From 1245805c56b13219bdde57cdea1d64e6827842b7 Mon Sep 17 00:00:00 2001
From: laoquy056 <doremifason2000@gmail.com>
Date: Sun, 24 May 2026 17:32:37 +0700
Subject: [PATCH] fix: prevent release overflow

---
 src/index.ts      |  6 ++++++
 test/sema.test.ts | 18 ++++++++++++++++++
 2 files changed, 24 insertions(+)

diff --git a/src/index.ts b/src/index.ts
index d584c64..82ec2f0 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -193,6 +193,12 @@ export class Sema {
 	}
 
 	release(token?: any): void {
+		if (this.waiting.length === 0 && this.free.length >= this.nrTokens) {
+			throw new Error(
+				'Sema#release() was called more times than Sema#acquire()'
+			);
+		}
+
 		this.releaseEmitter.emit('release', this.noTokens ? '1' : token);
 	}
 
diff --git a/test/sema.test.ts b/test/sema.test.ts
index 929a796..10c63ac 100644
--- a/test/sema.test.ts
+++ b/test/sema.test.ts
@@ -41,6 +41,24 @@ test('tryAcquire returns undefined', async () => {
 	expect(s.tryAcquire()).toBeUndefined();
 });
 
+test('release throws when called without an acquired token', () => {
+	const s = new Sema(1);
+
+	expect(() => s.release()).toThrow(
+		'Sema#release() was called more times than Sema#acquire()'
+	);
+});
+
+test('release does not increase available tokens beyond the limit', async () => {
+	const s = new Sema(1);
+
+	await s.acquire();
+	s.release();
+
+	expect(s.tryAcquire()).toBeDefined();
+	expect(s.tryAcquire()).toBeUndefined();
+});
+
 test('Pausing works', () => {
 	const pauseFn = jest.fn();
 	const resumeFn = jest.fn();