Add TimeoutCancellationToken

lib/CancellationTokenSource.php

@@ -117,13 +117,16 @@ final class CancellationTokenSource {
         return $this->token;
     }
 
-    public function cancel() {
+    /**
+     * @param \Throwable|null $previous Exception to be used as the previous exception to CancelledException.
+     */
+    public function cancel(\Throwable $previous = null) {
         if ($this->onCancel === null) {
             return;
         }
 
         $onCancel = $this->onCancel;
         $this->onCancel = null;
-        $onCancel(new CancelledException);
+        $onCancel(new CancelledException($previous));
     }
 }

lib/CancelledException.php

@@ -9,4 +9,7 @@ namespace Amp;
  * @see CancellationTokenSource
  */
 class CancelledException extends \Exception {
+    public function __construct(\Throwable $previous = null) {
+        parent::__construct("The operation was cancelled", 0, $previous);
+    }
 }

lib/TimeoutCancellationToken.php

@@ -0,0 +1,62 @@
+<?php
+
+namespace Amp;
+
+/**
+ * A TimeoutCancellationToken automatically requests cancellation after the timeout has elapsed.
+ */
+final class TimeoutCancellationToken implements CancellationToken {
+    /** @var string */
+    private $watcher;
+
+    /** @var \Amp\CancellationToken */
+    private $token;
+
+    /**
+     * @param int $timeout Milliseconds until cancellation is requested.
+     */
+    public function __construct(int $timeout) {
+        $source = new CancellationTokenSource;
+        $this->token = $source->getToken();
+
+        $this->watcher = Loop::delay($timeout, static function () use ($source) {
+            $source->cancel(new TimeoutException);
+        });
+        Loop::unreference($this->watcher);
+    }
+
+    /**
+     * Cancels the delay watcher.
+     */
+    public function __destruct() {
+        Loop::cancel($this->watcher);
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function subscribe(callable $callback): string {
+        return $this->token->subscribe($callback);
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function unsubscribe(string $id) {
+        $this->token->unsubscribe($id);
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function isRequested(): bool {
+        return $this->token->isRequested();
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function throwIfRequested() {
+        $this->token->throwIfRequested();
+    }
+}

test/TimeoutCancellationTokenTest.php

@@ -0,0 +1,37 @@
+<?php
+
+namespace Amp\Test;
+
+use Amp\CancelledException;
+use Amp\Delayed;
+use Amp\Loop;
+use Amp\PHPUnit\TestCase;
+use Amp\TimeoutCancellationToken;
+use Amp\TimeoutException;
+
+class TimeoutCancellationTokenTest extends TestCase {
+    public function testTimeout() {
+        Loop::run(function () {
+            $token = new TimeoutCancellationToken(10);
+
+            $this->assertFalse($token->isRequested());
+            yield new Delayed(20);
+            $this->assertTrue($token->isRequested());
+
+            try {
+                $token->throwIfRequested();
+            } catch (CancelledException $exception) {
+                $this->assertInstanceOf(TimeoutException::class, $exception->getPrevious());
+            }
+        });
+    }
+
+    public function testWatcherCancellation() {
+        Loop::run(function () {
+            $token = new TimeoutCancellationToken(1);
+            $this->assertSame(1, Loop::getInfo()["delay"]["enabled"]);
+            unset($token);
+            $this->assertSame(0, Loop::getInfo()["delay"]["enabled"]);
+        });
+    }
+}