register_shutdown_function()在PHP中用於在腳本終止時執(zhí)行指定函數，無論腳本如何結束。 1. 它適用於正常結束、錯誤或手動停止的情況；2. 可傳遞參數給註冊的函數；3. 可註冊多個函數，按註冊順序依次執(zhí)行；4. 常用於日誌記錄、清理任務、錯誤處理等場景；5. 注意避免依賴已釋放資源，不進行耗時操作，並確保輸出緩衝處理得當。

You can use register_shutdown_function() in PHP to execute a function when your script is about to terminate — whether it finishes normally, hits an error, or is manually stopped. It's useful for cleanup tasks, logging, or final output handling.

What Is register_shutdown_function() ?

register_shutdown_function() allows you to register one or more functions that will be called automatically when the script ends. This includes:

• Normal script termination
• Fatal errors (with some limitations)
• When exit() or die() is called

Example:

 function my_shutdown() {
    echo "Script is ending now.\n";
}

register_shutdown_function('my_shutdown');

This will print “Script is ending now.” no matter how the script ends — unless it crashes hard (like a segmentation fault).

How to Use It with Parameters

You can also pass parameters to your shutdown function. Just include them after the function name in the call to register_shutdown_function() .

Example:

 function log_shutdown($message) {
    file_put_contents('shutdown.log', $message . PHP_EOL, FILE_APPEND);
}

register_shutdown_function('log_shutdown', 'Script ended at ' . date('Ymd H:i:s'));

This logs a timestamped message every time the script ends.

Note: If you're passing variables, make sure they're not dependent on resources that might be freed before the shutdown function runs.

Registering Multiple Shutdown Functions

You can register more than one function. They will be called in the order they were registered.

Example:

 register_shutdown_function('first_shutdown');
register_shutdown_function('second_shutdown');

function first_shutdown() {
    echo "First shutdown function\n";
}

function second_shutdown() {
    echo "Second shutdown function\n";
}

Output:

 First shutdown function
Second shutdown function

This lets you organize different tasks like logging, cleanup, and notifications separately.

Common Use Cases

Here are a few real-world scenarios where register_shutdown_function() comes in handy:

• Logging final stats – eg, memory usage, execution time
• Cleanup tasks – closing files, database connections, temp data
• Error handling – catching fatal errors and sending alerts
• Custom shutdown messages – especially helpful during CLI script debugging

However, keep in mind:

• You can't output headers once the script has started sending output
• Some resources may already be unavailable by the time the function runs

Also, if you're using output buffering, make sure to flush it if needed.

Things to Watch Out For

There are a few gotchas to be aware of:

• Fatal errors : While shutdown functions run after many types of errors, some internal engine failures may prevent them from executing.
• Performance impact : Don't do heavy processing in shutdown functions — it blocks the script from fully exiting until done.
• Function scope : If you're using object methods, pass the array syntax ( [$object, 'method'] ) instead of just the method name as a string.
• Order matters : If one function depends on another, make sure they're registered in the correct sequence.

So while it's powerful, it's best used for lightweight, critical end-of-script tasks.

That's basically it — not too complex, but easy to misuse if you're not careful with what and how you register.

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