It gets me error at rand_r
undefined reference to 'rand_r'
It is my first program at c language
I must use rand_r to threads, but i don't know what to do.
Please help me. Thank you
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include "p3160062.h"
int cook;
int oven;
int prep;
int bake;
pthread_mutex_t lock;
pthread_t thread_id[100];
unsigned int seed;
int a;
void *myThread(void *vargp)
{
pthread_mutex_lock(&lock);
a=rand_r(&seed)%6;
while(a==0){
a=rand_r(&seed)%6;
}
printf("a=%d\n",a);
sleep(1);
printf("In thread\n");
pthread_mutex_unlock(&lock);
return NULL;
}
int main(void)
{
seed=1;
int i=0;
printf("Before Thread\n");
for(i=0;i<100;i++){
pthread_create(&(thread_id[i]), NULL, myThread, NULL);
pthread_join(thread_id[i], NULL);
seed++;
}
printf("After Thread\n");
pthread_mutex_destroy(&lock);
exit(0);
}
Related
This is the code I have so far for the newly modified version of nosmp.c.
#include <pthread.h>
#include <stdio.h>
#define NUM_THREADS 5
void *PrintHello(void *threadid)
{
long tid;
tid = (long)threadid;
printf("Hello World! It's me, thread #%ld!\n", tid);
pthread_exit(NULL);
}
int main (int argc, char *argv[])
{
pthread_t threads[NUM_THREADS];
int rc;
lng t;
for(t=0; t<NUM_THREADS; t++){
printf("In main: creating thread %ld\n", t);
rc = pthread_create(&threads[t], NULL, PrintHello, (void *)t);
if (rc){
printf("ERROR; return code from pthread_create() is %d\n", rc);
exit(-1);
}
}
pthread_exit(NULL);
}
The code below is the old nosmp.c code:
#include <stdio.h>
#include <pthread.h>
#include <semaphore.h>
#include <unistd.h>
void* thread(void* arg)
{
printf("\n Entered.., %c\n", *((char*)arg));
//critical section
sleep(4);
printf("\n Just Exiting.., %c\n", *((char*)arg));
}
int main()
{
pthread_t t1,t2;
pthread_create(&t1,NULL,thread,"1");
sleep(2);
pthread_create(&t2,NULL,thread,"2");
pthread_join(t1,NULL);
pthread_join(t2,NULL);
return 0;
}
For the modified version of the code above, I am trying to figure out where I would add the semaphore system calls into their proper lines to ensure that two threads will enter the critical section in order.
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
void *t1(){
long tid=9;
printf("thread ID %ld",tid);
}
void *t2(){
long tid=10;
printf("thread ID %ld",tid);
}
int main()
{
pthread_t thread1,thread2;
int rc;
int i=0;
rc =pthread_create(&thread1,NULL,t1,NULL);
if(rc)
{
printf("ERROR");
exit();
}
pthread_create(&thread2,NULL,t2,NULL);
return 0;
}
This is where I am at, I have created the threads and executed it but I don't know how to call those functions based on a timer.
I have 4 processed called A, B, C, D in 4 thread, They printf their name. I want use mutex to process A, B, C, D run in order A, B, C, D. This is my code but it don't work such as me think. How to they work?
