terraform: Adding a semaphore implementation

This commit is contained in:
Armon Dadgar 2014-10-16 10:04:07 -07:00
parent 8f98a79cf1
commit ad31023252
2 changed files with 73 additions and 1 deletions

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@ -1,5 +1,47 @@
package terraform
// Semaphore is a wrapper around a channel to provide
// utility methods to clarify that we are treating the
// channel as a semaphore
type Semaphore chan struct{}
// NewSemaphore creates a semaphore that allows up
// to a given limit of simultaneous acquisitions
func NewSemaphore(n int) Semaphore {
if n == 0 {
panic("semaphore with limit 0")
}
ch := make(chan struct{}, n)
return Semaphore(ch)
}
// Acquire is used to acquire an available slot.
// Blocks until available.
func (s Semaphore) Acquire() {
s <- struct{}{}
}
// TryAcquire is used to do a non-blocking acquire.
// Returns a bool indicating success
func (s Semaphore) TryAcquire() bool {
select {
case s <- struct{}{}:
return true
default:
return false
}
}
// Release is used to return a slot. Acquire must
// be called as a pre-condition.
func (s Semaphore) Release() {
select {
case <-s:
default:
panic("release without an acquire")
}
}
// strSliceContains checks if a given string is contained in a slice
// When anybody asks why Go needs generics, here you go.
func strSliceContains(haystack []string, needle string) bool {

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@ -1,6 +1,36 @@
package terraform
import "testing"
import (
"testing"
"time"
)
func TestSemaphore(t *testing.T) {
s := NewSemaphore(2)
timer := time.AfterFunc(time.Second, func() {
panic("deadlock")
})
defer timer.Stop()
s.Acquire()
if !s.TryAcquire() {
t.Fatalf("should acquire")
}
if s.TryAcquire() {
t.Fatalf("should not acquire")
}
s.Release()
s.Release()
// This release should panic
defer func() {
r := recover()
if r == nil {
t.Fatalf("should panic")
}
}()
s.Release()
}
func TestStrSliceContains(t *testing.T) {
if strSliceContains(nil, "foo") {