diff options
Diffstat (limited to 'dependencies/pkg/mod/golang.org/x/sync@v0.0.0-20210220032951-036812b2e83c/syncmap')
6 files changed, 936 insertions, 0 deletions
diff --git a/dependencies/pkg/mod/golang.org/x/sync@v0.0.0-20210220032951-036812b2e83c/syncmap/go19.go b/dependencies/pkg/mod/golang.org/x/sync@v0.0.0-20210220032951-036812b2e83c/syncmap/go19.go new file mode 100644 index 0000000..fa04dba --- /dev/null +++ b/dependencies/pkg/mod/golang.org/x/sync@v0.0.0-20210220032951-036812b2e83c/syncmap/go19.go @@ -0,0 +1,18 @@ +// Copyright 2019 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. + +//go:build go1.9 +// +build go1.9 + +package syncmap + +import "sync" // home to the standard library's sync.map implementation as of Go 1.9 + +// Map is a concurrent map with amortized-constant-time loads, stores, and deletes. +// It is safe for multiple goroutines to call a Map's methods concurrently. +// +// The zero Map is valid and empty. +// +// A Map must not be copied after first use. +type Map = sync.Map diff --git a/dependencies/pkg/mod/golang.org/x/sync@v0.0.0-20210220032951-036812b2e83c/syncmap/map.go b/dependencies/pkg/mod/golang.org/x/sync@v0.0.0-20210220032951-036812b2e83c/syncmap/map.go new file mode 100644 index 0000000..4b638cb --- /dev/null +++ b/dependencies/pkg/mod/golang.org/x/sync@v0.0.0-20210220032951-036812b2e83c/syncmap/map.go @@ -0,0 +1,8 @@ +// Copyright 2019 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 syncmap provides a concurrent map implementation. +// This was the prototype for sync.Map which was added to the standard library's +// sync package in Go 1.9. https://golang.org/pkg/sync/#Map. +package syncmap diff --git a/dependencies/pkg/mod/golang.org/x/sync@v0.0.0-20210220032951-036812b2e83c/syncmap/map_bench_test.go b/dependencies/pkg/mod/golang.org/x/sync@v0.0.0-20210220032951-036812b2e83c/syncmap/map_bench_test.go new file mode 100644 index 0000000..b279b4f --- /dev/null +++ b/dependencies/pkg/mod/golang.org/x/sync@v0.0.0-20210220032951-036812b2e83c/syncmap/map_bench_test.go @@ -0,0 +1,216 @@ +// 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 syncmap_test + +import ( + "fmt" + "reflect" + "sync/atomic" + "testing" + + "golang.org/x/sync/syncmap" +) + +type bench struct { + setup func(*testing.B, mapInterface) + perG func(b *testing.B, pb *testing.PB, i int, m mapInterface) +} + +func benchMap(b *testing.B, bench bench) { + for _, m := range [...]mapInterface{&DeepCopyMap{}, &RWMutexMap{}, &syncmap.Map{}} { + b.Run(fmt.Sprintf("%T", m), func(b *testing.B) { + m = reflect.New(reflect.TypeOf(m).Elem()).Interface().(mapInterface) + if bench.setup != nil { + bench.setup(b, m) + } + + b.ResetTimer() + + var i int64 + b.RunParallel(func(pb *testing.PB) { + id := int(atomic.AddInt64(&i, 1) - 1) + bench.perG(b, pb, id*b.N, m) + }) + }) + } +} + +func BenchmarkLoadMostlyHits(b *testing.B) { + const hits, misses = 1023, 1 + + benchMap(b, bench{ + setup: func(_ *testing.B, m mapInterface) { + for i := 0; i < hits; i++ { + m.LoadOrStore(i, i) + } + // Prime the map to get it into a steady state. + for i := 0; i < hits*2; i++ { + m.Load(i % hits) + } + }, + + perG: func(b *testing.B, pb *testing.PB, i int, m mapInterface) { + for ; pb.Next(); i++ { + m.Load(i % (hits + misses)) + } + }, + }) +} + +func BenchmarkLoadMostlyMisses(b *testing.B) { + const hits, misses = 1, 1023 + + benchMap(b, bench{ + setup: func(_ *testing.B, m mapInterface) { + for i := 0; i < hits; i++ { + m.LoadOrStore(i, i) + } + // Prime the map to get it into a steady state. + for i := 0; i < hits*2; i++ { + m.Load(i % hits) + } + }, + + perG: func(b *testing.B, pb *testing.PB, i int, m mapInterface) { + for ; pb.Next(); i++ { + m.Load(i % (hits + misses)) + } + }, + }) +} + +func BenchmarkLoadOrStoreBalanced(b *testing.B) { + const hits, misses = 128, 128 + + benchMap(b, bench{ + setup: func(b *testing.B, m mapInterface) { + if _, ok := m.