PHP并发写文件数据串行的问题

写日志代码：

$dir = rtrim($dir, '/') . '/' . ltrim($logFile, '/');

// 自动创建不存在的目录
$directory = dirname($dir);
if (!is_dir($directory)) {
    $oldUmask = umask(0);
    mkdir($directory, 0777, true);
    umask($oldUmask);
}   

$fd = fopen($dir, "a+");
if (!$fd) {
    error_log("Logger: Cannot open file ($dir)");
    return false;
}   

$logData = implode("\t", $data);

fwrite($fd, $logData. "\n");
fclose($fd);

同事反馈上报的日志格式错误，看了下日志，发现居然有串行的现象。

搜索一番才知道，当写的数据过大时，可能会产生串行的问题。

If handle was fopen()ed in append mode, fwrite()s are atomic (unless the size of string exceeds the filesystem's block size, on some platforms, and as long as the file is on a local filesystem). That is, there is no need to flock() a resource before calling fwrite(); all of the data will be written without interruption.

参考资料：
封装php的Log类