问题描述
我正在尝试寻找一种安全的方法来防止 cron 作业冲突(即，如果另一个实例已经在运行，则阻止它运行).
I'm trying to find a safe way to prevent a cron job collision (ie. prevent it from running if another instance is already running).
一些我发现推荐的选项 对文件使用锁.
这真的是一个安全的选择吗?例如，如果脚本死了会发生什么?锁会保留吗?
Is that really a safe option? What would happen if the script dies for example? Will the lock remain?
还有其他方法可以做到这一点吗?
Are there other ways of doing this?
推荐答案
此示例取自 http://php.net/flock 并稍作改动，这是一个正确的方式来做你想做的事:
This sample was taken at http://php.net/flock and changed a little and this is a correct way to do what you want:
$fp = fopen("/path/to/lock/file", "w+");
if (flock($fp, LOCK_EX | LOCK_NB)) { // do an exclusive lock
// do the work
flock($fp, LOCK_UN); // release the lock
} else {
echo "Couldn't get the lock!";
}
fclose($fp);
不要使用诸如 /tmp 或 /var/tmp 之类的位置，因为它们可能会被您的系统随时清除，因此根据文档弄乱了您的锁:
Do not use locations such as /tmp or /var/tmp as they could be cleaned up at any time by your system, thus messing with your lock as per the docs:
程序不得假定/tmp 中的任何文件或目录在程序调用之间都保留.
Programs must not assume that any files or directories in /tmp are preserved between invocations of the program.
https://refspecs.linuxfoundation.org/FHS_3.0/fhs/ch03s18.htmlhttps://refspecs.linuxfoundation.org/FHS_3.0/fhs/ch05s15.html
务必使用您可以控制的位置.
Do use a location that is under your control.
学分:
- Michal Perrin - 提议使用
w+而不是r+
- Michal Perrin - for proposing to use
w+instead ofr+
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