#include <stdio.h>
#include <pthread.h>
void processA();
void processB();
void processC();
void processD();
pthread_mutex_t mutex;
void main(){
pthread_t thread1;
pthread_t thread2;
pthread_t thread3;
pthread_t thread4;
pthread_mutex_init(&mutex,NULL);
pthread_create(&thread1, NULL, (void *)&processA,NULL);
pthread_create(&thread2, NULL, (void *)&processB,NULL);
pthread_create(&thread3, NULL, (void *)&processC,NULL);
pthread_create(&thread4, NULL, (void *)&processD,NULL);
pthread_join(thread1, NULL);
pthread_join(thread2, NULL);
pthread_join(thread3, NULL);
pthread_join(thread4, NULL);
pthread_mutex_destroy(&mutex);
}
void processA()
{
while (1)
{
pthread_mutex_lock(&mutex);
printf("A \n");
pthread_mutex_unlock(&mutex);
}
}
void processB()
{
while (1)
{
pthread_mutex_lock(&mutex);
printf("B \n");
pthread_mutex_unlock(&mutex);
}
}
void processC()
{
while (1)
{
pthread_mutex_lock(&mutex);
printf("C \n");
pthread_mutex_unlock(&mutex);
}
}
void processD()
{
pthread_mutex_lock(&mutex);
while (1)
{
pthread_mutex_lock(&mutex);
printf("D \n");
pthread_mutex_unlock(&mutex);
}
}
mutex is for creating mutual exclusion on some context. For example if you have an object that should be reached by one thread at a time, you can use mutex.
You should use 3 semaphores for implementing such feature. You can say:
//semaphore1 = up, semaphore2 = up, semaphore3 = up
//Thread A
//wait for semaphore1 is up
//work
//make semaphore1 down
//Thread B
//wait for semaphore1 is down
//work
//make semaphore2 down
//Thread C
//wait for semaphore2 is down
//work
//make semaphore3 down
//Thread D
//wait for semaphore3 is down
//work
Well this is how you can do it, you just use mutex for the mutual variable (f in this case) and a pthread conditional signal to trigger the action of one thread per second. All of the threads get the signal but only one can access the mutex.
#include <unistd.h>
#include <signal.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <sys/time.h>
#include <stdlib.h>
#include <memory.h>
#include <stdarg.h>
#include <pthread.h>
pthread_mutex_t v1 = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t v2 = PTHREAD_COND_INITIALIZER;
int f = 0;
void *processA(){
while(1){
pthread_mutex_lock(&v1);
pthread_cond_wait(&v2,&v1);
printf("A,%d\n",f);
f++;
pthread_mutex_unlock(&v1);
}
return NULL;
}
void *processB(){
while(1){
pthread_mutex_lock(&v1);
pthread_cond_wait(&v2,&v1);
printf("B,%d\n",f);
f++;
pthread_mutex_unlock(&v1);
}
return NULL;
}
void *processC(){
while(1){
pthread_mutex_lock(&v1);
pthread_cond_wait(&v2,&v1);
printf("C,%d\n",f);
f++;
pthread_mutex_unlock(&v1);
}
void main(){
pthread_t *h;
int i,ptnum = 3;
h = malloc(sizeof(pthread_t)*ptnum);
pthread_create(&h[0],NULL,processA,NULL);
pthread_create(&h[1],NULL,processB,NULL);
pthread_create(&h[2],NULL,processC,NULL);
while(f<=30){
pthread_cond_signal(&v2);
sleep(1);
}
pthread_mutex_lock(&v1);
printf("Main Mutex\n");
for(i=0;i<ptnum;i++){
pthread_join(&h[i],PTHREAD_CANCELED);
}
pthread_mutex_unlock(&v1);
return NULL;
}
in this example code below, where is the "critical section" exatly?. after "sem_wait()" ?
