An explanation of php flock usage examples

php flock usage example

bool flock ( resource $handle , int $operation [, int &$wouldblock ] )

flock()Allows the execution of a simple function that can be used on any platform Read/write model (including most Unix derivatives and windows)

Prior to PHP 5.3.2, the lock will be released by fclose() (will be called automatically after the script ends), now you need to manually unlock

operation

1. LOCK_SH Obtain shared lock (reading program)

2.LOCK_EX Obtain exclusive lock (writing program)

3.LOCK_UN Release the lock (whether shared or exclusive)

4.LOCK_NB Not locked when flock() Blocking

Example 1: A uses an exclusive lock to write the file, B reads the file, blocking

a.php

<?php
$file = &#39;test.txt&#39;;
$fp = fopen($file, &#39;w&#39;);
if(flock($fp, LOCK_EX)){            // 取得独占锁
    fwrite($fp, "Hello World\r\n"); // 写入数据
    sleep(10);                      // sleep 10秒，文件被锁定
    fwrite($fp, "Hello PHP\r\n");   // 写入数据
    flock($fp, LOCK_UN);            // 解锁
}
fclose($fp);
?>

b.php

<?php
$file = &#39;test.txt&#39;;
$fp = fopen($file, &#39;r&#39;);
if(flock($fp, LOCK_SH)){ // 取得贡献锁
    while(!feof($fp)){
        echo fread($fp, 100);
    }
    flock($fp, LOCK_UN);
}
fclose($fp);
?>

Execute a first .php, and then execute b.php

a to obtain the exclusive lock, b can only wait until a is executed and the lock is released before b can be executed, Blocking

Example 2: A and B both use shared locks and do not block

a.php

<?php
$file = &#39;test.txt&#39;;
$fp = fopen($file, &#39;r&#39;);
if(flock($fp, LOCK_SH)){ // 取得共享锁
    sleep(10);           // sleep 10秒
    while(!feof($fp)){
        echo fread($fp, 100);
    }
    flock($fp, LOCK_UN);
}
fclose($fp);
?>

b.php

<?php
$file = &#39;test.txt&#39;;
$fp = fopen($file, &#39;r&#39;);
if(flock($fp, LOCK_SH)){ // 取得共享锁
    while(!feof($fp)){
        echo fread($fp, 100);
    }
    flock($fp, LOCK_UN);
}
fclose($fp);
?>

Execute a first .php, and then execute b.php

b can output the file content without waiting for a to finish executing, non-blocking

Example 3: Both A and B use exclusive locks to write files, blocking

## a.php

<?php
$file = &#39;test.txt&#39;;
$fp = fopen($file, &#39;a&#39;);
if(flock($fp, LOCK_EX)){            // 取得独占锁
    fwrite($fp, "Hello World\r\n"); // 写入数据
    sleep(10);                      // sleep 10秒，文件被锁定
    fwrite($fp, "Hello PHP\r\n");   // 写入数据
    flock($fp, LOCK_UN);            // 解锁
}
fclose($fp);
?>

b.php

<?php
$file = &#39;test.txt&#39;;
$fp = fopen($file, &#39;a&#39;);
if(flock($fp, LOCK_EX)){                    // 取得独占锁
    fwrite($fp, "How Are You\r\n");         // 写入数据
    fwrite($fp, "Show Me The Money\r\n");   // 写入数据
    flock($fp, LOCK_UN);                    // 解锁
}
fclose($fp);
?>

Execute a.php first, Then execute b.php

b needs to wait for a to be executed before writing data, blocking

Example 4: LOCK_NB does not block or wait when locked

##a.php

<?php
$file = &#39;test.txt&#39;;
$fp = fopen($file, &#39;a&#39;);
if(flock($fp, LOCK_EX)){            // 取得独占锁
    fwrite($fp, "Hello World\r\n"); // 写入数据
    sleep(10);                      // sleep 10秒，文件被锁定
    fwrite($fp, "Hello PHP\r\n");   // 写入数据
    flock($fp, LOCK_UN);            // 解锁
}
fclose($fp);
?>

b.php

<?php
$file = &#39;test.txt&#39;;
$fp = fopen($file, &#39;a&#39;);
if(flock($fp, LOCK_EX|LOCK_NB)){            // 取得独占锁
    fwrite($fp, "How Are You\r\n");         // 写入数据
    fwrite($fp, "Show Me The Money\r\n");   // 写入数据
    flock($fp, LOCK_UN);                    // 解锁
}else{
    echo &#39;file locked&#39;;
}
fclose($fp);
?>

Execute a.php first, then b.php

b cannot obtain the exclusive lock. There is no need to wait for a to complete execution, but directly returns the prompt that the lock cannot be obtained.

Non-blocking

Summary:

Use shared lock

LOCK_SH. If it is reading, there is no need to wait, but if it is writing Enter, need to wait for the read to complete.

Using exclusive lock

LOCK_EX, both writing/reading need to wait.

LOCK_UN, regardless of whether a shared/read lock is used, it needs to be unlocked after use.

LOCK_NB, when locked, does not block, but prompts for lock.

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