10-05-2001
URGENT Help required regarding the use of FORK system call
I desperately wanted one of the UNIX Gurus to help me resolve my problem asap(I have to deliver the code to the client by Monday 08-oct).
I have a file with around 5 million records (50 lakhs). Now my original process was taking around 30 hours to read the complete file, process each and every record and write it to another file. we do a lot of calculations for each and every record so it takes that time.
Now I planned to implement PARALLEL processing in my program. So I am dividing the complete input file into 5 chunks (each of 1 million) and sending every chunk to every child process to process. Now every child process will process its own chunk and write it to its own temporary file. Finally in the parent process I am planning to merge all the temporary files together. By doing this I believe I shall save a lot of processing time.
What I am basically interested to know is that what are the side effects of using FORK in the C programs? Are there any SYSTEM level impacts by using FORK? Is there any system call to merge multiple files into ONE? I am interested in knowing what happens if a Child is killed? How can I reprocess the child that is killed? How do I ensure that there are no ZOMBIES or INFANT process created?
Can some one briefly advise how I can proceed with my Logic. I have already written the logic but I want to cross check if there is something I am missing in my logic.
Thanks,
Kumar
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FORK(2) System Calls Manual FORK(2)
NAME
fork, rfork - manipulate process resources
SYNOPSIS
#include <u.h>
#include <libc.h>
int fork(void)
int rfork(int flags)
DESCRIPTION
Forking is the only way new processes are created. The flags argument to rfork selects which resources of the invoking process (parent)
are shared by the new process (child) or initialized to their default values. The resources include the file name space, the open file
descriptor table (which, when shared, permits processes to open and close files for other processes), the set of environment variables (see
env(3)), the note group (the set of processes that receive notes written to a member's notepg file; see proc(3)), and open files. Flags is
the logical OR of some subset of
RFPROC If set a new process is created; otherwise changes affect the current process.
RFNOWAIT
If set, the child process will be dissociated from the parent. Upon exit the child will leave no Waitmsg (see wait(2)) for the par-
ent to collect.
RFNAMEG
If set, the new process inherits a copy of the parent's name space; otherwise the new process shares the parent's name space. The
tag space for rendezvous(2) is considered part of the name space. Is mutually exclusive with RFCNAMEG.
RFCNAMEG
If set, the new process starts with a clean name space. A new name space must be built from a mount of an open file descriptor. Is
mutually exclusive with RFNAMEG.
RFENVG If set, the environment variables are copied; otherwise the two processes share environment variables. Is mutually exclusive with
RFCENVG.
RFCENVG
If set, the new process starts with an empty environment. Is mutually exclusive with RFENVG.
RFNOTEG
Each process is a member of a group of processes that all receive notes when a note is written to any of their notepg files (see
proc(3)). The group of a new process is by default the same as its parent, but if RFNOTEG is set (regardless of RFPROC), the
process becomes the first in a new group, isolated from previous processes.
RFFDG If set, the invoker's file descriptor table (see intro(2)) is copied; otherwise the two processes share a single table.
RFCFDG If set, the new process starts with a clean file descriptor table. Is mutually exclusive with RFFDG.
RFMEM If set, the kernel will mark segments of type data and bss as shared. The child will then inherit all the shared segments the parent
process owns. Other segment types will be unaffected. Subsequent forks by the parent will then propagate the shared data and bss
between children. The stack segment is always split. May be set only with RFPROC.
File descriptors in a shared file descriptor table are kept open until either they are explicitly closed or all processes sharing the table
exit.
If RFPROC is set, the value returned in the parent process is the process id of the child process; the value returned in the child is zero.
Without RFPROC, the return value is zero. Process ids range from 1 to the maximum integer (int) value. Rfork will sleep, if necessary,
until required process resources are available.
Fork is just a call of rfork(RFFDG|RFPROC).
SOURCE
/sys/src/libc/9syscall
/sys/src/libc/9sys/fork.c
SEE ALSO
intro(2), proc(3),
DIAGNOSTICS
These functions set errstr.
FORK(2)