What are the concurrency methods in php

Several implementation methods to solve concurrency problems in PHP development:

Recommendation: php server

Option 1: Use File lock exclusive lock

Theflock function is used to obtain the file lock. This lock can only be obtained by one thread at the same time. Other threads that have not obtained the lock will either block or fail to obtain the lock

When acquiring the lock, first query the inventory. If the inventory is greater than 0, place an order, reduce the inventory, and then release the lock

Option 2: Use the pessimistic lock provided by the Mysql database

The Innodb storage engine supports row-level locks. When a row of data is locked, other processes cannot operate on the row of data.

Query and lock the row first:

select stock_num from table where id=1 for update
if(stock_num > 0){
//下订单
update table set stock_num=stock-1 where id=1
}

Option 3: Use queue

Save the user's order requests into a queue in sequence, and use a separate process in the background to process the order requests in the queue

Option 4: Use Redis

redis The operations are all atomic. You can store the inventory of the product in redis. Before placing an order, perform a decr operation on the inventory. If the returned value is greater than or equal to 0, you can place an order. Otherwise, you cannot place an order. This method is more efficient.

if(redis->get('stock_num') > 0){
 stock_num = redis->decr('stock_num')
 if(stock_num >= 0){
 //下订单
 }else{
 //库存不足
 }
}else{
//库存不足
}

Other concurrency issues:

In real applications, in many cases, data will be stored in the cache. When the cache fails, go to the database to retrieve the data and reset the cache. If the concurrency is exceeded at this time, It is very large. There will be many processes going to the database to get data at the same time, causing many requests to

penetrate to the database and causing the database to crash. File locks can be used to solve this problem

$data = $cache->get('key');
if(!$data){
  $fp = fopen('lockfile');
  if(flock($fp, LOCK_EX)){
    $data = $cache->get('key');//拿到锁后再次检查缓存，这时可能已经有了
    if(!$data){
      $data = mysql->query();
      $cache->set('key', $data);
    }
    flock($fp, LOCK_UN);
  }
  fclose($fp);
}

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