From d678f4ff0e04455e591eae4d66e80dc8ab7ce57c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Michael=20Vo=C5=99=C3=AD=C5=A1ek?= <mvorisek@mvorisek.cz>
Date: Sun, 29 Nov 2020 15:58:29 +0100
Subject: [PATCH 1/2] Limit max. sleep duration per loop iteration

---
 classes/util/Loop.php | 47 +++++++++++++++++--------------------------
 1 file changed, 18 insertions(+), 29 deletions(-)

diff --git a/classes/util/Loop.php b/classes/util/Loop.php
index e8203d00..ae1f1b9c 100644
--- a/classes/util/Loop.php
+++ b/classes/util/Loop.php
@@ -17,20 +17,6 @@
  */
 class Loop
 {
-    /**
-     * Minimum time that we want to wait, between lock checks. In micro seconds.
-     *
-     * @var double
-     */
-    private const MINIMUM_WAIT_US = 1e4; // 0.01 seconds
-
-    /**
-     * Maximum time that we want to wait, between lock checks. In micro seconds.
-     *
-     * @var double
-     */
-    private const MAXIMUM_WAIT_US = 5e5; // 0.50 seconds
-
     /**
      * @var int The timeout in seconds.
      */
@@ -92,35 +78,38 @@ public function execute(callable $code)
         $this->looping = true;
 
         // At this time, the lock will time out.
-        $deadline = microtime(true) + $this->timeout;
+        $deadlineTs = microtime(true) + $this->timeout;
+
+        $minWaitSecs = 0.1e-3; // 0.1 ms
+        $maxWaitSecs = max(0.05, min(25, $this->timeout / 120)); // 50 ms to 25 s, based on timeout
 
         $result = null;
-        for ($i = 0; $this->looping && microtime(true) < $deadline; ++$i) {
+        for ($i = 0; microtime(true) < $deadlineTs; ++$i) {
             $result = $code();
             if (!$this->looping) {
                 break;
             }
 
             // Calculate max time remaining, don't sleep any longer than that.
-            $usecRemaining = intval(($deadline - microtime(true)) * 1e6);
-
-            // We've ran out of time.
-            if ($usecRemaining <= 0) {
-                throw TimeoutException::create($this->timeout);
+            $remainingSecs = $deadlineTs - microtime(true);
+            if ($remainingSecs <= 0) {
+                break;
             }
 
-            $min = min(
-                (int) self::MINIMUM_WAIT_US * 1.25 ** $i,
-                self::MAXIMUM_WAIT_US
+            $minSecs = min(
+                $minWaitSecs * 1.5 ** $i,
+                max($minWaitSecs, $maxWaitSecs / 2)
+            );
+            $maxSecs = min($minSecs * 2, $maxWaitSecs);
+            $sleepMicros = min(
+                (int)($remainingSecs * 1e6),
+                random_int((int)($minSecs * 1e6), (int)($maxSecs * 1e6))
             );
-            $max = min($min * 2, self::MAXIMUM_WAIT_US);
-
-            $usecToSleep = min($usecRemaining, random_int((int)$min, (int)$max));
 
-            usleep($usecToSleep);
+            usleep($sleepMicros);
         }
 
-        if (microtime(true) >= $deadline) {
+        if (microtime(true) >= $deadlineTs) {
             throw TimeoutException::create($this->timeout);
         }
 

From b3d64bcdd8bdb7bfca0d9e23bdee443d770f5ec6 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Michael=20Vo=C5=99=C3=AD=C5=A1ek?= <mvorisek@mvorisek.cz>
Date: Sun, 29 Nov 2020 16:33:18 +0100
Subject: [PATCH 2/2] prevent looping with 0 us on systems with unprecise
 microtime

---
 classes/util/Loop.php | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/classes/util/Loop.php b/classes/util/Loop.php
index ae1f1b9c..0657568e 100644
--- a/classes/util/Loop.php
+++ b/classes/util/Loop.php
@@ -84,7 +84,7 @@ public function execute(callable $code)
         $maxWaitSecs = max(0.05, min(25, $this->timeout / 120)); // 50 ms to 25 s, based on timeout
 
         $result = null;
-        for ($i = 0; microtime(true) < $deadlineTs; ++$i) {
+        for ($i = 0; ; ++$i) {
             $result = $code();
             if (!$this->looping) {
                 break;
@@ -102,7 +102,7 @@ public function execute(callable $code)
             );
             $maxSecs = min($minSecs * 2, $maxWaitSecs);
             $sleepMicros = min(
-                (int)($remainingSecs * 1e6),
+                max(10, (int)($remainingSecs * 1e6)),
                 random_int((int)($minSecs * 1e6), (int)($maxSecs * 1e6))
             );