source: src/libcfa/concurrency/monitor.c @ 5ea06d6

//                              -*- 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"
#include "libhdr.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, monitor_desc * leader) {
                lock( &this->lock );
                thread_desc * thrd = this_thread();

                //Update the stack owner
                this->stack_owner = leader;

                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 );
                return;
        }

        // 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, monitor_desc * leader) {
                lock( &this->lock );

                thread_desc * thrd = this_thread();
                assert( thrd == this->owner || this->stack_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) {
                        this->stack_owner = leader;
                        unlock( &this->lock );
                        return;
                }
                        
                //If we don't own the signal stack then just leave it to the owner
                if( this->stack_owner ) {
                        this->stack_owner = leader;
                        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 );
                        this->stack_owner = leader;
                        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 );

                //Update the stack owner
                this->stack_owner = leader;

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

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

static inline void enter(monitor_desc ** monitors, int count) {
        __enter_monitor_desc( monitors[0], NULL );
        for(int i = 1; i < count; i++) {
                __enter_monitor_desc( monitors[i], monitors[0] );
        }
}

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

void ?{}( monitor_guard_t * this, monitor_desc ** m, int count ) {
        this->m = m;
        this->count = count;
        qsort(this->m, count);
        enter( this->m, this->count );

        this->prev_mntrs = this_thread()->current_monitors;
        this->prev_count = this_thread()->current_monitor_count;

        this_thread()->current_monitors      = m;
        this_thread()->current_monitor_count = count;
}

void ^?{}( monitor_guard_t * this ) {
        leave( this->m, this->count );

        this_thread()->current_monitors      = this->prev_mntrs;
        this_thread()->current_monitor_count = this->prev_count;
}

//-----------------------------------------------------------------------------
// Internal scheduling
void wait( condition * this ) {
        // LIB_DEBUG_FPRINTF("Waiting\n");
        thread_desc * this_thrd = this_thread();

        if( !this->monitors ) {
                this->monitors = this_thrd->current_monitors;
                this->monitor_count = this_thrd->current_monitor_count;
        }

        unsigned short count = this->monitor_count;

        //Check that everything is as expected
        assert( this->monitors != NULL );
        assert( this->monitor_count != 0 );

        unsigned int recursions[ count ];               //Save the current recursion levels to restore them later
        spinlock *   locks     [ count ];               //We need to pass-in an array of locks to ScheduleInternal

        // LIB_DEBUG_FPRINTF("Getting ready to wait\n");

        //Loop on all the monitors and release the owner
        for( unsigned int i = 0; i < count; i++ ) {
                monitor_desc * cur = this->monitors[i];

                assert( cur );

                // LIB_DEBUG_FPRINTF("cur %p lock %p\n", cur, &cur->lock);

                //Store the locks for later
                locks[i] = &cur->lock;

                //Protect the monitors
                lock( locks[i] );
                {               
                        //Save the recursion levels
                        recursions[i] = cur->recursion;

                        //Release the owner
                        cur->recursion = 0;
                        cur->owner = NULL;
                }
                //Release the monitor
                unlock( locks[i] );
        }

        // LIB_DEBUG_FPRINTF("Waiting now\n");

        //Everything is ready to go to sleep
        ScheduleInternal( locks, count );


        //WE WOKE UP


        //We are back, restore the owners and recursions
        for( unsigned int i = 0; i < count; i++ ) {
                monitor_desc * cur = this->monitors[i];

                //Protect the monitors
                lock( locks[i] );
                {
                        //Release the owner
                        cur->owner = this_thrd;
                        cur->recursion = recursions[i];
                }
                //Release the monitor
                unlock( locks[i] );
        }
}

static void __signal_internal( condition * this ) {
        if( !this->blocked.head ) return;

        //Check that everything is as expected
        assert( this->monitors );
        assert( this->monitor_count != 0 );
        
        LIB_DEBUG_DO(
                if ( this->monitors != this_thread()->current_monitors ) {
                        abortf( "Signal on condition %p made outside of the correct monitor(s)", this );
                } // if
        );

        monitor_desc * owner = this->monitors[0];
        lock( &owner->lock );
        {
                thread_desc * unblock = pop_head( &this->blocked );
                push( &owner->signal_stack, unblock );
        }
        unlock( &owner->lock );
}

void signal( condition * this ) {
        __signal_internal( this );
}