sem_acquire() acquires a System V semaphore, waiting unless nonblocking mode is requested. This guide explains the function with focused examples and the decisions that matter in real applications.
What Is sem_acquire() in PHP?
Acquires a System V semaphore, waiting unless nonblocking mode is requested.
A typical call looks like this:
<?php
sem_acquire($semaphore, [$non_blocking]);
The input arguments shown in the call identify the relevant connection, resource, value, path or configuration for the operation. Pay attention to argument order and to the return value demonstrated below.
Example 1: Basic Usage
This first example uses sem_acquire() directly to demonstrate its basic purpose.
<?php
$semaphore = sem_get(ftok(__FILE__, "a")); sem_acquire($semaphore); sem_release($semaphore);
The returned value illustrates acquires a System V semaphore, waiting unless nonblocking mode is requested. Always release acquired locks, even on exceptions.
Example 2: A Different Input or Option
The next example changes the input or option, showing another supported use of sem_acquire().
<?php
$semaphore = sem_get(ftok(__FILE__, "b")); var_dump(sem_acquire($semaphore, true)); sem_release($semaphore);
The returned value illustrates acquires a System V semaphore, waiting unless nonblocking mode is requested. Always release acquired locks, even on exceptions.
Practical Example: Applying the Function
In application code, sem_acquire() belongs in a controlled workflow with input validation, a checked result and cleanup where needed.
<?php
$semaphore = sem_get(ftok(__FILE__, "c")); if (sem_acquire($semaphore)) { try { echo "Critical section"; } finally { sem_release($semaphore); } }
The returned value illustrates acquires a System V semaphore, waiting unless nonblocking mode is requested. Always release acquired locks, even on exceptions.
Important Behavior and Edge Cases
- Main behavior: Acquires a System V semaphore, waiting unless nonblocking mode is requested.
- Important limitation: Always release acquired locks, even on exceptions.
- Requirements: System V IPC support and operating-system permissions are required.
Comparison With Related Functions
| Function or Approach | When to Use It |
|---|---|
sem_acquire() | Acquires a System V semaphore, waiting unless nonblocking mode is requested. |
sem_release | Releases a System V semaphore previously acquired by the process. |
Common Beginner Mistakes
| Mistake | Correct Approach |
|---|---|
Ignoring the specific limits or preconditions of sem_acquire(). | Always release acquired locks, even on exceptions. |
| Assuming every environment produces the same result. | System V IPC support and operating-system permissions are required. |
Key Takeaways
- Acquires a System V semaphore, waiting unless nonblocking mode is requested.
- Always release acquired locks, even on exceptions.
- System V IPC support and operating-system permissions are required.
Use sem_acquire() when its behavior matches your task, and verify the relevant return value before taking further action. The output depends on the local configuration when it uses resources, files or an interactive terminal.