(*DeepCopyMap); ok { + b.Skip("DeepCopyMap has quadratic running time.") + } + for i := 0; i < hits; i++ { + m.LoadOrStore(i, i) + } + // Prime the map to get it into a steady state. + for i := 0; i < hits*2; i++ { + m.Load(i % hits) + } + }, + + perG: func(b *testing.B, pb *testing.PB, i int, m mapInterface) { + for ; pb.Next(); i++ { + j := i % (hits + misses) + if j < hits { + if _, ok := m.LoadOrStore(j, i); !ok { + b.Fatalf("unexpected miss for %v", j) + } + } else { + if v, loaded := m.LoadOrStore(i, i); loaded { + b.Fatalf("failed to store %v: existing value %v", i, v) + } + } + } + }, + }) +} + +func BenchmarkLoadOrStoreUnique(b *testing.B) { + benchMap(b, bench{ + setup: func(b *testing.B, m mapInterface) { + if _, ok := m.(*DeepCopyMap); ok { + b.Skip("DeepCopyMap has quadratic running time.") + } + }, + + perG: func(b *testing.B, pb *testing.PB, i int, m mapInterface) { + for ; pb.Next(); i++ { + m.LoadOrStore(i, i) + } + }, + }) +} + +func BenchmarkLoadOrStoreCollision(b *testing.B) { + benchMap(b, bench{ + setup: func(_ *testing.B, m mapInterface) { + m.LoadOrStore(0, 0) + }, + + perG: func(b *testing.B, pb *testing.PB, i int, m mapInterface) { + for ; pb.Next(); i++ { + m.LoadOrStore(0, 0) + } + }, + }) +} + +func BenchmarkRange(b *testing.B) { + const mapSize = 1 << 10 + + benchMap(b, bench{ + setup: func(_ *testing.B, m mapInterface) { + for i := 0; i < mapSize; i++ { + m.Store(i, i) + } + }, + + perG: func(b *testing.B, pb *testing.PB, i int, m mapInterface) { + for ; pb.Next(); i++ { + m.Range(func(_, _ interface{}) bool { return true }) + } + }, + }) +} + +// BenchmarkAdversarialAlloc tests performance when we store a new value +// immediately whenever the map is promoted to clean and otherwise load a +// unique, missing key. +// +// This forces the Load calls to always acquire the map's mutex. +func BenchmarkAdversarialAlloc(b *testing.B) { + benchMap(b, bench{ + perG: func(b *testing.B, pb *testing.PB, i int, m mapInterface) { + var stores, loadsSinceStore int64 + for ; pb.Next(); i++ { + m.Load(i) + if loadsSinceStore++; loadsSinceStore > stores { + m.LoadOrStore(i, stores) + loadsSinceStore = 0 + stores++ + } + } + }, + }) +} + +// BenchmarkAdversarialDelete tests performance when we periodically delete +// one key and add a different one in a large map. +// +// This forces the Load calls to always acquire the map's mutex and periodically +// makes a full copy of the map despite changing only one entry. +func BenchmarkAdversarialDelete(b *testing.B) { + const mapSize = 1 << 10 + + benchMap(b, bench{ + setup: func(_ *testing.B, m mapInterface) { + for i := 0; i < mapSize; i++ { + m.Store(i, i) + } + }, + + perG: func(b *testing.B, pb *testing.PB, i int, m mapInterface) { + for ; pb.Next(); i++ { + m.Load(i) + + if i%mapSize == 0 { + m.Range(func(k, _ interface{}) bool { + m.Delete(k) + return false + }) + m.Store(i, i) + } + } + }, + }) +} diff --git a/dependencies/pkg/mod/golang.org/x/sync@v0.0.0-20210220032951-036812b2e83c/syncmap/map_reference_test.go b/dependencies/pkg/mod/golang.org/x/sync@v0.0.0-20210220032951-036812b2e83c/syncmap/map_reference_test.go new file mode 100644 index 0000000..923c51b --- /dev/null +++ b/dependencies/pkg/mod/golang.org/x/sync@v0.0.0-20210220032951-036812b2e83c/syncmap/map_reference_test.go @@ -0,0 +1,151 @@ +// 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 syncmap_test + +import ( + "sync" + "sync/atomic" +) + +// This file