How to "multithread" c code

I have a number crunching application written in C. It is kind of a main loop that for each value calls, for increasing values of "i", a function that performs some calculations. I read about multithreading, và I am considering learning a bit about it, in C. I wonder if somehow general code lượt thích mine could be automatically multithreaded & how.

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P.D. Lớn get an idea about my code, let"s say that it is something lượt thích this:


void get_result(float x,float y,float result) result=sqrt(log (x) + log (y) + cos (exp (x + y));(and some more similar mathematical operations)
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edited Oct 11, 2010 at 17:59
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asked Oct 11, 2010 at 16:19


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If the task is highly parallelizable and your compiler is modern, you could try OpenMP. Http://

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answered Oct 11, 2010 at 16:21

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One alternative lớn multithread your code would be using pthreads ( provides more precise control than OpenMP ).

Assuming x, y & result are global variable arrays,

#include ...void *get_result(void *param) // param is a dummy main(){...pthread_t *tid = malloc( ntimes * sizeof(pthread_t) );for( i=0; i(Compile your code with gcc prog.c -lpthread)

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answered Oct 16, 2010 at 17:25
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You should have a look at openMP for this. The C/C++ example on this page is similar lớn your code:

#include #define N 1000main (){int i;float a, b, c, d;/* Some initializations */for (i=0; i If you prefer not to lớn use openMP you could use either pthreads or clone/wait directly.

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No matter which route you choose you are just dividing up your arrays into chunks which each thread will process. If all of your processing is purely computational (as suggested by your example function) then you should vị well lớn have only as many threads as you have logical processors.

There is some overhead with adding threads to bởi vì parallel processing, so make sure that you give each thread enough work to biến hóa for it. Usually you will, but if each thread only ends up with 1 computation lớn do và the computations aren"t that difficult to vị then you may actually slow things down. You can always have fewer threads than you have processors if that is the case.

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If you bởi have some IO going on in your work then you may find that having more threads than processors is a win because while one thread may be blocking waiting for some IO lớn complete another thread can be doing its computations. You have lớn be careful doing IO to lớn the same file in threads, though.