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-rw-r--r--src/context/afterfunc_test.go141
-rw-r--r--src/context/benchmark_test.go190
-rw-r--r--src/context/context.go785
-rw-r--r--src/context/context_test.go297
-rw-r--r--src/context/example_test.go263
-rw-r--r--src/context/net_test.go21
-rw-r--r--src/context/x_test.go956
7 files changed, 2653 insertions, 0 deletions
diff --git a/src/context/afterfunc_test.go b/src/context/afterfunc_test.go
new file mode 100644
index 0000000..71f639a
--- /dev/null
+++ b/src/context/afterfunc_test.go
@@ -0,0 +1,141 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package context_test
+
+import (
+ "context"
+ "sync"
+ "testing"
+ "time"
+)
+
+// afterFuncContext is a context that's not one of the types
+// defined in context.go, that supports registering AfterFuncs.
+type afterFuncContext struct {
+ mu sync.Mutex
+ afterFuncs map[*struct{}]func()
+ done chan struct{}
+ err error
+}
+
+func newAfterFuncContext() context.Context {
+ return &afterFuncContext{}
+}
+
+func (c *afterFuncContext) Deadline() (time.Time, bool) {
+ return time.Time{}, false
+}
+
+func (c *afterFuncContext) Done() <-chan struct{} {
+ c.mu.Lock()
+ defer c.mu.Unlock()
+ if c.done == nil {
+ c.done = make(chan struct{})
+ }
+ return c.done
+}
+
+func (c *afterFuncContext) Err() error {
+ c.mu.Lock()
+ defer c.mu.Unlock()
+ return c.err
+}
+
+func (c *afterFuncContext) Value(key any) any {
+ return nil
+}
+
+func (c *afterFuncContext) AfterFunc(f func()) func() bool {
+ c.mu.Lock()
+ defer c.mu.Unlock()
+ k := &struct{}{}
+ if c.afterFuncs == nil {
+ c.afterFuncs = make(map[*struct{}]func())
+ }
+ c.afterFuncs[k] = f
+ return func() bool {
+ c.mu.Lock()
+ defer c.mu.Unlock()
+ _, ok := c.afterFuncs[k]
+ delete(c.afterFuncs, k)
+ return ok
+ }
+}
+
+func (c *afterFuncContext) cancel(err error) {
+ c.mu.Lock()
+ defer c.mu.Unlock()
+ if c.err != nil {
+ return
+ }
+ c.err = err
+ for _, f := range c.afterFuncs {
+ go f()
+ }
+ c.afterFuncs = nil
+}
+
+func TestCustomContextAfterFuncCancel(t *testing.T) {
+ ctx0 := &afterFuncContext{}
+ ctx1, cancel := context.WithCancel(ctx0)
+ defer cancel()
+ ctx0.cancel(context.Canceled)
+ <-ctx1.Done()
+}
+
+func TestCustomContextAfterFuncTimeout(t *testing.T) {
+ ctx0 := &afterFuncContext{}
+ ctx1, cancel := context.WithTimeout(ctx0, veryLongDuration)
+ defer cancel()
+ ctx0.cancel(context.Canceled)
+ <-ctx1.Done()
+}
+
+func TestCustomContextAfterFuncAfterFunc(t *testing.T) {
+ ctx0 := &afterFuncContext{}
+ donec := make(chan struct{})
+ stop := context.AfterFunc(ctx0, func() {
+ close(donec)
+ })
+ defer stop()
+ ctx0.cancel(context.Canceled)
+ <-donec
+}
+
+func TestCustomContextAfterFuncUnregisterCancel(t *testing.T) {
+ ctx0 := &afterFuncContext{}
+ _, cancel := context.WithCancel(ctx0)
+ if got, want := len(ctx0.afterFuncs), 1; got != want {
+ t.Errorf("after WithCancel(ctx0): ctx0 has %v afterFuncs, want %v", got, want)
+ }
+ cancel()
+ if got, want := len(ctx0.afterFuncs), 0; got != want {
+ t.Errorf("after canceling WithCancel(ctx0): ctx0 has %v afterFuncs, want %v", got, want)
+ }
+}
+
+func TestCustomContextAfterFuncUnregisterTimeout(t *testing.T) {
+ ctx0 := &afterFuncContext{}
+ _, cancel := context.WithTimeout(ctx0, veryLongDuration)
+ if got, want := len(ctx0.afterFuncs), 1; got != want {
+ t.Errorf("after WithTimeout(ctx0, d): ctx0 has %v afterFuncs, want %v", got, want)
+ }
+ cancel()
+ if got, want := len(ctx0.afterFuncs), 0; got != want {
+ t.Errorf("after canceling WithTimeout(ctx0, d): ctx0 has %v afterFuncs, want %v", got, want)
+ }
+}
+
+func TestCustomContextAfterFuncUnregisterAfterFunc(t *testing.T) {
+ ctx0 := &afterFuncContext{}
+ stop := context.AfterFunc(ctx0, func() {})
+ if got, want := len(ctx0.afterFuncs), 1; got != want {
+ t.Errorf("after AfterFunc(ctx0, f): ctx0 has %v afterFuncs, want %v", got, want)
+ }
+ stop()
+ if got, want := len(ctx0.afterFuncs), 0; got != want {
+ t.Errorf("after stopping AfterFunc(ctx0, f): ctx0 has %v afterFuncs, want %v", got, want)
+ }
+}
diff --git a/src/context/benchmark_test.go b/src/context/benchmark_test.go
new file mode 100644
index 0000000..144f473
--- /dev/null
+++ b/src/context/benchmark_test.go
@@ -0,0 +1,190 @@
+// Copyright 2014 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package context_test
+
+import (
+ . "context"
+ "fmt"
+ "runtime"
+ "sync"
+ "testing"
+ "time"
+)
+
+func BenchmarkCommonParentCancel(b *testing.B) {
+ root := WithValue(Background(), "key", "value")
+ shared, sharedcancel := WithCancel(root)
+ defer sharedcancel()
+
+ b.ResetTimer()
+ b.RunParallel(func(pb *testing.PB) {
+ x := 0
+ for pb.Next() {
+ ctx, cancel := WithCancel(shared)
+ if ctx.Value("key").(string) != "value" {
+ b.Fatal("should not be reached")
+ }
+ for i := 0; i < 100; i++ {
+ x /= x + 1
+ }
+ cancel()
+ for i := 0; i < 100; i++ {
+ x /= x + 1
+ }
+ }
+ })
+}
+
+func BenchmarkWithTimeout(b *testing.B) {
+ for concurrency := 40; concurrency <= 4e5; concurrency *= 100 {
+ name := fmt.Sprintf("concurrency=%d", concurrency)
+ b.Run(name, func(b *testing.B) {
+ benchmarkWithTimeout(b, concurrency)
+ })
+ }
+}
+
+func benchmarkWithTimeout(b *testing.B, concurrentContexts int) {
+ gomaxprocs := runtime.GOMAXPROCS(0)
+ perPContexts := concurrentContexts / gomaxprocs
+ root := Background()
+
+ // Generate concurrent contexts.
+ var wg sync.WaitGroup
+ ccf := make([][]CancelFunc, gomaxprocs)
+ for i := range ccf {
+ wg.Add(1)
+ go func(i int) {
+ defer wg.Done()
+ cf := make([]CancelFunc, perPContexts)
+ for j := range cf {
+ _, cf[j] = WithTimeout(root, time.Hour)
+ }
+ ccf[i] = cf
+ }(i)
+ }
+ wg.Wait()
+
+ b.ResetTimer()
+ b.RunParallel(func(pb *testing.PB) {
+ wcf := make([]CancelFunc, 10)
+ for pb.Next() {
+ for i := range wcf {
+ _, wcf[i] = WithTimeout(root, time.Hour)
+ }
+ for _, f := range wcf {
+ f()
+ }
+ }
+ })
+ b.StopTimer()
+
+ for _, cf := range ccf {
+ for _, f := range cf {
+ f()
+ }
+ }
+}
+
+func BenchmarkCancelTree(b *testing.B) {
+ depths := []int{1, 10, 100, 1000}
+ for _, d := range depths {
+ b.Run(fmt.Sprintf("depth=%d", d), func(b *testing.B) {
+ b.Run("Root=Background", func(b *testing.B) {
+ for i := 0; i < b.N; i++ {
+ buildContextTree(Background(), d)
+ }
+ })
+ b.Run("Root=OpenCanceler", func(b *testing.B) {
+ for i := 0; i < b.N; i++ {
+ ctx, cancel := WithCancel(Background())
+ buildContextTree(ctx, d)
+ cancel()
+ }
+ })
+ b.Run("Root=ClosedCanceler", func(b *testing.B) {
+ for i := 0; i < b.N; i++ {
+ ctx, cancel := WithCancel(Background())
+ cancel()
+ buildContextTree(ctx, d)
+ }
+ })
+ })
+ }
+}
+
+func buildContextTree(root Context, depth int) {
+ for d := 0; d < depth; d++ {
+ root, _ = WithCancel(root)
+ }
+}
+
+func BenchmarkCheckCanceled(b *testing.B) {
+ ctx, cancel := WithCancel(Background())
+ cancel()
+ b.Run("Err", func(b *testing.B) {
+ for i := 0; i < b.N; i++ {
+ ctx.Err()
+ }
+ })
+ b.Run("Done", func(b *testing.B) {
+ for i := 0; i < b.N; i++ {
+ select {
+ case <-ctx.Done():
+ default:
+ }
+ }
+ })
+}
+
+func BenchmarkContextCancelDone(b *testing.B) {
+ ctx, cancel := WithCancel(Background())
+ defer cancel()
+
+ b.RunParallel(func(pb *testing.PB) {
+ for pb.Next() {
+ select {
+ case <-ctx.Done():
+ default:
+ }
+ }
+ })
+}
+
+func BenchmarkDeepValueNewGoRoutine(b *testing.B) {
+ for _, depth := range []int{10, 20, 30, 50, 100} {
+ ctx := Background()
+ for i := 0; i < depth; i++ {
+ ctx = WithValue(ctx, i, i)
+ }
+
+ b.Run(fmt.Sprintf("depth=%d", depth), func(b *testing.B) {
+ for i := 0; i < b.N; i++ {
+ var wg sync.WaitGroup
+ wg.Add(1)
+ go func() {
+ defer wg.Done()
+ ctx.Value(-1)
+ }()
+ wg.Wait()
+ }
+ })
+ }
+}
+
+func BenchmarkDeepValueSameGoRoutine(b *testing.B) {
+ for _, depth := range []int{10, 20, 30, 50, 100} {
+ ctx := Background()
+ for i := 0; i < depth; i++ {
+ ctx = WithValue(ctx, i, i)
+ }
+
+ b.Run(fmt.Sprintf("depth=%d", depth), func(b *testing.B) {
+ for i := 0; i < b.N; i++ {
+ ctx.Value(-1)
+ }
+ })
+ }
+}
diff --git a/src/context/context.go b/src/context/context.go
new file mode 100644
index 0000000..ee66b43
--- /dev/null
+++ b/src/context/context.go
@@ -0,0 +1,785 @@
+// Copyright 2014 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package context defines the Context type, which carries deadlines,
+// cancellation signals, and other request-scoped values across API boundaries
+// and between processes.
