expvar: revise API.
Nuke RemoveAll from the public API.
Replace Iter functions with Do functions.
Fixes #2852.
R=rsc, r
CC=golang-dev
https://golang.org/cl/5622055
diff --git a/src/pkg/expvar/expvar.go b/src/pkg/expvar/expvar.go
index 5ced285..ee32eff 100644
--- a/src/pkg/expvar/expvar.go
+++ b/src/pkg/expvar/expvar.go
@@ -83,7 +83,7 @@
// 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 @@
}
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) 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) 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 @@
// 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 @@
}
}
-// 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 @@
}
// 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 @@
// 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 @@
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 init() {
- http.Handle("/debug/vars", http.HandlerFunc(expvarHandler))
+ http.HandleFunc("/debug/vars", expvarHandler)
Publish("cmdline", Func(cmdline))
Publish("memstats", Func(memstats))
}
