Locking Files for Concurrent Updates

When working with PHP, you may need to use flock to serialize writes to shared files. This guide explains the operation, shows what its arguments mean, and uses three separate examples to make the result easier to understand.

Locking Files for Concurrent Updates: This topic combines several operations. The code demonstrates the important sequence and its effect.

What Is Locking Files for Concurrent Updates in PHP?

Use flock to serialize writes to shared files. This topic combines several operations. The code demonstrates the important sequence and its effect.

Syntax:

See the complete PHP example below.

Parameters and return value: The signature above identifies the arguments and return type where the API has a single call. For topic guides, follow the sequence of calls in the examples. Always distinguish a returned value from an object or variable modified by reference.

Important: Locks are advisory and only work if every cooperating writer honors them. Network filesystems may have different semantics.

Example 1: Basic Usage

This example introduces the operation with a short and predictable input.

<?php

$file = tmpfile();
var_dump(flock($file, LOCK_EX));
flock($file, LOCK_UN);
fclose($file);

Output:

bool(true)

The code focuses on the main operation. This topic combines several operations. The code demonstrates the important sequence and its effect.

Example 2: Another Case

Now compare a different input, locale, date, or option to see another part of the behavior.

<?php

$file = tmpfile();
if (flock($file, LOCK_EX | LOCK_NB)) {
    fwrite($file, "Updated");
    flock($file, LOCK_UN);
}
fclose($file);

What changes? Locks are advisory and only work if every cooperating writer honors them. Network filesystems may have different semantics.

Practical Example: Applying It in an Application

Use the following separate example as a starting point for a small application task. Check any extension or environment requirements below before running it.

<?php

$filename = sys_get_temp_dir() . "/example-counter.lock";
$file = fopen($filename, "c+");
if ($file === false) {
    throw new RuntimeException("Cannot open shared file");
}
try {
    if (!flock($file, LOCK_EX)) {
        throw new RuntimeException("Cannot acquire lock");
    }
    rewind($file);
    $count = (int) stream_get_contents($file);
    rewind($file);
    ftruncate($file, 0);
    fwrite($file, (string) ($count + 1));
    fflush($file);
    flock($file, LOCK_UN);
} finally {
    fclose($file);
}

The practical example demonstrates how to apply this operation to multiple values, a reusable task, or a validated input. This topic combines several operations. The code demonstrates the important sequence and its effect.

Important Behavior and Edge Cases

• Core behavior: This topic combines several operations. The code demonstrates the important sequence and its effect.
• Inputs and results: Locks are advisory and only work if every cooperating writer honors them. Network filesystems may have different semantics.
• Alternatives: Database transactions are generally preferable for transactional shared business data.

Comparison With Related Functions

Common Beginner Mistakes

Key Takeaways

• Locking Files for Concurrent Updates helps you use flock to serialize writes to shared files.
• This topic combines several operations. The code demonstrates the important sequence and its effect.
• Locks are advisory and only work if every cooperating writer honors them. Network filesystems may have different semantics.

Use Locking Files for Concurrent Updates when you need to use flock to serialize writes to shared files. Start with the first example, compare the second, and adapt the practical example to your inputs. Confirm the return value and environment requirements before adding it to production code.