From dd84b9d64fb98746a230cd24233ff50a562c39c9 Mon Sep 17 00:00:00 2001
From: 简律纯 <hsiangnianian@outlook.com>
Date: Fri, 28 Apr 2023 01:36:44 +0800
Subject:

---
 cli/internal/util/semaphore.go | 43 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)
 create mode 100644 cli/internal/util/semaphore.go

(limited to 'cli/internal/util/semaphore.go')

diff --git a/cli/internal/util/semaphore.go b/cli/internal/util/semaphore.go
new file mode 100644
index 0000000..ef29df0
--- /dev/null
+++ b/cli/internal/util/semaphore.go
@@ -0,0 +1,43 @@
+package util
+
+// 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")
+	}
+}
-- 
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