Ensure promise is only cancelled if all derived promises cancel

README.md

@@ -268,7 +268,7 @@ If the resolver or canceller throw an exception, the promise will be rejected
 with that thrown exception as the rejection reason.
 
 The resolver function will be called immediately, the canceller function only
-once a consumer calls the `cancel()` method of the promise.
+once all consumers called the `cancel()` method of the promise.
 
 ### FulfilledPromise
 

src/Promise.php

@@ -10,6 +10,9 @@ class Promise implements PromiseInterface, CancellablePromiseInterface
     private $handlers = [];
     private $progressHandlers = [];
 
+    private $requiredCancelRequests = 0;
+    private $cancelRequests = 0;
+
     public function __construct(callable $resolver, callable $canceller = null)
     {
         $this->canceller = $canceller;
@@ -22,7 +25,13 @@ public function then(callable $onFulfilled = null, callable $onRejected = null,
             return $this->result->then($onFulfilled, $onRejected, $onProgress);
         }
 
+        $this->requiredCancelRequests++;
+
         return new static($this->resolver($onFulfilled, $onRejected, $onProgress), function($resolve, $reject, $progress) {
+            if (++$this->cancelRequests < $this->requiredCancelRequests) {
+                return;
+            }
+
             $this->cancel();
         });
     }

tests/PromiseTest/CancelTestTrait.php

@@ -157,4 +157,50 @@ public function cancelShouldCallCancellerFromDeepNestedPromiseChain()
 
         $promise->cancel();
     }
+
+    /** @test */
+    public function cancelCalledOnChildrenSouldOnlyCancelWhenAllChildrenCancelled()
+    {
+        $adapter = $this->getPromiseTestAdapter($this->expectCallableNever());
+
+        $child1 = $adapter->promise()
+            ->then()
+            ->then();
+
+        $adapter->promise()
+            ->then();
+
+        $child1->cancel();
+    }
+
+    /** @test */
+    public function cancelShouldTriggerCancellerWhenAllChildrenCancel()
+    {
+        $adapter = $this->getPromiseTestAdapter($this->expectCallableOnce());
+
+        $child1 = $adapter->promise()
+            ->then()
+            ->then();
+
+        $child2 = $adapter->promise()
+            ->then();
+
+        $child1->cancel();
+        $child2->cancel();
+    }
+
+    /** @test */
+    public function cancelShouldAlwaysTriggerCancellerWhenCalledOnRootPromise()
+    {
+        $adapter = $this->getPromiseTestAdapter($this->expectCallableOnce());
+
+        $adapter->promise()
+            ->then()
+            ->then();
+
+        $adapter->promise()
+            ->then();
+
+        $adapter->promise()->cancel();
+    }
 }