From cc440e4b6d48e7e97a504ebcd763f69493b66085 Mon Sep 17 00:00:00 2001
From: Niklas Keller <me@kelunik.com>
Date: Sat, 19 Aug 2023 15:39:44 +0200
Subject: [PATCH] Add re-entry support to synchronized (#26)

---
 src/functions.php         | 12 +++++++
 test/SynchronizedTest.php | 73 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 85 insertions(+)

diff --git a/src/functions.php b/src/functions.php
index 4513854..3090be9 100644
--- a/src/functions.php
+++ b/src/functions.php
@@ -4,6 +4,7 @@
 
 use Amp\Pipeline\Queue;
 use Amp\Sync\Internal\ConcurrentIteratorChannel;
+use Revolt\EventLoop\FiberLocal;
 
 /**
  * Invokes the given Closure while maintaining a lock from the provided mutex.
@@ -18,11 +19,22 @@
  */
 function synchronized(Semaphore $semaphore, \Closure $synchronized, mixed ...$args): mixed
 {
+    static $reentry;
+    $reentry ??= new FiberLocal(fn () => new \WeakMap());
+
+    /** @var \WeakMap<Semaphore, bool> $existingLocks */
+    $existingLocks = $reentry->get();
+    if ($existingLocks[$semaphore] ?? false) {
+        return $synchronized(...$args);
+    }
+
     $lock = $semaphore->acquire();
+    $existingLocks[$semaphore] = true;
 
     try {
         return $synchronized(...$args);
     } finally {
+        unset($existingLocks[$semaphore]);
         $lock->release();
     }
 }
diff --git a/test/SynchronizedTest.php b/test/SynchronizedTest.php
index 5b52d81..9f9db41 100644
--- a/test/SynchronizedTest.php
+++ b/test/SynchronizedTest.php
@@ -27,4 +27,77 @@ public function testSynchronized(): void
 
         self::assertEquals([0, 1, 2], await($futures));
     }
+
+    public function testSynchronizedReentry(): void
+    {
+        $mutex = new LocalMutex;
+        $count = 0;
+
+        synchronized($mutex, function () use ($mutex, &$count) {
+            $count++;
+
+            synchronized($mutex, function () use (&$count) {
+                $count++;
+            });
+        });
+
+        self::assertSame(2, $count);
+    }
+
+    public function testSynchronizedReentryAsync(): void
+    {
+        $mutex = new LocalMutex;
+        $count = 0;
+
+        synchronized($mutex, function () use ($mutex, &$count) {
+            async(function () use ($mutex, &$count) {
+                synchronized($mutex, function () use (&$count) {
+                    $count++;
+                });
+            });
+
+            delay(1);
+
+            $count = 10;
+        });
+
+        delay(2);
+
+        // The async synchronized block must be executed after $count = 10 is executed
+        self::assertSame(11, $count);
+    }
+
+    public function testSynchronizedReentryDifferentLocks(): void
+    {
+        $mutexA = new LocalMutex;
+        $mutexB = new LocalMutex;
+
+        $lock = $mutexB->acquire();
+
+        $op = async(function () use ($mutexA, $mutexB) {
+            print 'Before ';
+
+            synchronized($mutexA, function () use ($mutexB) {
+                print 'before ';
+
+                synchronized($mutexB, function () {
+                    print 'X ';
+                });
+
+                print 'after ';
+            });
+
+            print 'After ';
+        });
+
+        delay(1);
+
+        print 'Unlock ';
+
+        $lock->release();
+
+        $op->await();
+
+        self::expectOutputString('Before before Unlock X after After ');
+    }
 }