From fcdf36fbbc45137d5878a8d29a0566e4789ecdb2 Mon Sep 17 00:00:00 2001
From: "jian.han" <jian.han@neds.com>
Date: Fri, 12 Jan 2018 14:36:49 +1000
Subject: [PATCH] added sem pattern

---
 concurrency/semaphore/main.go | 63 +++++++++++++++++++++++++++++++++++
 1 file changed, 63 insertions(+)
 create mode 100644 concurrency/semaphore/main.go

diff --git a/concurrency/semaphore/main.go b/concurrency/semaphore/main.go
new file mode 100644
index 0000000..91d1b77
--- /dev/null
+++ b/concurrency/semaphore/main.go
@@ -0,0 +1,63 @@
+package main
+
+import (
+	"errors"
+	"time"
+
+	"github.com/davecgh/go-spew/spew"
+)
+
+func main() {
+	tickets, timeout := 1, 3*time.Second
+	s := New(tickets, timeout)
+	if err := s.Aquire(); err != nil {
+		panic(err)
+	}
+	// do important work
+	spew.Dump("Test")
+	if err := s.Release(); err != nil {
+		panic(err)
+	}
+}
+
+// https://github.com/tmrts/go-patterns/blob/master/synchronization/semaphore.md
+var (
+	ErrNoTickets      = errors.New("semaphore: could not aquire semaphore")
+	ErrIllegalRelease = errors.New("semaphore: Can not release the semaphore without acquiring it first")
+)
+
+type Interface interface {
+	Aquire() error
+	Release() error
+}
+
+type implementation struct {
+	sem     chan struct{}
+	timeout time.Duration
+}
+
+func (s *implementation) Aquire() error {
+	select {
+	case s.sem <- struct{}{}:
+		return nil
+	case <-time.After(s.timeout):
+		return ErrNoTickets
+	}
+}
+
+func (s *implementation) Release() error {
+	select {
+	case _ = <-s.sem:
+		return nil
+	case <-time.After(s.timeout):
+		return ErrIllegalRelease
+	}
+	return nil
+}
+
+func New(tickets int, timeout time.Duration) Interface {
+	return &implementation{
+		sem:     make(chan struct{}, tickets),
+		timeout: timeout,
+	}
+}