PHP uses Redis to implement methods to prevent secondary writing under large concurrency

This article mainly introduces the method of PHP using Redis to prevent secondary writing under large concurrency. It analyzes the read and write errors when PHP uses the lock mechanism to implement concurrent reading and writing of redis in the form of examples. Friends who need it can refer to it. Next

The example in this article describes how PHP uses Redis to prevent secondary writing under large concurrency. Share it with everyone for your reference, the details are as follows:

PHP calls redis to perform read and write operations. Under large concurrency, it will appear: read key1, and write the content if there is no content, but under large concurrency, multiple simultaneous operations will appear. In the case of writing by the PHP process, a lock needs to be added at this time, that is, the PHP process that obtains the lock has permission to write.

$lock_key = 'LOCK_PREFIX' . $redis_key;
$is_lock = $redis->setnx($lock_key, 1); // 加锁
if($is_lock == true){ // 获取锁权限
  $redis->setex($redis_key, $expire, $data); // 写入内容
  // 释放锁
  $redis->del($lock_key);
}else{
  return true; // 获取不到锁权限，直接返回
}

The idea is: Set the key of a lock, setnx is an atomic operation, only one process can write successfully, and return true if the write is successful ( Indicates obtaining the lock permission), then writing the content and then releasing the lock to delete the lock key. Processes that cannot obtain the lock return directly. But there is a situation here. The process that obtains the lock permission reports an error when running after obtaining the lock. As a result, the lock is not released, and the content cannot be written. In this case, the process that does not obtain the lock permission needs to judge the remaining validity time of the lock. , if it is -1, set the effective time of the lock to 5 seconds (5 seconds are reserved for the running time of the process that gets the lock, which is enough). Improved code:

$lock_key = 'LOCK_PREFIX' . $redis_key;
$is_lock = $redis->setnx($lock_key, 1); // 加锁
if($is_lock == true){ // 获取锁权限
  $redis->setex($redis_key, $expire, $data); // 写入内容
  // 释放锁
  $redis->del($lock_key);
}else{
  // 防止死锁
  if($redis->ttl($lock_key) == -1){
    $redis->expire($lock_key, 5);
  }
  return true; // 获取不到锁权限，直接返回
}

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