syncmap: add a synchronized map implementation.
This is a draft for the sync.Map API proposed in golang/go#18177.
It supports fast-path loads via an atomic variable, falling back to a
Mutex for stores. In order to keep stores amortized to O(1), loads
following a store follow the Mutex path until enough loads have
occurred to offset the cost of a deep copy.
For mostly-read loads, such as the maps in the reflect package in the
standard library, this significantly reduces cache-line contention vs.
a plain RWMutex with a map.
goos: linux
goarch: amd64
pkg: golang.org/x/sync/syncmap
BenchmarkLoadMostlyHits/*syncmap_test.DeepCopyMap 20000000 73.1 ns/op
BenchmarkLoadMostlyHits/*syncmap_test.DeepCopyMap-48 100000000 13.8 ns/op
BenchmarkLoadMostlyHits/*syncmap_test.RWMutexMap 20000000 87.7 ns/op
BenchmarkLoadMostlyHits/*syncmap_test.RWMutexMap-48 10000000 154 ns/op
BenchmarkLoadMostlyHits/*syncmap.Map 20000000 72.1 ns/op
BenchmarkLoadMostlyHits/*syncmap.Map-48 100000000 11.2 ns/op
BenchmarkLoadMostlyMisses/*syncmap_test.DeepCopyMap 20000000 63.2 ns/op
BenchmarkLoadMostlyMisses/*syncmap_test.DeepCopyMap-48 200000000 14.2 ns/op
BenchmarkLoadMostlyMisses/*syncmap_test.RWMutexMap 20000000 72.7 ns/op
BenchmarkLoadMostlyMisses/*syncmap_test.RWMutexMap-48 10000000 150 ns/op
BenchmarkLoadMostlyMisses/*syncmap.Map 30000000 56.4 ns/op
BenchmarkLoadMostlyMisses/*syncmap.Map-48 200000000 9.77 ns/op
BenchmarkLoadOrStoreBalanced/*syncmap_test.RWMutexMap 2000000 683 ns/op
BenchmarkLoadOrStoreBalanced/*syncmap_test.RWMutexMap-48 1000000 1394 ns/op
BenchmarkLoadOrStoreBalanced/*syncmap.Map 2000000 645 ns/op
BenchmarkLoadOrStoreBalanced/*syncmap.Map-48 1000000 1253 ns/op
BenchmarkLoadOrStoreUnique/*syncmap_test.RWMutexMap 1000000 1015 ns/op
BenchmarkLoadOrStoreUnique/*syncmap_test.RWMutexMap-48 1000000 1911 ns/op
BenchmarkLoadOrStoreUnique/*syncmap.Map 1000000 1018 ns/op
BenchmarkLoadOrStoreUnique/*syncmap.Map-48 1000000 1776 ns/op
BenchmarkLoadOrStoreCollision/*syncmap_test.DeepCopyMap 50000000 30.2 ns/op
BenchmarkLoadOrStoreCollision/*syncmap_test.DeepCopyMap-48 2000000000 1.24 ns/op
BenchmarkLoadOrStoreCollision/*syncmap_test.RWMutexMap 30000000 50.1 ns/op
BenchmarkLoadOrStoreCollision/*syncmap_test.RWMutexMap-48 5000000 451 ns/op
BenchmarkLoadOrStoreCollision/*syncmap.Map 30000000 36.8 ns/op
BenchmarkLoadOrStoreCollision/*syncmap.Map-48 2000000000 1.24 ns/op
BenchmarkAdversarialAlloc/*syncmap_test.DeepCopyMap 10000000 213 ns/op
BenchmarkAdversarialAlloc/*syncmap_test.DeepCopyMap-48 1000000 5012 ns/op
BenchmarkAdversarialAlloc/*syncmap_test.RWMutexMap 20000000 68.8 ns/op
BenchmarkAdversarialAlloc/*syncmap_test.RWMutexMap-48 5000000 429 ns/op
BenchmarkAdversarialAlloc/*syncmap.Map 5000000 229 ns/op
BenchmarkAdversarialAlloc/*syncmap.Map-48 2000000 600 ns/op
BenchmarkAdversarialDelete/*syncmap_test.DeepCopyMap 5000000 314 ns/op
BenchmarkAdversarialDelete/*syncmap_test.DeepCopyMap-48 2000000 726 ns/op
BenchmarkAdversarialDelete/*syncmap_test.RWMutexMap 20000000 63.2 ns/op
BenchmarkAdversarialDelete/*syncmap_test.RWMutexMap-48 5000000 469 ns/op
BenchmarkAdversarialDelete/*syncmap.Map 10000000 203 ns/op