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <pthread.h>
#include <semaphore.h>
void * thread_snd(void *arg);
void * thread_rcv(void *arg);
sem_t bin_sem;
int number=0;
char thread1[]="A Thread";
char thread2[]="B Thread";
char thread3[]="C Thread";
int main(int argc, char **argv)
{
pthread_t t1, t2, t3;
void *thread_result;
int state;
state = sem_init(&bin_sem, 0, 0);
pthread_create(&t1, NULL, thread_snd, &thread1);
pthread_create(&t2, NULL, thread_rcv, &thread2);
pthread_create(&t3, NULL, thread_rcv, &thread3);
pthread_join(t1, &thread_result);
pthread_join(t2, &thread_result);
pthread_join(t3, &thread_result);
printf("number : %d \n", number);
sem_destroy(&bin_sem);
return 0;
}
void * thread_snd(void * arg)
{
int i;
for(i=0; i<4; i++)
{
while(number != 0)
sleep(1);
number++;
printf("%s, number : %d \n", (char*)arg, number);
sem_post(&bin_sem);
}
}
void * thread_rcv(void * arg)
{
int i;
for(i=0; i<2; i++)
{
sem_wait(&bin_sem);
number--;
printf("%s, number : %d \n", (char*)arg, number);
}
}
There actually is no "critical section" in the provided code, there is only "sync point", and yes that is realized with the semaphore. The critical section can also be implemented with semaphore, but then the thread must use both sem_wait() and sem_post() but in most cases mutexes are used for critical sections (if only one thread is ever supposed to enter it).
I have a big problem, I can't figure out why mutexes in C don't work as I expect.
This is my code:
#include <stdlib.h>
#include <stdio.h>
#include <pthread.h>
pthread_t mythread;
pthread_mutex_t mymutex;
void *anotherFunc(void*)
{
pthread_mutex_lock(&mymutex);
for(int i = 0; i < 100; i++)
printf("anotherFunc\n");
pthread_mutex_unlock(&mymutex);
pthread_exit(NULL);
}
void *func(void*)
{
pthread_mutex_lock(&mymutex);
for(int i = 0; i < 100; i++)
printf("func\n");
pthread_mutex_unlock(&mymutex);
pthread_exit(NULL);
}
int main(int argc, char *argv[])
{
pthread_mutex_init(&mymutex, NULL);
pthread_create(&mythread, NULL, func, NULL);
pthread_create(&mythread, NULL, anotherFunc, NULL);
pthread_mutex_destroy(&mymutex);
pthread_exit(NULL);
return EXIT_SUCCESS;
}
What I expect to happen is the program to print first 100 "func" messages and then 100 "anotherFunc" messages. What I expect is execution to reach func and lock the mutex. When the execution reaches anotherFunc, I expect to wait until func unlocks the mutex. But I get interfered messages like
func
func
func
anotherFunc
anotherFunc
anotherFunc
func
anotherFunc
I don't understand how this thing works. Please help!
pthread_create(&mythread, NULL, func, NULL);
pthread_create(&mythread, NULL, anotherFunc, NULL);
pthread_mutex_destroy(&mymutex);
You're destroying the mutex before the threads are done with it, so all bets are off. You'll probably want to pthread_join the 2 threads before destroying it.
I got few comiplation errors
I couldn't declare int i in for loop
Used an argument name arg as an argument for threads "func" and "anotherFunc"
I have used pthread_join before destroying the mutex.
In this way I am destroying my mutex "mymutex" after both threads "func" and "anotherFunc" have completed their execution
Also each threads now has their own thread id "mythread1" and "mythread2" so in this way I can use pthread_join() function for each thread
#include <stdlib.h>
#include <stdio.h>
#include <pthread.h>
pthread_t mythread1, mythread2;
pthread_mutex_t mymutex;
void *anotherFunc(void *arg)
{
pthread_mutex_lock(&mymutex);
int i;
for(i = 0; i < 100; i++)
printf("anotherFunc\n");
pthread_mutex_unlock(&mymutex);
pthread_exit(NULL);
}
void *func(void *arg)
{
pthread_mutex_lock(&mymutex);
int i;
for(i = 0; i < 100; i++)
printf("func\n");
pthread_mutex_unlock(&mymutex);
pthread_exit(NULL);
}
int main(int argc, char *argv[])
{
pthread_mutex_init(&mymutex, NULL);
pthread_create(&mythread1, NULL, func, NULL);
pthread_create(&mythread2, NULL, anotherFunc, NULL);
pthread_join(mythread1, NULL);
pthread_join(mythread2, NULL);
pthread_mutex_destroy(&mymutex);
return EXIT_SUCCESS;
}