+//
+// Incoming requests to a server should create a [Context], and outgoing
+// calls to servers should accept a Context. The chain of function
+// calls between them must propagate the Context, optionally replacing
+// it with a derived Context created using [WithCancel], [WithDeadline],
+// [WithTimeout], or [WithValue]. When a Context is canceled, all
+// Contexts derived from it are also canceled.
+//
+// The [WithCancel], [WithDeadline], and [WithTimeout] functions take a
+// Context (the parent) and return a derived Context (the child) and a
+// [CancelFunc]. Calling the CancelFunc cancels the child and its
+// children, removes the parent's reference to the child, and stops
+// any associated timers. Failing to call the CancelFunc leaks the
+// child and its children until the parent is canceled or the timer
+// fires. The go vet tool checks that CancelFuncs are used on all
+// control-flow paths.
+//
+// The [WithCancelCause] function returns a [CancelCauseFunc], which
+// takes an error and records it as the cancellation cause. Calling
+// [Cause] on the canceled context or any of its children retrieves
+// the cause. If no cause is specified, Cause(ctx) returns the same
+// value as ctx.Err().
+//
+// Programs that use Contexts should follow these rules to keep interfaces
+// consistent across packages and enable static analysis tools to check context
+// propagation:
+//
+// Do not store Contexts inside a struct type; instead, pass a Context
+// explicitly to each function that needs it. The Context should be the first
+// parameter, typically named ctx:
+//
+// func DoSomething(ctx context.Context, arg Arg) error {
+// // ... use ctx ...
+// }
+//
+// Do not pass a nil [Context], even if a function permits it. Pass [context.TODO]
+// if you are unsure about which Context to use.
+//
+// Use context Values only for request-scoped data that transits processes and
+// APIs, not for passing optional parameters to functions.
+//
+// The same Context may be passed to functions running in different goroutines;
+// Contexts are safe for simultaneous use by multiple goroutines.
+//
+// See https://blog.golang.org/context for example code for a server that uses
+// Contexts.
+package context
+
+import (
+ "errors"
+ "internal/reflectlite"
+ "sync"
+ "sync/atomic"
+ "time"
+)
+
+// A Context carries a deadline, a cancellation signal, and other values across
+// API boundaries.
+//
+// Context's methods may be called by multiple goroutines simultaneously.
+type Context interface {
+ // Deadline returns the time when work done on behalf of this context
+ // should be canceled. Deadline returns ok==false when no deadline is
+ // set. Successive calls to Deadline return the same results.
+ Deadline() (deadline time.Time, ok bool)
+
+ // Done returns a channel that's closed when work done on behalf of this
+ // context should be canceled. Done may return nil if this context can
+ // never be canceled. Successive calls to Done return the same value.
+ // The close of the Done channel may happen asynchronously,
+ // after the cancel function returns.
+ //
+ // WithCancel arranges for Done to be closed when cancel is called;
+ // WithDeadline arranges for Done to be closed when the deadline
+ // expires; WithTimeout arranges for Done to be closed when the timeout
+ // elapses.
+ //
+ // Done is provided for use in select statements:
+ //
+ // // Stream generates values with DoSomething and sends them to out
+ // // until DoSomething returns an error or ctx.Done is closed.
+ // func Stream(ctx context.Context, out chan<- Value) error {
+ // for {
+ // v, err := DoSomething(ctx)
+ // if err != nil {
+ // return err
+ // }
+ // select {
+ // case <-ctx.Done():
+ // return ctx.Err()
+ // case out <- v:
+ // }
+ // }
+ // }
+ //
+ // See https://blog.golang.org/pipelines for more examples of how to use
+ // a Done channel for cancellation.
+ Done() <-chan struct{}
+
+ // If Done is not yet closed, Err returns nil.
+ // If Done is closed, Err returns a non-nil error explaining why:
+ // Canceled if the context was canceled
+ // or DeadlineExceeded if the context's deadline passed.
+ // After Err returns a non-nil error, successive calls to Err return the same error.
+ Err() error
+
+ // Value returns the value associated with this context for key, or nil
+ // if no value is associated with key. Successive calls to Value with
+ // the same key returns the same result.
+ //
+ // Use context values only for request-scoped data that transits
+ // processes and API boundaries, not for passing optional parameters to
+ // functions.
+ //
+ // A key identifies a specific value in a Context. Functions that wish
+ // to store values in Context typically allocate a key in a global
+ // variable then use that key as the argument to context.WithValue and
+ // Context.Value. A key can be any type that supports equality;
+ // packages should define keys as an unexported type to avoid
+ // collisions.
+ //
+ // Packages that define a Context key should provide type-safe accessors
+ // for the values stored using that key:
+ //
+ // // Package user defines a User type that's stored in Contexts.
+ // package user
+ //
+ // import "context"
+ //
+ // // User is the type of value stored in the Contexts.
+ // type User struct {...}
+ //
+ // // key is an unexported type for keys defined in this package.
+ // // This prevents collisions with keys defined in other packages.
+ // type key int
+ //
+ // // userKey is the key for user.User values in Contexts. It is
+ // // unexported; clients use user.NewContext and user.FromContext
+ // // instead of using this key directly.
+ // var userKey key
+ //
+ // // NewContext returns a new Context that carries value u.
+ // func NewContext(ctx context.Context, u *User) context.Context {
+ // return context.WithValue(ctx, userKey, u)
+ // }
+ //
+ // // FromContext returns the User value stored in ctx, if any.
+ // func FromContext(ctx context.Context) (*User, bool) {
+ // u, ok := ctx.Value(userKey).(*User)
+ // return u, ok
+ // }
+ Value(key any) any
+}
+
+// Canceled is the error returned by [Context.Err] when the context is canceled.
+var Canceled = errors.New("context canceled")
+
+// DeadlineExceeded is the error returned by [Context.Err] when the context's
+// deadline passes.
+var DeadlineExceeded error = deadlineExceededError{}
+
+type deadlineExceededError struct{}
+
+func (deadlineExceededError) Error() string { return "context deadline exceeded" }
+func (deadlineExceededError) Timeout() bool { return true }
+func (deadlineExceededError) Temporary() bool { return true }
+
+// An emptyCtx is never canceled, has no values, and has no deadline.
+// It is the common base of backgroundCtx and todoCtx.
+type emptyCtx struct{}
+
+func (emptyCtx) Deadline() (deadline time.Time, ok bool) {
+ return
+}
+
+func (emptyCtx) Done() <-chan struct{} {
+ return nil
+}
+
+func (emptyCtx) Err() error {
+ return nil
+}
+
+func (emptyCtx) Value(key any) any {
+ return nil
+}
+
+type backgroundCtx struct{ emptyCtx }
+
+func (backgroundCtx) String() string {
+ return "context.Background"
+}
+
+type todoCtx struct{ emptyCtx }
+
+func (todoCtx) String() string {
+ return "context.TODO"
+}
+
+// Background returns a non-nil, empty [Context]. It is never canceled, has no
+// values, and has no deadline. It is typically used by the main function,
+// initialization, and tests, and as the top-level Context for incoming
+// requests.
+func Background() Context {
+ return backgroundCtx{}
+}
+
+// TODO returns a non-nil, empty [Context]. Code should use context.TODO when
+// it's unclear which Context to use or it is not yet available (because the
+// surrounding function has not yet been extended to accept a Context
+// parameter).
+func TODO() Context {
+ return todoCtx{}
+}
+
+// A CancelFunc tells an operation to abandon its work.
+// A CancelFunc does not wait for the work to stop.
+// A CancelFunc may be called by multiple goroutines simultaneously.
+// After the first call, subsequent calls to a CancelFunc do nothing.
+type CancelFunc func()
+
+// WithCancel returns a copy of parent with a new Done channel. The returned
+// context's Done channel is closed when the returned cancel function is called
+// or when the parent context's Done channel is closed, whichever happens first.
+//
+// Canceling this context releases resources associated with it, so code should
+// call cancel as soon as the operations running in this Context complete.
+func WithCancel(parent Context) (ctx Context, cancel CancelFunc) {
+ c := withCancel(parent)
+ return c, func() { c.cancel(true, Canceled, nil) }
+}
+
+// A CancelCauseFunc behaves like a [CancelFunc] but additionally sets the cancellation cause.
+// This cause can be retrieved by calling [Cause] on the canceled Context or on
+// any of its derived Contexts.
+//
+// If the context has already been canceled, CancelCauseFunc does not set the cause.
+// For example, if childContext is derived from parentContext:
+// - if parentContext is canceled with cause1 before childContext is canceled with cause2,
+// then Cause(parentContext) == Cause(childContext) == cause1
+// - if childContext is canceled with cause2 before parentContext is canceled with cause1,
+// then Cause(parentContext) == cause1 and Cause(childContext) == cause2
+type CancelCauseFunc func(cause error)
+
+// WithCancelCause behaves like [WithCancel] but returns a [CancelCauseFunc] instead of a [CancelFunc].
+// Calling cancel with a non-nil error (the "cause") records that error in ctx;
+// it can then be retrieved using Cause(ctx).
+// Calling cancel with nil sets the cause to Canceled.
+//
+// Example use:
+//
+// ctx, cancel := context.WithCancelCause(parent)
+// cancel(myError)
+// ctx.Err() // returns context.Canceled
+// context.Cause(ctx) // returns myError
+func WithCancelCause(parent Context) (ctx Context, cancel CancelCauseFunc) {
+ c := withCancel(parent)
+ return c, func(cause error) { c.cancel(true, Canceled, cause) }
+}
+
+func withCancel(parent Context) *cancelCtx {
+ if parent == nil {
+ panic("cannot create context from nil parent")
+ }
+ c := &cancelCtx{}
+ c.propagateCancel(parent, c)
+ return c
+}
+
+// Cause returns a non-nil error explaining why c was canceled.
+// The first cancellation of c or one of its parents sets the cause.
+// If that cancellation happened via a call to CancelCauseFunc(err),
+// then [Cause] returns err.
+// Otherwise Cause(c) returns the same value as c.Err().
+// Cause returns nil if c has not been canceled yet.
+func Cause(c Context) error {
+ if cc, ok := c.Value(&cancelCtxKey).(*cancelCtx); ok {
+ cc.mu.Lock()
+ defer cc.mu.Unlock()
+ return cc.cause
+ }
+ return nil
+}
+
+// AfterFunc arranges to call f in its own goroutine after ctx is done
+// (cancelled or timed out).
