Rochester <[EMAIL PROTECTED]> wrote: > Hi, > > I just found out that the general open file mechanism doesn't work > for named pipes (fifo). Say I wrote something like this and it > simply hangs python:
...just as it would "hang" any other language...!-). Looks like you may not be fully cognizant of the semantics of fifos -- understandably, because the man pages on most systems are not too limpid on the subject. But there's a good one, e.g., at <http://opengroup.org/onlinepubs/007908799/xsh/open.html> , and I selectively quote...: """ O_RDWR Open for reading and writing. The result is undefined if this flag is applied to a FIFO. """ (which means that your open with r+ _might_ cause the system to make demons fly out of your nose, according to e.g. <http://everything2.com/index.pl?node_id=922462> ...:-); so, _don't_ use 'r+' to open your fifo. But, moreover...: """ O_NONBLOCK When opening a FIFO with O_RDONLY or O_WRONLY set: If O_NONBLOCK is set: An open() for reading only will return without delay. An open() for writing only will return an error if no process currently has the file open for reading. If O_NONBLOCK is clear: An open() for reading only will block the calling thread until a thread opens the file for writing. An open() for writing only will block the calling thread until a thread opens the file for reading. """ This last paragraph is the crucial one: the fundamental semantics of FIFOs in Unix is for the writing and reading processes (or more modernly "threads":-) to "rendezvous" around their respective calls to open (2), blocking until both of them reach the open point. The semantics in the nonblocking case(s) are somewhat weird (to my way of thinking, but then, my Unix background _is_ somewhat dated!-), but they wouldn't help you anyway, it seems to me -- looks like you'd like drastically different semantics (with neither open blocking, or just the reading one), but Unix just doesn't really offer them... Alex -- http://mail.python.org/mailman/listinfo/python-list
