Very Computer

I am new to pThreads. I am using pThreads Programmin by Bradford
Nichols from O'Reilly.

The code for an example demostrating Conditional veriables is as
follows:

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

#define TCOUNT 10
#define WATCH_COUNT 12

int count = 0;

pthread_mutex_t count_mutex = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t count_threshold_cv = PTHREAD_COND_INITIALIZER;

int thread_ids[3] = {0, 1, 2};

void watch_count(int *idp){

     pthread_mutex_lock(&count_mutex);
     while (count <= WATCH_COUNT){
         pthread_cond_wait(&count_threshold_cv, &count_mutex);
         printf("\n watch_count(): Thread %d, Count is %d \n", *idp,
count);
         }
     pthread_mutex_unlock(&count_mutex);
     }

void inc_count(int *idp){

     int i;
     for (i=0;i<TCOUNT; i++){
         pthread_mutex_lock(&count_mutex);
         count++;
         printf("\n inc_counter(): Thread %d, old count %d New Count
%d \n", *idp, count-1, count);
         if (count == WATCH_COUNT)
            pthread_cond_signal(&count_threshold_cv);
         pthread_mutex_unlock(&count_mutex);
         }
     }

main(){

     pthread_t threads[3];

     pthread_create(&threads[0], NULL, (void *(*)(void *))inc_count,
&thread_ids[0]);
     pthread_create(&threads[1], NULL, (void *(*)(void *))inc_count,
&thread_ids[1]);
     pthread_create(&threads[2], NULL, (void *(*)(void *))watch_count,
&thread_ids[2]);

     pthread_join(threads[0], NULL);
     pthread_join(threads[1], NULL);
     pthread_join(threads[2], NULL);

     }

I expected the o/p to contain
watch_count(): Thread 2 count:12
But, it did not. I traced the prog. and found out, by the time the
watch thread checks count - its already beyond 12. So I modified the
code such that the Watch thread - Thread 3 is created first. This
modified the o/p with the watch thread printing :
watch_count(): Thread 2 count: 20.

I am thinking that the watch thread is not able to lock the mutex till
the two threads are done. If it is, what is the use of the conditional
variable and the pthread_cond_signal().

o/p:
inc_counter(): Thread 0, old count 0 New Count 1

 inc_counter(): Thread 0, old count 1 New Count 2

 inc_counter(): Thread 0, old count 2 New Count 3

 inc_counter(): Thread 0, old count 3 New Count 4

 inc_counter(): Thread 0, old count 4 New Count 5

 inc_counter(): Thread 0, old count 5 New Count 6

 inc_counter(): Thread 0, old count 6 New Count 7

 inc_counter(): Thread 0, old count 7 New Count 8

 inc_counter(): Thread 0, old count 8 New Count 9

 inc_counter(): Thread 0, old count 9 New Count 10

 inc_counter(): Thread 1, old count 10 New Count 11

 inc_counter(): Thread 1, old count 11 New Count 12

 inc_counter(): Thread 1, old count 12 New Count 13

 inc_counter(): Thread 1, old count 13 New Count 14

 inc_counter(): Thread 1, old count 14 New Count 15

 inc_counter(): Thread 1, old count 15 New Count 16

 inc_counter(): Thread 1, old count 16 New Count 17

 inc_counter(): Thread 1, old count 17 New Count 18

 inc_counter(): Thread 1, old count 18 New Count 19

 inc_counter(): Thread 1, old count 19 New Count 20

 watch_count(): Thread 2, Count is 20

I am using Solaris 7.

Any suggestions would be very welcome.

regards,
=========
Chadalavada Kalyana Krishna,
National PARAM Super Computing Facility,
Center for Development of Advanced Computing,
Pune University Campus,
Pune - 411007
India.

Fax : +91-20-5694081.