+// If ctx is already done, AfterFunc calls f immediately in its own goroutine.
+//
+// Multiple calls to AfterFunc on a context operate independently;
+// one does not replace another.
+//
+// Calling the returned stop function stops the association of ctx with f.
+// It returns true if the call stopped f from being run.
+// If stop returns false,
+// either the context is done and f has been started in its own goroutine;
+// or f was already stopped.
+// The stop function does not wait for f to complete before returning.
+// If the caller needs to know whether f is completed,
+// it must coordinate with f explicitly.
+//
+// If ctx has a "AfterFunc(func()) func() bool" method,
+// AfterFunc will use it to schedule the call.
+func AfterFunc(ctx Context, f func()) (stop func() bool) {
+ a := &afterFuncCtx{
+ f: f,
+ }
+ a.cancelCtx.propagateCancel(ctx, a)
+ return func() bool {
+ stopped := false
+ a.once.Do(func() {
+ stopped = true
+ })
+ if stopped {
+ a.cancel(true, Canceled, nil)
+ }
+ return stopped
+ }
+}
+
+type afterFuncer interface {
+ AfterFunc(func()) func() bool
+}
+
+type afterFuncCtx struct {
+ cancelCtx
+ once sync.Once // either starts running f or stops f from running
+ f func()
+}
+
+func (a *afterFuncCtx) cancel(removeFromParent bool, err, cause error) {
+ a.cancelCtx.cancel(false, err, cause)
+ if removeFromParent {
+ removeChild(a.Context, a)
+ }
+ a.once.Do(func() {
+ go a.f()
+ })
+}
+
+// A stopCtx is used as the parent context of a cancelCtx when
+// an AfterFunc has been registered with the parent.
+// It holds the stop function used to unregister the AfterFunc.
+type stopCtx struct {
+ Context
+ stop func() bool
+}
+
+// goroutines counts the number of goroutines ever created; for testing.
+var goroutines atomic.Int32
+
+// &cancelCtxKey is the key that a cancelCtx returns itself for.
+var cancelCtxKey int
+
+// parentCancelCtx returns the underlying *cancelCtx for parent.
+// It does this by looking up parent.Value(&cancelCtxKey) to find
+// the innermost enclosing *cancelCtx and then checking whether
+// parent.Done() matches that *cancelCtx. (If not, the *cancelCtx
+// has been wrapped in a custom implementation providing a
+// different done channel, in which case we should not bypass it.)
+func parentCancelCtx(parent Context) (*cancelCtx, bool) {
+ done := parent.Done()
+ if done == closedchan || done == nil {
+ return nil, false
+ }
+ p, ok := parent.Value(&cancelCtxKey).(*cancelCtx)
+ if !ok {
+ return nil, false
+ }
+ pdone, _ := p.done.Load().(chan struct{})
+ if pdone != done {
+ return nil, false
+ }
+ return p, true
+}
+
+// removeChild removes a context from its parent.
+func removeChild(parent Context, child canceler) {
+ if s, ok := parent.(stopCtx); ok {
+ s.stop()
+ return
+ }
+ p, ok := parentCancelCtx(parent)
+ if !ok {
+ return
+ }
+ p.mu.Lock()
+ if p.children != nil {
+ delete(p.children, child)
+ }
+ p.mu.Unlock()
+}
+
+// A canceler is a context type that can be canceled directly. The
+// implementations are *cancelCtx and *timerCtx.
+type canceler interface {
+ cancel(removeFromParent bool, err, cause error)
+ Done() <-chan struct{}
+}
+
+// closedchan is a reusable closed channel.
+var closedchan = make(chan struct{})
+
+func init() {
+ close(closedchan)
+}
+
+// A cancelCtx can be canceled. When canceled, it also cancels any children
+// that implement canceler.
+type cancelCtx struct {
+ Context
+
+ mu sync.Mutex // protects following fields
+ done atomic.Value // of chan struct{}, created lazily, closed by first cancel call
+ children map[canceler]struct{} // set to nil by the first cancel call
+ err error // set to non-nil by the first cancel call
+ cause error // set to non-nil by the first cancel call
+}
+
+func (c *cancelCtx) Value(key any) any {
+ if key == &cancelCtxKey {
+ return c
+ }
+ return value(c.Context, key)
+}
+
+func (c *cancelCtx) Done() <-chan struct{} {
+ d := c.done.Load()
+ if d != nil {
+ return d.(chan struct{})
+ }
+ c.mu.Lock()
+ defer c.mu.Unlock()
+ d = c.done.Load()
+ if d == nil {
+ d = make(chan struct{})
+ c.done.Store(d)
+ }
+ return d.(chan struct{})
+}
+
+func (c *cancelCtx) Err() error {
+ c.mu.Lock()
+ err := c.err
+ c.mu.Unlock()
+ return err
+}
+
+// propagateCancel arranges for child to be canceled when parent is.
+// It sets the parent context of cancelCtx.
+func (c *cancelCtx) propagateCancel(parent Context, child canceler) {
+ c.Context = parent
+
+ done := parent.Done()
+ if done == nil {
+ return // parent is never canceled
+ }
+
+ select {
+ case <-done:
+ // parent is already canceled
+ child.cancel(false, parent.Err(), Cause(parent))
+ return
+ default:
+ }
+
+ if p, ok := parentCancelCtx(parent); ok {
+ // parent is a *cancelCtx, or derives from one.
+ p.mu.Lock()
+ if p.err != nil {
+ // parent has already been canceled
+ child.cancel(false, p.err, p.cause)
+ } else {
+ if p.children == nil {
+ p.children = make(map[canceler]struct{})
+ }
+ p.children[child] = struct{}{}
+ }
+ p.mu.Unlock()
+ return
+ }
+
+ if a, ok := parent.(afterFuncer); ok {
+ // parent implements an AfterFunc method.
+ c.mu.Lock()
+ stop := a.AfterFunc(func() {
+ child.cancel(false, parent.Err(), Cause(parent))
+ })
+ c.Context = stopCtx{
+ Context: parent,
+ stop: stop,
+ }
+ c.mu.Unlock()
+ return
+ }
+
+ goroutines.Add(1)
+ go func() {
+ select {
+ case <-parent.Done():
+ child.cancel(false, parent.Err(), Cause(parent))
+ case <-child.Done():
+ }
+ }()
+}
+
+type stringer interface {
+ String() string
+}
+
+func contextName(c Context) string {
+ if s, ok := c.(stringer); ok {
+ return s.String()
+ }
+ return reflectlite.TypeOf(c).String()
+}
+
+func (c *cancelCtx) String() string {
+ return contextName(c.Context) + ".WithCancel"
+}
+
+// cancel closes c.done, cancels each of c's children, and, if
+// removeFromParent is true, removes c from its parent's children.
+// cancel sets c.cause to cause if this is the first time c is canceled.
+func (c *cancelCtx) cancel(removeFromParent bool, err, cause error) {
+ if err == nil {
+ panic("context: internal error: missing cancel error")
+ }
+ if cause == nil {
+ cause = err
+ }
+ c.mu.Lock()
+ if c.err != nil {
+ c.mu.Unlock()
+ return // already canceled
+ }
+ c.err = err
+ c.cause = cause
+ d, _ := c.done.Load().(chan struct{})
+ if d == nil {
+ c.done.Store(closedchan)
+ } else {
+ close(d)
+ }
+ for child := range c.children {
+ // NOTE: acquiring the child's lock while holding parent's lock.
+ child.cancel(false, err, cause)
+ }
+ c.children = nil
+ c.mu.Unlock()
+
+ if removeFromParent {
+ removeChild(c.Context, c)
+ }
+}
+
+// WithoutCancel returns a copy of parent that is not canceled when parent is canceled.
+// The returned context returns no Deadline or Err, and its Done channel is nil.
+// Calling [Cause] on the returned context returns nil.
+func WithoutCancel(parent Context) Context {
+ if parent == nil {
+ panic("cannot create context from nil parent")
+ }
+ return withoutCancelCtx{parent}
+}
+
+type withoutCancelCtx struct {
+ c Context
+}
+
+func (withoutCancelCtx) Deadline() (deadline time.Time, ok bool) {
+ return
+}
+
+func (withoutCancelCtx) Done() <-chan struct{} {
+ return nil
+}
+
+func (withoutCancelCtx) Err() error {
+ return nil
+}
+
+func (c withoutCancelCtx) Value(key any) any {
+ return value(c, key)
+}
+
+func (c withoutCancelCtx) String() string {
+ return contextName(c.c) + ".WithoutCancel"
+}
+
+// WithDeadline returns a copy of the parent context with the deadline adjusted
+// to be no later than d. If the parent's deadline is already earlier than d,
+// WithDeadline(parent, d) is semantically equivalent to parent. The returned
+// [Context.Done] channel is closed when the deadline expires, when the returned
+// cancel function is called, or when the parent context's Done channel is
+// closed, whichever happens first.
+//
+// Canceling this context releases resources associated with it, so code should
+// call cancel as soon as the operations running in this [Context] complete.
+func WithDeadline(parent Context, d time.Time) (Context, CancelFunc) {
+ return WithDeadlineCause(parent, d, nil)
+}
+
+// WithDeadlineCause behaves like [WithDeadline] but also sets the cause of the
+// returned Context when the deadline is exceeded. The returned [CancelFunc] does
+// not set the cause.
+func WithDeadlineCause(parent Context, d time.Time, cause error) (Context, CancelFunc) {
+ if parent == nil {
+ panic("cannot create context from nil parent")
+ }
+ if cur, ok := parent.Deadline(); ok && cur.Before(d) {
+ // The current deadline is already sooner than the new one.
+ return WithCancel(parent)
+ }
+ c := &timerCtx{
+ deadline: d,
+ }
+ c.cancelCtx.propagateCancel(parent, c)
+ dur := time.Until(d)
+ if dur <= 0 {
+ c.cancel(true, DeadlineExceeded, cause) // deadline has already passed
+ return c, func() { c.cancel(false, Canceled, nil) }
+ }
+ c.mu.Lock()
+ defer c.mu.Unlock()
+ if c.err == nil {
+ c.timer = time.AfterFunc(dur, func() {
+ c.cancel(true, DeadlineExceeded, cause)
+ })
+ }
+ return c, func() { c.cancel(true, Canceled, nil) }
+}
+
+// A timerCtx carries a timer and a deadline. It embeds a cancelCtx to
+// implement Done and Err. It implements cancel by stopping its timer then
+// delegating to cancelCtx.cancel.
+type timerCtx struct {
+ cancelCtx
+ timer *time.Timer // Under cancelCtx.mu.
