fseek-fread error

[ahmetbm]

Hi;

I have a c program that uses mpi library to run on parallel arhitecture. First i coded serial program and it worked perfectly. But the parallel one did not run. I found the error but could not solve it.

The error is: the "fseek" and "fread" functions does not return the correct values.

fseek(wav_fp,40L,SEEK_SET);fread(&str,4,1,wav_fp);

this code must return "str" = "81913" but i get "-442495"

Thanks.

[weaknessforcats]

Are you reading as text or as binary??

[mehmetbm]

Are you reading as text or as binary??

As binary..

In serial version of this code runs true as parallel program with mpi library can not get the right result.

[weaknessforcats]

Then you have a multithreading race operating.

If this file is a shared resource, you may have to access it within a critical section.

[ahmetbm]

no, it is not multithreading program, it is a parallel program, the fseek's offset value is long type and this is causing segmentation fault problem.

[weaknessforcats]

I'm sorry but what is the difference between a parallel program and a multi-threaded one??

[ahmetbm]

in parallel programing a processor executes a part of the job, but in multi-thread programming whole job is done by one processor.

[weaknessforcats]

in parallel programing a processor executes a part of the job, but in multi-thread programming whole job is done by one processor.

This statement is absolutely false.

A parallel program is a program where sections are run in parallel in real time. This requires multiple processors. Each processor runs a section. Each section is called a thread.

A multi-threaded program is a program that can be run as a parallel program. It can also be run using one processsor but only one thread executes at a time. The operating system will multi-task to make it appear that there is more than one processor giving the illusion that the threads are running in parallel.

You have to be certain that any data shared between threads is protected by a critical section, mutex, sempaphore, spin-lock or something that prevents two threads from writing simultaneously to the same resource.