From 07437f705b52888cea0fa282401b6df15ab860ce Mon Sep 17 00:00:00 2001
From: David Flatz
Date: Thu, 11 May 2023 09:31:37 +0200
Subject: Use flock for locking to prevent stale locks, when process gets
 killed

---
 it_url.class | 31 ++++++++++++++++++++-----------
 1 file changed, 20 insertions(+), 11 deletions(-)

diff --git a/it_url.class b/it_url.class
index 014610c..cfa2bef 100644
--- a/it_url.class
+++ b/it_url.class
@@ -605,7 +605,7 @@ static function get_cache($p = array())
 	{
 		$fileexists = $filemtime !== true;
 
-		if ($lock = !$p['lock'] ?: it_url::_lock($path))
+		if ($lock = !$p['lock'] ?: it_url::_lock($path, $p))
 		{
 			# Touch existing file to prevent locking other getters while refreshing
 			if ($fileexists)
@@ -657,7 +657,7 @@ static function get_cache($p = array())
 
 		if ($filemtime = $isnewfile ? true : it_url::_expired($path, $p['maxage']))	# Outdated(non-zero int) or non-existant(true)?
 		{
-			if ($lock = !$p['lock'] ?: it_url::_lock($path))
+			if ($lock = !$p['lock'] ?: it_url::_lock($path, $p))
 			{
 				# Touch existing file to prevent locking other getters while refreshing
 				if ($filemtime !== true)
@@ -759,10 +759,20 @@ static function _expired($path, $maxage, $randomexpire = 0)
  * @param $path File to lock
  * @return Lock handle if successfully locked file
  */
-static function _lock($path)
+static function _lock($path, $p = [])
 {
-	$force = EDC('nocache') || (($mtime = @filemtime("$path.lock")) && (time() - $mtime > 30)); # expire forgotten locks
-	return @it::fopen("$path.lock", $force ? "w" : "x");
+	if (!($fh = it::fopen("$path.lock", "w")))
+		return false;
+
+	if (!flock($fh, LOCK_EX | LOCK_NB))
+	{
+		if (($mtime = @filemtime("$path.lock")) && (time() - $mtime > 30))
+			it::error((array)$p['it_error'] + ['title' => "stale lock epired for $path"]); # FIXME 2023-07 DF remove stale lock expiration if never triggered
+		else
+			return false;
+	}
+
+	return $fh;
 }
 
 /**
@@ -790,16 +800,15 @@ static function _waitforlockedfile($path, $p)
 	$sleeptime = 0.1; # seconds to wait per pass
 
 	# wait until cache is ready, then read from cache
-	for ($maxpasses = $p['timeout'] / $sleeptime, $passes = 0; ($lockedbyother = file_exists("$path.lock")) && ($passes < $maxpasses); ++$passes)
-	{
+	for ($maxpasses = $p['timeout'] / $sleeptime, $passes = 0; !($lock = self::_lock("$path", $p)) && ($passes < $maxpasses); ++$passes)
 		usleep($sleeptime * 1000000);
-		clearstatcache();
-	}
 
-	if ($lockedbyother)
+	if (!$lock)
 		it::error((array)$p['it_error'] + ['title' => ($passes < $maxpasses ? "error getting url" : "timeout") . " in it_url::get_cache(): url={$p['url']}, passes=$passes, maxpasses=$maxpasses, path=$path"]);
+	else
+		self::_unlock($path, $lock);
 
-	return !$lockedbyother && file_exists($path);
+	return $lock && file_exists($path);
 }
 
 /**
-- 
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