+
+ deadline time.Time
+}
+
+func (c *timerCtx) Deadline() (deadline time.Time, ok bool) {
+ return c.deadline, true
+}
+
+func (c *timerCtx) String() string {
+ return contextName(c.cancelCtx.Context) + ".WithDeadline(" +
+ c.deadline.String() + " [" +
+ time.Until(c.deadline).String() + "])"
+}
+
+func (c *timerCtx) cancel(removeFromParent bool, err, cause error) {
+ c.cancelCtx.cancel(false, err, cause)
+ if removeFromParent {
+ // Remove this timerCtx from its parent cancelCtx's children.
+ removeChild(c.cancelCtx.Context, c)
+ }
+ c.mu.Lock()
+ if c.timer != nil {
+ c.timer.Stop()
+ c.timer = nil
+ }
+ c.mu.Unlock()
+}
+
+// WithTimeout returns WithDeadline(parent, time.Now().Add(timeout)).
+//
+// Canceling this context releases resources associated with it, so code should
+// call cancel as soon as the operations running in this [Context] complete:
+//
+// func slowOperationWithTimeout(ctx context.Context) (Result, error) {
+// ctx, cancel := context.WithTimeout(ctx, 100*time.Millisecond)
+// defer cancel() // releases resources if slowOperation completes before timeout elapses
+// return slowOperation(ctx)
+// }
+func WithTimeout(parent Context, timeout time.Duration) (Context, CancelFunc) {
+ return WithDeadline(parent, time.Now().Add(timeout))
+}
+
+// WithTimeoutCause behaves like [WithTimeout] but also sets the cause of the
+// returned Context when the timeout expires. The returned [CancelFunc] does
+// not set the cause.
+func WithTimeoutCause(parent Context, timeout time.Duration, cause error) (Context, CancelFunc) {
+ return WithDeadlineCause(parent, time.Now().Add(timeout), cause)
+}
+
+// WithValue returns a copy of parent in which the value associated with key is
+// val.
+//
+// Use context Values only for request-scoped data that transits processes and
+// APIs, not for passing optional parameters to functions.
+//
+// The provided key must be comparable and should not be of type
+// string or any other built-in type to avoid collisions between
+// packages using context. Users of WithValue should define their own
+// types for keys. To avoid allocating when assigning to an
+// interface{}, context keys often have concrete type
+// struct{}. Alternatively, exported context key variables' static
+// type should be a pointer or interface.
+func WithValue(parent Context, key, val any) Context {
+ if parent == nil {
+ panic("cannot create context from nil parent")
+ }
+ if key == nil {
+ panic("nil key")
+ }
+ if !reflectlite.TypeOf(key).Comparable() {
+ panic("key is not comparable")
+ }
+ return &valueCtx{parent, key, val}
+}
+
+// A valueCtx carries a key-value pair. It implements Value for that key and
+// delegates all other calls to the embedded Context.
+type valueCtx struct {
+ Context
+ key, val any
+}
+
+// stringify tries a bit to stringify v, without using fmt, since we don't
+// want context depending on the unicode tables. This is only used by
+// *valueCtx.String().
+func stringify(v any) string {
+ switch s := v.(type) {
+ case stringer:
+ return s.String()
+ case string:
+ return s
+ }
+ return "<not Stringer>"
+}
+
+func (c *valueCtx) String() string {
+ return contextName(c.Context) + ".WithValue(type " +
+ reflectlite.TypeOf(c.key).String() +
+ ", val " + stringify(c.val) + ")"
+}
+
+func (c *valueCtx) Value(key any) any {
+ if c.key == key {
+ return c.val
+ }
+ return value(c.Context, key)
+}
+
+func value(c Context, key any) any {
+ for {
+ switch ctx := c.(type) {
+ case *valueCtx:
+ if key == ctx.key {
+ return ctx.val
+ }
+ c = ctx.Context
+ case *cancelCtx:
+ if key == &cancelCtxKey {
+ return c
+ }
+ c = ctx.Context
+ case withoutCancelCtx:
+ if key == &cancelCtxKey {
+ // This implements Cause(ctx) == nil
+ // when ctx is created using WithoutCancel.
+ return nil
+ }
+ c = ctx.c
+ case *timerCtx:
+ if key == &cancelCtxKey {
+ return &ctx.cancelCtx
+ }
+ c = ctx.Context
+ case backgroundCtx, todoCtx:
+ return nil
+ default:
+ return c.Value(key)
+ }
+ }
+}
diff --git a/src/context/context_test.go b/src/context/context_test.go
new file mode 100644
index 0000000..57066c9
--- /dev/null
+++ b/src/context/context_test.go
@@ -0,0 +1,297 @@
+// Copyright 2014 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package context
+
+// Tests in package context cannot depend directly on package testing due to an import cycle.
+// If your test does requires access to unexported members of the context package,
+// add your test below as `func XTestFoo(t testingT)` and add a `TestFoo` to x_test.go
+// that calls it. Otherwise, write a regular test in a test.go file in package context_test.
+
+import (
+ "time"
+)
+
+type testingT interface {
+ Deadline() (time.Time, bool)
+ Error(args ...any)
+ Errorf(format string, args ...any)
+ Fail()
+ FailNow()
+ Failed() bool
+ Fatal(args ...any)
+ Fatalf(format string, args ...any)
+ Helper()
+ Log(args ...any)
+ Logf(format string, args ...any)
+ Name() string
+ Parallel()
+ Skip(args ...any)
+ SkipNow()
+ Skipf(format string, args ...any)
+ Skipped() bool
+}
+
+const veryLongDuration = 1000 * time.Hour // an arbitrary upper bound on the test's running time
+
+func contains(m map[canceler]struct{}, key canceler) bool {
+ _, ret := m[key]
+ return ret
+}
+
+func XTestParentFinishesChild(t testingT) {
+ // Context tree:
+ // parent -> cancelChild
+ // parent -> valueChild -> timerChild
+ // parent -> afterChild
+ parent, cancel := WithCancel(Background())
+ cancelChild, stop := WithCancel(parent)
+ defer stop()
+ valueChild := WithValue(parent, "key", "value")
+ timerChild, stop := WithTimeout(valueChild, veryLongDuration)
+ defer stop()
+ afterStop := AfterFunc(parent, func() {})
+ defer afterStop()
+
+ select {
+ case x := <-parent.Done():
+ t.Errorf("<-parent.Done() == %v want nothing (it should block)", x)
+ case x := <-cancelChild.Done():
+ t.Errorf("<-cancelChild.Done() == %v want nothing (it should block)", x)
+ case x := <-timerChild.Done():
+ t.Errorf("<-timerChild.Done() == %v want nothing (it should block)", x)
+ case x := <-valueChild.Done():
+ t.Errorf("<-valueChild.Done() == %v want nothing (it should block)", x)
+ default:
+ }
+
+ // The parent's children should contain the three cancelable children.
+ pc := parent.(*cancelCtx)
+ cc := cancelChild.(*cancelCtx)
+ tc := timerChild.(*timerCtx)
+ pc.mu.Lock()
+ var ac *afterFuncCtx
+ for c := range pc.children {
+ if a, ok := c.(*afterFuncCtx); ok {
+ ac = a
+ break
+ }
+ }
+ if len(pc.children) != 3 || !contains(pc.children, cc) || !contains(pc.children, tc) || ac == nil {
+ t.Errorf("bad linkage: pc.children = %v, want %v, %v, and an afterFunc",
+ pc.children, cc, tc)
+ }
+ pc.mu.Unlock()
+
+ if p, ok := parentCancelCtx(cc.Context); !ok || p != pc {
+ t.Errorf("bad linkage: parentCancelCtx(cancelChild.Context) = %v, %v want %v, true", p, ok, pc)
+ }
+ if p, ok := parentCancelCtx(tc.Context); !ok || p != pc {
+ t.Errorf("bad linkage: parentCancelCtx(timerChild.Context) = %v, %v want %v, true", p, ok, pc)
+ }
+ if p, ok := parentCancelCtx(ac.Context); !ok || p != pc {
+ t.Errorf("bad linkage: parentCancelCtx(afterChild.Context) = %v, %v want %v, true", p, ok, pc)
+ }
+
+ cancel()
+
+ pc.mu.Lock()
+ if len(pc.children) != 0 {
+ t.Errorf("pc.cancel didn't clear pc.children = %v", pc.children)
+ }
+ pc.mu.Unlock()
+
+ // parent and children should all be finished.
+ check := func(ctx Context, name string) {
+ select {
+ case <-ctx.Done():
+ default:
+ t.Errorf("<-%s.Done() blocked, but shouldn't have", name)
+ }
+ if e := ctx.Err(); e != Canceled {
+ t.Errorf("%s.Err() == %v want %v", name, e, Canceled)
+ }
+ }
+ check(parent, "parent")
+ check(cancelChild, "cancelChild")
+ check(valueChild, "valueChild")
+ check(timerChild, "timerChild")
+
+ // WithCancel should return a canceled context on a canceled parent.
+ precanceledChild := WithValue(parent, "key", "value")
+ select {
+ case <-precanceledChild.Done():
+ default:
+ t.Errorf("<-precanceledChild.Done() blocked, but shouldn't have")
+ }
+ if e := precanceledChild.Err(); e != Canceled {
+ t.Errorf("precanceledChild.Err() == %v want %v", e, Canceled)
+ }
+}
+
+func XTestChildFinishesFirst(t testingT) {
+ cancelable, stop := WithCancel(Background())
+ defer stop()
+ for _, parent := range []Context{Background(), cancelable} {
+ child, cancel := WithCancel(parent)
+
+ select {
+ case x := <-parent.Done():
+ t.Errorf("<-parent.Done() == %v want nothing (it should block)", x)
+ case x := <-child.Done():
+ t.Errorf("<-child.Done() == %v want nothing (it should block)", x)
+ default:
+ }
+
+ cc := child.(*cancelCtx)
+ pc, pcok := parent.(*cancelCtx) // pcok == false when parent == Background()
+ if p, ok := parentCancelCtx(cc.Context); ok != pcok || (ok && pc != p) {
+ t.Errorf("bad linkage: parentCancelCtx(cc.Context) = %v, %v want %v, %v", p, ok, pc, pcok)
+ }
+
+ if pcok {
+ pc.mu.Lock()
+ if len(pc.children) != 1 || !contains(pc.children, cc) {
+ t.Errorf("bad linkage: pc.children = %v, cc = %v", pc.children, cc)
+ }
+ pc.mu.Unlock()
+ }
+
+ cancel()
+
+ if pcok {
+ pc.mu.Lock()
+ if len(pc.children) != 0 {
+ t.Errorf("child's cancel didn't remove self from pc.children = %v", pc.children)
+ }
+ pc.mu.Unlock()
+ }
+
+ // child should be finished.
+ select {
+ case <-child.Done():
+ default:
+ t.Errorf("<-child.Done() blocked, but shouldn't have")
+ }
+ if e := child.Err(); e != Canceled {
+ t.Errorf("child.Err() == %v want %v", e, Canceled)
+ }
+
+ // parent should not be finished.
