Hello every one I want to ask a question about flockfile function I was reading the description and came to know that it is used in threads. but I am doing forking which means that there will be different process not threads can I use flockfile with different process does it make any difference?
大家好我想问一个关于flockfile函数的问题我正在阅读描述并且知道它是在线程中使用的。但我正在做分叉这意味着将有不同的进程而不是线程我可以使用flockfile与不同的进程它有什么区别?
Thanks
2 个解决方案
#1
3
The flockfile function doesn't lock a file but the FILE data structure that a process uses to access a file. So this is about the representation in address space that a process has of the file, not necessarily about the file itself.
flockfile函数不会锁定文件,而是锁定进程用来访问文件的FILE数据结构。所以这是关于进程对文件的地址空间中的表示,而不一定是文件本身。
Even in a process if you have different FILEs open on the same file, you can write simultaneously to that file, even if you have locked each of the FILEs by means of flockfile.
即使在一个进程中,如果您在同一文件上打开了不同的FILE,也可以同时写入该文件,即使您已通过flockfile锁定了每个FILE。
For locking on the file itself have a look into flock and lockf but beware that the rules of their effects for access files through different threads of the same process are complicated.
要锁定文件本身,请查看flock和lockf,但要注意,通过同一进程的不同线程访问文件的效果规则很复杂。
#2
1
These functions can only be used within one process.
这些功能只能在一个进程中使用。
From the POSIX docs:
来自POSIX文档:
In summary, threads sharing stdio streams with other threads can use flockfile() and funlockfile() to cause sequences of I/O performed by a single thread to be kept bundled.
总之,与其他线程共享stdio流的线程可以使用flockfile()和funlockfile()来使单个线程执行的I / O序列保持捆绑。
All the rest of that page talks about mutual exclusion between threads. Different processes will have different input/output buffers for file streams, this locking wouldn't really make sense/be effective.
该页面的所有其余部分都讨论了线程之间的互斥问题。不同的进程将为文件流提供不同的输入/输出缓冲区,这种锁定实际上没有意义/有效。
#1
3
The flockfile function doesn't lock a file but the FILE data structure that a process uses to access a file. So this is about the representation in address space that a process has of the file, not necessarily about the file itself.
flockfile函数不会锁定文件,而是锁定进程用来访问文件的FILE数据结构。所以这是关于进程对文件的地址空间中的表示,而不一定是文件本身。
Even in a process if you have different FILEs open on the same file, you can write simultaneously to that file, even if you have locked each of the FILEs by means of flockfile.
即使在一个进程中,如果您在同一文件上打开了不同的FILE,也可以同时写入该文件,即使您已通过flockfile锁定了每个FILE。
For locking on the file itself have a look into flock and lockf but beware that the rules of their effects for access files through different threads of the same process are complicated.
要锁定文件本身,请查看flock和lockf,但要注意,通过同一进程的不同线程访问文件的效果规则很复杂。
#2
1
These functions can only be used within one process.
这些功能只能在一个进程中使用。
From the POSIX docs:
来自POSIX文档:
In summary, threads sharing stdio streams with other threads can use flockfile() and funlockfile() to cause sequences of I/O performed by a single thread to be kept bundled.
总之,与其他线程共享stdio流的线程可以使用flockfile()和funlockfile()来使单个线程执行的I / O序列保持捆绑。
All the rest of that page talks about mutual exclusion between threads. Different processes will have different input/output buffers for file streams, this locking wouldn't really make sense/be effective.
该页面的所有其余部分都讨论了线程之间的互斥问题。不同的进程将为文件流提供不同的输入/输出缓冲区,这种锁定实际上没有意义/有效。