PHP uses file locks to solve high concurrency problems

This time I will bring you Tphp's use of file locks to solve high concurrency problems. What are the precautions for PHP's use of file locks to solve high concurrency problems? The following is a practical case, let's take a look.

Create a new .txt file without writing anything in the file.

【一】.Blocking (waiting) mode: (As long as other processes have locked the file, the current process will wait for other processes to unlock the file)

<span style="font-family: 微软雅黑, "Microsoft YaHei"; font-size: 14px;">     <?php<br/>     //连接数据库<br/>     $con=mysqli_connect("192.168.2.186","root","root","test");<br/>     //查询商品数量是否大于0,大于0才能下单,并减少库存<br/>     $fp = fopen("lock.txt", "r");<br/>     //加锁<br/>     if(flock($fp,LOCK_EX))<br/>{ <br/>   $res=mysqli_fetch_assoc(mysqli_query($con,&#39;SELECT total FROM shop WHERE id=1 LIMIT 1&#39;)); <br/>      if($res[&#39;total&#39;]>0){mysqli_query($con,&#39;UPDATE shop SET total=total-1  WHERE id=1&#39;);}    //执行完成解锁<br/>    flock($fp,LOCK_UN);<br/>}<br/>//关闭文件<br/>fclose($fp);<br/>unset($res);<br/>mysqli_close($con);<br/>?><br/></span>

【二】.Non-blocking (waiting) mode: (As long as other processes have locked the file, the current process will not wait for other processes to unlock the file and return directly)

<span style="font-family: 微软雅黑, "Microsoft YaHei"; font-size: 14px;">   <?php<br/>   //连接数据库<br/>   $con=mysqli_connect("192.168.2.186","root","root","test");<br/>   //查询商品数量是否大于0,大于0才能下单,并减少库存<br/>   $fp = fopen("lock.txt", "r");<br/>   //加锁if(flock($fp,LOCK_EX | LOCK_NB))<br/>{ <br/>   $res=mysqli_fetch_assoc(mysqli_query($con,&#39;SELECT total FROM shop WHERE id=1 LIMIT 1&#39;));   <br/>    if($res[&#39;total&#39;]>0){mysqli_query($con,&#39;UPDATE shop SET total=total-1  WHERE id=1&#39;);}   <br/>     //执行完成解锁<br/>    flock($fp,LOCK_UN);<br/>}//关闭文件<br/>fclose($fp);<br/>unset($res);<br/>mysqli_close($con);<br/>?></span>

If connecting to the database takes time, there is a simple demo below for a more intuitive understanding.

   demo.php
   <?php$fp = fopen("file_lock.txt", "r");
   // 加锁
   if(flock($fp, LOCK_EX))
{
    sleep(10);
    echo 1;    
    //执行完成解锁
    flock($fp,LOCK_UN);
} else {  
  echo 2;
}
//关闭文件
fclose($fp);
demo2.php
<?php
$fp = fopen("file_lock.txt", "r");
// 加锁（如果改成flock($fp, LOCK_EX | LOCK_NB)，demo2.php会直接返回2，否则会等待demo.php执行完返回1）
if(flock($fp, LOCK_EX))
{    echo 1;
} else {   
 echo 2;
}
//关闭文件
fclose($fp);

Run two files at the same time, and then modify the locking mechanism in demo2, you can see that blocking (waiting) mode and non-blocking (waiting) ) mode
difference.

But this will cause the queue to be blocked. If 10 people write to the database at the same second, it will be blocked. The 10th person will wait for the first 9 to be executed before executing!

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