How can PHP scripts prevent multiple instances from running simultaneously?

To prevent multiple instances of a PHP script from running simultaneously, you can use a lock file mechanism. When the script starts, it checks for the existence of a lock file. If the lock file exists, it means another instance is already running, so the script exits. If the lock file doesn't exist, the script creates the lock file and proceeds with its execution. Once the script finishes, it deletes the lock file to allow other instances to run. 

$lockFile = 'script.lock';

if (file_exists($lockFile)) {
    echo "Another instance is already running. Exiting.";
    exit;
}

file_put_contents($lockFile, '');

// Your script code here

unlink($lockFile);

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PHP script prevent multiple instances running simultaneously

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