source: libcfa/src/concurrency/locks.cfa @ 03cdad6

//
// Cforall Version 1.0.0 Copyright (C) 2021 University of Waterloo
//
// The contents of this file are covered under the licence agreement in the
// file "LICENCE" distributed with Cforall.
//
// locks.hfa -- LIBCFATHREAD
// Runtime locks that used with the runtime thread system.
//
// Author           : Colby Alexander Parsons
// Created On       : Thu Jan 21 19:46:50 2021
// Last Modified By :
// Last Modified On :
// Update Count     :
//

#define __cforall_thread__
#define _GNU_SOURCE

#include "locks.hfa"
#include "kernel_private.hfa"

#include <kernel.hfa>
#include <stdlib.hfa>

//-----------------------------------------------------------------------------
// info_thread
forall(L & | is_blocking_lock(L)) {
        struct info_thread {
                // used to put info_thread on a dl queue
                inline dlink(info_thread(L));

                // waiting thread
                struct thread$ * t;

                // shadow field
                uintptr_t info;

                // lock that is passed to wait() (if one is passed)
                L * lock;

                // true when signalled and false when timeout wakes thread
                bool signalled;
        };
        P9_EMBEDDED( info_thread(L), dlink(info_thread(L)) )

        void ?{}( info_thread(L) & this, thread$ * t, uintptr_t info, L * l ) {
                this.t = t;
                this.info = info;
                this.lock = l;
        }

        void ^?{}( info_thread(L) & this ) {}
}

//-----------------------------------------------------------------------------
// Blocking Locks
void ?{}( blocking_lock & this, bool multi_acquisition, bool strict_owner ) {
        this.lock{};
        this.blocked_threads{};
        this.wait_count = 0;
        this.multi_acquisition = multi_acquisition;
        this.strict_owner = strict_owner;
        this.owner = 0p;
        this.recursion_count = 0;
}

void ^?{}( blocking_lock & this ) {}


void lock( blocking_lock & this ) with( this ) {
        lock( lock __cfaabi_dbg_ctx2 );
        thread$ * thrd = active_thread();

        // single acquisition lock is held by current thread
        /* paranoid */ verifyf( owner != thrd || multi_acquisition, "Single acquisition lock holder (%p) attempted to reacquire the lock %p resulting in a deadlock.", owner, &this );

        // lock is held by some other thread
        if ( owner != 0p && owner != thrd ) {
                insert_last( blocked_threads, *thrd );
                wait_count++;
                unlock( lock );
                park( );
        }
        // multi acquisition lock is held by current thread
        else if ( owner == thrd && multi_acquisition ) {
                recursion_count++;
                unlock( lock );
        }
        // lock isn't held
        else {
                owner = thrd;
                recursion_count = 1;
                unlock( lock );
        }
}

bool try_lock( blocking_lock & this ) with( this ) {
        bool ret = false;
        lock( lock __cfaabi_dbg_ctx2 );

        // lock isn't held
        if ( owner == 0p ) {
                owner = active_thread();
                recursion_count = 1;
                ret = true;
        }
        // multi acquisition lock is held by current thread
        else if ( owner == active_thread() && multi_acquisition ) {
                recursion_count++;
                ret = true;
        }

        unlock( lock );
        return ret;
}

void pop_and_set_new_owner( blocking_lock & this ) with( this ) {
        thread$ * t = &try_pop_front( blocked_threads );
        owner = t;
        recursion_count = ( t ? 1 : 0 );
        if ( t ) wait_count--;
        unpark( t );
}

void unlock( blocking_lock & this ) with( this ) {
        lock( lock __cfaabi_dbg_ctx2 );
        /* paranoid */ verifyf( owner != 0p, "Attempt to release lock %p that isn't held", &this );
        /* paranoid */ verifyf( owner == active_thread() || !strict_owner , "Thread %p other than the owner %p attempted to release owner lock %p", owner, active_thread(), &this );
        /* paranoid */ verifyf( recursion_count == 1 || multi_acquisition, "Thread %p attempted to release owner lock %p which is not recursive but has a recursive count of %zu", active_thread(), &this, recursion_count );