BenchmarkAdversarialDelete/*syncmap.Map-48 10000000 253 ns/op
goos: linux
goarch: ppc64le
pkg: golang.org/x/sync/syncmap
BenchmarkLoadMostlyHits/*syncmap_test.DeepCopyMap 5000000 253 ns/op
BenchmarkLoadMostlyHits/*syncmap_test.DeepCopyMap-48 50000000 26.2 ns/op
BenchmarkLoadMostlyHits/*syncmap_test.RWMutexMap 5000000 505 ns/op
BenchmarkLoadMostlyHits/*syncmap_test.RWMutexMap-48 3000000 443 ns/op
BenchmarkLoadMostlyHits/*syncmap.Map 10000000 200 ns/op
BenchmarkLoadMostlyHits/*syncmap.Map-48 100000000 18.1 ns/op
BenchmarkLoadMostlyMisses/*syncmap_test.DeepCopyMap 10000000 162 ns/op
BenchmarkLoadMostlyMisses/*syncmap_test.DeepCopyMap-48 100000000 23.8 ns/op
BenchmarkLoadMostlyMisses/*syncmap_test.RWMutexMap 10000000 195 ns/op
BenchmarkLoadMostlyMisses/*syncmap_test.RWMutexMap-48 3000000 531 ns/op
BenchmarkLoadMostlyMisses/*syncmap.Map 10000000 182 ns/op
BenchmarkLoadMostlyMisses/*syncmap.Map-48 100000000 15.8 ns/op
BenchmarkLoadOrStoreBalanced/*syncmap_test.RWMutexMap 1000000 1664 ns/op
BenchmarkLoadOrStoreBalanced/*syncmap_test.RWMutexMap-48 1000000 1768 ns/op
BenchmarkLoadOrStoreBalanced/*syncmap.Map 1000000 2128 ns/op
BenchmarkLoadOrStoreBalanced/*syncmap.Map-48 1000000 1903 ns/op
BenchmarkLoadOrStoreUnique/*syncmap_test.RWMutexMap 1000000 2657 ns/op
BenchmarkLoadOrStoreUnique/*syncmap_test.RWMutexMap-48 1000000 2577 ns/op
BenchmarkLoadOrStoreUnique/*syncmap.Map 1000000 1714 ns/op
BenchmarkLoadOrStoreUnique/*syncmap.Map-48 1000000 2484 ns/op
BenchmarkLoadOrStoreCollision/*syncmap_test.DeepCopyMap 10000000 130 ns/op
BenchmarkLoadOrStoreCollision/*syncmap_test.DeepCopyMap-48 100000000 11.3 ns/op
BenchmarkLoadOrStoreCollision/*syncmap_test.RWMutexMap 3000000 426 ns/op
BenchmarkLoadOrStoreCollision/*syncmap_test.RWMutexMap-48 2000000 930 ns/op
BenchmarkLoadOrStoreCollision/*syncmap.Map 10000000 131 ns/op
BenchmarkLoadOrStoreCollision/*syncmap.Map-48 300000000 4.07 ns/op
BenchmarkAdversarialAlloc/*syncmap_test.DeepCopyMap 3000000 447 ns/op
BenchmarkAdversarialAlloc/*syncmap_test.DeepCopyMap-48 300000 4159 ns/op
BenchmarkAdversarialAlloc/*syncmap_test.RWMutexMap 10000000 191 ns/op
BenchmarkAdversarialAlloc/*syncmap_test.RWMutexMap-48 3000000 535 ns/op
BenchmarkAdversarialAlloc/*syncmap.Map 2000000 525 ns/op
BenchmarkAdversarialAlloc/*syncmap.Map-48 1000000 1000 ns/op
BenchmarkAdversarialDelete/*syncmap_test.DeepCopyMap 2000000 711 ns/op
BenchmarkAdversarialDelete/*syncmap_test.DeepCopyMap-48 2000000 900 ns/op
BenchmarkAdversarialDelete/*syncmap_test.RWMutexMap 3000000 354 ns/op
BenchmarkAdversarialDelete/*syncmap_test.RWMutexMap-48 3000000 473 ns/op
BenchmarkAdversarialDelete/*syncmap.Map 2000000 1357 ns/op
BenchmarkAdversarialDelete/*syncmap.Map-48 5000000 334 ns/op
Updates golang/go#18177
Change-Id: I8d561b617b1cd2ca03a8e68a5d5a28a519a0ce38
Reviewed-on: https://go-review.googlesource.com/33912
Reviewed-by: Russ Cox <rsc@golang.org>
diff --git a/syncmap/map.go b/syncmap/map.go
new file mode 100644
index 0000000..1efbcb2
--- /dev/null
+++ b/syncmap/map.go
@@ -0,0 +1,192 @@
+// 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 provides a concurrent map implementation.
