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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-28 12:36:04 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-28 12:36:04 +0000 |
commit | b09c6d56832eb1718c07d74abf3bc6ae3fe4e030 (patch) | |
tree | d2caec2610d4ea887803ec9e9c3cd77136c448ba /dependencies/pkg/mod/golang.org/x/sync@v0.0.0-20210220032951-036812b2e83c/singleflight/singleflight.go | |
parent | Initial commit. (diff) | |
download | icingadb-b09c6d56832eb1718c07d74abf3bc6ae3fe4e030.tar.xz icingadb-b09c6d56832eb1718c07d74abf3bc6ae3fe4e030.zip |
Adding upstream version 1.1.0.upstream/1.1.0upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'dependencies/pkg/mod/golang.org/x/sync@v0.0.0-20210220032951-036812b2e83c/singleflight/singleflight.go')
-rw-r--r-- | dependencies/pkg/mod/golang.org/x/sync@v0.0.0-20210220032951-036812b2e83c/singleflight/singleflight.go | 212 |
1 files changed, 212 insertions, 0 deletions
diff --git a/dependencies/pkg/mod/golang.org/x/sync@v0.0.0-20210220032951-036812b2e83c/singleflight/singleflight.go b/dependencies/pkg/mod/golang.org/x/sync@v0.0.0-20210220032951-036812b2e83c/singleflight/singleflight.go new file mode 100644 index 0000000..690eb85 --- /dev/null +++ b/dependencies/pkg/mod/golang.org/x/sync@v0.0.0-20210220032951-036812b2e83c/singleflight/singleflight.go @@ -0,0 +1,212 @@ +// Copyright 2013 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 singleflight provides a duplicate function call suppression +// mechanism. +package singleflight // import "golang.org/x/sync/singleflight" + +import ( + "bytes" + "errors" + "fmt" + "runtime" + "runtime/debug" + "sync" +) + +// errGoexit indicates the runtime.Goexit was called in +// the user given function. +var errGoexit = errors.New("runtime.Goexit was called") + +// A panicError is an arbitrary value recovered from a panic +// with the stack trace during the execution of given function. +type panicError struct { + value interface{} + stack []byte +} + +// Error implements error interface. +func (p *panicError) Error() string { + return fmt.Sprintf("%v\n\n%s", p.value, p.stack) +} + +func newPanicError(v interface{}) error { + stack := debug.Stack() + + // The first line of the stack trace is of the form "goroutine N [status]:" + // but by the time the panic reaches Do the goroutine may no longer exist + // and its status will have changed. Trim out the misleading line. + if line := bytes.IndexByte(stack[:], '\n'); line >= 0 { + stack = stack[line+1:] + } + return &panicError{value: v, stack: stack} +} + +// call is an in-flight or completed singleflight.Do call +type call struct { + wg sync.WaitGroup + + // These fields are written once before the WaitGroup is done + // and are only read after the WaitGroup is done. + val interface{} + err error + + // forgotten indicates whether Forget was called with this call's key + // while the call was still in flight. + forgotten bool + + // These fields are read and written with the singleflight + // mutex held before the WaitGroup is done, and are read but + // not written after the WaitGroup is done. + dups int + chans []chan<- Result +} + +// Group represents a class of work and forms a namespace in +// which units of work can be executed with duplicate suppression. +type Group struct { + mu sync.Mutex // protects m + m map[string]*call // lazily initialized +} + +// Result holds the results of Do, so they can be passed +// on a channel. +type Result struct { + Val interface{} + Err error + Shared bool +} + +// Do executes and returns the results of the given function, making +// sure that only one execution is in-flight for a given key at a +// time. If a duplicate comes in, the duplicate caller waits for the +// original to complete and receives the same results. +// The return value shared indicates whether v was given to multiple callers. +func (g *Group) Do(key string, fn func() (interface{}, error)) (v interface{}, err error, shared bool) { + g.mu.Lock() + if g.m == nil { + g.m = make(map[string]*call) + } + if c, ok := g.m[key]; ok { + c.dups++ + g.mu.Unlock() + c.wg.Wait() + + if e, ok := c.err.(*panicError); ok { + panic(e) + } else if c.err == errGoexit { + runtime.Goexit() + } + return c.val, c.err, true + } + c := new(call) + c.wg.Add(1) + g.m[key] = c + g.mu.Unlock() + + g.doCall(c, key, fn) + return c.val, c.err, c.dups > 0 +} + +// DoChan is like Do but returns a channel that will receive the +// results when they are ready. +// +// The returned channel will not be closed. +func (g *Group) DoChan(key string, fn func() (interface{}, error)) <-chan Result { + ch := make(chan Result, 1) + g.mu.Lock() + if g.m == nil { + g.m = make(map[string]*call) + } + if c, ok := g.m[key]; ok { + c.dups++ + c.chans = append(c.chans, ch) + g.mu.Unlock() + return ch + } + c := &call{chans: []chan<- Result{ch}} + c.wg.Add(1) + g.m[key] = c + g.mu.Unlock() + + go g.doCall(c, key, fn) + + return ch +} + +// doCall handles the single call for a key. +func (g *Group) doCall(c *call, key string, fn func() (interface{}, error)) { + normalReturn := false + recovered := false + + // use double-defer to distinguish panic from runtime.Goexit, + // more details see https://golang.org/cl/134395 + defer func() { + // the given function invoked runtime.Goexit + if !normalReturn && !recovered { + c.err = errGoexit + } + + c.wg.Done() + g.mu.Lock() + defer g.mu.Unlock() + if !c.forgotten { + delete(g.m, key) + } + + if e, ok := c.err.(*panicError); ok { + // In order to prevent the waiting channels from being blocked forever, + // needs to ensure that this panic cannot be recovered. + if len(c.chans) > 0 { + go panic(e) + select {} // Keep this goroutine around so that it will appear in the crash dump. + } else { + panic(e) + } + } else if c.err == errGoexit { + // Already in the process of goexit, no need to call again + } else { + // Normal return + for _, ch := range c.chans { + ch <- Result{c.val, c.err, c.dups > 0} + } + } + }() + + func() { + defer func() { + if !normalReturn { + // Ideally, we would wait to take a stack trace until we've determined + // whether this is a panic or a runtime.Goexit. + // + // Unfortunately, the only way we can distinguish the two is to see + // whether the recover stopped the goroutine from terminating, and by + // the time we know that, the part of the stack trace relevant to the + // panic has been discarded. + if r := recover(); r != nil { + c.err = newPanicError(r) + } + } + }() + + c.val, c.err = fn() + normalReturn = true + }() + + if !normalReturn { + recovered = true + } +} + +// Forget tells the singleflight to forget about a key. Future calls +// to Do for this key will call the function rather than waiting for +// an earlier call to complete. +func (g *Group) Forget(key string) { + g.mu.Lock() + if c, ok := g.m[key]; ok { + c.forgotten = true + } + delete(g.m, key) + g.mu.Unlock() +} |