General purpose thread-safe cache function

loadCacheFile.php

<?php

/**
 * @param  string   $file
 * @param  callable $tryLoad   (string $file, mixed & $data): bool
 * @param  callable $isExpired (string $file): bool
 * @param  callable $fallback  (string $file): string
 * @return mixed
 */
function loadCacheFile($file, $tryLoad, $isExpired, $fallback)
{
	if (!$isExpired($file) && $tryLoad($file, $data)) {
		return $data;
	}

	if (!is_dir(dirname($file))) {
		@mkdir(dirname($file)); // @ - directory may already exist
	}

	$handle = fopen("$file.lock", 'c+');
	if (!$handle || !flock($handle, LOCK_EX)) {
		throw new \RuntimeException("Unable to acquire exclusive lock '$file.lock'.");
	}

	if (!is_file($file) || $isExpired($file)) {
		$data = $fallback($file);
		if (file_put_contents("$file.tmp", $data) !== strlen($data) || !rename("$file.tmp", $file)) {
			@unlink("$file.tmp"); // @ - file may not exist
			throw new \RuntimeException("Unable to create '$file'.");
		}
	}

	if (!$tryLoad($file, $data)) {
		throw new \RuntimeException("Unable to load '$file'.");
	}

	flock($handle, LOCK_UN);
	return $data;
}