contains reference map implementations for unit-tests. + +// mapInterface is the interface Map implements. +type mapInterface interface { + Load(interface{}) (interface{}, bool) + Store(key, value interface{}) + LoadOrStore(key, value interface{}) (actual interface{}, loaded bool) + Delete(interface{}) + Range(func(key, value interface{}) (shouldContinue bool)) +} + +// RWMutexMap is an implementation of mapInterface using a sync.RWMutex. +type RWMutexMap struct { + mu sync.RWMutex + dirty map[interface{}]interface{} +} + +func (m *RWMutexMap) Load(key interface{}) (value interface{}, ok bool) { + m.mu.RLock() + value, ok = m.dirty[key] + m.mu.RUnlock() + return +} + +func (m *RWMutexMap) Store(key, value interface{}) { + m.mu.Lock() + if m.dirty == nil { + m.dirty = make(map[interface{}]interface{}) + } + m.dirty[key] = value + m.mu.Unlock() +} + +func (m *RWMutexMap) LoadOrStore(key, value interface{}) (actual interface{}, loaded bool) { + m.mu.Lock() + actual, loaded = m.dirty[key] + if !loaded { + actual = value + if m.dirty == nil { + m.dirty = make(map[interface{}]interface{}) + } + m.dirty[key] = value + } + m.mu.Unlock() + return actual, loaded +} + +func (m *RWMutexMap) Delete(key interface{}) { + m.mu.Lock() + delete(m.dirty, key) + m.mu.Unlock() +} + +func (m *RWMutexMap) Range(f func(key, value interface{}) (shouldContinue bool)) { + m.mu.RLock() + keys := make([]interface{}, 0, len(m.dirty)) + for k := range m.dirty { + keys = append(keys, k) + } + m.mu.RUnlock() + + for _, k := range keys { + v, ok := m.Load(k) + if !ok { + continue + } + if !f(k, v) { + break + } + } +} + +// DeepCopyMap is an implementation of mapInterface using a Mutex and +// atomic.Value. It makes deep copies of the map on every write to avoid +// acquiring the Mutex in Load. +type DeepCopyMap struct { + mu sync.Mutex + clean atomic.Value +} + +func (m *DeepCopyMap) Load(key interface{}) (value interface{}, ok bool) { + clean, _ := m.clean.Load().(map[interface{}]interface{}) + value, ok = clean[key] + return value, ok +} + +func (m *DeepCopyMap) Store(key, value interface{}) { + m.mu.Lock() + dirty := m.dirty() + dirty[key] = value + m.clean.Store(dirty) + m.mu.Unlock() +} + +func (m *DeepCopyMap) LoadOrStore(key, value interface{}) (actual interface{}, loaded bool) { + clean, _ := m.clean.Load().(map[interface{}]interface{}) + actual, loaded = clean[key] + if loaded { + return actual, loaded + } + + m.mu.Lock() + // Reload clean in case it changed while we were waiting on m.mu. + clean, _ = m.clean.Load().(map[interface{}]interface{}) + actual, loaded = clean[key] + if !loaded { + dirty := m.dirty() + dirty[key] = value + actual = value + m.clean.Store(dirty) + } + m.mu.Unlock() + return actual, loaded +} + +func (m *DeepCopyMap) Delete(key interface{}) { + m.mu.Lock() + dirty := m.dirty() + delete(dirty, key) + m.clean.Store(dirty) + m.mu.Unlock() +} + +func (m *DeepCopyMap) Range(f func(key, value interface{}) (shouldContinue bool)) { + clean, _ := m.clean.Load().(map[interface{}]interface{}) + for k, v := range clean { + if !f(k, v) { + break + } + } +} + +func (m *DeepCopyMap) dirty() map[interface{}]interface{} { + clean, _ := m.clean.Load().