+ select {
+ case x := <-parent.Done():
+ t.Errorf("<-parent.Done() == %v want nothing (it should block)", x)
+ default:
+ }
+ if e := parent.Err(); e != nil {
+ t.Errorf("parent.Err() == %v want nil", e)
+ }
+ }
+}
+
+func XTestCancelRemoves(t testingT) {
+ checkChildren := func(when string, ctx Context, want int) {
+ if got := len(ctx.(*cancelCtx).children); got != want {
+ t.Errorf("%s: context has %d children, want %d", when, got, want)
+ }
+ }
+
+ ctx, _ := WithCancel(Background())
+ checkChildren("after creation", ctx, 0)
+ _, cancel := WithCancel(ctx)
+ checkChildren("with WithCancel child ", ctx, 1)
+ cancel()
+ checkChildren("after canceling WithCancel child", ctx, 0)
+
+ ctx, _ = WithCancel(Background())
+ checkChildren("after creation", ctx, 0)
+ _, cancel = WithTimeout(ctx, 60*time.Minute)
+ checkChildren("with WithTimeout child ", ctx, 1)
+ cancel()
+ checkChildren("after canceling WithTimeout child", ctx, 0)
+
+ ctx, _ = WithCancel(Background())
+ checkChildren("after creation", ctx, 0)
+ stop := AfterFunc(ctx, func() {})
+ checkChildren("with AfterFunc child ", ctx, 1)
+ stop()
+ checkChildren("after stopping AfterFunc child ", ctx, 0)
+}
+
+type myCtx struct {
+ Context
+}
+
+type myDoneCtx struct {
+ Context
+}
+
+func (d *myDoneCtx) Done() <-chan struct{} {
+ c := make(chan struct{})
+ return c
+}
+func XTestCustomContextGoroutines(t testingT) {
+ g := goroutines.Load()
+ checkNoGoroutine := func() {
+ t.Helper()
+ now := goroutines.Load()
+ if now != g {
+ t.Fatalf("%d goroutines created", now-g)
+ }
+ }
+ checkCreatedGoroutine := func() {
+ t.Helper()
+ now := goroutines.Load()
+ if now != g+1 {
+ t.Fatalf("%d goroutines created, want 1", now-g)
+ }
+ g = now
+ }
+
+ _, cancel0 := WithCancel(&myDoneCtx{Background()})
+ cancel0()
+ checkCreatedGoroutine()
+
+ _, cancel0 = WithTimeout(&myDoneCtx{Background()}, veryLongDuration)
+ cancel0()
+ checkCreatedGoroutine()
+
+ checkNoGoroutine()
+ defer checkNoGoroutine()
+
+ ctx1, cancel1 := WithCancel(Background())
+ defer cancel1()
+ checkNoGoroutine()
+
+ ctx2 := &myCtx{ctx1}
+ ctx3, cancel3 := WithCancel(ctx2)
+ defer cancel3()
+ checkNoGoroutine()
+
+ _, cancel3b := WithCancel(&myDoneCtx{ctx2})
+ defer cancel3b()
+ checkCreatedGoroutine() // ctx1 is not providing Done, must not be used
+
+ ctx4, cancel4 := WithTimeout(ctx3, veryLongDuration)
+ defer cancel4()
+ checkNoGoroutine()
+
+ ctx5, cancel5 := WithCancel(ctx4)
+ defer cancel5()
+ checkNoGoroutine()
+
+ cancel5()
+ checkNoGoroutine()
+
+ _, cancel6 := WithTimeout(ctx5, veryLongDuration)
+ defer cancel6()
+ checkNoGoroutine()
+
+ // Check applied to canceled context.
+ cancel6()
+ cancel1()
+ _, cancel7 := WithCancel(ctx5)
+ defer cancel7()
+ checkNoGoroutine()
+}
diff --git a/src/context/example_test.go b/src/context/example_test.go
new file mode 100644
index 0000000..03333b5
--- /dev/null
+++ b/src/context/example_test.go
@@ -0,0 +1,263 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package context_test
+
+import (
+ "context"
+ "errors"
+ "fmt"
+ "net"
+ "sync"
+ "time"
+)
+
+var neverReady = make(chan struct{}) // never closed
+
+// This example demonstrates the use of a cancelable context to prevent a
+// goroutine leak. By the end of the example function, the goroutine started
+// by gen will return without leaking.
+func ExampleWithCancel() {
+ // gen generates integers in a separate goroutine and
+ // sends them to the returned channel.
+ // The callers of gen need to cancel the context once
+ // they are done consuming generated integers not to leak
+ // the internal goroutine started by gen.
+ gen := func(ctx context.Context) <-chan int {
+ dst := make(chan int)
+ n := 1
+ go func() {
+ for {
+ select {
+ case <-ctx.Done():
+ return // returning not to leak the goroutine
+ case dst <- n:
+ n++
+ }
+ }
+ }()
+ return dst
+ }
+
+ ctx, cancel := context.WithCancel(context.Background())
+ defer cancel() // cancel when we are finished consuming integers
+
+ for n := range gen(ctx) {
+ fmt.Println(n)
+ if n == 5 {
+ break
+ }
+ }
+ // Output:
+ // 1
+ // 2
+ // 3
+ // 4
+ // 5
+}
+
+// This example passes a context with an arbitrary deadline to tell a blocking
+// function that it should abandon its work as soon as it gets to it.
+func ExampleWithDeadline() {
+ d := time.Now().Add(shortDuration)
+ ctx, cancel := context.WithDeadline(context.Background(), d)
+
+ // Even though ctx will be expired, it is good practice to call its
+ // cancellation function in any case. Failure to do so may keep the
+ // context and its parent alive longer than necessary.
+ defer cancel()
+
+ select {
+ case <-neverReady:
+ fmt.Println("ready")
+ case <-ctx.Done():
+ fmt.Println(ctx.Err())
+ }
+
+ // Output:
+ // context deadline exceeded
+}
+
+// This example passes a context with a timeout to tell a blocking function that
+// it should abandon its work after the timeout elapses.
+func ExampleWithTimeout() {
+ // Pass a context with a timeout to tell a blocking function that it
+ // should abandon its work after the timeout elapses.
+ ctx, cancel := context.WithTimeout(context.Background(), shortDuration)
+ defer cancel()
+
+ select {
+ case <-neverReady:
+ fmt.Println("ready")
+ case <-ctx.Done():
+ fmt.Println(ctx.Err()) // prints "context deadline exceeded"
+ }
+
+ // Output:
+ // context deadline exceeded
+}
+
+// This example demonstrates how a value can be passed to the context
+// and also how to retrieve it if it exists.
+func ExampleWithValue() {
+ type favContextKey string
+
+ f := func(ctx context.Context, k favContextKey) {
+ if v := ctx.Value(k); v != nil {
+ fmt.Println("found value:", v)
+ return
+ }
+ fmt.Println("key not found:", k)
+ }
+
+ k := favContextKey("language")
+ ctx := context.WithValue(context.Background(), k, "Go")
+
+ f(ctx, k)
+ f(ctx, favContextKey("color"))
+
+ // Output:
+ // found value: Go
+ // key not found: color
+}
+
+// This example uses AfterFunc to define a function which waits on a sync.Cond,
+// stopping the wait when a context is canceled.
+func ExampleAfterFunc_cond() {
+ waitOnCond := func(ctx context.Context, cond *sync.Cond, conditionMet func() bool) error {
+ stopf := context.AfterFunc(ctx, func() {
+ // We need to acquire cond.L here to be sure that the Broadcast
+ // below won't occur before the call to Wait, which would result
+ // in a missed signal (and deadlock).
+ cond.L.Lock()
+ defer cond.L.Unlock()
+
+ // If multiple goroutines are waiting on cond simultaneously,
+ // we need to make sure we wake up exactly this one.
+ // That means that we need to Broadcast to all of the goroutines,
+ // which will wake them all up.
+ //
+ // If there are N concurrent calls to waitOnCond, each of the goroutines
+ // will spuriously wake up O(N) other goroutines that aren't ready yet,
+ // so this will cause the overall CPU cost to be O(N²).
+ cond.Broadcast()
+ })
+ defer stopf()
+
+ // Since the wakeups are using Broadcast instead of Signal, this call to
+ // Wait may unblock due to some other goroutine's context becoming done,
+ // so to be sure that ctx is actually done we need to check it in a loop.
+ for !conditionMet() {
+ cond.Wait()
+ if ctx.Err() != nil {
+ return ctx.Err()
+ }
+ }
+
+ return nil
+ }
+
+ cond := sync.NewCond(new(sync.Mutex))
+
+ var wg sync.WaitGroup
+ for i := 0; i < 4; i++ {
+ wg.Add(1)
+ go func() {
+ defer wg.Done()
+
+ ctx, cancel := context.WithTimeout(context.Background(), 1*time.Millisecond)
+ defer cancel()
+
+ cond.L.Lock()
+ defer cond.L.Unlock()
+
+ err := waitOnCond(ctx, cond, func() bool { return false })
+ fmt.Println(err)
+ }()
+ }
+ wg.Wait()
+
+ // Output:
+ // context deadline exceeded
+ // context deadline exceeded
+ // context deadline exceeded
+ // context deadline exceeded
+}
+
+// This example uses AfterFunc to define a function which reads from a net.Conn,
+// stopping the read when a context is canceled.
+func ExampleAfterFunc_connection() {
+ readFromConn := func(ctx context.Context, conn net.Conn, b []byte) (n int, err error) {
+ stopc := make(chan struct{})
+ stop := context.AfterFunc(ctx, func() {
+ conn.SetReadDeadline(time.Now())
+ close(stopc)
+ })
+ n, err = conn.Read(b)
+ if !stop() {
+ // The AfterFunc was started.
+ // Wait for it to complete, and reset the Conn's deadline.
+ <-stopc
+ conn.SetReadDeadline(time.Time{})
+ return n, ctx.Err()
+ }
+ return n, err
+ }
+
+ listener, err := net.Listen("tcp", ":0")
+ if err != nil {
+ fmt.Println(err)
+ return
+ }
+ defer listener.Close()
+
+ conn, err := net.Dial(listener.Addr().Network(), listener.Addr().String())
+ if err != nil {
+ fmt.Println(err)
+ return
+ }
+ defer conn.Close()
+
+ ctx, cancel := context.WithTimeout(context.Background(), 1*time.Millisecond)
+ defer cancel()
+
+ b := make([]byte, 1024)
+ _, err = readFromConn(ctx, conn, b)
+ fmt.Println(err)
+
+ // Output:
+ // context deadline exceeded
+}
+
+// This example uses AfterFunc to define a function which combines
+// the cancellation signals of two Contexts.
+func ExampleAfterFunc_merge() {
+ // mergeCancel returns a context that contains the values of ctx,
+ // and which is canceled when either ctx or cancelCtx is canceled.
