How to realise barrier synchronization between threads?

[rweickelt]

Hi,

I've started a set of threads with the par{} statement. How can I achieve a synchronisation barrier between those threads? The architecture manual mentions msync and ssync instructions, but I was hoping to find a more high-level solution.

Thanks

[segher]

Just use channels :-)

[rweickelt]

Thank You for taking the time to answer. The concept of channels is still very new to me and I have problems to get my head around this. May I ask for a small example, e.g. with 3 threads? Or a hint to existing code that involves more than 2 threads?

I am also looking for an easy-to-use solution, that would not be bound to XC and hide the usage of XCORE primitives. The following example reflects what I had in mind.

Code: Select all

// main.xc
int main()
{
    par {
        thread0();
        thread1();
        thread2();
    }

    return 0;
}


// threads.h
extern "C" {
    void thread0();
    void thread1();
    void thread2();
}


// threads.cpp
Barrier<3> barrier;

void thread0()
{
    // do something
    barrier.signalAndWait();
    // do some more
    barrier.signalAndWait();
    // ...
}

void thread1()
{
    // do something
    barrier.signalAndWait();
    // do some more
    barrier.signalAndWait();
    // ...
}

void thread2()
{
    // do something
    barrier.signalAndWait();
    // do some more
    barrier.signalAndWait();
    // ...
}

 

Barrier could be a template class, but still, I have no idea, how to realize the low-level backend.

[rweickelt]

Thanks to this thread pointing to this code I was able to replace the par construct with a thread group and got a working synchronization barrier.