MultiThreading in C Tutorial - Part 6(Attributes)

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We know that the second argument we pass to the pthread_create is attributes,when we pass it NULL it will take the default attributes.We will see what are the default state of the attributes.

 Example code to print the default attributes:

 #include <stdio.h>
#include <pthread.h>
#include <stdlib.h>

void attr_dump(pthread_t thread_id)
{

pthread_attr_t attr;
void *stkaddr;
size_t stksize, guardsize;
int thread_state, schedpolicy;
/*
* pthread_getattr_np : gets the attributes of the thread specified
* in the first argument
*/
pthread_getattr_np(thread_id, &attr);
printf("Printing Default Attributes\n");
/*
* Read stack size and stack address
*/
pthread_attr_getstack(&attr, &stkaddr, &stksize);
printf("Stack Size:%d bytes\n",stksize);
printf("Stack Address:%p\n",stkaddr);

/*
* Read whether it is detached state or joinable state
  */
pthread_attr_getdetachstate(&attr, &thread_state);
if (thread_state == PTHREAD_CREATE_JOINABLE)
printf("Thread state:Joinable\n");
else
printf("Thread state:Detached\n");

/*
* Read stack guard size
*/
pthread_attr_getguardsize(&attr, &guardsize);
printf("Default stack guard size:%d\n", guardsize);

/*
  * Read Scheduling Policy
*/
pthread_attr_getschedpolicy(&attr, &schedpolicy);

if (schedpolicy == SCHED_OTHER)
printf("Scheduling Policy:SCHED_OTHER(Preemptive fair-share sscheduler)\n");
else if (schedpolicy == SCHED_RR)
printf("Scheduling Policy:SCHED_RR(Static Priority Round Robin)\n");
else if (schedpolicy == SCHED_FIFO)
printf("Scheduling Policy:SCHED_FIFO(static Priority Preemptive Cooperative scheduler)\n");

}


void *threadFn(void *arg)
{
pthread_detach(pthread_self());
attr_dump(pthread_self());

}




int main(int argc, char *argv[])
{

pthread_t tid;
int ret;

ret = pthread_create(&tid, NULL, threadFn, NULL);
if (ret != 0){
printf("Error in creating thread\n");
exit(1);
}else
printf("Thread Created Successfully\n");
pthread_exit(NULL);

}

O/P:
Thread Created Successfully
Printing Default Attributes
Stack Size:8392704 bytes
Stack Address:0xb6d70000
Thread state:Detached
Default stack guard size:4096
Scheduling Policy:SCHED_OTHER(Preemptive fair-share sscheduler)


 Example Code to change the default attributes:

 #include <stdio.h>
#include <pthread.h>
#include <stdlib.h>

pthread_t tid, tid1;

void attr_dump(pthread_t thread_id)
{

pthread_attr_t attr;
void *stkaddr;
size_t stksize, guardsize;
int thread_state, schedpolicy;
/*
* pthread_getattr_np : gets the attributes of the thread specified
* in the first argument
*/
pthread_getattr_np(thread_id, &attr);
printf("Printing Default Attributes\n");
/*
* Read stack size and stack address
*/
pthread_attr_getstack(&attr, &stkaddr, &stksize);
printf("Stack Size:%d bytes\n",stksize);
printf("Stack Address:%p\n",stkaddr);

/*
* Read whether it is detached state or joinable state
  */
pthread_attr_getdetachstate(&attr, &thread_state);
if (thread_state == PTHREAD_CREATE_JOINABLE)
printf("Thread state:Joinable\n");
else
printf("Thread state:Detached\n");

/*
* Read stack guard size
*/
pthread_attr_getguardsize(&attr, &guardsize);
printf("Default stack guard size:%d\n", guardsize);

/*
  * Read Scheduling Policy
*/
pthread_attr_getschedpolicy(&attr, &schedpolicy);

if (schedpolicy == SCHED_OTHER)
printf("Scheduling Policy:SCHED_OTHER(Preemptive fair-share sscheduler)\n");
else if (schedpolicy == SCHED_RR)
printf("Scheduling Policy:SCHED_RR(Static Priority Round Robin)\n");
else if (schedpolicy == SCHED_FIFO)
printf("Scheduling Policy:SCHED_FIFO(static Priority Preemptive Cooperative scheduler)\n");
}


void *threadFn(void *arg)
{
int ret;

if (pthread_equal(pthread_self(), tid))
printf("\nPrinting Thread 1 Contents\n");
else{
ret = pthread_join(tid, NULL);
if (ret != 0) {
perror("Error in joining thread\n");
exit(1);
}
printf("\nPrinting Thread 2 Contents\n");
}
attr_dump(pthread_self());
pthread_exit(NULL);
}


int main(int argc, char *argv[])
{

pthread_attr_t attr;
int ret, schedpolicy;

