Thanks all for the response.
I thought of constructing a conditional wait using semaphores as follows:
//global flag = 0.
void *text(void *arg)
{
int n = *(int*)arg;
while(flag != n)
{
sem_wait(&mutex);
internal_flag = 1;
}
if(internal_flag)
sem_post(&mutex);
.....................................
//We can take a lock on this also.
flag++;
pthread_exit(0);
}
//Rest of the code for
On Mon, Nov 26, 2012 at 10:08 AM, Sachin Maheshwari <
sachin.maheshw...@gmail.com> wrote:
> Hi Jagannath,
> pthread_join function call will suspend the execution of the current
> thread till the new thread (whose id you provide to this function) has
> completed.
>
> So in your example when you say pthread_join(tid[i],NULL), the current
> thread (ie the main thread) will remain suspended till thread created by
> you in the previous line pthread_create (with thread id tid[i]) completes.
>
> Regards,
> Sachin
>
>
> On Mon, Nov 26, 2012 at 9:46 AM, Jagannath Prasad Das <jpdasi...@gmail.com
> > wrote:
>
>> @Naveen: I didn't understand your point . Can you please throw more light
>> on join operation
>>
>> On Sun, Nov 25, 2012 at 10:47 PM, vIGNESH v <v.v.07121...@gmail.com>wrote:
>>
>>> You can use mutex instead of semaphores if you need to execute only one
>>> case at a time.
>>>
>>> FROM,
>>>
>>> V.VIGNESH.
>>> M.Sc Theoretical Computer Science.
>>> PSG College of Technology
>>>
>>>
>>>
>>> On 25 November 2012 22:37, jagannath <jpdasi...@gmail.com> wrote:
>>>
>>>> Folks, I have one pthread question.I know that its not the right place
>>>> but i thought this is the right place to post this. Code snippet:
>>>> #include <stdlib.h>
>>>> #include <stdio.h>
>>>>
>>>> #include <unistd.h> /* defines _POSIX_THREADS if pthreads are available
>>>> */
>>>> #ifdef _POSIX_THREADS
>>>> # include <pthread.h>
>>>> #endif
>>>>
>>>> #include <semaphore.h>
>>>>
>>>> void *text(void *arg);
>>>>
>>>> int code[] = { 4, 6, 3, 1, 5, 0, 2 };
>>>>
>>>> int main()
>>>> {
>>>> int i;
>>>> pthread_t tid[7];
>>>>
>>>> for (i = 0; i < 7; i++)
>>>> {
>>>> pthread_create(&tid[i], NULL, text, (void*)&code[i]);
>>>> pthread_join(tid[i],NULL);
>>>> }
>>>>
>>>> return 0;
>>>> }
>>>>
>>>> void *text(void *arg)
>>>> {
>>>> int n = *(int*)arg;
>>>>
>>>> switch (n)
>>>> {
>>>> case 0:
>>>> printf("A semaphore S is an integer-valued variable which can take only
>>>> non-negative\n");
>>>> printf("values. Exactly two operations are defined on a
>>>> semaphore:\n\n");
>>>> break;
>>>>
>>>> case 1:
>>>> printf("Signal(S): If there are processes that have been suspended on
>>>> this semaphore,\n");
>>>> printf(" wake one of them, else S := S+1.\n\n");
>>>> break;
>>>>
>>>> case 2:
>>>> printf("Wait(S): If S>0 then S:=S-1, else suspend the execution of this
>>>> process.\n");
>>>> printf(" The process is said to be suspended on the semaphore S.\n\n");
>>>> break;
>>>>
>>>> case 3:
>>>> printf("The semaphore has the following properties:\n\n");
>>>> break;
>>>>
>>>> case 4:
>>>> printf("1. Signal(S) and Wait(S) are atomic instructions. In
>>>> particular, no\n");
>>>> printf(" instructions can be interleaved between the test that S>0 and
>>>> the\n");
>>>> printf(" decrement of S or the suspension of the calling
>>>> process.\n\n");
>>>> break;
>>>>
>>>> case 5:
>>>> printf("2. A semaphore must be given an non-negative initial
>>>> value.\n\n");
>>>> break;
>>>>
>>>> case 6:
>>>> printf("3. The Signal(S) operation must waken one of the suspended
>>>> processes. The\n");
>>>> printf(" definition does not specify which process will be
>>>> awakened.\n\n");
>>>> break;
>>>> }
>>>>
>>>> pthread_exit(0);
>>>> }
>>>>
>>>> The threads are not synchronized and therefore the text output is
>>>> garbled. How to add semaphores of POSIX to this program to synchronize the
>>>> threads.?
>>>>
>>>> primitives to rejig your memory:
>>>>
>>>> sem_init(), sem_wait(),sem_post(),sem_destroy().
>>>>
>>>> --
>>>>
>>>>
>>>>
>>>
>>> --
>>>
>>>
>>>
>>
>> --
>>
>>
>>
>
>
>
> --
> Regards,
> Sachin Maheshwari
> Cell phone: +91.7259917298
>
> "If we admit that human life can be ruled by reason; the possibility of
> life is destroyed." - Alexander Supertramp
>
> --
>
>
>
--
