pthread_getspecific()--Get Thread Local Storage Value by Key
Syntax:
#include <pthread.h> void *pthread_getspecific(pthread_key_t key);Service Program Name: QP0WPTHR
Default Public Authority: *USE
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 by the key.
Authorities and Locks
None.
Parameters
- key
- (Input) The thread local storage key returned from pthread_key_create()
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.
Error Conditions
None.
Related Information
- The <pthread.h> header file. See Header files for Pthread functions.
- pthread_key_create()--Create Thread Local Storage
Key
- pthread_key_delete()--Delete Thread Local Storage
Key
- pthread_setspecific()--Set Thread Local Storage by Key
Example
Note: By using the code examples, you agree to the terms of the Code license and disclaimer information.
#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; }
Output:
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
API introduced: V4R3
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