butdub.com/hardforums/showthread.php?t=499867">srsrgg3
I've come up with the code but it does not work. I can't figure out how to use all three threads to run at the same time.
#include
#include
#include
int i = 0;
void* hello(void* p) {
while (i < 1) {
printf("Hi\n");
usleep(1000);
i++;
}
}
int main(void) {
pthread_t h, a, b;
pthread_create(&b, NULL, hello, NULL);
pthread_create(&a, NULL, hello, NULL);
pthread_create(&h, NULL, hello, NULL);
}
Thanks.
A:
You are probably creating your threads without a stack.
By default, all threads that start out of the box without parameters are created with a stack of 512 bytes.
When you are calling pthread_create, you can provide the size of the stack for each thread to use. Using this stack size as a base, the stack will grow when it is full. The stack size is not a limit on how large it can grow; it only dictates how large it can grow. Once the stack reaches its limit, the thread will simply start executing into a memory region that is not executable, crashing the program.
You can change the stack size by specifying a different value to the argument you pass to pthread_attr_create:
pthread_attr_t attr;
pthread_attr_init(&attr);
pthread_attr_setstacksize(&attr, 8192);
Now your threads have a stack of 8192 bytes each. Make sure to set the stacksize on all threads, or your program will still crash.
A:
To expand on David's answer, here's a test program that illustrates how you might set up and wait for multiple threads on a Unix system using a set of pthreads.
It uses three threads, one that sleeps, one that runs forever, and one that sleeps forever then terminates. I also illustrate a mechanism to wait for the threads using pthread_join, to ensure that the threads do what you want them to do.
This is compiled in gcc with the following:
gcc -o test main.c -lpthread
Sample output
Started all threads
Hello from thread: 1, num thread = 3, sleep time = 0
Hello from thread: 0, num thread = 3, sleep time = 0
Hello from thread: 2, num thread = 3, sleep time = 0
Ended all threads
waiting on thread: 1
waiting on thread: 2
Thread 2 terminated
Thread 1 terminated
Main ended
Press any key to continue . . .
#include
#include
#include
#define NUM_THREADS 3
void * doHello(void *param);
void * doHelloForever(void *param);
void * doHelloWithWait(void *param);
int main(void)
{
pthread_t myThread[NUM_THREADS];
pthread_attr_t threadAttr;
int count;
pthread_attr_init(&threadAttr);
for (count = 0; count < NUM_THREADS; count++)
{
pthread_create(&myThread[count], &threadAttr, doHello, NULL);
printf("%d started\n", count+1);
pthread_join(myThread[count], NULL);
}
pthread_attr_destroy(&threadAttr);
return 0;
}
void doHello(void *param)
{
printf("Hello from thread: %d, num thread = %d, sleep time = %d\n",
param+1, param+1, param+1);
}
void doHelloForever(void *param)
{
printf("Hello from thread: %d, num thread = %d, sleep time = %d\n",
param+1, param+1, param+1);
}
void doHelloWithWait(void *param)
{
int status;
printf("Waiting on thread: %d\n", param+1);
status = pthread_join(pthread_self(), NULL);
if (status == 0)
{
printf("Thread %d terminated\n", param+1);
}
else
{
printf("Error joining thread: %d\n", param+1);
}
}
Here is a sample session:
$ cat test.c
#include
#include
#include
#define NUM_THREADS 3
void * doHello(void *param);
void * doHelloForever(void *param);
void * doHelloWithWait(void *param);
int main(void)
{
pthread_t myThread[NUM_THREADS];
pthread_attr_t threadAttr;
int count;
pthread_attr_init(&threadAttr);
for (count = 0; count < NUM_THREADS; count++)
{
pthread_create(&myThread[count], &threadAttr, doHello, NULL);
printf("%d started\n", count+1);
pthread_join(myThread[count], NULL);
}
pthread_attr_destroy(&threadAttr);
return 0;
}
void doHello(void *param)
{
printf("Hello from thread: %d, num thread = %d, sleep time = %d\n",
param+1, param+1, param+1);
}
$ gcc -o test main.c -lpthread
$ ./test
Started all threads
Hello from thread: 1, num thread = 3, sleep time = 0
Hello from thread: 0, num thread = 3, sleep time = 0
Hello from thread: 2, num thread = 3, sleep time = 0
Ended all threads
Waiting on thread: 1
Waiting on thread: 2
Thread 2 terminated
Thread 1 terminated
Main ended
Press any key to continue . . .
As you can see, the thread ids start at 1, then the main program ends.
