golang 实现cas

相比sync.WaitGroup里面的互斥锁，cas可以实现无锁等待一组任务执行完成后释放，示例代码如下

func TestCAS(t *testing.T) {
	var count int32 = 10000
	for i := 0; i < int(count); {
		go func() {
			defer func() { atomic.AddInt32(&count, -1) }()
			//do something
			//...
		}()
	}
	for atomic.LoadInt32(&count) > 0 {
	}
	t.Log("task exec finished")
}