11-07-2010
Playing with the named pipe on the shell first is instructional (mknod path p). One party needs to be opening to read before one opens to write or one read may get many write. There is no wait, just blocking. Beware ccc>pipe as your login hangs, do (xxx >pipe)& after (yyy <pipe)&.
Named pipes are more a client-server or shell thing, as pipe() suffices for fork()/exec(), and popen() makes life simpler.
Last edited by DGPickett; 11-07-2010 at 06:37 AM..
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FORK(2) System Calls Manual FORK(2)
NAME
fork - spawn new process
SYNOPSIS
fork( )
DESCRIPTION
Fork is the only way new processes are created. The new process's core image is a copy of that of the caller of fork. The only distinc-
tion is the fact that the value returned in the old (parent) process contains the process ID of the new (child) process, while the value
returned in the child is 0. Process ID's range from 1 to 30,000. This process ID is used by wait(2).
Files open before the fork are shared, and have a common read-write pointer. In particular, this is the way that standard input and output
files are passed and also how pipes are set up.
SEE ALSO
wait(2), exec(2)
DIAGNOSTICS
Returns -1 and fails to create a process if: there is inadequate swap space, the user is not super-user and has too many processes, or the
system's process table is full. Only the super-user can take the last process-table slot.
ASSEMBLER
(fork = 2.)
sys fork
(new process return)
(old process return, new process ID in r0)
The return locations in the old and new process differ by one word. The C-bit is set in the old process if a new process could not be cre-
ated.
FORK(2)