concurrent_monitor.h

Go to the documentation of this file.

/*
    Copyright (c) 2005-2020 Intel Corporation

    Licensed under the Apache License, Version 2.0 (the "License");
    you may not use this file except in compliance with the License.
    You may obtain a copy of the License at

        http://www.apache.org/licenses/LICENSE-2.0

    Unless required by applicable law or agreed to in writing, software
    distributed under the License is distributed on an "AS IS" BASIS,
    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    See the License for the specific language governing permissions and
    limitations under the License.
*/

#ifndef __TBB_concurrent_monitor_H
#define __TBB_concurrent_monitor_H

#include "tbb/tbb_stddef.h"
#include "tbb/atomic.h"
#include "tbb/spin_mutex.h"
#include "tbb/tbb_exception.h"
#include "tbb/aligned_space.h"

#include "semaphore.h"

namespace tbb {
namespace internal {


class circular_doubly_linked_list_with_sentinel : no_copy {
public:
    struct node_t {
        node_t* next;
        node_t* prev;
        explicit node_t() : next((node_t*)(uintptr_t)0xcdcdcdcd), prev((node_t*)(uintptr_t)0xcdcdcdcd) {}
    };

    // ctor
    circular_doubly_linked_list_with_sentinel() {clear();}
    // dtor
    ~circular_doubly_linked_list_with_sentinel() {__TBB_ASSERT( head.next==&head && head.prev==&head, "the list is not empty" );}

    inline size_t  size()  const {return count;}
    inline bool    empty() const {return size()==0;}
    inline node_t* front() const {return head.next;}
    inline node_t* last()  const {return head.prev;}
    inline node_t* begin() const {return front();}
    inline const node_t* end() const {return &head;}

    inline void add( node_t* n ) {
        __TBB_store_relaxed(count, __TBB_load_relaxed(count) + 1);
        n->prev = head.prev;
        n->next = &head;
        head.prev->next = n;
        head.prev = n;
    }

    inline void remove( node_t& n ) {
        __TBB_ASSERT( count > 0, "attempt to remove an item from an empty list" );
        __TBB_store_relaxed(count, __TBB_load_relaxed(count) - 1);
        n.prev->next = n.next;
        n.next->prev = n.prev;
    }

    inline void flush_to( circular_doubly_linked_list_with_sentinel& lst ) {
        if( const size_t l_count = __TBB_load_relaxed(count) ) {
            __TBB_store_relaxed(lst.count, l_count);
            lst.head.next = head.next;
            lst.head.prev = head.prev;
            head.next->prev = &lst.head;
            head.prev->next = &lst.head;
            clear();
        }
    }

    void clear() {head.next = head.prev = &head; __TBB_store_relaxed(count, 0);}
private:
    __TBB_atomic size_t count;
    node_t head;
};

typedef circular_doubly_linked_list_with_sentinel waitset_t;
typedef circular_doubly_linked_list_with_sentinel::node_t waitset_node_t;


class concurrent_monitor : no_copy {
public:
    class thread_context : waitset_node_t, no_copy {
        friend class concurrent_monitor;
    public:
        thread_context() : skipped_wakeup(false), aborted(false), ready(false), context(0) {
            epoch = 0;
            in_waitset = false;
        }
        ~thread_context() {
            if (ready) {
                if( skipped_wakeup ) semaphore().P();
                semaphore().~binary_semaphore();
            }
        }
        binary_semaphore& semaphore() { return *sema.begin(); }
    private:
        //  Inlining of the method is undesirable, due to extra instructions for
        //  exception support added at caller side.
        __TBB_NOINLINE( void init() );
        tbb::aligned_space<binary_semaphore> sema;
        __TBB_atomic unsigned epoch;
        tbb::atomic<bool> in_waitset;
        bool  skipped_wakeup;
        bool  aborted;
        bool  ready;
        uintptr_t context;
    };

    concurrent_monitor() {__TBB_store_relaxed(epoch, 0);}

    ~concurrent_monitor() ;

    void prepare_wait( thread_context& thr, uintptr_t ctx = 0 );


    inline bool commit_wait( thread_context& thr ) {
        const bool do_it = thr.epoch == __TBB_load_relaxed(epoch);
        // this check is just an optimization
        if( do_it ) {
            __TBB_ASSERT( thr.ready, "use of commit_wait() without prior prepare_wait()");
            thr.semaphore().P();
            __TBB_ASSERT( !thr.in_waitset, "still in the queue?" );
            if( thr.aborted )
                throw_exception( eid_user_abort );
        } else {
            cancel_wait( thr );
        }
        return do_it;
    }
    void cancel_wait( thread_context& thr );

    template<typename WaitUntil, typename Context>
    void wait( WaitUntil until, Context on );

    void notify_one() {atomic_fence(); notify_one_relaxed();}

    void notify_one_relaxed();

    void notify_all() {atomic_fence(); notify_all_relaxed();}

    void notify_all_relaxed();

    template<typename P> void notify( const P& predicate ) {atomic_fence(); notify_relaxed( predicate );}

    template<typename P> void notify_relaxed( const P& predicate );

    void abort_all() {atomic_fence(); abort_all_relaxed(); }

    void abort_all_relaxed();

private:
    tbb::spin_mutex mutex_ec;
    waitset_t       waitset_ec;
    __TBB_atomic unsigned epoch;
    thread_context* to_thread_context( waitset_node_t* n ) { return static_cast<thread_context*>(n); }
};

template<typename WaitUntil, typename Context>
void concurrent_monitor::wait( WaitUntil until, Context on )
{
    bool slept = false;
    thread_context thr_ctx;
    prepare_wait( thr_ctx, on() );
    while( !until() ) {
        if( (slept = commit_wait( thr_ctx ) )==true )
            if( until() ) break;
        slept = false;
        prepare_wait( thr_ctx, on() );
    }
    if( !slept )
        cancel_wait( thr_ctx );
}

template<typename P>
void concurrent_monitor::notify_relaxed( const P& predicate ) {
        if( waitset_ec.empty() )
            return;
        waitset_t temp;
        waitset_node_t* nxt;
        const waitset_node_t* end = waitset_ec.end();
        {
            tbb::spin_mutex::scoped_lock l( mutex_ec );
            __TBB_store_relaxed(epoch, __TBB_load_relaxed(epoch) + 1);
            for( waitset_node_t* n=waitset_ec.last(); n!=end; n=nxt ) {
                nxt = n->prev;
                thread_context* thr = to_thread_context( n );
                if( predicate( thr->context ) ) {
                    waitset_ec.remove( *n );
                    thr->in_waitset = false;
                    temp.add( n );
                }
            }
        }

        end = temp.end();
        for( waitset_node_t* n=temp.front(); n!=end; n=nxt ) {
            nxt = n->next;
            to_thread_context(n)->semaphore().V();
        }
#if TBB_USE_ASSERT
        temp.clear();
#endif
}

} // namespace internal
} // namespace tbb

#endif /* __TBB_concurrent_monitor_H */