clusterfudge · August 23, 2013 22:58 · Aug 23, 2013
diff --git a/lock.js b/lock.js
@@ -0,0 +1,55 @@
+var Lock = function() {
+    this.readLocks = [];
+    this.writeLocks = [];
+}
+
+Lock.prototype.getReadLock = function(callback) {
+    var self = this;
+    if (this.writeLocks.length > 0) {
+        setTimeout(function() {self.getReadLock(callback);}, 5);
+    } else {
+        self.readLocks.push(true);
+        var released = false;
+        try {
+            if (callback) {
+                callback(function() {
+                    self.readLocks.pop();
+                    released = true;
+                });
+            }
+        } catch (ex) {
+            if (!released) {
+                self.readLocks.pop();
+            }
+            throw ex;
+        }
+    }
+}
+
+Lock.prototype.getWriteLock = function(callback) {
+    var self = this;
+    var release = function() {
+        self.writeLocks.shift();
+    }
+    if (self.writeLocks.length > 0) {
+        setTimeout(function() {self.getWriteLock(callback);}, 10);
+        return;
+    }
+    self.writeLocks.push(function() {callback(release);});
+    var invokeWriteCallback = function() {
+        if (self.readLocks.length == 0) {
+            var cb = self.writeLocks[0];
+            if (cb) {
+                self.writeLocks[0] = null;
+                cb();
+            } else {
+                setTimeout(invokeWriteCallback, 10);
+            }
+        } else {
+            setTimeout(invokeWriteCallback, 10);
+        }
+    }
+    invokeWriteCallback();
+
+
+}