4_sync.cpp

Synchronization primitives example.

Synchronization primitives example.This program will print something like this:

Other fiber
fiber 3 outside of critical section
 { fiber 3 at start of critical section
fiber 2 outside of critical section
fiber 1 outside of critical section
Other fiber
 } fiber 3 at end of critical section
 { fiber 2 at start of critical section
Other fiber
fiber 3 outside of critical section
 } fiber 2 at end of critical section
 { fiber 1 at start of critical section
Other fiber
fiber 2 outside of critical section
 } fiber 1 at end of critical section
 { fiber 3 at start of critical section
Other fiber
fiber 1 outside of critical section
 } fiber 3 at end of critical section
 { fiber 2 at start of critical section
Other fiber
fiber 3 outside of critical section
 } fiber 2 at end of critical section
 { fiber 1 at start of critical section
Other fiber
fiber 2 outside of critical section
 } fiber 1 at end of critical section
 { fiber 3 at start of critical section
Other fiber
fiber 1 outside of critical section
 } fiber 3 at end of critical section
 { fiber 2 at start of critical section
Other fiber
 } fiber 2 at end of critical section
 { fiber 1 at start of critical section
Other fiber
 } fiber 1 at end of critical section
Other fiber

/*
 * SPDX-FileCopyrightText: 2019-2026 Jochem Rutgers
 *
 * SPDX-License-Identifier: CC0-1.0
 */
 
#include <zth>
 
#include <cstdio>
 
// Even though all code within a fiber is executed atomically when not yielded,
// sometimes it is required to yield within a (long) critical section anyway.
// If you have many fibers, but only a few may be trying to access the critical
// section, it is still nice to yield.  In that case, synchronization
// primitives are required. Zth offers a few, namely a mutex, signal (a.k.a.
// condition), and a semaphore.  Their interface is straight-forward. Here, we
// only show an example with a mutex.
 
static zth::Mutex mutex;
 
void fiber(int id)
{
        for(int i = 0; i < 3; i++) {
                printf("fiber %d outside of critical section\n", id);
 
                zth::Locked l(mutex);
 
                printf(" { fiber %d at start of critical section\n", id);
                // It does not matter how and how often we yield, other fibers
                // trying to lock the mutex will not be scheduled, but others
                // may.
                zth::yield();
                zth::outOfWork();
                printf(" } fiber %d at end of critical section\n", id);
 
                zth::outOfWork();
        }
}
zth_fiber(fiber)
 
static bool stopOther = false;
 
void otherFiber()
{
        while(!stopOther) {
                printf("Other fiber\n");
                zth::outOfWork();
        }
}
zth_fiber(otherFiber)
 
int main_fiber(int /*argc*/, char** /*argv*/)
{
        fiber_future f1 = zth_async fiber(1);
        fiber_future f2 = zth_async fiber(2);
        fiber_future f3 = zth_async fiber(3);
        zth_async otherFiber();
        f1->wait();
        f2->wait();
        f3->wait();
        stopOther = true;
        return 0;
}