Add option to retrieve current max depth

src/Loop/AbstractLoop.php

@@ -238,7 +238,7 @@ public function queue(callable $callback, array $args = [])
     /**
      * {@inheritdoc}
      */
-    public function maxQueueDepth($depth)
+    public function maxQueueDepth($depth = null)
     {
         return $this->callableQueue->maxDepth($depth);
     }

src/Loop/Loop.php

@@ -62,11 +62,12 @@ public function reInit();
     /**
      * Sets the maximum number of callbacks set with Loop::queue() that will be executed per tick.
      *
-     * @param int $depth Maximum number of functions to execute each tick. Use 0 for unlimited.
+     * @param int|null $depth Maximum number of functions to execute each tick. Use 0 for unlimited. Use null to
+     *     retrieve the current max depth.
      *
      * @return int Previous max depth.
      */
-    public function maxQueueDepth($depth);
+    public function maxQueueDepth($depth = null);
 
     /**
      * Queue a callback function to be run after all I/O has been handled in the current tick.

src/Loop/Structures/CallableQueue.php

@@ -77,12 +77,17 @@ public function clear()
     /**
      * Sets the maximum number of functions that can be called when the queue is called.
      *
-     * @param int $depth Maximum number of functions to execute when the queue is called. Use 0 for unlimited.
+     * @param int|null $depth Maximum number of functions to execute when the queue is called. Use 0 for unlimited.
+     *     Use null to just retrieve the current max depth.
      *
      * @return int Previous max depth.
      */
-    public function maxDepth($depth)
+    public function maxDepth($depth = null)
     {
+        if (null === $depth) {
+            return $this->maxDepth;
+        }
+
         $previous = $this->maxDepth;
 
         $depth = (int) $depth;

src/Loop/functions.php

@@ -83,11 +83,12 @@ function queue(callable $callback /* , ...$args */)
     /**
      * Sets the maximum number of callbacks set with queue() that will be executed per tick.
      *
-     * @param int $depth Maximum number of functions to execute each tick. Use 0 for unlimited.
+     * @param int|null $depth Maximum number of functions to execute each tick. Use 0 for unlimited. Use null to
+     *     retrieve the current max depth.
      *
      * @return int Previous max depth.
      */
-    function maxQueueDepth($depth)
+    function maxQueueDepth($depth = null)
     {
         return loop()->maxQueueDepth($depth);
     }

tests/Loop/Structures/CallableQueueTest.php

@@ -99,6 +99,8 @@ public function testInvoke()
     public function testMaxDepth()
     {
         $previous = $this->queue->maxDepth(1);
+
+        $this->assertSame(1, $this->queue->maxDepth());
 
         $this->queue->insert($this->createCallback(1));
         $this->queue->insert($this->createCallback(1));