How does the php interface handle concurrency?

For concurrency scenarios such as product rushes, overselling may occur. At this time, it is necessary to solve the problems caused by concurrency.

There is no native provision in the PHP language Concurrency solutions require other ways to achieve concurrency control.

Option 1: Use file lock exclusive lock

Theflock function is used to obtain the file lock. This lock It can only be acquired by one thread at the same time. Other threads that have not acquired the lock are either blocked or the acquisition fails.

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 (recommended learning: PHP video tutorial)

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

Innodb storage The engine supports row-level locking. 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

Store the user’s order requests in a queue in sequence, and use a separate process in the background to process the order requests in the queue

Option 4: Using Redis

The operations of redis are all atomic. You can store the inventory of goods in redis. Before placing an order, perform a decr operation on the inventory. If the returned value is greater than or equal to 0, etc. 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
}

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