+ mergeCancel := func(ctx, cancelCtx context.Context) (context.Context, context.CancelFunc) {
+ ctx, cancel := context.WithCancelCause(ctx)
+ stop := context.AfterFunc(cancelCtx, func() {
+ cancel(context.Cause(cancelCtx))
+ })
+ return ctx, func() {
+ stop()
+ cancel(context.Canceled)
+ }
+ }
+
+ ctx1, cancel1 := context.WithCancelCause(context.Background())
+ defer cancel1(errors.New("ctx1 canceled"))
+
+ ctx2, cancel2 := context.WithCancelCause(context.Background())
+
+ mergedCtx, mergedCancel := mergeCancel(ctx1, ctx2)
+ defer mergedCancel()
+
+ cancel2(errors.New("ctx2 canceled"))
+ <-mergedCtx.Done()
+ fmt.Println(context.Cause(mergedCtx))
+
+ // Output:
+ // ctx2 canceled
+}
diff --git a/src/context/net_test.go b/src/context/net_test.go
new file mode 100644
index 0000000..a007689
--- /dev/null
+++ b/src/context/net_test.go
@@ -0,0 +1,21 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package context_test
+
+import (
+ "context"
+ "net"
+ "testing"
+)
+
+func TestDeadlineExceededIsNetError(t *testing.T) {
+ err, ok := context.DeadlineExceeded.(net.Error)
+ if !ok {
+ t.Fatal("DeadlineExceeded does not implement net.Error")
+ }
+ if !err.Timeout() || !err.Temporary() {
+ t.Fatalf("Timeout() = %v, Temporary() = %v, want true, true", err.Timeout(), err.Temporary())
+ }
+}
diff --git a/src/context/x_test.go b/src/context/x_test.go
new file mode 100644
index 0000000..57fe60b
--- /dev/null
+++ b/src/context/x_test.go
@@ -0,0 +1,956 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package context_test
+
+import (
+ . "context"
+ "errors"
+ "fmt"
+ "math/rand"
+ "runtime"
+ "strings"
+ "sync"
+ "testing"
+ "time"
+)
+
+// Each XTestFoo in context_test.go must be called from a TestFoo here to run.
+func TestParentFinishesChild(t *testing.T) {
+ XTestParentFinishesChild(t) // uses unexported context types
+}
+func TestChildFinishesFirst(t *testing.T) {
+ XTestChildFinishesFirst(t) // uses unexported context types
+}
+func TestCancelRemoves(t *testing.T) {
+ XTestCancelRemoves(t) // uses unexported context types
+}
+func TestCustomContextGoroutines(t *testing.T) {
+ XTestCustomContextGoroutines(t) // reads the context.goroutines counter
+}
+
+// The following are regular tests in package context_test.
+
+// otherContext is a Context that's not one of the types defined in context.go.
+// This lets us test code paths that differ based on the underlying type of the
+// Context.
+type otherContext struct {
+ Context
+}
+
+const (
+ shortDuration = 1 * time.Millisecond // a reasonable duration to block in a test
+ veryLongDuration = 1000 * time.Hour // an arbitrary upper bound on the test's running time
+)
+
+// quiescent returns an arbitrary duration by which the program should have
+// completed any remaining work and reached a steady (idle) state.
+func quiescent(t *testing.T) time.Duration {
+ deadline, ok := t.Deadline()
+ if !ok {
+ return 5 * time.Second
+ }
+
+ const arbitraryCleanupMargin = 1 * time.Second
+ return time.Until(deadline) - arbitraryCleanupMargin
+}
+func TestBackground(t *testing.T) {
+ c := Background()
+ if c == nil {
+ t.Fatalf("Background returned nil")
+ }
+ select {
+ case x := <-c.Done():
+ t.Errorf("<-c.Done() == %v want nothing (it should block)", x)
+ default:
+ }
+ if got, want := fmt.Sprint(c), "context.Background"; got != want {
+ t.Errorf("Background().String() = %q want %q", got, want)
+ }
+}
+
+func TestTODO(t *testing.T) {
+ c := TODO()
+ if c == nil {
+ t.Fatalf("TODO returned nil")
+ }
+ select {
+ case x := <-c.Done():
+ t.Errorf("<-c.Done() == %v want nothing (it should block)", x)
+ default:
+ }
+ if got, want := fmt.Sprint(c), "context.TODO"; got != want {
+ t.Errorf("TODO().String() = %q want %q", got, want)
+ }
+}
+
+func TestWithCancel(t *testing.T) {
+ c1, cancel := WithCancel(Background())
+
+ if got, want := fmt.Sprint(c1), "context.Background.WithCancel"; got != want {
+ t.Errorf("c1.String() = %q want %q", got, want)
+ }
+
+ o := otherContext{c1}
+ c2, _ := WithCancel(o)
+ contexts := []Context{c1, o, c2}
+
+ for i, c := range contexts {
+ if d := c.Done(); d == nil {
+ t.Errorf("c[%d].Done() == %v want non-nil", i, d)
+ }
+ if e := c.Err(); e != nil {
+ t.Errorf("c[%d].Err() == %v want nil", i, e)
+ }
+
+ select {
+ case x := <-c.Done():
+ t.Errorf("<-c.Done() == %v want nothing (it should block)", x)
+ default:
+ }
+ }
+
+ cancel() // Should propagate synchronously.
+ for i, c := range contexts {
+ select {
+ case <-c.Done():
+ default:
+ t.Errorf("<-c[%d].Done() blocked, but shouldn't have", i)
+ }
+ if e := c.Err(); e != Canceled {
+ t.Errorf("c[%d].Err() == %v want %v", i, e, Canceled)
+ }
+ }
+}
+
+func testDeadline(c Context, name string, t *testing.T) {
+ t.Helper()
+ d := quiescent(t)
+ timer := time.NewTimer(d)
+ defer timer.Stop()
+ select {
+ case <-timer.C:
+ t.Fatalf("%s: context not timed out after %v", name, d)
+ case <-c.Done():
+ }
+ if e := c.Err(); e != DeadlineExceeded {
+ t.Errorf("%s: c.Err() == %v; want %v", name, e, DeadlineExceeded)
+ }
+}
+
+func TestDeadline(t *testing.T) {
+ t.Parallel()
+
+ c, _ := WithDeadline(Background(), time.Now().Add(shortDuration))
+ if got, prefix := fmt.Sprint(c), "context.Background.WithDeadline("; !strings.HasPrefix(got, prefix) {
+ t.Errorf("c.String() = %q want prefix %q", got, prefix)
+ }
+ testDeadline(c, "WithDeadline", t)
+
+ c, _ = WithDeadline(Background(), time.Now().Add(shortDuration))
+ o := otherContext{c}
+ testDeadline(o, "WithDeadline+otherContext", t)
+
+ c, _ = WithDeadline(Background(), time.Now().Add(shortDuration))
+ o = otherContext{c}
+ c, _ = WithDeadline(o, time.Now().Add(veryLongDuration))
+ testDeadline(c, "WithDeadline+otherContext+WithDeadline", t)
+
+ c, _ = WithDeadline(Background(), time.Now().Add(-shortDuration))
+ testDeadline(c, "WithDeadline+inthepast", t)
+
+ c, _ = WithDeadline(Background(), time.Now())
+ testDeadline(c, "WithDeadline+now", t)
+}
+
+func TestTimeout(t *testing.T) {
+ t.Parallel()
+
+ c, _ := WithTimeout(Background(), shortDuration)
+ if got, prefix := fmt.Sprint(c), "context.Background.WithDeadline("; !strings.HasPrefix(got, prefix) {
+ t.Errorf("c.String() = %q want prefix %q", got, prefix)
+ }
+ testDeadline(c, "WithTimeout", t)
+
+ c, _ = WithTimeout(Background(), shortDuration)
+ o := otherContext{c}
+ testDeadline(o, "WithTimeout+otherContext", t)
+
+ c, _ = WithTimeout(Background(), shortDuration)
+ o = otherContext{c}
+ c, _ = WithTimeout(o, veryLongDuration)
+ testDeadline(c, "WithTimeout+otherContext+WithTimeout", t)
+}
+
+func TestCanceledTimeout(t *testing.T) {
+ c, _ := WithTimeout(Background(), time.Second)
+ o := otherContext{c}
+ c, cancel := WithTimeout(o, veryLongDuration)
+ cancel() // Should propagate synchronously.
+ select {
+ case <-c.Done():
+ default:
+ t.Errorf("<-c.Done() blocked, but shouldn't have")
+ }
+ if e := c.Err(); e != Canceled {
+ t.Errorf("c.Err() == %v want %v", e, Canceled)
+ }
+}
+
+type key1 int
+type key2 int
+
+var k1 = key1(1)
+var k2 = key2(1) // same int as k1, different type
+var k3 = key2(3) // same type as k2, different int
+
+func TestValues(t *testing.T) {
+ check := func(c Context, nm, v1, v2, v3 string) {
+ if v, ok := c.Value(k1).(string); ok == (len(v1) == 0) || v != v1 {
+ t.Errorf(`%s.Value(k1).(string) = %q, %t want %q, %t`, nm, v, ok, v1, len(v1) != 0)
+ }
+ if v, ok := c.Value(k2).(string); ok == (len(v2) == 0) || v != v2 {
+ t.Errorf(`%s.Value(k2).(string) = %q, %t want %q, %t`, nm, v, ok, v2, len(v2) != 0)
+ }
+ if v, ok := c.Value(k3).(string); ok == (len(v3) == 0) || v != v3 {
+ t.Errorf(`%s.Value(k3).(string) = %q, %t want %q, %t`, nm, v, ok, v3, len(v3) != 0)
+ }
+ }
+
+ c0 := Background()
+ check(c0, "c0", "", "", "")
+
+ c1 := WithValue(Background(), k1, "c1k1")
+ check(c1, "c1", "c1k1", "", "")
+
+ if got, want := fmt.Sprint(c1), `context.Background.WithValue(type context_test.key1, val c1k1)`; got != want {
+ t.Errorf("c.String() = %q want %q", got, want)
+ }
+
+ c2 := WithValue(c1, k2, "c2k2")
+ check(c2, "c2", "c1k1", "c2k2", "")
+
+ c3 := WithValue(c2, k3, "c3k3")
+ check(c3, "c2", "c1k1", "c2k2", "c3k3")
+
+ c4 := WithValue(c3, k1, nil)
+ check(c4, "c4", "", "c2k2", "c3k3")
+
+ o0 := otherContext{Background()}
+ check(o0, "o0", "", "", "")
+
+ o1 := otherContext{WithValue(Background(), k1, "c1k1")}
+ check(o1, "o1", "c1k1", "", "")
+
+ o2 := WithValue(o1, k2, "o2k2")
+ check(o2, "o2", "c1k1", "o2k2", "")
+
+ o3 := otherContext{c4}
+ check(o3, "o3", "", "c2k2", "c3k3")
+
+ o4 := WithValue(o3, k3, nil)
+ check(o4, "o4", "", "c2k2", "")
+}
+
+func TestAllocs(t *testing.T) {
+ bg := Background()
+ for _, test := range []struct {
+ desc string
+ f func()
+ limit float64
+ gccgoLimit float64
+ }{
+ {
+ desc: "Background()",
+ f: func() { Background() },
+ limit: 0,
+ gccgoLimit: 0,
+ },
+ {
+ desc: fmt.Sprintf("WithValue(bg, %v, nil)", k1),
+ f: func() {
+ c := WithValue(bg, k1, nil)
+ c.Value(k1)
+ },
+ limit: 3,
+ gccgoLimit: 3,
+ },
+ {
+ desc: "WithTimeout(bg, 1*time.Nanosecond)",
+ f: func() {
+ c, _ := WithTimeout(bg, 1*time.Nanosecond)
+ <-c.Done()
+ },
+ limit: 12,
+ gccgoLimit: 15,
+ },
+ {
+ desc: "WithCancel(bg)",
+ f: func() {
+ c, cancel := WithCancel(bg)
+ cancel()
+ <-c.Done()
+ },
+ limit: 5,
+ gccgoLimit: 8,
+ },
+ {
+ desc: "WithTimeout(bg, 5*time.Millisecond)",
+ f: func() {
+ c, cancel := WithTimeout(bg, 5*time.Millisecond)
+ cancel()
+ <-c.Done()
+ },
+ limit: 8,
+ gccgoLimit: 25,
+ },
+ } {
+ limit := test.limit
+ if runtime.Compiler == "gccgo" {
+ // gccgo does not yet do escape analysis.
