56 lines
1.3 KiB
Go
56 lines
1.3 KiB
Go
// Copyright 2012, Google Inc. 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 sync2
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// What's in a name? Channels have all you need to emulate a counting
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// semaphore with a boatload of extra functionality. However, in some
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// cases, you just want a familiar API.
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import (
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"time"
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)
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// Semaphore is a counting semaphore with the option to
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// specify a timeout.
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type Semaphore struct {
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slots chan struct{}
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timeout time.Duration
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}
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// NewSemaphore creates a Semaphore. The count parameter must be a positive
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// number. A timeout of zero means that there is no timeout.
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func NewSemaphore(count int, timeout time.Duration) *Semaphore {
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sem := &Semaphore{
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slots: make(chan struct{}, count),
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timeout: timeout,
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}
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for i := 0; i < count; i++ {
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sem.slots <- struct{}{}
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}
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return sem
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}
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// Acquire returns true on successful acquisition, and
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// false on a timeout.
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func (sem *Semaphore) Acquire() bool {
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if sem.timeout == 0 {
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<-sem.slots
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return true
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}
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select {
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case <-sem.slots:
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return true
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case <-time.After(sem.timeout):
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return false
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}
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}
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// Release releases the acquired semaphore. You must
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// not release more than the number of semaphores you've
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// acquired.
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func (sem *Semaphore) Release() {
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sem.slots <- struct{}{}
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}
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