[FEATURE] Acquire a non-blocking lock should throw LockAcquireWouldBlockException

LockAcquireWouldBlockException should be thrown if non-blocking
lock would block according to the TYPO3 locking api.

Classes/Strategy/MutexAdapterStrategy.php

@@ -68,11 +68,20 @@ class MutexAdapterStrategy implements LockingStrategyInterface
     public function acquire($mode = self::LOCK_CAPABILITY_EXCLUSIVE)
     {
         $timeout = null;
-        if ($mode & static::LOCK_CAPABILITY_NOBLOCK) {
+        $isNonBlockingMode = $mode & static::LOCK_CAPABILITY_NOBLOCK;
+        if ($isNonBlockingMode) {
             $timeout = 0;
         }
 
-        return $this->mutex->acquireLock($timeout);
+        $isAcquired = $this->mutex->acquireLock($timeout);
+        if ($isNonBlockingMode && ! $isAcquired) {
+            throw new LockAcquireWouldBlockException(
+                'Failed to acquire lock because the request would block.',
+                1428700748
+            );
+        }
+
+        return $isAcquired;
     }
 
     /**

Tests/Unit/Strategy/MutexAdapterStrategyTest.php

@@ -98,6 +98,25 @@ class MutexAdapterStrategyTest extends UnitTestCase
         $this->assertTrue($sut->acquire($mode));
     }
 
+    /**
+     * @test
+     * @expectedException \TYPO3\CMS\Core\Locking\Exception\LockAcquireWouldBlockException
+     * @expectedExceptionMessage Failed to acquire lock because the request would block.
+     * @expectedExceptionCode 1428700748
+     */
+    public function itThrowsALockAcquireWouldBlockExceptionIfNonBlockingLockWhouldBlock()
+    {
+        $mode = LockingStrategyInterface::LOCK_CAPABILITY_EXCLUSIVE | LockingStrategyInterface::LOCK_CAPABILITY_NOBLOCK;
+        $mutex = $this->prophesize(Mutex::class);
+        $mutex
+            ->acquireLock(0)
+            ->shouldBeCalled()
+            ->willReturn(false);
+        $sut = new MutexAdapterStrategy($mutex->reveal());
+
+        $sut->acquire($mode);
+    }
+
     /**
      * @test
      */