source: tests/io/away_fair.cfa@ 2dcd80a

//
// 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.
//
// away_fair.cfa -- Test that spinning doesn't cause submissions to get stuck.
//                  This test should work without io_uring but isn't very useful without
//
// Author           : Thierry Delisle
// Created On       : Wed Mar 2 12:56:51 2022
// Last Modified By :
// Last Modified On :
// Update Count     :
//

#include <bits/defs.hfa>
#include <fstream.hfa>
#include <kernel.hfa>
#include <thread.hfa>
#include <iofwd.hfa>

Duration default_preemption() {
        return 0;
}

enum { TIMES = 1000 };

volatile unsigned counter = 0;

// ----- Spinner -----
// spins trying to prevent other threads from getting to this processor
thread Spinner {};
void ^?{}(Spinner &mutex ) {}
void main(Spinner &) {
        unsigned last = 0;
        for() {
                unsigned curr = __atomic_load_n(&counter, __ATOMIC_SEQ_CST);

                if(curr >= TIMES) return;

                if(last == curr) {
                        sched_yield();
                        continue;
                }

                last = curr;
                yield();
        }
}

// ----- Submitter -----
// try to submit io but yield so that it's likely we are moved to the slow path
thread Submitter {};
void ^?{}(Submitter &mutex ) {}
void main(Submitter & this) {
        for(TIMES) {
                #if CFA_HAVE_LINUX_IO_URING_H
                        io_future_t f;
                        struct io_uring_sqe * sqe;
                        __u32 idx;
                        struct io_context$ * ctx = cfa_io_allocate(&sqe, &idx, 1);

                        zero_sqe(sqe);
                        sqe->opcode = IORING_OP_NOP;
                        sqe->user_data = (uintptr_t)&f;
                #endif

                yield( prng( this, 15 ) );

                #if CFA_HAVE_LINUX_IO_URING_H
                        // Submit everything
                        asm volatile("": : :"memory");
                        cfa_io_submit( ctx, &idx, 1, false );
                #endif

                unsigned i = __atomic_add_fetch( &counter, 1, __ATOMIC_SEQ_CST );
                if(0 == (i % 100)) sout | i;

                #if CFA_HAVE_LINUX_IO_URING_H
                        wait( f );
                #endif
        }
}

// ----- Yielder -----
// Add some chaos into the mix
thread Yielder {};
void ^?{}(Yielder &mutex ) {}
void main(Yielder&) {
        while(TIMES > __atomic_load_n(&counter, __ATOMIC_SEQ_CST)) {
                yield();
        }
}


int main() {
        processor p;
        sout | "starting";
        {
                Yielder y;
                Spinner s;
                Submitter io;
        }
        sout | "done";
}