Example: One-time initialization in Pthread programs
This example shows a Pthread program that dynamically initializes an integer using the one-time initialization support.
Note: By using the code examples, you agree to the terms of the Code license and disclaimer information.
/*
Filename: ATEST20.QCSRC
The output of this example is as follows:
Enter Testcase - LIBRARY/ATEST20
Create/start threads
Wait for the threads to complete, and release their resources
Thread 00000000 00000007: Entered
Thread 00000000 00000000: INITIALIZE RESOURCE
Thread 00000000 00000007: The resource is 42
Thread 00000000 00000006: Entered
Thread 00000000 00000009: Entered
Thread 00000000 00000008: Entered
Thread 00000000 0000000a: Entered
Thread 00000000 00000006: The resource is 42
Thread 00000000 0000000a: The resource is 42
Thread 00000000 00000009: The resource is 42
Thread 00000000 00000008: The resource is 42
Main completed
*/
#define _MULTI_THREADED
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>t
#include <unistd.h>
#define checkResults(string, val) { \
if (val) { \
printf("Failed with %d at %s", val, string); \
exit(1); \
} \
}
#define NUMTHREADS 5
pthread_once_t oneTimeInit = PTHREAD_ONCE_INIT;
int initialized = 0;
int resource = 0;
void initFunction(void)
{
printf("Thread %.8x %.8x: INITIALIZE RESOURCE\n");
resource = 42;
/* Ensure that all initialization is complete and flushed */
/* to storage before turning on this boolean flag */
/* Perhaps call a function or register an exception */
/* that causes an optimization boundary */
initialized = 1;
}
void *theThread(void *parm)
{
int rc;
printf("Thread %.8x %.8x: Entered\n", pthread_getthreadid_np());
if (!initialized) {
rc = pthread_once(&oneTimeInit, initFunction);
checkResults("pthread_once()\n", rc);
}
printf("Thread %.8x %.8x: The resource is %d\n",
pthread_getthreadid_np(), resource);
return NULL;
}
int main(int argc, char **argv)
{
pthread_t thread[NUMTHREADS];
int rc=0;
int i;
printf("Enter Testcase - %s\n", argv[0]);
printf("Create/start threads\n");
for (i=0; i <NUMTHREADS; ++i) {
rc = pthread_create(&thread[i], NULL, theThread, NULL);
checkResults("pthread_create()\n", rc);
}
printf("Wait for the threads to complete, and release their resources\n");
for (i=0; i <NUMTHREADS; ++i) {
rc = pthread_join(thread[i], NULL);
checkResults("pthread_join()\n", rc);
}
printf("Main completed\n");
return 0;
}