Use a custom priority queue for timers

Fixes #220 by allowing immediate removal of the watcher from the queue. Insert and extract is O(log(n)), peeking is O(1), and removal is O(n).

lib/Loop/Internal/TimerQueue.php

@@ -0,0 +1,125 @@
+<?php
+
+namespace Amp\Loop\Internal;
+
+use Amp\Loop\Watcher;
+
+/**
+ * Uses a binary tree stored in an array to implement a heap.
+ */
+class TimerQueue
+{
+    /** @var TimerQueueEntry[] */
+    private $data = [];
+
+    /**
+     * Inserts the watcher into the queue. Time complexity: O(log(n)).
+     *
+     * @param Watcher $watcher
+     * @param int $expiration
+     */
+    public function insert(Watcher $watcher, int $expiration)
+    {
+        $entry = new TimerQueueEntry;
+        $entry->watcher = $watcher;
+        $entry->expiration = $expiration;
+
+        $node = \count($this->data);
+        $this->data[$node] = $entry;
+
+        while ($node !== 0 && $entry->expiration < $this->data[$parent = ($node - 1) >> 1]->expiration) {
+            $this->data[$node] = $this->data[$parent];
+            $this->data[$parent] = $entry;
+
+            $node = $parent;
+        }
+    }
+
+    /**
+     * Removes the given watcher from the queue. Time complexity: O(n).
+     *
+     * @param Watcher $watcher
+     */
+    public function remove(Watcher $watcher)
+    {
+        foreach ($this->data as $node => $entry) {
+            if ($entry->watcher === $watcher) {
+                $this->removeAndRebuild($node);
+                return;
+            }
+        }
+    }
+
+    /**
+     * Deletes and returns the Watcher on top of the heap. Time complexity: O(log(n)).
+     *
+     * @return  [Watcher, int] Tuple of the watcher and the expiration time.
+     */
+    public function extract(): array
+    {
+        if ($this->isEmpty()) {
+            throw new \Error('No data left in the heap.');
+        }
+
+        $data = $this->removeAndRebuild(0);
+
+        return [$data->watcher, $data->expiration];
+    }
+
+    /**
+     * @param int $node Remove the given node and then rebuild the data array from that node downward.
+     *
+     * @return TimerQueueEntry Removed entry.
+     */
+    private function removeAndRebuild(int $node): TimerQueueEntry
+    {
+        $length = \count($this->data) - 1;
+        $data = $this->data[$node];
+        $this->data[$node] = $this->data[$length];
+        unset($this->data[$length]);
+
+        while (($child = ($node << 1) + 1) < $length) {
+            if ($this->data[$child]->expiration < $this->data[$node]->expiration
+                && ($child + 1 >= $length || $this->data[$child]->expiration < $this->data[$child + 1]->expiration)
+            ) {
+                // Left child is less than parent and right child.
+                $swap = $child;
+            } elseif ($child + 1 < $length && $this->data[$child + 1]->expiration < $this->data[$node]->expiration) {
+                // Right child is less than parent and left child.
+                $swap = $child + 1;
+            } else { // Left and right child are greater than parent.
+                break;
+            }
+
+            $temp = $this->data[$node];
+            $this->data[$node] = $this->data[$swap];
+            $this->data[$swap] = $temp;
+            $node = $swap;
+        }
+
+        return $data;
+    }
+
+    /**
+     * Returns the value at the top of the heap (without removing it). Time complexity: O(1).
+     *
+     * @return  [Watcher, int] Tuple of the watcher and the expiration time.
+     */
+    public function peek(): array
+    {
+        if ($this->isEmpty()) {
+            throw new \Error('No data in the heap.');
+        }
+
+        return [$this->data[0]->watcher, $this->data[0]->expiration];
+    }
+
+    /**
+     * Determines if the heap is empty.
+     * @return  bool
+     */
+    public function isEmpty(): bool
+    {
+        return empty($this->data);
+    }
+}

lib/Loop/Internal/TimerQueueEntry.php

@@ -0,0 +1,17 @@
+<?php
+
+namespace Amp\Loop\Internal;
+
+use Amp\Loop\Watcher;
+use Amp\Struct;
+
+class TimerQueueEntry
+{
+    use Struct;
+
+    /** @var Watcher */
+    public $watcher;
+
+    /** @var int */
+    public $expiration;
+}

lib/Loop/NativeDriver.php

@@ -22,10 +22,7 @@ class NativeDriver extends Driver
     /** @var \Amp\Loop\Watcher[][] */
     private $writeWatchers = [];
 
