자바스크립트 : Mutex

.gitignore

@@ -1 +1,2 @@
-/**/tempCodeRunnerFile.js
+/**/tempCodeRunnerFile.js
+/**/node_modules

자바스크립트/concurrent/my-mutex.js

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+/**
+ * Promise.all을 사용하는 경우, 한번에 모든 Promise를 처리하므로, mutex를 걸어준다.
+ * 혹은 forEach, map 대신 reduce를 사용하거나, for문 사용해도 가능하다.
+ */
+
+class Mutex {
+  constructor() {
+    this._isLocked = false;
+  }
+
+  lock() {
+    this._isLocked = true;
+  }
+
+  unlock() {
+    this._isLocked = false;
+  }
+
+  release() {
+    this.unlock();
+  }
+
+  async acquire(count = 0) {
+    if (count >= 10) throw new Error("Mutex lock count exceeded");
+
+    const isLocked = this._isLocked;
+    if (!isLocked) {
+      this.lock();
+      return Promise.resolve();
+    } else {
+      return new Promise((resolve) => {
+        setTimeout(() => {
+          this.acquire(count + 1).then(resolve);
+        }, 100);
+      });
+    }
+  }
+}
+
+let sum = 0;
+const mutex = new Mutex();
+
+const wait = () =>
+  new Promise((resolve) => setTimeout(resolve, Math.random() * 50));
+
+async function add(order) {
+  await mutex.acquire();
+  console.log(`[${order}] start`);
+
+  await wait(); // async logic
+  sum += 1;
+
+  console.log(`[${order}] end`);
+  mutex.release();
+}
+
+async function main() {
+  console.log("start");
+  await Promise.all([add(1), add(2), add(3)]);
+  console.log("end");
+}
+
+main();

자바스크립트/concurrent/recursive-async.js

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+async function recursiveAsync(count = 0) {
+  console.log("count is", count);
+  return new Promise((resolve) =>
+    setTimeout(async () => {
+      await recursiveAsync(count + 1);
+      resolve();
+    }, 500)
+  );
+}
+
+async function main() {
+  console.log("start");
+  await recursiveAsync();
+  console.log("end");
+}
+
+main();