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// 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
// Once is an object that will perform exactly one action.
type Once struct {
m Mutex
done bool
}
// Do calls the function f if and only if the method is being called for the
// first time with this receiver. In other words, given
// var once Once
// if 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.
//
func (o *Once) Do(f func()) {
o.m.Lock()
defer o.m.Unlock()
if !o.done {
o.done = true
f()
}
}
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