source: tests/concurrency/readyQ/leader_spin.cfa @ e8b5ba4

//
// Cforall Version 1.0.0 Copyright (C) 2022 University of Waterloo
//
// The contents of this file are covered under the licence agreement in the
// file "LICENCE" distributed with Cforall.
//
// leader_spin.cfa -- validates ready queue fairness
//
// Author           : Thierry Delisle
// Created On       : Fri Apr 01 11:39:09 2022
// Last Modified By :
// Last Modified On :
// Update Count     :
//

#include <stdlib.hfa>
#include <fstream.hfa>
#include <thread.hfa>

// Test validates that all cores being constantly active doesn't prevent starvation.
// This test is very similar to the transfer benchmark, without all the benchmark bells and whistle.

// Deactivate preemption because it could fix starvation issues.
Duration default_preemption() {
        return 0;
}

PRNG64 lead_rng;
volatile unsigned leader;
volatile size_t lead_idx;

const uint64_t nthreads = 17;
const uint64_t stop_count = 327;

thread$ * the_main;

thread __attribute__((aligned(128))) MyThread {
        unsigned id;
        volatile size_t idx;
};

void ?{}( MyThread & this, unsigned id ) {
        this.id = id;
        this.idx = 0;
}

MyThread ** threads;

static void waitgroup() {
        for(i; nthreads) {
                while( threads[i]->idx != lead_idx ) {
                        sched_yield();
                }
        }
}

static void lead(MyThread & this) {
        this.idx = ++lead_idx;
        if(lead_idx > stop_count) {
                sout | "Leader done";
                unpark( the_main );
                return;
        }

        waitgroup();

        unsigned nleader = prng( lead_rng, nthreads );
        __atomic_store_n( &leader, nleader, __ATOMIC_SEQ_CST );
}

static void wait(MyThread & this) {
        yield();
        if(lead_idx == this.idx) {
                return;
        }

        assert( (lead_idx - 1) == this.idx );
        __atomic_add_fetch( &this.idx, 1, __ATOMIC_SEQ_CST );
        yield();
}

void main(MyThread & this) {
        park();

        unsigned me = this.id;

        for() {
                if(leader == me) {
                        lead( this );
                }
                else {
                        wait( this );
                }
                if(lead_idx > stop_count) break;
        }
}

// ==================================================
int main(int argc, char * argv[]) {
        lead_idx = 0;
        leader = prng( lead_rng, nthreads );

        the_main = active_thread();
        processor procs[2];
        {
                threads = alloc(nthreads);
                for(i; nthreads) {
                        threads[i] = malloc();
                        (*threads[i]){
                                i
                        };
                }

                for(i; nthreads) unpark(*threads[i]);

                park();

                for(i; nthreads) {
                        MyThread * thrd = threads[i];
                        join(*thrd);
                        ^( *thrd ){};
                        free(thrd);
                }

                free(threads);
        }
        sout | "done";
}