(map[interface{}]interface{}) + dirty := make(map[interface{}]interface{}, len(clean)+1) + for k, v := range clean { + dirty[k] = v + } + return dirty +} diff --git a/dependencies/pkg/mod/golang.org/x/sync@v0.0.0-20210220032951-036812b2e83c/syncmap/map_test.go b/dependencies/pkg/mod/golang.org/x/sync@v0.0.0-20210220032951-036812b2e83c/syncmap/map_test.go new file mode 100644 index 0000000..c883f17 --- /dev/null +++ b/dependencies/pkg/mod/golang.org/x/sync@v0.0.0-20210220032951-036812b2e83c/syncmap/map_test.go @@ -0,0 +1,172 @@ +// 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 syncmap_test + +import ( + "math/rand" + "reflect" + "runtime" + "sync" + "testing" + "testing/quick" + + "golang.org/x/sync/syncmap" +) + +type mapOp string + +const ( + opLoad = mapOp("Load") + opStore = mapOp("Store") + opLoadOrStore = mapOp("LoadOrStore") + opDelete = mapOp("Delete") +) + +var mapOps = [...]mapOp{opLoad, opStore, opLoadOrStore, opDelete} + +// mapCall is a quick.Generator for calls on mapInterface. +type mapCall struct { + op mapOp + k, v interface{} +} + +func (c mapCall) apply(m mapInterface) (interface{}, bool) { + switch c.op { + case opLoad: + return m.Load(c.k) + case opStore: + m.Store(c.k, c.v) + return nil, false + case opLoadOrStore: + return m.LoadOrStore(c.k, c.v) + case opDelete: + m.Delete(c.k) + return nil, false + default: + panic("invalid mapOp") + } +} + +type mapResult struct { + value interface{} + ok bool +} + +func randValue(r *rand.Rand) interface{} { + b := make([]byte, r.Intn(4)) + for i := range b { + b[i] = 'a' + byte(rand.Intn(26)) + } + return string(b) +} + +func (mapCall) Generate(r *rand.Rand, size int) reflect.Value { + c := mapCall{op: mapOps[rand.Intn(len(mapOps))], k: randValue(r)} + switch c.op { + case opStore, opLoadOrStore: + c.v = randValue(r) + } + return reflect.ValueOf(c) +} + +func applyCalls(m mapInterface, calls []mapCall) (results []mapResult, final map[interface{}]interface{}) { + for _, c := range calls { + v, ok := c.apply(m) + results = append(results, mapResult{v, ok}) + } + + final = make(map[interface{}]interface{}) + m.Range(func(k, v interface{}) bool { + final[k] = v + return true + }) + + return results, final +} + +func applyMap(calls []mapCall) ([]mapResult, map[interface{}]interface{}) { + return applyCalls(new(syncmap.Map), calls) +} + +func applyRWMutexMap(calls []mapCall) ([]mapResult, map[interface{}]interface{}) { + return applyCalls(new(RWMutexMap), calls) +} + +func applyDeepCopyMap(calls []mapCall) ([]mapResult, map[interface{}]interface{}) { + return applyCalls(new(DeepCopyMap), calls) +} + +func TestMapMatchesRWMutex(t *testing.T) { + if err := quick.CheckEqual(applyMap, applyRWMutexMap, nil); err != nil { + t.Error(err) + } +} + +func TestMapMatchesDeepCopy(t *testing.T) { + if err := quick.CheckEqual(applyMap, applyDeepCopyMap, nil); err != nil { + t.Error(err) + } +} + +func TestConcurrentRange(t *testing.T) { + const mapSize = 1 << 10 + + m := new(syncmap.Map) + for n := int64(1); n <= mapSize; n++ { + m.Store(n, int64(n)) + } + + done := make(chan struct{}) + var wg sync.WaitGroup + defer func() { + close(done) + wg.Wait() + }() + for g := int64(runtime.GOMAXPROCS(0)); g > 0; g-- { + r := rand.New(rand.NewSource(g)) + wg.Add(1) + go func(g int64) { + defer wg.Done() + for i := int64(0); ; i++ { + select { + case <-done: + return + default: + } + for n := int64(1); n < mapSize; n++ { + if r.Int63n(mapSize) == 0 { + m.Store(n, n*i*g) + } else { + m.Load(n) + } + } + } + }(g) + } + + iters := 1 << 10 + if testing.Short() { + iters = 16 + } + for n := iters; n > 0; n-- { + seen := make(map[int64]bool, mapSize) + + m.Range(func(ki, vi interface{}) bool { + k, v := ki.(int64), vi.