fopen(file，w +)在我可以检查文件是否被flock()锁定之前将其截断

问题描述

我有一个函数，该函数接收文件名和json对象以写入文本文件.

I have a function which receives a filename and a json object to write to a text file.

对象已更新，需要完全替换文件的当前内容.每个站点访问者都有自己的文件.多次快速更改会导致以下情况:文件被fopen(file,w+)截断，然后由于被锁定而未被写入.最终结果是空文件.

The object is updated and needs to entirely replace the current contents of the file. Each site visitor has their own file. Multiple rapid changes create a situation where the file is truncated by fopen(file,w+), then not written to as it's locked. End result is empty file.

我敢肯定有一种简单的标准方法可以做到这一点，因为它是一种通常的活动.理想情况下，我正在寻找的是一种在w+模式下用fopen截断文件之前检查文件是否具有锁定的方法，或者是一种切换模式的方法.

I'm sure there's a standard simply way to do this as it's such a usual activity. Ideally what I'm looking for is a way to check if a file has a lock before truncating the file with fopen in w+ mode or a way to switch modes.

您似乎不得不用fopen()截断文件以使文件句柄传递给flock()来检查它是否被锁定，这似乎很奇怪-但您只是将其截断了，所以有什么用呢?

It seems strange that you would have to truncate the file with fopen() to get a file handle to pass to flock() to check if it's locked -- but you just truncated it, so what's the point?

这是我到目前为止拥有的功能:

Here's the function I have so far:

function updateFile($filename, $jsonFileData) {
    $fp = fopen($filename,"w+");
    if (flock($fp, LOCK_EX)) {
        fwrite($fp, $jsonFileData);
        flock($fp, LOCK_UN);
        fclose($fp);
        return true;
    } else {
        fclose($fp);
        return false;
    }
}

推荐答案

PHP手册只需稍作修改即可完成您想要的操作.使用 "c"模式打开文件进行创建如果它不存在，也不要截断它.

Example #1 from the PHP manual will do what you want with a slight modification. Use the "c" mode to open the file for writing, create it if it doesn't exist, and don't truncate it.

$fp = fopen("/tmp/lock.txt", "c");

if (flock($fp, LOCK_EX)) {  // acquire an exclusive lock
    ftruncate($fp, 0);      // truncate file
    fwrite($fp, "Write something here\n");
    fflush($fp);            // flush output before releasing the lock
    flock($fp, LOCK_UN);    // release the lock
} else {
    echo "Couldn't get the lock!";
}

fclose($fp);

"c"模式的完整说明:

Full description of the "c" mode:

它看起来好像不是您需要的，但是如果您想同时读写，还可以使用相应的"c+"模式.

It doesn't look like you need it, but there's also a corresponding "c+" mode if you want to both read and write.

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