Solutions to common concurrency scenarios in PHP

Common solutions are as follows:

1. Use a queue, start an additional process to handle the queue, and put all concurrent requests into the queue. If additional processes are processed serially, the concurrency problem will not exist. However, additional process support is required and the processing delay is serious. This article will not discuss this method first.

2. Use the transaction characteristics of the database to perform atomic updates. This method needs to rely on the transaction characteristics of the database.

3. With the help of file exclusive lock, when processing an order request, use flock to lock a file. Only those who successfully obtain the lock can process the order.

1. Utilize Redis transaction features

Redis transactions are atomic operations, which can ensure that the data is not modified by other concurrent processes during order processing.

Sample code:

<?php
$http = new swoole_http_server("0.0.0.0", 9509);  // 监听 9509
 
$http->set(array(
  &#39;reactor_num&#39; => 2, //reactor thread num
  &#39;worker_num&#39; => 4  //worker process num
));
 
$http->on(&#39;request&#39;, function (swoole_http_request $request, swoole_http_response $response) {
  $uniqid = uniqid(&#39;uid-&#39;, TRUE);  // 模拟唯一用户ID
  $redis = new Redis();
  $redis->connect(&#39;127.0.0.1&#39;, 6379);  // 连接 redis
 
  $redis->watch(&#39;rest_count&#39;); // 监测 rest_count 是否被其它的进程更改
 
  $rest_count = intval($redis->get("rest_count")); // 模拟唯一订单ID
  if($rest_count > 0){
    $value = "{$rest_count}-{$uniqid}"; // 表示当前订单，被当前用户抢到了
 
    // do something ... 主要是模拟用户抢到单后可能要进行的一些密集运算
    $rand = rand(100, 1000000);
    $sum=0;
    for ($i=0;$i<$rand;$i++){ $sum+=$i; }
 
   // redis 事务
    $redis->multi();
    $redis->lPush(&#39;uniqids&#39;, $value);
    $redis->decr(&#39;rest_count&#39;);
    $replies = $redis->exec(); // 执行以上 redis 事务
 
   // 如果 rest_count 的值被其它的并发进程更改了，以上事务将回滚
    if(!$replies){
      echo "订单 {$value} 回滚".PHP_EOL;
    }
  }
  $redis->unwatch();
});
 
$http->start();

Use ab test

$ ab -t 20 -c 10 http://192.168.1.104:9509/

2. Use file exclusive lock (blocking mode)

In blocking mode, if a process acquires a file exclusive lock while other processes are occupying the lock, the process will hang up and wait for other processes to release the lock, acquire the lock itself, and then proceed.

Sample code:

<?php
$http = new swoole_http_server("0.0.0.0", 9510);
 
$http->set(array(
  &#39;reactor_num&#39; => 2, //reactor thread num
  &#39;worker_num&#39; => 4  //worker process num
));
 
$http->on(&#39;request&#39;, function (swoole_http_request $request, swoole_http_response $response) {
 
  $uniqid = uniqid(&#39;uid-&#39;, TRUE);
  $redis = new Redis();
  $redis->connect(&#39;127.0.0.1&#39;, 6379);
 
  $fp = fopen("lock.txt", "w+");
 
  // 阻塞(等待)模式， 要取得独占锁定（写入的程序）
  if(flock($fp,LOCK_EX))  //锁定当前指针
  {
   // 成功取得锁后，放心处理订单
    $rest_count = intval($redis->get("rest_count"));
    $value = "{$rest_count}-{$uniqid}";
    if($rest_count > 0){
      // do something ...
      $rand = rand(100, 1000000);
      $sum=0;
      for ($i=0;$i<$rand;$i++){ $sum+=$i; }
 
      $redis->lPush(&#39;uniqids&#39;, $value);
      $redis->decr(&#39;rest_count&#39;);
    }
 
   // 订单处理完成后，再释放锁
    flock($fp,LOCK_UN);
  }
  fclose($fp);
 
});
 
$http->start();

Use ab test

$ ab -t 20 -c 10 http://192.168.1.104:9510/

Recommended tutorial: PHP tutorial

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