f8d9fa9e80
This upgrades all of libgo other than the runtime package to the Go 1.4 release. In Go 1.4 much of the runtime was rewritten into Go. Merging that code will take more time and will not change the API, so I'm putting it off for now. There are a few runtime changes anyhow, to accomodate other packages that rely on minor modifications to the runtime support. The compiler changes slightly to add a one-bit flag to each type descriptor kind that is stored directly in an interface, which for gccgo is currently only pointer types. Another one-bit flag (gcprog) is reserved because it is used by the gc compiler, but gccgo does not currently use it. There is another error check in the compiler since I ran across it during testing. gotools/: * Makefile.am (go_cmd_go_files): Sort entries. Add generate.go. * Makefile.in: Rebuild. From-SVN: r219627
47 lines
1.3 KiB
Go
47 lines
1.3 KiB
Go
// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package sync
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import (
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"sync/atomic"
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)
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// Once is an object that will perform exactly one action.
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type Once struct {
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m Mutex
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done uint32
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}
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// Do calls the function f if and only if Do is being called for the
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// first time for this instance of Once. In other words, given
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// var once Once
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// if once.Do(f) is called multiple times, only the first call will invoke f,
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// even if f has a different value in each invocation. A new instance of
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// Once is required for each function to execute.
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//
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// Do is intended for initialization that must be run exactly once. Since f
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// is niladic, it may be necessary to use a function literal to capture the
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// arguments to a function to be invoked by Do:
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// config.once.Do(func() { config.init(filename) })
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//
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// Because no call to Do returns until the one call to f returns, if f causes
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// Do to be called, it will deadlock.
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//
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// If f panics, Do considers it to have returned; future calls of Do return
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// without calling f.
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//
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func (o *Once) Do(f func()) {
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if atomic.LoadUint32(&o.done) == 1 {
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return
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}
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// Slow-path.
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o.m.Lock()
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defer o.m.Unlock()
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if o.done == 0 {
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defer atomic.StoreUint32(&o.done, 1)
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f()
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}
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}
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