        // if recursion count is zero release lock and set new owner if one is waiting
        recursion_count--;
        if ( recursion_count == 0 ) {
                pop_and_set_new_owner( this );
        }
        unlock( lock );
}

size_t wait_count( blocking_lock & this ) with( this ) {
        return wait_count;
}

void on_notify( blocking_lock & this, thread$ * t ) with( this ) {
        lock( lock __cfaabi_dbg_ctx2 );
        // lock held
        if ( owner != 0p ) {
                insert_last( blocked_threads, *t );
                wait_count++;
                unlock( lock );
        }
        // lock not held
        else {
                owner = t;
                recursion_count = 1;
                unpark( t );
                unlock( lock );
        }
}

size_t on_wait( blocking_lock & this ) with( this ) {
        lock( lock __cfaabi_dbg_ctx2 );
        /* paranoid */ verifyf( owner != 0p, "Attempt to release lock %p that isn't held", &this );
        /* paranoid */ verifyf( owner == active_thread() || !strict_owner, "Thread %p other than the owner %p attempted to release owner lock %p", owner, active_thread(), &this );

        size_t ret = recursion_count;

        pop_and_set_new_owner( this );
        unlock( lock );
        return ret;
}

void on_wakeup( blocking_lock & this, size_t recursion ) with( this ) {
        recursion_count = recursion;
}

//-----------------------------------------------------------------------------
// alarm node wrapper
forall(L & | is_blocking_lock(L)) {
        struct alarm_node_wrap {
                alarm_node_t alarm_node;
                condition_variable(L) * cond;
                info_thread(L) * info_thd;
        };

        void ?{}( alarm_node_wrap(L) & this, Duration alarm, Duration period, Alarm_Callback callback, condition_variable(L) * c, info_thread(L) * i ) {
                this.alarm_node{ callback, alarm, period };
                this.cond = c;
                this.info_thd = i;
        }

        void ^?{}( alarm_node_wrap(L) & this ) { }

        void timeout_handler ( alarm_node_wrap(L) & this ) with( this ) {
                // This condition_variable member is called from the kernel, and therefore, cannot block, but it can spin.
                lock( cond->lock __cfaabi_dbg_ctx2 );

                // this check is necessary to avoid a race condition since this timeout handler
                //      may still be called after a thread has been removed from the queue but
                //      before the alarm is unregistered
                if ( (*info_thd)`isListed ) {   // is thread on queue
                        info_thd->signalled = false;
                        // remove this thread O(1)
                        remove( *info_thd );
                        cond->count--;
                        if( info_thd->lock ) {
                                // call lock's on_notify if a lock was passed
                                on_notify(*info_thd->lock, info_thd->t);
                        } else {
                                // otherwise wake thread
                                unpark( info_thd->t );
                        }
                }
                unlock( cond->lock );
        }

        // this casts the alarm node to our wrapped type since we used type erasure
        void alarm_node_wrap_cast( alarm_node_t & a ) { timeout_handler( (alarm_node_wrap(L) &)a ); }
}

//-----------------------------------------------------------------------------
// condition variable
forall(L & | is_blocking_lock(L)) {

        void ?{}( condition_variable(L) & this ){
                this.lock{};
                this.blocked_threads{};
                this.count = 0;
        }

        void ^?{}( condition_variable(L) & this ){ }

        void process_popped( condition_variable(L) & this, info_thread(L) & popped ) with( this ) {
                if(&popped != 0p) {
                        popped.signalled = true;
                        count--;
                        if (popped.lock) {
                                // if lock passed call on_notify
                                on_notify(*popped.lock, popped.t);
                        } else {
                                // otherwise wake thread
                                unpark(popped.t);
                        }
                }
        }

        bool notify_one( condition_variable(L) & this ) with( this ) {
                lock( lock __cfaabi_dbg_ctx2 );
                bool ret = ! blocked_threads`isEmpty;
                process_popped(this, try_pop_front( blocked_threads ));
                unlock( lock );
                return ret;
        }

        bool notify_all( condition_variable(L) & this ) with(this) {
                lock( lock __cfaabi_dbg_ctx2 );
                bool ret = ! blocked_threads`isEmpty;
                while( ! blocked_threads`isEmpty ) {
                        process_popped(this, try_pop_front( blocked_threads ));
                }
                unlock( lock );
                return ret;
        }

        uintptr_t front( condition_variable(L) & this ) with(this) {
                return blocked_threads`isEmpty ? NULL : blocked_threads`first.info;
        }

        bool empty( condition_variable(L) & this ) with(this) {
                lock( lock __cfaabi_dbg_ctx2 );
                bool ret = blocked_threads`isEmpty;
                unlock( lock );
                return ret;
        }

        int counter( condition_variable(L) & this ) with(this) { return count; }

        size_t queue_and_get_recursion( condition_variable(L) & this, info_thread(L) * i ) with(this) {
                // add info_thread to waiting queue
                insert_last( blocked_threads, *i );
                count++;
                size_t recursion_count = 0;
                if (i->lock) {
                        // if lock was passed get recursion count to reset to after waking thread
                        recursion_count = on_wait( *i->lock );
                }
                return recursion_count;
        }