+ // TODO(iant): Remove this when gccgo does do escape analysis.
+ limit = test.gccgoLimit
+ }
+ numRuns := 100
+ if testing.Short() {
+ numRuns = 10
+ }
+ if n := testing.AllocsPerRun(numRuns, test.f); n > limit {
+ t.Errorf("%s allocs = %f want %d", test.desc, n, int(limit))
+ }
+ }
+}
+
+func TestSimultaneousCancels(t *testing.T) {
+ root, cancel := WithCancel(Background())
+ m := map[Context]CancelFunc{root: cancel}
+ q := []Context{root}
+ // Create a tree of contexts.
+ for len(q) != 0 && len(m) < 100 {
+ parent := q[0]
+ q = q[1:]
+ for i := 0; i < 4; i++ {
+ ctx, cancel := WithCancel(parent)
+ m[ctx] = cancel
+ q = append(q, ctx)
+ }
+ }
+ // Start all the cancels in a random order.
+ var wg sync.WaitGroup
+ wg.Add(len(m))
+ for _, cancel := range m {
+ go func(cancel CancelFunc) {
+ cancel()
+ wg.Done()
+ }(cancel)
+ }
+
+ d := quiescent(t)
+ stuck := make(chan struct{})
+ timer := time.AfterFunc(d, func() { close(stuck) })
+ defer timer.Stop()
+
+ // Wait on all the contexts in a random order.
+ for ctx := range m {
+ select {
+ case <-ctx.Done():
+ case <-stuck:
+ buf := make([]byte, 10<<10)
+ n := runtime.Stack(buf, true)
+ t.Fatalf("timed out after %v waiting for <-ctx.Done(); stacks:\n%s", d, buf[:n])
+ }
+ }
+ // Wait for all the cancel functions to return.
+ done := make(chan struct{})
+ go func() {
+ wg.Wait()
+ close(done)
+ }()
+ select {
+ case <-done:
+ case <-stuck:
+ buf := make([]byte, 10<<10)
+ n := runtime.Stack(buf, true)
+ t.Fatalf("timed out after %v waiting for cancel functions; stacks:\n%s", d, buf[:n])
+ }
+}
+
+func TestInterlockedCancels(t *testing.T) {
+ parent, cancelParent := WithCancel(Background())
+ child, cancelChild := WithCancel(parent)
+ go func() {
+ <-parent.Done()
+ cancelChild()
+ }()
+ cancelParent()
+ d := quiescent(t)
+ timer := time.NewTimer(d)
+ defer timer.Stop()
+ select {
+ case <-child.Done():
+ case <-timer.C:
+ buf := make([]byte, 10<<10)
+ n := runtime.Stack(buf, true)
+ t.Fatalf("timed out after %v waiting for child.Done(); stacks:\n%s", d, buf[:n])
+ }
+}
+
+func TestLayersCancel(t *testing.T) {
+ testLayers(t, time.Now().UnixNano(), false)
+}
+
+func TestLayersTimeout(t *testing.T) {
+ testLayers(t, time.Now().UnixNano(), true)
+}
+
+func testLayers(t *testing.T, seed int64, testTimeout bool) {
+ t.Parallel()
+
+ r := rand.New(rand.NewSource(seed))
+ errorf := func(format string, a ...any) {
+ t.Errorf(fmt.Sprintf("seed=%d: %s", seed, format), a...)
+ }
+ const (
+ minLayers = 30
+ )
+ type value int
+ var (
+ vals []*value
+ cancels []CancelFunc
+ numTimers int
+ ctx = Background()
+ )
+ for i := 0; i < minLayers || numTimers == 0 || len(cancels) == 0 || len(vals) == 0; i++ {
+ switch r.Intn(3) {
+ case 0:
+ v := new(value)
+ ctx = WithValue(ctx, v, v)
+ vals = append(vals, v)
+ case 1:
+ var cancel CancelFunc
+ ctx, cancel = WithCancel(ctx)
+ cancels = append(cancels, cancel)
+ case 2:
+ var cancel CancelFunc
+ d := veryLongDuration
+ if testTimeout {
+ d = shortDuration
+ }
+ ctx, cancel = WithTimeout(ctx, d)
+ cancels = append(cancels, cancel)
+ numTimers++
+ }
+ }
+ checkValues := func(when string) {
+ for _, key := range vals {
+ if val := ctx.Value(key).(*value); key != val {
+ errorf("%s: ctx.Value(%p) = %p want %p", when, key, val, key)
+ }
+ }
+ }
+ if !testTimeout {
+ select {
+ case <-ctx.Done():
+ errorf("ctx should not be canceled yet")
+ default:
+ }
+ }
+ if s, prefix := fmt.Sprint(ctx), "context.Background."; !strings.HasPrefix(s, prefix) {
+ t.Errorf("ctx.String() = %q want prefix %q", s, prefix)
+ }
+ t.Log(ctx)
+ checkValues("before cancel")
+ if testTimeout {
+ d := quiescent(t)
+ timer := time.NewTimer(d)
+ defer timer.Stop()
+ select {
+ case <-ctx.Done():
+ case <-timer.C:
+ errorf("ctx should have timed out after %v", d)
+ }
+ checkValues("after timeout")
+ } else {
+ cancel := cancels[r.Intn(len(cancels))]
+ cancel()
+ select {
+ case <-ctx.Done():
+ default:
+ errorf("ctx should be canceled")
+ }
+ checkValues("after cancel")
+ }
+}
+
+func TestWithCancelCanceledParent(t *testing.T) {
+ parent, pcancel := WithCancelCause(Background())
+ cause := fmt.Errorf("Because!")
+ pcancel(cause)
+
+ c, _ := WithCancel(parent)
+ select {
+ case <-c.Done():
+ default:
+ t.Errorf("child not done immediately upon construction")
+ }
+ if got, want := c.Err(), Canceled; got != want {
+ t.Errorf("child not canceled; got = %v, want = %v", got, want)
+ }
+ if got, want := Cause(c), cause; got != want {
+ t.Errorf("child has wrong cause; got = %v, want = %v", got, want)
+ }
+}
+
+func TestWithCancelSimultaneouslyCanceledParent(t *testing.T) {
+ // Cancel the parent goroutine concurrently with creating a child.
+ for i := 0; i < 100; i++ {
+ parent, pcancel := WithCancelCause(Background())
+ cause := fmt.Errorf("Because!")
