mirror of git://gcc.gnu.org/git/gcc.git
47 lines
1.3 KiB
Go
47 lines
1.3 KiB
Go
// Copyright 2009 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"
|
|
)
|
|
|
|
// Once is an object that will perform exactly one action.
|
|
type Once struct {
|
|
m Mutex
|
|
done uint32
|
|
}
|
|
|
|
// Do calls the function f if and only if Do is being called for the
|
|
// first time for this instance of Once. In other words, given
|
|
// var once Once
|
|
// if once.Do(f) is called multiple times, only the first call will invoke f,
|
|
// even if f has a different value in each invocation. A new instance of
|
|
// Once is required for each function to execute.
|
|
//
|
|
// Do is intended for initialization that must be run exactly once. Since f
|
|
// is niladic, it may be necessary to use a function literal to capture the
|
|
// arguments to a function to be invoked by Do:
|
|
// config.once.Do(func() { config.init(filename) })
|
|
//
|
|
// Because no call to Do returns until the one call to f returns, if f causes
|
|
// Do to be called, it will deadlock.
|
|
//
|
|
// If f panics, Do considers it to have returned; future calls of Do return
|
|
// without calling f.
|
|
//
|
|
func (o *Once) Do(f func()) {
|
|
if atomic.LoadUint32(&o.done) == 1 {
|
|
return
|
|
}
|
|
// Slow-path.
|
|
o.m.Lock()
|
|
defer o.m.Unlock()
|
|
if o.done == 0 {
|
|
defer atomic.StoreUint32(&o.done, 1)
|
|
f()
|
|
}
|
|
}
|