(int64) + if v%k != 0 { + t.Fatalf("while Storing multiples of %v, Range saw value %v", k, v) + } + if seen[k] { + t.Fatalf("Range visited key %v twice", k) + } + seen[k] = true + return true + }) + + if len(seen) != mapSize { + t.Fatalf("Range visited %v elements of %v-element Map", len(seen), mapSize) + } + } +} diff --git a/dependencies/pkg/mod/golang.org/x/sync@v0.0.0-20210220032951-036812b2e83c/syncmap/pre_go19.go b/dependencies/pkg/mod/golang.org/x/sync@v0.0.0-20210220032951-036812b2e83c/syncmap/pre_go19.go new file mode 100644 index 0000000..5bba413 --- /dev/null +++ b/dependencies/pkg/mod/golang.org/x/sync@v0.0.0-20210220032951-036812b2e83c/syncmap/pre_go19.go @@ -0,0 +1,371 @@ +// 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. + +//go:build !go1.9 +// +build !go1.9 + +package syncmap + +import ( + "sync" + "sync/atomic" + "unsafe" +) + +// Map is a concurrent map with amortized-constant-time loads, stores, and deletes. +// It is safe for multiple goroutines to call a Map's methods concurrently. +// +// The zero Map is valid and empty. +// +// A Map must not be copied after first use. +type Map struct { + mu sync.Mutex + + // read contains the portion of the map's contents that are safe for + // concurrent access (with or without mu held). + // + // The read field itself is always safe to load, but must only be stored with + // mu held. + // + // Entries stored in read may be updated concurrently without mu, but updating + // a previously-expunged entry requires that the entry be copied to the dirty + // map and unexpunged with mu held. + read atomic.Value // readOnly + + // dirty contains the portion of the map's contents that require mu to be + // held. To ensure that the dirty map can be promoted to the read map quickly, + // it also includes all of the non-expunged entries in the read map. + // + // Expunged entries are not stored in the dirty map. An expunged entry in the + // clean map must be unexpunged and added to the dirty map before a new value + // can be stored to it. + // + // If the dirty map is nil, the next write to the map will initialize it by + // making a shallow copy of the clean map, omitting stale entries. + dirty map[interface{}]*entry + + // misses counts the number of loads since the read map was last updated that + // needed to lock mu to determine whether the key was present. + // + // Once enough misses have occurred to cover the cost of copying the dirty + // map, the dirty map will be promoted to the read map (in the unamended + // state) and the next store to the map will make a new dirty copy. + misses int +} + +// readOnly is an immutable struct stored atomically in the Map.read field. +type readOnly struct { + m map[interface{}]*entry + amended bool // true if the dirty map contains some key not in m. +} + +// expunged is an arbitrary pointer that marks entries which have been deleted +// from the dirty map. +var expunged = unsafe.Pointer(new(interface{})) + +// An entry is a slot in the map corresponding to a particular key. +type entry struct { + // p points to the interface{} value stored for the entry. + // + // If p == nil, the entry has been deleted and m.dirty == nil. + // + // If p == expunged, the entry has been deleted, m.dirty != nil, and the entry + // is missing from m.dirty. + // + // Otherwise, the entry is valid and recorded in m.read.m[key] and, if m.dirty + // != nil, in m.dirty[key]. + // + // An entry can be deleted by atomic replacement with nil: when m.dirty is + // next created, it will atomically replace nil with expunged and leave + // m.dirty[key] unset. + // + // An entry's associated value can be updated by atomic replacement, provided + // p != expunged. If p == expunged, an entry's associated value can be updated + // only after first setting m.dirty[key] = e so that lookups using the dirty + // map find the entry. + p unsafe.Pointer // *interface{} +} + +func newEntry(i interface{}) *entry { + return &entry{p: unsafe.Pointer(&i)} +} + +// Load returns the value stored in the map for a key, or nil if no +// value is present. +// The ok result indicates whether value was found in the map. +func (m *Map) Load(key interface{}) (value interface{}, ok bool) { + read, _ := m.read.Load().