Taskgroup construct

When a running task meets taskgroup construct:

#pragma omp taskgroup new-line
    structured-block

It will pause, and won't execute again until all child and descendant tasks in taskgroup finish. Check the following example:

#include <stdio.h>
#include <omp.h>
#include <unistd.h>

int main(void)
{    
    #pragma omp task
    {
        printf("Thread %d is in the beginning of main task\n", omp_get_thread_num());
        #pragma omp taskgroup
        {
            #pragma omp task
            {
                sleep(1);
                printf("Thread %d is in running sub-task 1\n", omp_get_thread_num());
            }
            #pragma omp task
            {
                sleep(1);
                printf("Thread %d is in running sub-task 2\n", omp_get_thread_num());
            }
        }
        printf("Thread %d is in the ending of main task\n", omp_get_thread_num());
    }

    return 0;
}

Build and run it:

# gcc -fopenmp parallel.c
# ./a.out
Thread 0 is in the beginning of main task
Thread 0 is in running sub-task 1
Thread 0 is in running sub-task 2
Thread 0 is in the ending of main task

We can see even though the sub-tasks in taskgroup will sleep (call sleep), the main task won't be scheduled to run. The main task will wait all tasks in taskgroup end.