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Critical Sections

Posted on 2002-04-16
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Last Modified: 2010-04-15
I'm writting a C program which is supposed to run on multiple platforms (Windows, AIX ,..),This program is multithreaded, There are sections in the program that i want to restrict only one thread at a time to execute those sections(Critical Sections), I know that the solution is to use MUTEX.
Anyone can tell me wether the language C supports MUTEX or Not???
if yes , Tell me the details.
or if anyone has a different solution, pls tell me.
I want to confirm that i can't use a platform dependent solution.
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Question by:fattien
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5 Comments
 
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Expert Comment

by:BlackDiamond
ID: 6945190
Yes, you can use mutexes in C.  It is dependant on the thread library that you are using as to how you implement them.  What thread library are you using?

If you are using pthread, then the function you are looking for pthread_mutex_lock.
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Expert Comment

by:thienpnguyen
ID: 6945729
C/C++ doesn't support "synchronization" stuff as Critical Sections, Mutex .... . You need to use a platform dependent solution for "multi thread" .
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Expert Comment

by:makerp
ID: 6947263
WINDOZZZZZZZE

/* either have this global, a class member or pass it to the function(s) that will use it */
HANDLE mutex = CreateMutex(NULL,FALSE,NULL)

void my_fn()
{
  if(WaitForSingleObject(mutex,my_timeout_in_millis /* use the INFINITE constant to wait for ever */) == WAIT_OBJECT_0)
  {
    // do your stuff here
    ReleaseMutex(mutex);
  }
  else
  {
    // your request for the mutex timed out
  }
}

it will be very similar on other platforms. if the mutex only need local process scope then use CRITICAL_SECTION instead as they are more light weight. these have the same semantics and are similar to use..........

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Expert Comment

by:arul_m
ID: 6953623
It is possible to implement Mutex independent of platform by locking an OS resource with platform independent C Runtime API. I have implemented mutex by locking/unlocking the file. Find below the code skeleton for the same:

Mutex Locking:
^^^^^^^^^^^^^^
while(true)
{
 /* Try to remove the 'locked' file.
    This will throw an error if a
    thread/process has already opened
    the file */

  if (remove(filename)==0)
    break;

  // Wait for a while before trying again
  sleep(delay);
}
file = fopen(filename,"w");


Unlocking the mutex:
^^^^^^^^^^^^^^^^^^^
fclose(file);
file = NULL;

In the above example, you need to share the 'filename' across threads.
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