#23: Improved double checked locking

- The `then` method now returns the return value of the locked code
callable.
- The `check` method now returns false if check fails.
- Updated tests for double checked locking.

Author: TheLevti

classes/util/DoubleCheckedLocking.php

@@ -56,7 +56,14 @@ public function setCheck(callable $check)
      * Both the check and the code execution are locked by a mutex.
      * Only if the check fails the method returns before acquiring a lock.
      *
-     * @param callable $code The locked code.
+     * If then returns boolean FALSE, the check did not pass before or after
+     * acquiring the lock. A boolean FALSE can also be returned from the
+     * synchronized code to indicate that processing did not occure or has
+     * failed. It is up to the user to decide.
+     *
+     * @param  callable $code The locked code.
+     * @return mixed Boolean FALSE if check did not pass or mixed for what ever
+     *               the synchronized code returns.
      *
      * @throws \Exception The execution block or the check threw an exception.
      * @throws LockAcquireException The mutex could not be acquired.
@@ -65,12 +72,15 @@ public function setCheck(callable $check)
     public function then(callable $code)
     {
         if (!call_user_func($this->check)) {
-            return;
+            return false;
         }
-        $this->mutex->synchronized(function () use ($code) {
-            if (call_user_func($this->check)) {
-                call_user_func($code);
+
+        return $this->mutex->synchronized(function () use ($code) {
+            if (!call_user_func($this->check)) {
+                return false;
             }
+
+            return call_user_func($code);
         });
     }
 }

tests/util/DoubleCheckedLockingTest.php

@@ -44,9 +44,12 @@ public function testCheckFailsAcquiresNoLock()
         $this->checkedLocking->setCheck(function () {
             return false;
         });
-        $this->checkedLocking->then(function () {
+        $result = $this->checkedLocking->then(function () {
             $this->fail();
         });
+
+        // Failed check should return false.
+        $this->assertFalse($result);
     }
 
     /**
@@ -63,23 +66,31 @@ public function testLockedCheckAndExecution()
                 ->method("synchronized")
                 ->willReturnCallback(function (callable $block) use (&$lock) {
                     $lock++;
-                    call_user_func($block);
+                    $result = call_user_func($block);
                     $lock++;
+
+                    return $result;
                 });
 
         $this->checkedLocking->setCheck(function () use (&$lock, &$check) {
             if ($check == 1) {
                 $this->assertEquals(1, $lock);
             }
             $check++;
+
             return true;
         });
 
-        $this->checkedLocking->then(function () use (&$lock) {
+        $result = $this->checkedLocking->then(function () use (&$lock) {
             $this->assertEquals(1, $lock);
+
+            return 'test';
         });
 
         $this->assertEquals(2, $check);
+
+        // Synchronized code should return a test string.
+        $this->assertEquals('test', $result);
     }
 
     /**
@@ -98,9 +109,12 @@ public function testCodeNotExecuted(callable $check)
                 });
 
         $this->checkedLocking->setCheck($check);
-        $this->checkedLocking->then(function () {
+        $result = $this->checkedLocking->then(function () {
             $this->fail();
         });
+
+        // Each failed check should return false.
+        $this->assertFalse($result);
     }
 
     /**
@@ -142,9 +156,13 @@ public function testCodeExecuted()
         });
 
         $executed = false;
-        $this->checkedLocking->then(function () use (&$executed) {
+        $result = $this->checkedLocking->then(function () use (&$executed) {
             $executed = true;
+
+            return 'test';
         });
+
         $this->assertTrue($executed);
+        $this->assertEquals('test', $result);
     }
 }