source: src/libcfa/concurrency/monitor.c @ cc7f4b1

//                              -*- Mode: CFA -*-
//
// Cforall Version 1.0.0 Copyright (C) 2016 University of Waterloo
//
// The contents of this file are covered under the licence agreement in the
// file "LICENCE" distributed with Cforall.
//
// __monitor_t.c --
//
// Author           : Thierry Delisle
// Created On       : Thd Feb 23 12:27:26 2017
// Last Modified By : Thierry Delisle
// Last Modified On : --
// Update Count     : 0
//

#include "monitor"

#include "kernel_private.h"

void enter(__monitor_t * this) {
        lock( &this->lock );
        thread * thrd = this_thread();

        if( !this->owner ) {
                //No one has the monitor, just take it
                this->owner = thrd;
                this->recursion = 1;
        }
        else if( this->owner == thrd) {
                //We already have the monitor, just not how many times we took it
                assert( this->recursion > 0 );
                this->recursion += 1;
        }
        else {
                //Some one else has the monitor, wait in line for it
                append( &this->entry_queue, thrd );
                ScheduleInternal( &this->lock );

                //ScheduleInternal will unlock spinlock, no need to unlock ourselves
                return; 
        }

        unlock( &this->lock );
}

void leave(__monitor_t * this) {
        lock( &this->lock );

        thread * thrd = this_thread();
        assert( thrd == this->owner );

        //Leaving a recursion level, decrement the counter
        this->recursion -= 1;

        //If we left the last level of recursion it means we are changing who owns the monitor
        thread * new_owner = 0;
        if( this->recursion == 0) {
                //Get the next thread in the list
                new_owner = this->owner = pop_head( &this->entry_queue );

                //We are passing the monitor to someone else, which means recursion level is not 0
                this->recursion = new_owner ? 1 : 0;
        }       

        unlock( &this->lock );

        //If we have a new owner, we need to wake-up the thread
        if( new_owner ) {
                ScheduleThread( new_owner );
        }
}