Add Loop::supports to check for optional features

Author: kelunik

src/Loop.php

@@ -210,6 +210,18 @@ public static function unreference($eventIdentifier)
         self::get()->unreference($eventIdentifier);
     }
 
+    /**
+     * Check whether an optional feature is supported by the current event loop
+     * driver.
+     *
+     * @param int $feature Loop::FEATURE_* constant
+     *
+     * @return bool
+     */
+    public static function supports($feature) {
+        return self::get()->supports($feature);
+    }
+
     /**
      * Disable construction as this is a static class.
      */

src/LoopDriver.php

@@ -4,6 +4,8 @@
 
 interface LoopDriver
 {
+    const FEATURE_SIGNAL_HANDLING = 0b001;
+
     /**
      * Start the event loop.
      *
@@ -135,4 +137,18 @@ public function reference($eventIdentifier);
      * @return void
      */
     public function unreference($eventIdentifier);
+
+    /**
+     * Check whether an optional features is supported by this implementation
+     * and system.
+     *
+     * Example: If the implementation can handle signals using PCNTL, but the
+     * PCNTL extension is not available, the feature MUST NOT be marked as
+     * supported.
+     *
+     * @param int $feature FEATURE constant
+     *
+     * @return bool
+     */
+    public function supports($feature);
 }

src/UnsupportedFeatureException.php

@@ -0,0 +1,9 @@
+<?php
+
+use Interop\Async\EventLoop;
+
+/**
+ * Must be thrown if an optional feature is not supported by the current driver
+ * or system.
+ */
+class UnsupportedFeatureException extends \RuntimeException { }