On 07Apr2009 10:08, akineko <akin...@gmail.com> wrote: | I'm trying to use named pipes to fuse a Python program and a C | program. | One side creates pipes using os.mkfifo() and both sides use the same | named pipes (one side reads, another side writes). The read side uses | select.select() to wait for incoming messages and read the message | when select.select() says it is ready. | The length of the message is unknown to the read side.
That's a serious flaw in the message protocol. | I cannot use file.read() because it will block waiting for an EOF. | I cannot use file.readline() because how many lines have arrived is | unknown. | So, I needed to use os.read() with the exact number of characters to | read. No! You should use os.read() with the maximum size of a message. It _should_ return with the number of bytes in the message, provided the C program writes messages with a single OS-level write() call. Forget all the fstat() stuff - it's racy. Personally, I'd use a thread to just do continuous blocking os.read()s of the pipe, and putting the resulting messages on a Queue for collection by your main program. If you're the only consumer of a Queue it's safe to poll it for emptiness or not, or to use a no-wait get(). All the above is untested, but absent a size in the protocol or other ways of parsing message boundaries in data stream, you can only rely on the C program writing messages with a single write() and collect using a large os.read(), which should return with what is there. Cheers, -- Cameron Simpson <c...@zip.com.au> DoD#743 http://www.cskk.ezoshosting.com/cs/ Language... has created the word "loneliness" to express the pain of being alone. And it has created the word "solitude" to express the glory of being alone. - Paul Johannes Tillich -- http://mail.python.org/mailman/listinfo/python-list
