pthread_lock_global_np()--Lock Global Mutex

 #include <pthread.h>
 int pthread_lock_global_np(void);  

The pthread_lock_global_np() function locks a global mutex provided by the pthreads run-time. The global mutex is a recursive mutex with a name of "QP0W_GLOBAL_MTX". The global mutex is not currently used by the pthreads run-time to serialize access to any system resources, and is provided for application use only.

The maximum number of recursive locks by the owning thread is 32,767. After which, attempts to lock the mutex will return the ERECURSE error.

Note: This function is not portable

Authorities and Locks

None.

Parameters

None.

Return Value

0

pthread_lock_global_np() was successful.

value

pthread_lock_global_np() was not successful. value is set to indicate the error condition.

Error Conditions

If pthread_lock_global_np() was not successful, the error condition returned usually indicates one of the following errors. Under some conditions, the value returned could indicate an error other than those listed here.

[EINVAL]

The value specified for the argument is not correct.

[ERECURSE]

The recursive mutex cannot be recursively locked again.

Related Information

• The <pthread.h> header file. See Header files for Pthread functions.
  
  
• pthread_unlock_global_np()--Unlock Global Mutex

Example

See Code disclaimer information for information pertaining to code examples.

#include <pthread.h>
#include <stdio.h>
#include "check.h"
/*
  This example shows the corruption that can result if no
  serialization is done and also shows the use of
  pthread_lock_global_np(). Call this test with no parameters
  to use pthread_lock_gloabl_np() to protect the critical data,
  between more than one (possibly unrelated) functions.
  Use 1 or more parameters to skip locking and
  show data corruption that occurs without locking.
   */
#define            LOOPCONSTANT     50000
#define            THREADS          10

int                i,j,k,l;
int                uselock=1;

void secondFunction(void)
{
  int rc;
  if (uselock) {
    rc = pthread_lock_global_np();
    checkResults("pthread_lock_global_np()\n", rc);
  }
  --i; --j; --k; --l;
  if (uselock) {
    rc = pthread_unlock_global_np();
    checkResults("pthread_unlock_global_np()\n", rc);
  } 
}

void *threadfunc(void *parm)
{
  int   loop = 0;
  int   rc;

  for (loop=0; loop<LOOPCONSTANT; ++loop) {
    if (uselock) {
      rc = pthread_lock_global_np();
      checkResults("pthread_lock_global_np()\n", rc);
    }
    ++i; ++j; ++k; ++l;
    secondFunction();
    ++i; ++j; ++k; ++l;
    if (uselock) {
      rc = pthread_unlock_global_np();
      checkResults("pthread_unlock_global_np()\n", rc);
    }
  }
  return NULL;
}

int main(int argc, char **argv)
{
  pthread_t             threadid[THREADS];
  int                   rc=0;
  int                   loop=0;

  printf("Enter Testcase - %s\n", argv[0]);
  printf("Give any number of parameters to show data corruption\n");
  if (argc != 1) {
    printf("A parameter was specified, no serialization is being done!\n");
    uselock = 0;
  }

  if (uselock) {
    rc = pthread_lock_global_np();
    checkResults("pthread_lock_global_np() (main)\n", rc);
  }

  printf("Creating %d threads\n", THREADS);
  for (loop=0; loop<THREADS; ++loop) {
    rc = pthread_create(&threadid[loop], NULL, threadfunc, NULL);
    checkResults("pthread_create()\n", rc);
  }

  sleep(5);
  if (uselock) {
    rc = pthread_unlock_global_np();
    checkResults("pthread_unlock_global_np() (main)\n", rc);
  }

  printf("Wait for results\n");
  for (loop=0; loop<THREADS; ++loop) {
    rc = pthread_join(threadid[loop], NULL);
    checkResults("pthread_join()\n", rc);
  }

  printf("\nUsing %d threads and LOOPCONSTANT = %d\n",
         THREADS, LOOPCONSTANT);
  printf("Values are: (should be %d)\n", THREADS * LOOPCONSTANT);
  printf(" ==>%d, %d, %d, %d\n", i, j, k, l);

  printf("Main completed\n");
  return 0;
}

Output:

Enter Testcase - QP0WTEST/TPMTXGLB0
Give any number of parameters to show data corruption
Creating 10 threads
Wait for results
Using 10 threads and LOOPCONSTANT = 50000
Values are: (should be 500000)
  ==>500000, 500000, 500000, 500000
Main completed