Content
First Wayflock helpcrontab config
Second WayAttention Programing LanguageReference
Two ways of crontab avoiding multiple executions. The first way is to use the shell command
flock to implement, The second way is to use
ps aux | grep'pid'.
First Way
flock help
$ flock -h
Usage:
flock [options] <file>|<directory> <command> [<argument>...]
flock [options] <file>|<directory> -c <command>
flock [options] <file descriptor number>
Manage file locks from shell scripts.
Options:
-s, --shared get a shared lock
-x, --exclusive get an exclusive lock (default)
-u, --unlock remove a lock
-n, --nonblock fail rather than wait
-w, --timeout <secs> wait for a limited amount of time
-E, --conflict-exit-code <number> exit code after conflict or timeout
-o, --close close file descriptor before running command
-c, --command <command> run a single command string through the shell
-F, --no-fork execute command without forking
--verbose increase verbosity
-h, --help display this help
-V, --version display version
For more details see flock(1).
crontab config
* * * * * flock -xn /tmp/my_lock -c "php test.php"
Second Way
<?php
crontab_avoid_multi_exec($argv[0]);
//Do Something
sleep(20);
function crontab_avoid_multi_exec($filename) {
//Querying and storing PID can use memcached, files, redis, and so on.
$command = "ps aux | grep '{$filename}' | grep -v 'grep' | wc -l";
exec($command, $count);
if ( $count[0] > 1 ) {
die("Crontab job can only run one!");
}
}
?>
Attention Programing Language
When the parent process uses flock, the child process reuses the file descriptor as well.
Reference
https://www.php.net/manual/en/function.exec.php https://www.cnblogs.com/wangxusummer/p/4933492.html