(readOnly) + e, ok := read.m[key] + if !ok && read.amended { + m.mu.Lock() + // Avoid reporting a spurious miss if m.dirty got promoted while we were + // blocked on m.mu. (If further loads of the same key will not miss, it's + // not worth copying the dirty map for this key.) + read, _ = m.read.Load().(readOnly) + e, ok = read.m[key] + if !ok && read.amended { + e, ok = m.dirty[key] + // Regardless of whether the entry was present, record a miss: this key + // will take the slow path until the dirty map is promoted to the read + // map. + m.missLocked() + } + m.mu.Unlock() + } + if !ok { + return nil, false + } + return e.load() +} + +func (e *entry) load() (value interface{}, ok bool) { + p := atomic.LoadPointer(&e.p) + if p == nil || p == expunged { + return nil, false + } + return *(*interface{})(p), true +} + +// Store sets the value for a key. +func (m *Map) Store(key, value interface{}) { + read, _ := m.read.Load().(readOnly) + if e, ok := read.m[key]; ok && e.tryStore(&value) { + return + } + + m.mu.Lock() + read, _ = m.read.Load().(readOnly) + if e, ok := read.m[key]; ok { + if e.unexpungeLocked() { + // The entry was previously expunged, which implies that there is a + // non-nil dirty map and this entry is not in it. + m.dirty[key] = e + } + e.storeLocked(&value) + } else if e, ok := m.dirty[key]; ok { + e.storeLocked(&value) + } else { + if !read.amended { + // We're adding the first new key to the dirty map. + // Make sure it is allocated and mark the read-only map as incomplete. + m.dirtyLocked() + m.read.Store(readOnly{m: read.m, amended: true}) + } + m.dirty[key] = newEntry(value) + } + m.mu.Unlock() +} + +// tryStore stores a value if the entry has not been expunged. +// +// If the entry is expunged, tryStore returns false and leaves the entry +// unchanged. +func (e *entry) tryStore(i *interface{}) bool { + p := atomic.LoadPointer(&e.p) + if p == expunged { + return false + } + for { + if atomic.CompareAndSwapPointer(&e.p, p, unsafe.Pointer(i)) { + return true + } + p = atomic.LoadPointer(&e.p) + if p == expunged { + return false + } + } +} + +// unexpungeLocked ensures that the entry is not marked as expunged. +// +// If the entry was previously expunged, it must be added to the dirty map +// before m.mu is unlocked. +func (e *entry) unexpungeLocked() (wasExpunged bool) { + return atomic.CompareAndSwapPointer(&e.p, expunged, nil) +} + +// storeLocked unconditionally stores a value to the entry. +// +// The entry must be known not to be expunged. +func (e *entry) storeLocked(i *interface{}) { + atomic.StorePointer(&e.p, unsafe.Pointer(i)) +} + +// LoadOrStore returns the existing value for the key if present. +// Otherwise, it stores and returns the given value. +// The loaded result is true if the value was loaded, false if stored. +func (m *Map) LoadOrStore(key, value interface{}) (actual interface{}, loaded bool) { + // Avoid locking if it's a clean hit. + read, _ := m.read.Load().(readOnly) + if e, ok := read.m[key]; ok { + actual, loaded, ok := e.tryLoadOrStore(value) + if ok { + return actual, loaded + } + } + + m.mu.Lock() + read, _ = m.read.Load().