Can I lock and unlock a fifo (named pipe) in C?

Question

I have two progress, p1 and p2, and a named pipe var for ipc between 2 progress.
I want to lock var's rw for p2 when p1 writes, and unlock var when p1 finished write.

ps:

I using select for nonblocking, so p2 will get readable when p1 put anything to var.Can I let var become readable when p1 finish write?

Did you try to put your thoughts and come up with some design ? — Srikanth, Dec 04 '13 at 09:25
On POSIX systems (like Linux and OSX) named pipes are files in the file system, and files can be locked. Though I don't know if they will work for pipes. Have you tried to search for file locking functions? — Some programmer dude, Dec 04 '13 at 09:27
Now I have a big amount of data, and I need write it to pipe. but another progress shouldnt read it until all data has written — KaMeTang, Dec 04 '13 at 09:28
I using select for nonblocking, and `p2` will identify pipe is readable when `p1` put anything to pipe, althought it not completely written of whole data. — KaMeTang, Dec 04 '13 at 09:31
Remember that a pipe is not limitless, it can fill up and block the writing application. — Some programmer dude, Dec 04 '13 at 09:32
When I lock file that means `p1` and `p2` both cant write? I only want lock for `p2`. — KaMeTang, Dec 04 '13 at 09:35
Use two pipes? One for p1-to-p2 communication, and one for p2-to-p1 communication. — Some programmer dude, Dec 04 '13 at 09:39

score 1 · Accepted Answer · answered Dec 04 '13 at 09:35

1

You could use signals (e.g. SIGUSR1). The writer makes it pipe non-blocking (so it won't block when the pipe becomes full), writes until it can't write anymore, then send the signal to the other process. The reading process reads all (from its non-blocking pipe), then sends a signal to the writer who then continues to write.

However, this is really not needed. The writer can just write, and the reader just read. If the pipe becomes full the writer will block until it can write more. And the same for the reader, it will block if there's nothing to read. Then when the writer has written all data, it will simply close its end of the pipe, which the reader will detect with a read call that returns zero bytes read.

answered Dec 04 '13 at 09:35

Some programmer dude

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File lock give me some sense. I will test fcntl later. – KaMeTang Dec 04 '13 at 09:54
I think I need to use two pipes, one for signal, the other for data. I just try to lock, but I cant lock. Maybe cant lock `mkfifo`'s file? – KaMeTang Dec 04 '13 at 12:32
@KaMeTang I suspected it was not possible to lock the FIFO file. And yes, one pipe for data in one direction, and one pipe for commands (or signals) in the other. – Some programmer dude Dec 04 '13 at 12:39

Can I lock and unlock a fifo (named pipe) in C?

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