/*
    Copyright (c) 2005-2019 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_parallel_while
#define __TBB_parallel_while

#include "task.h"
#include <new>

namespace tbb {

template<typename Body>
class parallel_while;

//! @cond INTERNAL
namespace internal {

    template<typename Stream, typename Body> class while_task;

    //! For internal use only.
    /** Executes one iteration of a while.
        @ingroup algorithms */
    template<typename Body>
    class while_iteration_task: public task {
        const Body& my_body;
        typename Body::argument_type my_value;
        task* execute() __TBB_override {
            my_body(my_value);
            return NULL;
        }
        while_iteration_task( const typename Body::argument_type& value, const Body& body ) :
            my_body(body), my_value(value)
        {}
        template<typename Body_> friend class while_group_task;
        friend class tbb::parallel_while<Body>;
    };

    //! For internal use only
    /** Unpacks a block of iterations.
        @ingroup algorithms */
    template<typename Body>
    class while_group_task: public task {
        static const size_t max_arg_size = 4;
        const Body& my_body;
        size_t size;
        typename Body::argument_type my_arg[max_arg_size];
        while_group_task( const Body& body ) : my_body(body), size(0) {}
        task* execute() __TBB_override {
            typedef while_iteration_task<Body> iteration_type;
            __TBB_ASSERT( size>0, NULL );
            task_list list;
            task* t;
            size_t k=0;
            for(;;) {
                t = new( allocate_child() ) iteration_type(my_arg[k],my_body);
                if( ++k==size ) break;
                list.push_back(*t);
            }
            set_ref_count(int(k+1));
            spawn(list);
            spawn_and_wait_for_all(*t);
            return NULL;
        }
        template<typename Stream, typename Body_> friend class while_task;
    };

    //! For internal use only.
    /** Gets block of iterations from a stream and packages them into a while_group_task.
        @ingroup algorithms */
    template<typename Stream, typename Body>
    class while_task: public task {
        Stream& my_stream;
        const Body& my_body;
        empty_task& my_barrier;
        task* execute() __TBB_override {
            typedef while_group_task<Body> block_type;
            block_type& t = *new( allocate_additional_child_of(my_barrier) ) block_type(my_body);
            size_t k=0;
            while( my_stream.pop_if_present(t.my_arg[k]) ) {
                if( ++k==block_type::max_arg_size ) {
                    // There might be more iterations.
                    recycle_to_reexecute();
                    break;
                }
            }
            if( k==0 ) {
                destroy(t);
                return NULL;
            } else {
                t.size = k;
                return &t;
            }
        }
        while_task( Stream& stream, const Body& body, empty_task& barrier ) :
            my_stream(stream),
            my_body(body),
            my_barrier(barrier)
        {}
        friend class tbb::parallel_while<Body>;
    };

} // namespace internal
//! @endcond

//! Parallel iteration over a stream, with optional addition of more work.
/** The Body b has the requirement: \n
        "b(v)"                      \n
        "b.argument_type"           \n
    where v is an argument_type
    @ingroup algorithms */
template<typename Body>
class parallel_while: internal::no_copy {
public:
    //! Construct empty non-running parallel while.
    parallel_while() : my_body(NULL), my_barrier(NULL) {}

    //! Destructor cleans up data members before returning.
    ~parallel_while() {
        if( my_barrier ) {
            my_barrier->destroy(*my_barrier);
            my_barrier = NULL;
        }
    }

    //! Type of items
    typedef typename Body::argument_type value_type;

    //! Apply body.apply to each item in the stream.
    /** A Stream s has the requirements \n
         "S::value_type"                \n
         "s.pop_if_present(value) is convertible to bool */
    template<typename Stream>
    void run( Stream& stream, const Body& body );

    //! Add a work item while running.
    /** Should be executed only by body.apply or a thread spawned therefrom. */
    void add( const value_type& item );

private:
    const Body* my_body;
    empty_task* my_barrier;
};

template<typename Body>
template<typename Stream>
void parallel_while<Body>::run( Stream& stream, const Body& body ) {
    using namespace internal;
    empty_task& barrier = *new( task::allocate_root() ) empty_task();
    my_body = &body;
    my_barrier = &barrier;
    my_barrier->set_ref_count(2);
    while_task<Stream,Body>& w = *new( my_barrier->allocate_child() ) while_task<Stream,Body>( stream, body, barrier );
    my_barrier->spawn_and_wait_for_all(w);
    my_barrier->destroy(*my_barrier);
    my_barrier = NULL;
    my_body = NULL;
}

template<typename Body>
void parallel_while<Body>::add( const value_type& item ) {
    __TBB_ASSERT(my_barrier,"attempt to add to parallel_while that is not running");
    typedef internal::while_iteration_task<Body> iteration_type;
    iteration_type& i = *new( task::allocate_additional_child_of(*my_barrier) ) iteration_type(item,*my_body);
    task::self().spawn( i );
}

} // namespace

#endif /* __TBB_parallel_while */
