Question

I have written a small program to create thread and change their default stack size but in my case . When i am printing the stacksize after changing the attribute, i am still getting stacksize displayed as default stack size .

        # include<iostream>
        # include<pthread.h>
        # include<stdio.h>
        # define size 10
        using namespace std;
        pthread_attr_t attr;

        void* sum(void * threadid)
        {
          static int sum =0;
          sum=sum+5;
          long id=(long)threadid;
          size_t mystacksize;
          pthread_attr_getstacksize(&attr,&mystacksize);
          cout << " stack size  "<< mystacksize <<endl;
        }
        int main()
        {
         int rc;
         long t=0;
         pthread_t threads[5];  //number of different thread to br creatd
         size_t stacksize;
         pthread_attr_init(&attr);
         pthread_attr_getstacksize(&attr,&stacksize);   //gets the default stack size 
                                                        //allocated for thread
         cout <<" Default stack size is : " << stacksize <<endl; 
         stacksize=size;
         pthread_attr_setstacksize(&attr,stacksize);  //sets a new stacksize for thread
           for(t=0;t<5;t++)
            {
              rc=pthread_create(&threads[t],&attr,sum,(void*)t);
              if(rc)
              cout << "thread creation failed with id : " << t <<endl;
            }
         pthread_exit(NULL);
        return 0;
        }

output is :-

           Default stack size is : 8388608
           stack size  : 8388608
           stack size  : 8388608
           stack size  : 8388608
           stack size  : 8388608
           stack size  : 8388608

Also note that if i try and increase the stacksize greater than default size i am successfully able to do so .

Answer 1

It’s crazy to expect to be able to use a stack size of ten bytes.

Did you read the pthread_attr_setstacksize man page? Did you check the return value of calling pthread_attr_setstacksize?

On my system (GNU/Linux) the man page says:

   pthread_attr_setstacksize() can fail with the following error:

   EINVAL The stack size is less than PTHREAD_STACK_MIN (16384) bytes.