+// It is a prototype for a proposed addition to the sync package
+// in the standard library.
+// (https://golang.org/issue/18177)
+package syncmap
+
+import (
+ "sync"
+ "sync/atomic"
+)
+
+// Map is a concurrent map with amortized-constant-time operations.
+// 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
+
+ // clean is a copy of the map's contents that will never be overwritten, and
+ // is thus safe for concurrent lookups without additional synchronization.
+ //
+ // A nil clean map indicates that the current map contents are stored in the
+ // dirty field instead.
+ // If clean is non-nil, its contents are up-to-date.
+ //
+ // clean is always safe to load, but must only be stored with mu held.
+ clean atomic.Value // map[interface{}]interface{}
+
+ // dirty is a copy of the map to which all writes occur.
+ //
+ // A nil dirty map indicates that the current map contents are either empty or
+ // stored in the clean field.
+ //
+ // If the dirty map is nil, the next write to the map will initialize it by
+ // making a deep copy of the clean map, then setting the clean map to nil.
+ dirty map[interface{}]interface{}
+
+ // misses counts the number of Load calls for which the clean map was nil
+ // since the last write.
+ //
+ // Once enough Load misses have occurred to cover the cost of a copy, the
+ // dirty map will be promoted to clean and any subsequent writes will make
+ // a new copy.
+ misses int
+}
+
+// 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) {
+ clean, _ := m.clean.Load().(map[interface{}]interface{})
+ if clean != nil {
+ value, ok = clean[key]
+ return value, ok
+ }
+
+ m.mu.Lock()
+ if m.dirty == nil {
+ clean, _ := m.clean.Load().(map[interface{}]interface{})
+ if clean == nil {
+ // Completely empty — promote to clean immediately.
+ m.clean.Store(map[interface{}]interface{}{})
+ } else {
+ value, ok = clean[key]
+ }
+ m.mu.Unlock()
+ return value, ok
+ }
+ value, ok = m.dirty[key]
+ m.missLocked()
+ m.mu.Unlock()
+ return value, ok
+}
+
+// Store sets the value for a key.
+func (m *Map) Store(key, value interface{}) {
+ m.mu.Lock()
+ m.dirtyLocked()
+ m.dirty[key] = value
+ m.mu.Unlock()
+}
+
+// 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.
+ clean, _ := m.clean.Load().(map[interface{}]interface{})
+ actual, loaded = clean[key]
+ if loaded {
+ return actual, true
+ }
+
+ m.mu.Lock()
+ if m.dirty == nil {
+ // 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 {
+ m.mu.Unlock()
+ return actual, true
+ }
+ } else {
+ actual, loaded = m.dirty[key]
+ if loaded {
+ m.missLocked()
+ m.mu.Unlock()
+ return actual, true
+ }
+ }
+
+ m.dirtyLocked()
+ m.dirty[key] = value
+ actual = value
+ m.mu.Unlock()
+ return actual, false
+}
+
+// Delete deletes the value for a key.
+func (m *Map) Delete(key interface{}) {
+ m.mu.Lock()
+ m.dirtyLocked()
+ delete(m.dirty, key)
+ m.mu.Unlock()
+}
+
+// Range calls f sequentially for each key and value present in the map.
+// If f returns false, range stops the iteration.
+//
+// Calls to other Map methods may block until Range returns.
+// The function f must not call any other methods on the Map.
+//
+// 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.
+func (m *Map) Range(f func(key, value interface{}) bool) {
+ clean, _ := m.clean.Load().(map[interface{}]interface{})
+ if clean == nil {
+ m.mu.Lock()
+ if m.dirty == nil {
+ clean, _ = m.clean.Load().(map[interface{}]interface{})
+ if clean == nil {
+ // Completely empty — add an empty map to bypass m.mu next time.
+ m.clean.Store(map[interface{}]interface{}{})
+ }
+ } else {
+ // Range is already O(N), so a call to Range amortizes an entire copy of
+ // the map. If it is dirty, we can promote it to clean immediately!
