#include <pthread.h>
void *pthread_getspecific(pthread_key_t key);
Threadsafe: Yes
Signal Safe: Yes

The pthread_getspecific() function retrieves the thread local storage value associated with the key. pthread_getspecific() may be called from a data destructor.

The thread local storage value is a variable of type void * that is local to a thread, but global to all of the functions called within that thread. It is accessed via the key.

Parameters

key

(Input) The thread local storage key returned from pthread_key_create().

None.

Return Value

value

pthread_getspecific() was successful. value is set to indicate the current thread specific data pointer stored at the key location.

NULL

pthread_getspecific() returned the null thread specific data value stored at the key location or the key was out of range.

None.

Related Information

• The <pthread.h> header file. See Header files for Pthread functions
• pthread_key_create()--Create a Thread Local Storage Key
• pthread_key_delete()--Delete Thread Local Storage Key
• pthread_setspecific()--Set Thread Local Storage by Key

#define _MULTI_THREADED
#include <pthread.h>
#include <stdio.h>
#include "check.h"

#define         NUMTHREADS    3
pthread_key_t   tlsKey = 0;

void globalDestructor(void *value)
{
  printf("In the globalDestructor\n");
  free(value);
  pthread_setspecific(tlsKey, NULL);
}


void showGlobal(void)
{
  void                 *global;
  pthread_id_np_t       tid;

  global  = pthread_getspecific(tlsKey);
  pthread_getunique_np((pthread_t *)global, &tid);
  printf("showGlobal: global data stored for thread 0x%.8x%.8x\n",
         tid);
}

void *threadfunc(void *parm)
{
  int           rc;
  int          *myThreadDataStructure;
  pthread_t     me = pthread_self();

  printf("Inside secondary thread\n");

  myThreadDataStructure = malloc(sizeof(pthread_t) + sizeof(int) * 10);
  memcpy(myThreadDataStructure, &me, sizeof(pthread_t));
  pthread_setspecific(tlsKey, myThreadDataStructure);
  showGlobal();
  pthread_exit(NULL);
}

int main(int argc, char **argv)
{
  pthread_t             thread[NUMTHREADS];
  int                   rc=0;
  int                   i=0;

  printf("Enter Testcase - %s\n", argv[0]);

  printf("Create a thread local storage key\n");
  rc = pthread_key_create(&tlsKey, globalDestructor);
  checkResults("pthread_key_create()\n", rc);
  /* The key can now be used from all threads */

  printf("Create %d threads using joinable attributes\n",
         NUMTHREADS);
  for (i=0; i<NUMTHREADS; ++i) {
    rc = pthread_create(&thread[i], NULL, threadfunc, NULL);
    checkResults("pthread_create()\n", rc);
  }

  printf("Join to threads\n");
  for (i=0; i<NUMTHREADS; ++i) {
    rc = pthread_join(thread[i], NULL);
    checkResults("pthread_join()\n", rc);
  }

  printf("Delete a thread local storage key\n");
  rc = pthread_key_delete(tlsKey);
  checkResults("pthread_key_delete()\n", rc);
  /* The key and any remaining values are now gone. */
  printf("Main completed\n");
  return 0;
}

Enter Testcase - QP0WTEST/TPGETS0
Create a thread local storage key
Create 3 threads using joinable attributes
Join to threads
Inside secondary thread
showGlobal: global data stored for thread 0x000000000000000b
In the globalDestructor
Inside secondary thread
showGlobal: global data stored for thread 0x000000000000000d
In the globalDestructor
Inside secondary thread
showGlobal: global data stored for thread 0x000000000000000c
In the globalDestructor
Delete a thread local storage key
Main completed