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