PIPE(3)PIPE(3)NAMEpipe - two-way interprocess communication
SYNOPSIS
bind '#|'dir
dir/data
dir/data1
DESCRIPTION
A pipe provides a mechanism for interprocess I/O by reading and writing
file descriptors (see sys-read(2)). An attach(5), typically via sys-
pipe(2) or sys-bind(2), allocates two files that are cross-connected:
data written to one can be read back from the other, in the same order.
Write boundaries are preserved: each read terminates when the read buf‐
fer is full or after reading the last byte of a write, whichever comes
first. In particular, a write of zero bytes will result in a zero-
length read, which is usually interpreted by readers as end-of-file,
but could be used to delimit the data stream for other purposes.
Written data is buffered by the kernel and stored on internal queues
(see qio(10.2)). The maximum block size is 128k bytes; larger writes
will be split across several blocks, which are queued separately. Each
read will return data from at most one block. Concurrent writers are
therefore guaranteed that their data will not be interleaved with data
from other writers (ie, will be written atomically) only when each
write is less than the maximum buffer size. Writers to pipe interfaces
on remotely mounted portions of the namespace have their guarantee of
atomicity lowered to Sys->ATOMICIO bytes by mnt(3).
The system mediates between producer and consumer. Writers will block
when buffered data reaches a high-water mark, currently 32k bytes,
until a reader has reduced it by half. The length returned by sys-
stat(2) on each name gives the number of bytes waiting to be read on
the corresponding end of the pipe.
When all file descriptors on one side of the pipe have been closed, and
after any remaining data has been read, a reader on the other side sees
end-of-file (count of zero) on a subsequent read. Once both ends are
closed, the pipe can be reused.
A pipe persists until it is unmounted and no processes have either end
open.
SOURCE
/emu/port/devpipe.c
/os/port/devpipe.c
SEE ALSOsys-file2chan(2), sys-pipe(2)DIAGNOSTICS
Writes to a closed pipe generate an exception `write on closed pipe'.
Persistently reading a closed pipe after reading end-of-file will
result in a read error.
PIPE(3)