+ clean = m.dirty
+ m.clean.Store(clean)
+ m.dirty = nil
+ }
+ m.mu.Unlock()
+ }
+
+ for k, v := range clean {
+ if !f(k, v) {
+ break
+ }
+ }
+}
+
+func (m *Map) missLocked() {
+ if m.misses++; m.misses >= len(m.dirty) {
+ m.clean.Store(m.dirty)
+ m.dirty = nil
+ }
+}
+
+// dirtyLocked prepares the map for a subsequent write.
+// It ensures that the dirty field is non-nil and clean is nil by making a deep
+// copy of clean.
+func (m *Map) dirtyLocked() {
+ m.misses = 0
+ if m.dirty != nil {
+ return
+ }
+
+ clean, _ := m.clean.Load().(map[interface{}]interface{})
+ m.dirty = make(map[interface{}]interface{}, len(clean))
+ for k, v := range clean {
+ m.dirty[k] = v
+ }
+ m.clean.Store(map[interface{}]interface{}(nil))
+}
diff --git a/syncmap/map_bench_test.go b/syncmap/map_bench_test.go
new file mode 100644
index 0000000..ac06274
--- /dev/null
+++ b/syncmap/map_bench_test.go
@@ -0,0 +1,199 @@
+// 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)
+ }
+ },
+ })
+}
+
+// BenchmarkAdversarialAlloc tests performance when we store a new value
+// immediately whenever the map is promoted to clean.
+//
+// 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 delete and restore a
+// value immediately after a large map has been promoted.
+//
+// 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 {
+ var key int
+ m.Range(func(k, _ interface{}) bool {
+ key = k.(int)
+ return false
+ })
+ m.Delete(key)
+ m.Store(key, key)
+ }
+ }
+ },
+ })
+}
diff --git a/syncmap/map_reference_test.go b/syncmap/map_reference_test.go
new file mode 100644
index 0000000..f3a4977
--- /dev/null
+++ b/syncmap/map_reference_test.go
@@ -0,0 +1,142 @@
+// 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()
+ defer m.mu.RUnlock()
+ for k, v := range m.dirty {
+ 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/syncmap/map_test.go b/syncmap/map_test.go
new file mode 100644
index 0000000..54448a0
--- /dev/null
+++ b/syncmap/map_test.go
@@ -0,0 +1,116 @@
+// 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"
+ "math/rand"
+ "reflect"
+ "testing"
+ "testing/quick"
+
+ "golang.org/x/sync/syncmap"
+)
+
+// mapCall is a quick.Generator for calls on mapInterface.
+type mapCall struct {
+ key interface{}
+ apply func(mapInterface) (interface{}, bool)
+ desc string
+}
+
+type mapResult struct {
+ value interface{}
+ ok bool
+}
+
+var stringType = reflect.TypeOf("")
+
+func randValue(r *rand.Rand) interface{} {
+ k, ok := quick.Value(stringType, r)
+ if !ok {
+ panic(fmt.Sprintf("quick.Value(%v, _) failed", stringType))
+ }
+ return k.Interface()
+}
+
+func (mapCall) Generate(r *rand.Rand, size int) reflect.Value {
+ k := randValue(r)
+
+ var (
+ app func(mapInterface) (interface{}, bool)
+ desc string
+ )
+ switch rand.Intn(4) {
+ case 0:
+ app = func(m mapInterface) (interface{}, bool) {
+ return m.Load(k)
+ }
+ desc = fmt.Sprintf("Load(%q)", k)
+
+ case 1:
+ v := randValue(r)
+ app = func(m mapInterface) (interface{}, bool) {
+ m.Store(k, v)
+ return nil, false
+ }
+ desc = fmt.Sprintf("Store(%q, %q)", k, v)
+
+ case 2:
+ v := randValue(r)
+ app = func(m mapInterface) (interface{}, bool) {
+ return m.LoadOrStore(k, v)
+ }
+ desc = fmt.Sprintf("LoadOrStore(%q, %q)", k, v)
+
+ case 3:
+ app = func(m mapInterface) (interface{}, bool) {
+ m.Delete(k)
+ return nil, false
+ }
+ desc = fmt.Sprintf("Delete(%q)", k)
+ }
+
+ return reflect.ValueOf(mapCall{k, app, desc})
+}
+
+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, applyRWMutexMap, nil); err != nil {
+ t.Error(err)
+ }
+}
