Hi
I need to use shared memory and fork to do this:
Multipling random 512x512 matrixes using 4 processes and shared memory.
I know how to fork one child but
How can I fork 4 processes that do 1/4 of work?
Thanks
views:
68answers:
3You also need to somehow communicate to the forked processes which set of processing they need to do. While not rocket science, Borealid's answer gives a nice, elegant method.
Michael Burr
2010-07-08 22:42:17
@Micheal: sure, just thought that he could figure that out by himself or rephrase his question in a more precise manner. Guess the `homework` tag is missing, no?
Jens Gustedt
2010-07-09 05:16:30
+3
A:
ct = 0;
while (ct < 3 && fork() == 0) {
ct++;
}
ct will tell you which thread you are. You should probably check for a return of -1 from fork(), though.
Borealid
2010-07-08 20:31:01
The thing I don't Understand is 3! Why always we fork one less than number of required processes? Why 3 and not 4?
Snigger
2010-07-08 20:38:52
The first one is 0. The second one is 1. The third one is 2. When 2 forks, that one (the fourth) becomes 3, and short-circuits the while statement to not fork again.
Borealid
2010-07-08 20:40:18
@Snigger: one process you already have from the start, so you only have to launch the missing 3 other ones.
Jens Gustedt
2010-07-08 20:41:19
@Snigger: after forking, there's no real distinction between the original and the children. Just do 1/4 the work in each of your four processes, and then (probably) combine the results in one of them.
Borealid
2010-07-08 20:43:53
+1
A:
How about this: Read the chapter in your textbook again, ask your classmates for the notes you missed, attack your TA while he or she is sneaking out of his office, then ask your professor during their office hours!
John
2010-07-08 20:35:45