Implement ifAvailable option

lib/locks.js

@@ -44,24 +44,35 @@ class Mutex {
     this.current = null;
   }
 
-  enter(callback) {
-    this.queue.push(callback);
+  enter(lock) {
+    this.queue.push(lock);
     this.trying = true;
     return this.tryEnter();
   }
 
   tryEnter() {
     if (this.queue.length === 0) return;
     const prev = Atomics.exchange(this.flag, 0, LOCKED);
-    if (prev === UNLOCKED) {
-      this.owner = true;
-      this.trying = false;
-      const lock = this.queue.shift();
-      this.current = lock;
-      return lock.callback(lock).then(() => {
-        this.leave();
-      });
-    }
+    if (prev === LOCKED) return;
+    this.owner = true;
+    this.trying = false;
+    const lock = this.queue.shift();
+    this.current = lock;
+    return lock.callback(lock).then(() => {
+      this.leave();
+    });
+  }
+
+  enterIfAvailable(lock) {
+    if (this.owner) return lock.callback();
+    const prev = Atomics.exchange(this.flag, 0, LOCKED);
+    if (prev === LOCKED) return lock.callback();
+    this.owner = true;
+    this.trying = false;
+    this.current = lock;
+    return lock.callback(lock).then(() => {
+      this.leave();
+    });
   }
 
   leave() {
@@ -70,6 +81,7 @@ class Mutex {
     this.owner = false;
     this.current = null;
     sendMessage({ kind: 'leave', resourceName: this.name });
+    this.tryEnter();
   }
 }
 
@@ -82,6 +94,7 @@ const request = (resourceName, options, callback) => {
     resources.set(resourceName, mutex);
     sendMessage({ kind: 'create', resourceName, buffer });
   }
+  if (lock.ifAvailable) return mutex.enterIfAvailable(lock);
   return mutex.enter(lock);
 };