Pthread: wake a thread from 4 threads - c++

Question

I have a problem with waking a thread in C++. I have 4 running threads. I want to wake my sleeping thread when the 4 running threads are completed. I did it with condition wait operation but it doesn't look good. How can I do this process in a better quality way?
4 tasks are triggered by broadcast and starts working on different cores at the same time. At the end of each task, it sets the flag of its own taskID to 1 and sends a signal to the sleeping task. The task in sleep state wakes up every time it receives a signal and checks the flag of each task. If the 4 task flag is 1, it continues and does its own work.
void *thread_sleep( void *arg )
{
pthread_mutex_lock(&mutex_sleep);
while(flag_task[0] == 0 || flag_task[1] == 0 || flag_task[2] == 0 || flag_task[3] == 0)
pthread_cond_wait(&cond_sleep, &mutex_sleep);
/*
.
.
.
.
*/
flag_task[0] = 0;
flag_task[1] = 0;
flag_task[2] = 0;
flag_task[3] = 0;
pthread_mutex_unlock(&mutex_sleep);
}
void *thread( void *arg)
{
int taskID = *(char *)arg - '0';
while(1)
{
pthread_mutex_lock(&mutex[taskID]);
pthread_cond_wait(&cond, &mutex[taskID]);
/*
.
.
.
.
*/
pthread_mutex_unlock(&mutex[taskID]);
flag_task[taskID] = 1;
pthread_cond_signal(&cond_sleep);
}
}
int main()
{
pthread_create( &pthread1, NULL, thread, (void *)"0" );
pthread_create( &pthread2, NULL, thread, (void *)"1" );
pthread_create( &pthread3, NULL, thread, (void *)"2" );
pthread_create( &pthread4, NULL, thread, (void *)"3" );
pthread_create( &pthread5, NULL, thread_sleep, (void *)"4" );
pthread_cond_broadcast(&cond);
}

Answer 1

I solved using barrier. Thank you #Quimby.
void *thread_sleep( void *arg )
{
pthread_mutex_lock(&mutex_sleep);
pthread_cond_wait(&cond_sleep, &mutex_sleep);
/*
.
.
.
.
*/
pthread_mutex_unlock(&mutex_sleep);
}
void *thread( void *arg)
{
int taskID = *(char *)arg - '0';
while(1)
{
pthread_mutex_lock(&mutex[taskID]);
pthread_cond_wait(&cond, &mutex[taskID]);
/*
.
.
.
.
*/
pthread_mutex_unlock(&mutex[taskID]);
pthread_barrier_wait(&barrier);
pthread_cond_signal(&cond_sleep);
}
}
int main()
{
pthread_barrier_init(&barrier, NULL, 4);
pthread_create( &pthread1, NULL, thread, (void *)"0" );
pthread_create( &pthread2, NULL, thread, (void *)"1" );
pthread_create( &pthread3, NULL, thread, (void *)"2" );
pthread_create( &pthread4, NULL, thread, (void *)"3" );
pthread_create( &pthread5, NULL, thread_sleep, (void *)"4" );
sleep(1);
pthread_cond_broadcast(&cond);
}