+ go pcancel(cause)
+
+ c, _ := WithCancel(parent)
+ <-c.Done()
+ if got, want := c.Err(), Canceled; got != want {
+ t.Errorf("child not canceled; got = %v, want = %v", got, want)
+ }
+ if got, want := Cause(c), cause; got != want {
+ t.Errorf("child has wrong cause; got = %v, want = %v", got, want)
+ }
+ }
+}
+
+func TestWithValueChecksKey(t *testing.T) {
+ panicVal := recoveredValue(func() { _ = WithValue(Background(), []byte("foo"), "bar") })
+ if panicVal == nil {
+ t.Error("expected panic")
+ }
+ panicVal = recoveredValue(func() { _ = WithValue(Background(), nil, "bar") })
+ if got, want := fmt.Sprint(panicVal), "nil key"; got != want {
+ t.Errorf("panic = %q; want %q", got, want)
+ }
+}
+
+func TestInvalidDerivedFail(t *testing.T) {
+ panicVal := recoveredValue(func() { _, _ = WithCancel(nil) })
+ if panicVal == nil {
+ t.Error("expected panic")
+ }
+ panicVal = recoveredValue(func() { _, _ = WithDeadline(nil, time.Now().Add(shortDuration)) })
+ if panicVal == nil {
+ t.Error("expected panic")
+ }
+ panicVal = recoveredValue(func() { _ = WithValue(nil, "foo", "bar") })
+ if panicVal == nil {
+ t.Error("expected panic")
+ }
+}
+
+func recoveredValue(fn func()) (v any) {
+ defer func() { v = recover() }()
+ fn()
+ return
+}
+
+func TestDeadlineExceededSupportsTimeout(t *testing.T) {
+ i, ok := DeadlineExceeded.(interface {
+ Timeout() bool
+ })
+ if !ok {
+ t.Fatal("DeadlineExceeded does not support Timeout interface")
+ }
+ if !i.Timeout() {
+ t.Fatal("wrong value for timeout")
+ }
+}
+func TestCause(t *testing.T) {
+ var (
+ forever = 1e6 * time.Second
+ parentCause = fmt.Errorf("parentCause")
+ childCause = fmt.Errorf("childCause")
+ tooSlow = fmt.Errorf("tooSlow")
+ finishedEarly = fmt.Errorf("finishedEarly")
+ )
+ for _, test := range []struct {
+ name string
+ ctx func() Context
+ err error
+ cause error
+ }{
+ {
+ name: "Background",
+ ctx: Background,
+ err: nil,
+ cause: nil,
+ },
+ {
+ name: "TODO",
+ ctx: TODO,
+ err: nil,
+ cause: nil,
+ },
+ {
+ name: "WithCancel",
+ ctx: func() Context {
+ ctx, cancel := WithCancel(Background())
+ cancel()
+ return ctx
+ },
+ err: Canceled,
+ cause: Canceled,
+ },
+ {
+ name: "WithCancelCause",
+ ctx: func() Context {
+ ctx, cancel := WithCancelCause(Background())
+ cancel(parentCause)
+ return ctx
+ },
+ err: Canceled,
+ cause: parentCause,
+ },
+ {
+ name: "WithCancelCause nil",
+ ctx: func() Context {
+ ctx, cancel := WithCancelCause(Background())
+ cancel(nil)
+ return ctx
+ },
+ err: Canceled,
+ cause: Canceled,
+ },
+ {
+ name: "WithCancelCause: parent cause before child",
+ ctx: func() Context {
+ ctx, cancelParent := WithCancelCause(Background())
+ ctx, cancelChild := WithCancelCause(ctx)
+ cancelParent(parentCause)
+ cancelChild(childCause)
+ return ctx
+ },
+ err: Canceled,
+ cause: parentCause,
+ },
+ {
+ name: "WithCancelCause: parent cause after child",
+ ctx: func() Context {
+ ctx, cancelParent := WithCancelCause(Background())
+ ctx, cancelChild := WithCancelCause(ctx)
+ cancelChild(childCause)
+ cancelParent(parentCause)
+ return ctx
+ },
+ err: Canceled,
+ cause: childCause,
+ },
+ {
+ name: "WithCancelCause: parent cause before nil",
+ ctx: func() Context {
+ ctx, cancelParent := WithCancelCause(Background())
+ ctx, cancelChild := WithCancel(ctx)
+ cancelParent(parentCause)
+ cancelChild()
+ return ctx
+ },
+ err: Canceled,
+ cause: parentCause,
+ },
+ {
+ name: "WithCancelCause: parent cause after nil",
+ ctx: func() Context {
+ ctx, cancelParent := WithCancelCause(Background())
+ ctx, cancelChild := WithCancel(ctx)
+ cancelChild()
+ cancelParent(parentCause)
+ return ctx
+ },
+ err: Canceled,
+ cause: Canceled,
+ },
+ {
+ name: "WithCancelCause: child cause after nil",
+ ctx: func() Context {
+ ctx, cancelParent := WithCancel(Background())
+ ctx, cancelChild := WithCancelCause(ctx)
+ cancelParent()
+ cancelChild(childCause)
+ return ctx
+ },
+ err: Canceled,
+ cause: Canceled,
+ },
+ {
+ name: "WithCancelCause: child cause before nil",
+ ctx: func() Context {
+ ctx, cancelParent := WithCancel(Background())
+ ctx, cancelChild := WithCancelCause(ctx)
+ cancelChild(childCause)
+ cancelParent()
+ return ctx
+ },
+ err: Canceled,
+ cause: childCause,
+ },
+ {
+ name: "WithTimeout",
+ ctx: func() Context {
+ ctx, cancel := WithTimeout(Background(), 0)
+ cancel()
+ return ctx
+ },
+ err: DeadlineExceeded,
+ cause: DeadlineExceeded,
+ },
+ {
+ name: "WithTimeout canceled",
+ ctx: func() Context {
+ ctx, cancel := WithTimeout(Background(), forever)
+ cancel()
+ return ctx
+ },
+ err: Canceled,
+ cause: Canceled,
+ },
+ {
+ name: "WithTimeoutCause",
+ ctx: func() Context {
+ ctx, cancel := WithTimeoutCause(Background(), 0, tooSlow)
+ cancel()
+ return ctx
+ },
+ err: DeadlineExceeded,
+ cause: tooSlow,
+ },
+ {
+ name: "WithTimeoutCause canceled",
+ ctx: func() Context {
+ ctx, cancel := WithTimeoutCause(Background(), forever, tooSlow)
+ cancel()
+ return ctx
+ },
+ err: Canceled,
+ cause: Canceled,
+ },
+ {
+ name: "WithTimeoutCause stacked",
+ ctx: func() Context {
+ ctx, cancel := WithCancelCause(Background())
+ ctx, _ = WithTimeoutCause(ctx, 0, tooSlow)
+ cancel(finishedEarly)
+ return ctx
+ },
+ err: DeadlineExceeded,
+ cause: tooSlow,
+ },
+ {
+ name: "WithTimeoutCause stacked canceled",
+ ctx: func() Context {
+ ctx, cancel := WithCancelCause(Background())
+ ctx, _ = WithTimeoutCause(ctx, forever, tooSlow)
+ cancel(finishedEarly)
+ return ctx
+ },
+ err: Canceled,
+ cause: finishedEarly,
+ },
+ {
+ name: "WithoutCancel",
+ ctx: func() Context {
+ return WithoutCancel(Background())
+ },
+ err: nil,
+ cause: nil,
+ },
+ {
+ name: "WithoutCancel canceled",
+ ctx: func() Context {
+ ctx, cancel := WithCancelCause(Background())
+ ctx = WithoutCancel(ctx)
+ cancel(finishedEarly)
+ return ctx
+ },
+ err: nil,
+ cause: nil,
+ },
+ {
+ name: "WithoutCancel timeout",
+ ctx: func() Context {
+ ctx, cancel := WithTimeoutCause(Background(), 0, tooSlow)
+ ctx = WithoutCancel(ctx)
+ cancel()
+ return ctx
+ },
+ err: nil,
+ cause: nil,
+ },
+ } {
+ test := test
+ t.Run(test.name, func(t *testing.T) {
+ t.Parallel()
+ ctx := test.ctx()
+ if got, want := ctx.Err(), test.err; want != got {
+ t.Errorf("ctx.Err() = %v want %v", got, want)
+ }
+ if got, want := Cause(ctx), test.cause; want != got {
+ t.Errorf("Cause(ctx) = %v want %v", got, want)
+ }
+ })
+ }
+}
+
+func TestCauseRace(t *testing.T) {
+ cause := errors.New("TestCauseRace")
+ ctx, cancel := WithCancelCause(Background())
+ go func() {
+ cancel(cause)
+ }()
+ for {
+ // Poll Cause, rather than waiting for Done, to test that
+ // access to the underlying cause is synchronized properly.
+ if err := Cause(ctx); err != nil {
+ if err != cause {
+ t.Errorf("Cause returned %v, want %v", err, cause)
+ }
+ break
+ }
+ runtime.Gosched()
+ }
+}
+
+func TestWithoutCancel(t *testing.T) {
+ key, value := "key", "value"
+ ctx := WithValue(Background(), key, value)
+ ctx = WithoutCancel(ctx)
+ if d, ok := ctx.Deadline(); !d.IsZero() || ok != false {
+ t.Errorf("ctx.Deadline() = %v, %v want zero, false", d, ok)
+ }
+ if done := ctx.Done(); done != nil {
+ t.Errorf("ctx.Deadline() = %v want nil", done)
+ }
+ if err := ctx.Err(); err != nil {
+ t.Errorf("ctx.Err() = %v want nil", err)
+ }
+ if v := ctx.Value(key); v != value {
+ t.Errorf("ctx.Value(%q) = %q want %q", key, v, value)
+ }
+}
+
+type customDoneContext struct {
+ Context
+ donec chan struct{}
+}
+
+func (c *customDoneContext) Done() <-chan struct{} {
+ return c.donec
+}
+
+func TestCustomContextPropagation(t *testing.T) {
+ cause := errors.New("TestCustomContextPropagation")
+ donec := make(chan struct{})
+ ctx1, cancel1 := WithCancelCause(Background())
+ ctx2 := &customDoneContext{
+ Context: ctx1,
+ donec: donec,
+ }
+ ctx3, cancel3 := WithCancel(ctx2)
+ defer cancel3()
+
+ cancel1(cause)
+ close(donec)
+
+ <-ctx3.Done()
+ if got, want := ctx3.Err(), Canceled; got != want {
+ t.Errorf("child not canceled; got = %v, want = %v", got, want)
+ }
+ if got, want := Cause(ctx3), cause; got != want {
+ t.Errorf("child has wrong cause; got = %v, want = %v", got, want)
+ }
+}
+
+func TestAfterFuncCalledAfterCancel(t *testing.T) {
+ ctx, cancel := WithCancel(Background())
+ donec := make(chan struct{})
+ stop := AfterFunc(ctx, func() {
+ close(donec)
+ })
+ select {
+ case <-donec:
+ t.Fatalf("AfterFunc called before context is done")
+ case <-time.After(shortDuration):
+ }
+ cancel()
+ select {
+ case <-donec:
+ case <-time.After(veryLongDuration):
+ t.Fatalf("AfterFunc not called after context is canceled")
+ }
+ if stop() {
+ t.Fatalf("stop() = true, want false")
+ }
+}
+
+func TestAfterFuncCalledAfterTimeout(t *testing.T) {
+ ctx, cancel := WithTimeout(Background(), shortDuration)
+ defer cancel()
+ donec := make(chan struct{})
+ AfterFunc(ctx, func() {
+ close(donec)
+ })
+ select {
+ case <-donec:
+ case <-time.After(veryLongDuration):
+ t.Fatalf("AfterFunc not called after context is canceled")
+ }
+}
+
+func TestAfterFuncCalledImmediately(t *testing.T) {
+ ctx, cancel := WithCancel(Background())
+ cancel()
+ donec := make(chan struct{})
+ AfterFunc(ctx, func() {
+ close(donec)
+ })
+ select {
+ case <-donec:
+ case <-time.After(veryLongDuration):
+ t.Fatalf("AfterFunc not called for already-canceled context")
+ }
+}
+
+func TestAfterFuncNotCalledAfterStop(t *testing.T) {
+ ctx, cancel := WithCancel(Background())
+ donec := make(chan struct{})
+ stop := AfterFunc(ctx, func() {
+ close(donec)
+ })
+ if !stop() {
+ t.Fatalf("stop() = false, want true")
+ }
+ cancel()
+ select {
+ case <-donec:
+ t.Fatalf("AfterFunc called for already-canceled context")
+ case <-time.After(shortDuration):
+ }
+ if stop() {
+ t.Fatalf("stop() = true, want false")
+ }
+}
+
+// This test verifies that cancelling a context does not block waiting for AfterFuncs to finish.
+func TestAfterFuncCalledAsynchronously(t *testing.T) {
+ ctx, cancel := WithCancel(Background())
+ donec := make(chan struct{})
+ stop := AfterFunc(ctx, func() {
+ // The channel send blocks until donec is read from.
+ donec <- struct{}{}
+ })
+ defer stop()
+ cancel()
+ // After cancel returns, read from donec and unblock the AfterFunc.
+ select {
+ case <-donec:
+ case <-time.After(veryLongDuration):
+ t.Fatalf("AfterFunc not called after context is canceled")
+ }
+}
generated by cgit v1.2.3 (git 2.39.1) at 2024-11-30 23:58:52 +0000