停止PHP脚本的并行执行

Question

I am trying to stop my cron script from allowing it to run in parallel. I need it so that if there is no current execution of it, the script will be allowed to run until it is complete, the script timesout or an exception occurs.

I have been trying to use the PHP flock function to engage a file lock, run the script and then release the lock. However, it still looks like I am able to run the script multiple times in parallel. Am I missing something?

Btw, I am developing on Mac OS X with the Mac filesystem, maybe this is the reason the file locks are being ignored? Though the PHP documentation only looks about NTFS filesystems?

        // Construct cron lock file path
    $cronLockFilePath = realpath(APPLICATION_PATH . '/locks/cron');

    // Get cron lock file
    $cronLockFile = fopen($cronLockFilePath, 'r');

    // Lock cron lock file
    if (flock($cronLockFile, LOCK_EX)) {

echo 'lock';
sleep(10);

    } else {

echo 'no lock';
    }

Answer 1

Your idea is basically correct, but tinkering with file locks generally leads to strange behaviour.

Just create a file on script start and delete it in the end. The presense of the file will indicate if the cron is already running. Make absolutely sure, that the file is deleted in the end, even if the cron runs into an error halfway through.