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82 lines
2.0 KiB
Go
82 lines
2.0 KiB
Go
// Copyright (c) 2018 Shivaram Lingamneni
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// released under the MIT license
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package utils
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import (
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"context"
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"log"
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"runtime/debug"
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"time"
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)
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// Semaphore is a counting semaphore.
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// A semaphore of capacity 1 can be used as a trylock.
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type Semaphore (chan empty)
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// Initialize initializes a semaphore to a given capacity.
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func (semaphore *Semaphore) Initialize(capacity int) {
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*semaphore = make(chan empty, capacity)
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}
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// Acquire acquires a semaphore, blocking if necessary.
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func (semaphore *Semaphore) Acquire() {
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(*semaphore) <- empty{}
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}
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// TryAcquire tries to acquire a semaphore, returning whether the acquire was
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// successful. It never blocks.
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func (semaphore *Semaphore) TryAcquire() (acquired bool) {
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select {
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case (*semaphore) <- empty{}:
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return true
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default:
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return false
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}
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}
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// AcquireWithTimeout tries to acquire a semaphore, blocking for a maximum
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// of approximately `d` while waiting for it. It returns whether the acquire
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// was successful.
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func (semaphore *Semaphore) AcquireWithTimeout(timeout time.Duration) (acquired bool) {
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if timeout < 0 {
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return semaphore.TryAcquire()
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}
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timer := time.NewTimer(timeout)
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select {
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case (*semaphore) <- empty{}:
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acquired = true
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case <-timer.C:
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acquired = false
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}
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timer.Stop()
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return
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}
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// AcquireWithContext tries to acquire a semaphore, blocking at most until
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// the context expires. It returns whether the acquire was successful.
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// Note that if the context is already expired, the acquire may succeed anyway.
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func (semaphore *Semaphore) AcquireWithContext(ctx context.Context) (acquired bool) {
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select {
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case (*semaphore) <- empty{}:
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acquired = true
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case <-ctx.Done():
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acquired = false
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}
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return
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}
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// Release releases a semaphore. It never blocks. (This is not a license
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// to program spurious releases.)
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func (semaphore *Semaphore) Release() {
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select {
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case <-(*semaphore):
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// good
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default:
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// spurious release
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log.Printf("spurious semaphore release (full to capacity %d)", cap(*semaphore))
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debug.PrintStack()
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}
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}
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