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Diffstat (limited to 'src/sync/mutex.go')
-rw-r--r--src/sync/mutex.go40
1 files changed, 35 insertions, 5 deletions
diff --git a/src/sync/mutex.go b/src/sync/mutex.go
index e12bf40c1..59f320d5d 100644
--- a/src/sync/mutex.go
+++ b/src/sync/mutex.go
@@ -3,10 +3,12 @@ package sync
import (
"internal/task"
_ "unsafe"
+
+ "runtime/volatile"
)
type Mutex struct {
- locked bool
+ state uint8 // Set to non-zero if locked.
blocked task.Stack
}
@@ -14,18 +16,18 @@ type Mutex struct {
func scheduleTask(*task.Task)
func (m *Mutex) Lock() {
- if m.locked {
+ if m.islocked() {
// Push self onto stack of blocked tasks, and wait to be resumed.
m.blocked.Push(task.Current())
task.Pause()
return
}
- m.locked = true
+ m.setlock(true)
}
func (m *Mutex) Unlock() {
- if !m.locked {
+ if !m.islocked() {
panic("sync: unlock of unlocked Mutex")
}
@@ -33,8 +35,36 @@ func (m *Mutex) Unlock() {
if t := m.blocked.Pop(); t != nil {
scheduleTask(t)
} else {
- m.locked = false
+ m.setlock(false)
+ }
+}
+
+// TryLock tries to lock m and reports whether it succeeded.
+//
+// Note that while correct uses of TryLock do exist, they are rare,
+// and use of TryLock is often a sign of a deeper problem
+// in a particular use of mutexes.
+func (m *Mutex) TryLock() bool {
+ if m.islocked() {
+ return false
+ }
+ m.Lock()
+ return true
+}
+
+func (m *Mutex) islocked() bool {
+ return volatile.LoadUint8(&m.state) != 0
+}
+
+func (m *Mutex) setlock(b bool) {
+ volatile.StoreUint8(&m.state, boolToU8(b))
+}
+
+func boolToU8(b bool) uint8 {
+ if b {
+ return 1
}
+ return 0
}
type RWMutex struct {