/*
* Initializes the atttribute object with the default values.
*/
ret = pthread_attr_init(&attr);
if (ret != 0) {
perror("Error Initializing attributes\n");
exit(1);
}

ret = pthread_create(&tid, &attr, threadFn, NULL);
if (ret != 0) {
perror("Error creating thread\n");
exit(1);

}


ret = pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
if (ret != 0) {
perror("Error setting state\n");
exit(1);
}

ret = pthread_attr_setschedpolicy(&attr, SCHED_RR);
if (ret != 0) {
perror("Error setting scheduling policy\n");
exit(1);
}


ret  = pthread_create(&tid1, &attr, threadFn, NULL);
if (ret != 0) {
perror("Error creating thread\n");
exit(1);
}

pthread_exit(NULL);
}

Example Code of pthread_attr_destroy :

 #include <stdio.h>
#include <pthread.h>
#include <stdlib.h>

pthread_t tid, tid1;

void attr_dump(pthread_t thread_id)
{

pthread_attr_t attr;
void *stkaddr;
size_t stksize, guardsize;
int thread_state, schedpolicy;
/*
* pthread_getattr_np : gets the attributes of the thread specified
* in the first argument
*/
pthread_getattr_np(thread_id, &attr);
printf("Printing Default Attributes\n");
/*
* Read stack size and stack address
*/
pthread_attr_getstack(&attr, &stkaddr, &stksize);
printf("Stack Size:%d bytes\n",stksize);
printf("Stack Address:%p\n",stkaddr);

/*
* Read whether it is detached state or joinable state
  */
pthread_attr_getdetachstate(&attr, &thread_state);
if (thread_state == PTHREAD_CREATE_JOINABLE)
printf("Thread state:Joinable\n");
else
printf("Thread state:Detached\n");

/*
* Read stack guard size
*/
pthread_attr_getguardsize(&attr, &guardsize);
printf("Default stack guard size:%d\n", guardsize);

/*
  * Read Scheduling Policy
*/
pthread_attr_getschedpolicy(&attr, &schedpolicy);

if (schedpolicy == SCHED_OTHER)
printf("Scheduling Policy:SCHED_OTHER(Preemptive fair-share sscheduler)\n");
else if (schedpolicy == SCHED_RR)
printf("Scheduling Policy:SCHED_RR(Static Priority Round Robin)\n");
else if (schedpolicy == SCHED_FIFO)
printf("Scheduling Policy:SCHED_FIFO(static Priority Preemptive Cooperative scheduler)\n");
}


void *threadFn(void *arg)
{
int ret;

if (pthread_equal(pthread_self(), tid))
printf("\nPrinting Thread 1 Contents\n");
else{
ret = pthread_join(tid, NULL);
if (ret != 0) {
perror("Error in joining thread\n");
exit(1);
}
printf("\nPrinting Thread 2 Contents\n");
}
attr_dump(pthread_self());
pthread_exit(NULL);
}


int main(int argc, char *argv[])
{

pthread_attr_t attr;
int ret, schedpolicy;

/*
* Initializes the atttribute object with the default values.
*/
ret = pthread_attr_init(&attr);
if (ret != 0) {
perror("Error Initializing attributes\n");
exit(1);
}

ret = pthread_create(&tid, &attr, threadFn, NULL);
if (ret != 0) {
perror("Error creating thread\n");
exit(1);

}


ret = pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
if (ret != 0) {
perror("Error setting state\n");
exit(1);
}

ret = pthread_attr_setschedpolicy(&attr, SCHED_RR);
if (ret != 0) {
perror("Error setting scheduling policy\n");
exit(1);
}


ret  = pthread_create(&tid1, &attr, threadFn, NULL);
if (ret != 0) {
perror("Error creating thread\n");
exit(1);
}


/*
  * When a thread attributes object is no longer, it should be destroyed using
  * the pthread_attr_destroy() function. Destroying a thread attributes object
  * has no effect on threads that were created using that object.
  */
if (pthread_attr_destroy(&attr) != 0)
perror("Error destroying attribute\n");
pthread_exit(NULL);
}






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