72 lines
1.7 KiB
Go
72 lines
1.7 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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"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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// NewSemaphore creates and initializes a semaphore to a given capacity.
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func NewSemaphore(capacity int) Semaphore {
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return 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.
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func (semaphore Semaphore) Release() {
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<-semaphore
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}
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