        // helper for wait()'s' with no timeout
        void queue_info_thread( condition_variable(L) & this, info_thread(L) & i ) with(this) {
                lock( lock __cfaabi_dbg_ctx2 );
                size_t recursion_count = queue_and_get_recursion(this, &i);
                unlock( lock );

                // blocks here
                park( );

                // resets recursion count here after waking
                if (i.lock) on_wakeup(*i.lock, recursion_count);
        }

        #define WAIT( u, l ) \
                info_thread( L ) i = { active_thread(), u, l }; \
                queue_info_thread( this, i );

        // helper for wait()'s' with a timeout
        void queue_info_thread_timeout( condition_variable(L) & this, info_thread(L) & info, Duration t, Alarm_Callback callback ) with(this) {
                lock( lock __cfaabi_dbg_ctx2 );
                size_t recursion_count = queue_and_get_recursion(this, &info);
                alarm_node_wrap(L) node_wrap = { t, 0`s, callback, &this, &info };
                register_self( &node_wrap.alarm_node );
                unlock( lock );

                // blocks here
                park();

                // unregisters alarm so it doesn't go off if this happens first
                unregister_self( &node_wrap.alarm_node );

                // resets recursion count here after waking
                if (info.lock) on_wakeup(*info.lock, recursion_count);
        }

        #define WAIT_TIME( u, l, t ) \
                info_thread( L ) i = { active_thread(), u, l }; \
                queue_info_thread_timeout(this, i, t, alarm_node_wrap_cast ); \
                return i.signalled;

        void wait( condition_variable(L) & this                        ) with(this) { WAIT( 0, 0p    ) }
        void wait( condition_variable(L) & this, uintptr_t info        ) with(this) { WAIT( info, 0p ) }
        void wait( condition_variable(L) & this, L & l                 ) with(this) { WAIT( 0, &l    ) }
        void wait( condition_variable(L) & this, L & l, uintptr_t info ) with(this) { WAIT( info, &l ) }

        bool wait( condition_variable(L) & this, Duration duration                        ) with(this) { WAIT_TIME( 0   , 0p , duration ) }
        bool wait( condition_variable(L) & this, uintptr_t info, Duration duration        ) with(this) { WAIT_TIME( info, 0p , duration ) }
        bool wait( condition_variable(L) & this, L & l, Duration duration                 ) with(this) { WAIT_TIME( 0   , &l , duration ) }
        bool wait( condition_variable(L) & this, L & l, uintptr_t info, Duration duration ) with(this) { WAIT_TIME( info, &l , duration ) }
}

//-----------------------------------------------------------------------------
// Semaphore
void  ?{}( semaphore & this, int count = 1 ) {
        (this.lock){};
        this.count = count;
        (this.waiting){};
}
void ^?{}(semaphore & this) {}

bool P(semaphore & this) with( this ){
        lock( lock __cfaabi_dbg_ctx2 );
        count -= 1;
        if ( count < 0 ) {
                // queue current task
                append( waiting, active_thread() );

                // atomically release spin lock and block
                unlock( lock );
                park();
                return true;
        }
        else {
            unlock( lock );
            return false;
        }
}

thread$ * V (semaphore & this, const bool doUnpark ) with( this ) {
        thread$ * thrd = 0p;
        lock( lock __cfaabi_dbg_ctx2 );
        count += 1;
        if ( count <= 0 ) {
                // remove task at head of waiting list
                thrd = pop_head( waiting );
        }

        unlock( lock );

        // make new owner
        if( doUnpark ) unpark( thrd );

        return thrd;
}

bool V(semaphore & this) with( this ) {
        thread$ * thrd = V(this, true);
        return thrd != 0p;
}

bool V(semaphore & this, unsigned diff) with( this ) {
        thread$ * thrd = 0p;
        lock( lock __cfaabi_dbg_ctx2 );
        int release = max(-count, (int)diff);
        count += diff;
        for(release) {
                unpark( pop_head( waiting ) );
        }

        unlock( lock );

        return thrd != 0p;
}