From cfd83425b68d40c7a2229fee3831a496783585d6 Mon Sep 17 00:00:00 2001
From: Tamer Tas <contact@tmrts.com>
Date: Wed, 23 Dec 2015 15:45:48 +0200
Subject: [PATCH] Add semaphore pattern

---
 semaphore.go | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)
 create mode 100644 semaphore.go

diff --git a/semaphore.go b/semaphore.go
new file mode 100644
index 0000000..766e76f
--- /dev/null
+++ b/semaphore.go
@@ -0,0 +1,46 @@
+package semaphore
+
+import (
+	"errors"
+	"time"
+)
+
+var (
+	ErrNoTickets      = errors.New("semaphore: could not aquire semaphore")
+	ErrIllegalRelease = errors.New("semaphore: can't release the semaphore without acquiring it first")
+)
+
+type Interface interface {
+	Acquire() error
+	Release() error
+}
+
+type semaphore struct {
+	sem     chan struct{}
+	timeout time.Duration
+}
+
+func New(tickets int, timeout time.Duration) Semaphore {
+	return &semaphore{
+		sem:     make(chan struct{}, tickets),
+		timeout: timeout,
+	}
+}
+
+func (s *semaphore) Acquire() error {
+	select {
+	case s.sem <- struct{}{}:
+		return nil
+	case <-time.After(s.timeout):
+		return ErrNoTickets
+	}
+}
+
+func (s *semaphore) Release() error {
+	_, ok := <-s.sem
+	if !ok {
+		return ErrIllegalRelease
+	}
+
+	return nil
+}