On 2023-07-15 20:36, наб wrote: > Which don't behave like you may expect them to; > unprimed, I expected the natural extension of either: > files (being a filesystem object), always returning 0 if no data, or > sockets (being an IPC mechanism), always EAGAINing if no data. > > The pipe semantics make sense of course ‒ pipes can be modelled as > sockets if there aren't writers, but files if there are; indeed, > this makes sense as the writer continuously appending a sliding > "window" over a file ‒ but they're unique amongst the UNIX file types, > but arriving at that specific interaction table is non-obvious, > especially to a user. > > Quoth Issue 8 Draft 3: > 60746 When attempting to read from an empty pipe or FIFO: > 60747 • If no process has the pipe open for writing, read( ) shall return 0 to indicate end-of-file. > 60748 • If some process has the pipe open for writing and O_NONBLOCK is set, read( ) shall return > 60749 −1 and set errno to [EAGAIN]. > 60750 • If some process has the pipe open for writing and O_NONBLOCK is clear, read( ) shall > 60751 block the calling thread until some data is written or the pipe is closed by all processes that > 60752 had the pipe open for writing. > > Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@xxxxxxxxxxxxxxxxxx> Applied. Thanks! > --- > man7/pipe.7 | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/man7/pipe.7 b/man7/pipe.7 > index c3e06bdab..91554fa3c 100644 > --- a/man7/pipe.7 > +++ b/man7/pipe.7 > @@ -56,12 +56,19 @@ .SS I/O on pipes and FIFOs > .BR write (2) > blocks until sufficient data has been read from the pipe > to allow the write to complete. > +.PP > Nonblocking I/O is possible by using the > .BR fcntl (2) > .B F_SETFL > operation to enable the > .B O_NONBLOCK > -open file status flag. > +open file status flag or by opening a > +.BR fifo (7) > +with > +.BR O_NONBLOCK . > +If any process has the pipe open for writing, reads fail with > +.BR EAGAIN ; > +otherwise\[em]with no potential writers\[em]reads succeed and return empty. > .PP > The communication channel provided by a pipe is a > .IR "byte stream" : -- <http://www.alejandro-colomar.es/> GPG key fingerprint: A9348594CE31283A826FBDD8D57633D441E25BB5
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