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Merge pull request #503 from slingamn/acquire_timeout.1
add AcquireWithTimeout for semaphores
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commit
a1b30290e3
@ -1,10 +1,12 @@
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// 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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"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. Note that a capacity of n requires O(n) storage.
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@ -35,6 +37,25 @@ func (semaphore *Semaphore) TryAcquire() (acquired bool) {
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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):
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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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// 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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48
irc/utils/semaphores_test.go
Normal file
48
irc/utils/semaphores_test.go
Normal file
@ -0,0 +1,48 @@
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// Copyright (c) 2019 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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"testing"
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"time"
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)
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func TestTryAcquire(t *testing.T) {
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count := 3
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var sem Semaphore
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sem.Initialize(count)
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for i := 0; i < count; i++ {
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assertEqual(sem.TryAcquire(), true, t)
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}
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// used up the capacity
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assertEqual(sem.TryAcquire(), false, t)
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sem.Release()
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// got one slot back
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assertEqual(sem.TryAcquire(), true, t)
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}
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func TestAcquireWithTimeout(t *testing.T) {
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var sem Semaphore
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sem.Initialize(1)
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assertEqual(sem.TryAcquire(), true, t)
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// cannot acquire the held semaphore
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assertEqual(sem.AcquireWithTimeout(100*time.Millisecond), false, t)
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sem.Release()
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// can acquire the released semaphore
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assertEqual(sem.AcquireWithTimeout(100*time.Millisecond), true, t)
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sem.Release()
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// XXX this test could fail if the machine is extremely overloaded
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sem.Acquire()
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go func() {
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time.Sleep(100 * time.Millisecond)
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sem.Release()
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}()
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// we should acquire successfully after approximately 100 msec
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assertEqual(sem.AcquireWithTimeout(1*time.Second), true, t)
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}
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