-    /** @var int[] */
+    /** @var Internal\TimerQueue */
-    private $timerExpires = [];
-
-    /** @var \SplPriorityQueue */
     private $timerQueue;
 
     /** @var \Amp\Loop\Watcher[][] */
@@ -45,7 +42,7 @@ class NativeDriver extends Driver
 
     public function __construct()
     {
-        $this->timerQueue = new \SplPriorityQueue();
+        $this->timerQueue = new Internal\TimerQueue;
         $this->signalHandling = \extension_loaded("pcntl");
         $this->nowOffset = getCurrentTime();
         $this->now = \random_int(0, $this->nowOffset);
@@ -97,21 +94,13 @@ class NativeDriver extends Driver
             $blocking ? $this->getTimeout() : 0
         );
 
-        if (!empty($this->timerExpires)) {
         $scheduleQueue = [];
 
         try {
             while (!$this->timerQueue->isEmpty()) {
-                    list($watcher, $expiration) = $this->timerQueue->top();
+                list($watcher, $expiration) = $this->timerQueue->peek();
 
-                    $id = $watcher->id;
+                if ($expiration > $this->now()) { // Timer at top of queue has not expired.
-
-                    if (!isset($this->timerExpires[$id]) || $expiration !== $this->timerExpires[$id]) {
-                        $this->timerQueue->extract(); // Timer was removed from queue.
-                        continue;
-                    }
-
-                    if ($this->timerExpires[$id] > $this->now()) { // Timer at top of queue has not expired.
                     break;
                 }
 
@@ -119,15 +108,14 @@ class NativeDriver extends Driver
 
                 if ($watcher->type & Watcher::REPEAT) {
                     $expiration = $this->now() + $watcher->value;
-                        $this->timerExpires[$watcher->id] = $expiration;
                     $scheduleQueue[] = [$watcher, $expiration];
                 } else {
-                        $this->cancel($id);
+                    $this->cancel($watcher->id);
                 }
 
                 try {
                     // Execute the timer.
-                        $result = ($watcher->callback)($id, $watcher->data);
+                    $result = ($watcher->callback)($watcher->id, $watcher->data);
 
                     if ($result === null) {
                         continue;
@@ -145,8 +133,9 @@ class NativeDriver extends Driver
                 }
             }
         } finally {
-                foreach ($scheduleQueue as $item) {
+            foreach ($scheduleQueue as list($watcher, $expiration)) {
-                    $this->timerQueue->insert($item, -$item[1]);
+                if ($watcher->enabled) {
+                    $this->timerQueue->insert($watcher, $expiration);
                 }
             }
         }
@@ -266,24 +255,15 @@ class NativeDriver extends Driver
      */
     private function getTimeout(): int
     {
-        while (!$this->timerQueue->isEmpty()) {
+        if (!$this->timerQueue->isEmpty()) {
-            list($watcher, $expiration) = $this->timerQueue->top();
+            list($watcher, $expiration) = $this->timerQueue->peek();
 
-            $id = $watcher->id;
+            $expiration -= getCurrentTime() - $this->nowOffset;
-
-            if (!isset($this->timerExpires[$id]) || $expiration !== $this->timerExpires[$id]) {
-                $this->timerQueue->extract(); // Timer was removed from queue.
-                continue;
-            }
-
-            $expiration -= $this->now();
 
             if ($expiration < 0) {
                 return 0;
             }
 
-            $this->nowUpdateNeeded = true; // Loop will block, so trigger now update after blocking.
-
             return $expiration;
         }
 
@@ -312,8 +292,7 @@ class NativeDriver extends Driver
                 case Watcher::DELAY:
                 case Watcher::REPEAT:
                     $expiration = $this->now() + $watcher->value;
-                    $this->timerExpires[$watcher->id] = $expiration;
+                    $this->timerQueue->insert($watcher, $expiration);
-                    $this->timerQueue->insert([$watcher, $expiration], -$expiration);
                     break;
 
                 case Watcher::SIGNAL:
@@ -362,7 +341,7 @@ class NativeDriver extends Driver
 
             case Watcher::DELAY:
             case Watcher::REPEAT:
-                unset($this->timerExpires[$watcher->id]);
+                $this->timerQueue->remove($watcher);
                 break;
 
             case Watcher::SIGNAL: