golang cond 代码
文件路径：/src/sync/cond.go
/ Copyright 2011 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 sync
import (
"sync/atomic"
"unsafe"
)
/ Cond implements a condition variable, a rendezvous point
/ for goroutines waiting for or announcing the occurrence
/ of an event.
/
/ Each Cond has an associated Locker L (often a *Mutex or *RWMutex),
/ which must be held when changing the condition and
/ when calling the Wait method.
/
/ A Cond must not be copied after first use.
/
/ In the terminology of the Go memory model, Cond arranges that
/ a call to Broadcast or Signal “synchronizes before” any Wait call
/ that it unblocks.
/
/ For many simple use cases, users will be better off using channels than a
/ Cond (Broadcast corresponds to closing a channel, and Signal corresponds to
/ sending on a channel).
/
/ For more on replacements for sync.Cond, see [Roberto Clapis's series on
/ advanced concurrency patterns], as well as [Bryan Mills's talk on concurrency
/ patterns].
/
/ [Roberto Clapis's series on advanced concurrency patterns]: https://blogtitle.github.io/categories/concurrency/
/ [Bryan Mills's talk on concurrency patterns]: https://drive.google.com/file/d/1nPdvhB0PutEJzdCq5ms6UI58dp50fcAN/view
type Cond struct {
noCopy noCopy
/ L is held while observing or changing the condition
L Locker
notify notifyList
checker copyChecker
}
/ NewCond returns a new Cond with Locker l.
func NewCond(l Locker) *Cond {
return &Cond{L: l}
}
/ Wait atomically unlocks c.L and suspends execution
/ of the calling goroutine. After later resuming execution,
/ Wait locks c.L before returning. Unlike in other systems,
/ Wait cannot return unless awoken by Broadcast or Signal.
/
/ Because c.L is not locked when Wait first resumes, the caller
/ typically cannot assume that the condition is true when
/ Wait returns. Instead, the caller should Wait in a loop:
/
/ c.L.Lock()
/ for !condition() {
/ c.Wait()
/ }
/ ... make use of condition ...
/ c.L.Unlock()
func (c *Cond) Wait() {
c.checker.check()
t := runtime_notifyListAdd(&c.notify)
c.L.Unlock()
runtime_notifyListWait(&c.notify, t)
c.L.Lock()
}
/ Signal wakes one goroutine waiting on c, if there is any.
/
/ It is allowed but not required for the caller to hold c.L
/ during the call.
/
/ Signal() does not affect goroutine scheduling priority; if other goroutines
/ are attempting to lock c.L, they may be awoken before a "waiting" goroutine.
func (c *Cond) Signal() {
c.checker.check()
runtime_notifyListNotifyOne(&c.notify)
}
/ Broadcast wakes all goroutines waiting on c.
/
/ It is allowed but not required for the caller to hold c.L
/ during the call.
func (c *Cond) Broadcast() {
c.checker.check()
runtime_notifyListNotifyAll(&c.notify)
}
/ copyChecker holds back pointer to itself to detect object copying.
type copyChecker uintptr
func (c *copyChecker) check() {
if uintptr(*c) != uintptr(unsafe.Pointer(c)) &&
!atomic.CompareAndSwapUintptr((*uintptr)(c), 0, uintptr(unsafe.Pointer(c))) &&
uintptr(*c) != uintptr(unsafe.Pointer(c)) {
panic("sync.Cond is copied")
}
}
/ noCopy may be added to structs which must not be copied
/ after the first use.
/
/ See https://golang.org/issues/8005#issuecomment-190753527
/ for details.
/
/ Note that it must not be embedded, due to the Lock and Unlock methods.
type noCopy struct{}
/ Lock is a no-op used by -copylocks checker from `go vet`.
func (*noCopy) Lock() {}
func (*noCopy) Unlock() {}