source: tests/io/comp_fair.cfa@ a76202d

//
// 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.
//
// comp_fair.cfa -- Test that spinning doesn't cause completions to get stuck.
//                  This test should work without io_uring but isn't very useful without
//
// Author           : Thierry Delisle
// Created On       : Thu Mar 10 15:06:50 2022
// Last Modified By :
// Last Modified On :
// Update Count     :
//


#include <concurrency/locks.hfa>
#include <fstream.hfa>
#include <iofwd.hfa>
#include <kernel.hfa>
#include <thread.hfa>

#include <errno.h>
#include <string.h>
#include <unistd.h>

struct {
      semaphore sem;
      int pipe[2];

} globals;

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 main(Spinner &) {
        unsigned last = 0;
        for() {
                unsigned curr = __atomic_load_n(&counter, __ATOMIC_SEQ_CST);

                if(curr >= TIMES) return;

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

                last = curr;
                yield();
        }
}

// ----- Reader -----
// Reader from the pipe to test completion doesn't starve
thread Reader {};
void main(Reader & this) {
      bool do_read = has_user_level_blocking( (fptr_t)async_read );

      for(TIMES) {
                yield( prng( this, 15 ) );

            io_future_t f;
            if ( do_read ) {
                  char thrash[1];
                  async_read(f, globals.pipe[0], thrash, 1, 0);
            } else {
                  fulfil(f, 0); // If we don't have user-level blocking just play along
            }

            P( globals.sem );

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

            wait( f );

            if(f.result < 0)
                  abort | "Read error" | -f.result | ":" | strerror(-f.result);
      }

      P( globals.sem );
}

// ----- Writer -----
// Writes to the pipe so the Reader can unblock
// takes its sweet time so the Reader has to block
thread Writer {};
void main(Writer & this) {
      for(TIMES) {
            yield( prng( this, 15 ) );

            V( globals.sem );

            sleep( 1`us );

            char buf[1] = { '+' };
            int ret = write( globals.pipe[1], buf, 1 );
            if(ret < 0)
                  abort | "Write error" | errno | ":" | strerror(errno);

      }
}

// ----- 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() {
      int ret = pipe(globals.pipe);
      if(ret != 0)
            abort | "Pipe error" | errno | ":" | strerror(errno);

        processor p;
        sout | "starting";
        {
                Yielder y;
                Spinner s;
                Reader ior;
            Writer iow;
        }
        sout | "done";
}