+In Go 1, the RemoveAll function has been removed.
+The Iter function and Iter method on *Map have
+been replaced by
+Do
+and
+(*Map).Do.
+
+Updating:
+Most code using expvar will not need changing. The rare code that used
+Iter can be updated to pass a closure to Do to achieve the same effect.
+
diff --git a/doc/go1.tmpl b/doc/go1.tmpl index 3287e137f28..c4f486bac30 100644 --- a/doc/go1.tmpl +++ b/doc/go1.tmpl @@ -817,6 +817,23 @@ to be implemented in the future. No changes will be needed.
+
+In Go 1, the RemoveAll function has been removed.
+The Iter function and Iter method on *Map have
+been replaced by
+Do
+and
+(*Map).Do.
+
+Updating:
+Most code using expvar will not need changing. The rare code that used
+Iter can be updated to pass a closure to Do to achieve the same effect.
+
diff --git a/src/pkg/expvar/expvar.go b/src/pkg/expvar/expvar.go index 5ced285804c..ee32eff9ea3 100644 --- a/src/pkg/expvar/expvar.go +++ b/src/pkg/expvar/expvar.go @@ -83,7 +83,7 @@ func (v *Float) Set(value float64) { // Map is a string-to-Var map variable that satisfies the Var interface. type Map struct { m map[string]Var - mu sync.Mutex + mu sync.RWMutex } // KeyValue represents a single entry in a Map. @@ -93,8 +93,8 @@ type KeyValue struct { } func (v *Map) String() string { - v.mu.Lock() - defer v.mu.Unlock() + v.mu.RLock() + defer v.mu.RUnlock() b := new(bytes.Buffer) fmt.Fprintf(b, "{") first := true @@ -115,8 +115,8 @@ func (v *Map) Init() *Map { } func (v *Map) Get(key string) Var { - v.mu.Lock() - defer v.mu.Unlock() + v.mu.RLock() + defer v.mu.RUnlock() return v.m[key] } @@ -127,12 +127,17 @@ func (v *Map) Set(key string, av Var) { } func (v *Map) Add(key string, delta int64) { - v.mu.Lock() - defer v.mu.Unlock() + v.mu.RLock() av, ok := v.m[key] + v.mu.RUnlock() if !ok { - av = new(Int) - v.m[key] = av + // check again under the write lock + v.mu.Lock() + if _, ok = v.m[key]; !ok { + av = new(Int) + v.m[key] = av + } + v.mu.Unlock() } // Add to Int; ignore otherwise. @@ -143,12 +148,17 @@ func (v *Map) Add(key string, delta int64) { // AddFloat adds delta to the *Float value stored under the given map key. func (v *Map) AddFloat(key string, delta float64) { - v.mu.Lock() - defer v.mu.Unlock() + v.mu.RLock() av, ok := v.m[key] + v.mu.RUnlock() if !ok { - av = new(Float) - v.m[key] = av + // check again under the write lock + v.mu.Lock() + if _, ok = v.m[key]; !ok { + av = new(Float) + v.m[key] = av + } + v.mu.Unlock() } // Add to Float; ignore otherwise. @@ -157,18 +167,15 @@ func (v *Map) AddFloat(key string, delta float64) { } } -// TODO(rsc): Make sure map access in separate thread is safe. -func (v *Map) iterate(c chan<- KeyValue) { +// Do calls f for each entry in the map. +// The map is locked during the iteration, +// but existing entries may be concurrently updated. +func (v *Map) Do(f func(KeyValue)) { + v.mu.RLock() + defer v.mu.RUnlock() for k, v := range v.m { - c <- KeyValue{k, v} + f(KeyValue{k, v}) } - close(c) -} - -func (v *Map) Iter() <-chan KeyValue { - c := make(chan KeyValue) - go v.iterate(c) - return c } // String is a string variable, and satisfies the Var interface. @@ -190,8 +197,10 @@ func (f Func) String() string { } // All published variables. -var vars map[string]Var = make(map[string]Var) -var mutex sync.Mutex +var ( + mutex sync.RWMutex + vars map[string]Var = make(map[string]Var) +) // Publish declares a named exported variable. This should be called from a // package's init function when it creates its Vars. If the name is already @@ -207,17 +216,11 @@ func Publish(name string, v Var) { // Get retrieves a named exported variable. func Get(name string) Var { + mutex.RLock() + defer mutex.RUnlock() return vars[name] } -// RemoveAll removes all exported variables. -// This is for tests; don't call this on a real server. -func RemoveAll() { - mutex.Lock() - defer mutex.Unlock() - vars = make(map[string]Var) -} - // Convenience functions for creating new exported variables. func NewInt(name string) *Int { @@ -244,31 +247,28 @@ func NewString(name string) *String { return v } -// TODO(rsc): Make sure map access in separate thread is safe. -func iterate(c chan<- KeyValue) { +// Do calls f for each exported variable. +// The global variable map is locked during the iteration, +// but existing entries may be concurrently updated. +func Do(f func(KeyValue)) { + mutex.RLock() + defer mutex.RUnlock() for k, v := range vars { - c <- KeyValue{k, v} + f(KeyValue{k, v}) } - close(c) -} - -func Iter() <-chan KeyValue { - c := make(chan KeyValue) - go iterate(c) - return c } func expvarHandler(w http.ResponseWriter, r *http.Request) { w.Header().Set("Content-Type", "application/json; charset=utf-8") fmt.Fprintf(w, "{\n") first := true - for name, value := range vars { + Do(func(kv KeyValue) { if !first { fmt.Fprintf(w, ",\n") } first = false - fmt.Fprintf(w, "%q: %s", name, value) - } + fmt.Fprintf(w, "%q: %s", kv.Key, kv.Value) + }) fmt.Fprintf(w, "\n}\n") } @@ -281,7 +281,7 @@ func memstats() interface{} { } func init() { - http.Handle("/debug/vars", http.HandlerFunc(expvarHandler)) + http.HandleFunc("/debug/vars", expvarHandler) Publish("cmdline", Func(cmdline)) Publish("memstats", Func(memstats)) } diff --git a/src/pkg/expvar/expvar_test.go b/src/pkg/expvar/expvar_test.go index fc607274b28..bbd9dd8d6e9 100644 --- a/src/pkg/expvar/expvar_test.go +++ b/src/pkg/expvar/expvar_test.go @@ -9,6 +9,14 @@ import ( "testing" ) +// RemoveAll removes all exported variables. +// This is for tests only. +func RemoveAll() { + mutex.Lock() + defer mutex.Unlock() + vars = make(map[string]Var) +} + func TestInt(t *testing.T) { reqs := NewInt("requests") if reqs.i != 0 {