4_sync.cpp

Synchronization primitives example.

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

fiber 1 outside of critical section
fiber 2 outside of critical section
fiber 3 outside of critical section
Other fiber
Other fiber
 { fiber 1 at start of critical section
Other fiber
Other fiber
Other fiber
 } fiber 1 at end of critical section
fiber 1 outside of critical section
Other fiber
 { fiber 2 at start of critical section
Other fiber
Other fiber
Other fiber
 } fiber 2 at end of critical section
fiber 2 outside of critical section
Other fiber
 { fiber 3 at start of critical section
Other fiber
Other fiber
Other fiber
 } fiber 3 at end of critical section
fiber 3 outside of critical section
Other fiber
 { fiber 1 at start of critical section
Other fiber
Other fiber
Other fiber
 } fiber 1 at end of critical section
fiber 1 outside of critical section
Other fiber
 { fiber 2 at start of critical section
Other fiber
Other fiber
Other fiber
 } fiber 2 at end of critical section
fiber 2 outside of critical section
Other fiber
 { fiber 3 at start of critical section
Other fiber
Other fiber
Other fiber
 } fiber 3 at end of critical section
fiber 3 outside of critical section
Other fiber
 { fiber 1 at start of critical section
Other fiber
Other fiber
Other fiber
 } fiber 1 at end of critical section
Other fiber
 { fiber 2 at start of critical section
Other fiber
Other fiber
Other fiber
 } fiber 2 at end of critical section
Other fiber
 { fiber 3 at start of critical section
Other fiber
Other fiber
Other fiber
 } fiber 3 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;
static zth::Gate gate(4);
 
static void fiber(int id)
{
        zth::currentFiber().setName(zth::format("fiber %d", id));
 
        for(int i = 0; i < 3; i++) {
                printf("fiber %d outside of critical section\n", id);
 
                zth::outOfWork();
                zth::outOfWork();
 
                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();
                zth::outOfWork();
                zth::outOfWork();
                printf(" } fiber %d at end of critical section\n", id);
        }
 
        gate.pass();
}
 
static bool stopOther = false;
 
static void otherFiber()
{
        zth::currentFiber().setName("other fiber");
 
        while(!stopOther) {
                printf("Other fiber\n");
                zth::outOfWork();
        }
}
 
int main_fiber(int /*argc*/, char** /*argv*/)
{
        zth::fiber(fiber, 1);
        zth::fiber(fiber, 2);
        zth::fiber(fiber, 3);
        zth::fiber(otherFiber);
 
        gate.wait();
 
        stopOther = true;
        return 0;
}