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flock与命名管道读写引发的死锁

 2 years ago
source link: https://www.lujun9972.win/blog/2019/02/15/flock%E4%B8%8E%E5%91%BD%E5%90%8D%E7%AE%A1%E9%81%93%E8%AF%BB%E5%86%99%E5%BC%95%E5%8F%91%E7%9A%84%E6%AD%BB%E9%94%81/index.html
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flock与命名管道读写引发的死锁

尝试用shell写一个多进程爬虫的时候，发现死锁了。代码简化如下: 

# 创建命名管道
mkfifo /tmp/ff
exec 99<> /tmp/ff
# 创建生产进程往管道中写入数据
(while :
 do
     flock /tmp/ff -c 'seq 1 10 > /tmp/ff'
 done
) &

# 创建消费进程从管道读取数据
(while :
 do
     flock /tmp/ff -c 'read i </tmp/ff;echo $i'
 done
) &

当消费者进程消费速度快于生产进程时就会发生下面步骤:

  1. 消费者进程持有锁0
  2. 消费者进程从管道读取消息，被阻塞
  3. 生产者往管道发送数据前需要先获取锁0,但是该锁被消费者进程持有，导致生产者也被阻塞。

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