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) BSD System Calls Manual FORK(2)
NAME
fork -- create a new process
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <unistd.h>
pid_t
fork(void);
DESCRIPTION
The fork() system call causes creation of a new process. The new process (child process) is an exact copy of the calling process (parent
process) except for the following:
o The child process has a unique process ID.
o The child process has a different parent process ID (i.e., the process ID of the parent process).
o The child process has its own copy of the parent's descriptors. These descriptors reference the same underlying objects, so that,
for instance, file pointers in file objects are shared between the child and the parent, so that an lseek(2) on a descriptor in the
child process can affect a subsequent read(2) or write(2) by the parent. This descriptor copying is also used by the shell to
establish standard input and output for newly created processes as well as to set up pipes.
o The child process' resource utilizations are set to 0; see setrlimit(2).
o All interval timers are cleared; see setitimer(2).
o The child process has only one thread, corresponding to the calling thread in the parent process. If the process has more than one
thread, locks and other resources held by the other threads are not released and therefore only async-signal-safe functions (see
sigaction(2)) are guaranteed to work in the child process until a call to execve(2) or a similar function.
RETURN VALUES
Upon successful completion, fork() returns a value of 0 to the child process and returns the process ID of the child process to the parent
process. Otherwise, a value of -1 is returned to the parent process, no child process is created, and the global variable errno is set to
indicate the error.
ERRORS
The fork() system call will fail and no child process will be created if:
[EAGAIN] The system-imposed limit on the total number of processes under execution would be exceeded. The limit is given by the
sysctl(3) MIB variable KERN_MAXPROC. (The limit is actually ten less than this except for the super user).
[EAGAIN] The user is not the super user, and the system-imposed limit on the total number of processes under execution by a single
user would be exceeded. The limit is given by the sysctl(3) MIB variable KERN_MAXPROCPERUID.
[EAGAIN] The user is not the super user, and the soft resource limit corresponding to the resource argument RLIMIT_NPROC would be
exceeded (see getrlimit(2)).
[ENOMEM] There is insufficient swap space for the new process.
SEE ALSO
execve(2), rfork(2), setitimer(2), setrlimit(2), sigaction(2), vfork(2), wait(2)
HISTORY
The fork() function appeared in Version 6 AT&T UNIX.
BSD
May 31, 2013 BSD