(readOnly) + if e, ok := read.m[key]; ok { + if e.unexpungeLocked() { + m.dirty[key] = e + } + actual, loaded, _ = e.tryLoadOrStore(value) + } else if e, ok := m.dirty[key]; ok { + actual, loaded, _ = e.tryLoadOrStore(value) + m.missLocked() + } else { + if !read.amended { + // We're adding the first new key to the dirty map. + // Make sure it is allocated and mark the read-only map as incomplete. + m.dirtyLocked() + m.read.Store(readOnly{m: read.m, amended: true}) + } + m.dirty[key] = newEntry(value) + actual, loaded = value, false + } + m.mu.Unlock() + + return actual, loaded +} + +// tryLoadOrStore atomically loads or stores a value if the entry is not +// expunged. +// +// If the entry is expunged, tryLoadOrStore leaves the entry unchanged and +// returns with ok==false. +func (e *entry) tryLoadOrStore(i interface{}) (actual interface{}, loaded, ok bool) { + p := atomic.LoadPointer(&e.p) + if p == expunged { + return nil, false, false + } + if p != nil { + return *(*interface{})(p), true, true + } + + // Copy the interface after the first load to make this method more amenable + // to escape analysis: if we hit the "load" path or the entry is expunged, we + // shouldn't bother heap-allocating. + ic := i + for { + if atomic.CompareAndSwapPointer(&e.p, nil, unsafe.Pointer(&ic)) { + return i, false, true + } + p = atomic.LoadPointer(&e.p) + if p == expunged { + return nil, false, false + } + if p != nil { + return *(*interface{})(p), true, true + } + } +} + +// Delete deletes the value for a key. +func (m *Map) Delete(key interface{}) { + read, _ := m.read.Load().(readOnly) + e, ok := read.m[key] + if !ok && read.amended { + m.mu.Lock() + read, _ = m.read.Load().(readOnly) + e, ok = read.m[key] + if !ok && read.amended { + delete(m.dirty, key) + } + m.mu.Unlock() + } + if ok { + e.delete() + } +} + +func (e *entry) delete() (hadValue bool) { + for { + p := atomic.LoadPointer(&e.p) + if p == nil || p == expunged { + return false + } + if atomic.CompareAndSwapPointer(&e.p, p, nil) { + return true + } + } +} + +// Range calls f sequentially for each key and value present in the map. +// If f returns false, range stops the iteration. +// +// Range does not necessarily correspond to any consistent snapshot of the Map's +// contents: no key will be visited more than once, but if the value for any key +// is stored or deleted concurrently, Range may reflect any mapping for that key +// from any point during the Range call. +// +// Range may be O(N) with the number of elements in the map even if f returns +// false after a constant number of calls. +func (m *Map) Range(f func(key, value interface{}) bool) { + // We need to be able to iterate over all of the keys that were already + // present at the start of the call to Range. + // If read.amended is false, then read.m satisfies that property without + // requiring us to hold m.mu for a long time. + read, _ := m.read.Load().(readOnly) + if read.amended { + // m.dirty contains keys not in read.m. Fortunately, Range is already O(N) + // (assuming the caller does not break out early), so a call to Range + // amortizes an entire copy of the map: we can promote the dirty copy + // immediately! + m.mu.Lock() + read, _ = m.read.Load().(readOnly) + if read.amended { + read = readOnly{m: m.dirty} + m.read.Store(read) + m.dirty = nil + m.misses = 0 + } + m.mu.Unlock() + } + + for k, e := range read.m { + v, ok := e.load() + if !ok { + continue + } + if !f(k, v) { + break + } + } +} + +func (m *Map) missLocked() { + m.misses++ + if m.misses < len(m.dirty) { + return + } + m.read.Store(readOnly{m: m.dirty}) + m.dirty = nil + m.misses = 0 +} + +func (m *Map) dirtyLocked() { + if m.dirty != nil { + return + } + + read, _ := m.read.Load().(readOnly) + m.dirty = make(map[interface{}]*entry, len(read.m)) + for k, e := range read.m { + if !e.tryExpungeLocked() { + m.dirty[k] = e + } + } +} + +func (e *entry) tryExpungeLocked() (isExpunged bool) { + p := atomic.LoadPointer(&e.p) + for p == nil { + if atomic.CompareAndSwapPointer(&e.p, nil, expunged) { + return true + } + p = atomic.LoadPointer(&e.p) + } + return p == expunged +} |