source: src/libcfa/concurrency/monitor.c @ 78d3dd5

//                              -*- 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_desc.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 set_owner( monitor_desc * this, thread_desc * owner ) {
        //Pass the monitor appropriately
        this->owner = owner;

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

extern "C" {
        void __enter_monitor_desc(monitor_desc * this) {
                lock( &this->lock );
                thread_desc * 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 );
        }

        // leave pseudo code :
        //      decrement level
        //      leve == 0 ?
        //              no : done
        //              yes :
        //                      signal stack empty ?
        //                              has leader :
        //                                      bulk acquiring means we don't own the signal stack
        //                                      ignore it but don't release the monitor
        //                              yes :
        //                                      next in entry queue is new owner
        //                              no :
        //                                      top of the signal stack is the owner
        //                                      context switch to him right away
        //
        void __leave_monitor_desc(monitor_desc * this) {
                lock( &this->lock );

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

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

                //If we haven't left the last level of recursion
                //it means we don't need to do anything
                if( this->recursion != 0) {
                        unlock( &this->lock );
                        return;
                }
                        
                //If we don't own the signal stack then just leave it to the owner
                if( this->stack_owner ) {
                        assert( this->owner == this->stack_owner );
                        unlock( &this->lock );
                        return;
                }

                //We are the stack owner and have left the last recursion level.
                //We are in charge of passing the monitor
                thread_desc * new_owner = 0;

                //Check the signaller stack
                new_owner = pop( &this->signal_stack );
                if( new_owner ) {
                        //The signaller stack is not empty,
                        //transfer control immediately
                        set_owner( this, new_owner );
                        ScheduleInternal( &this->lock, new_owner );
                        return;
                }
                
                // No signaller thread
                // Get the next thread in the entry_queue
                new_owner = pop_head( &this->entry_queue );
                set_owner( this, new_owner );

                //We can now let other threads in safely
                unlock( &this->lock );

                //We need to wake-up the thread
                ScheduleThread( new_owner );
        }
}

void enter(monitor_desc ** monitors, int count) {
        for(int i = 0; i < count; i++) {
                __enter_monitor_desc( monitors[i] );
        }
}

void leave(monitor_desc ** monitors, int count) {
        for(int i = count - 1; i >= 0; i--) {
                __leave_monitor_desc( monitors[i] );
        }
}