parallel_scan.h

/*
    Copyright 2005-2016 Intel Corporation.  All Rights Reserved.

    This file is part of Threading Building Blocks. Threading Building Blocks is free software;
    you can redistribute it and/or modify it under the terms of the GNU General Public License
    version 2  as  published  by  the  Free Software Foundation.  Threading Building Blocks is
    distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the
    implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
    See  the GNU General Public License for more details.   You should have received a copy of
    the  GNU General Public License along with Threading Building Blocks; if not, write to the
    Free Software Foundation, Inc.,  51 Franklin St,  Fifth Floor,  Boston,  MA 02110-1301 USA

    As a special exception,  you may use this file  as part of a free software library without
    restriction.  Specifically,  if other files instantiate templates  or use macros or inline
    functions from this file, or you compile this file and link it with other files to produce
    an executable,  this file does not by itself cause the resulting executable to be covered
    by the GNU General Public License. This exception does not however invalidate any other
    reasons why the executable file might be covered by the GNU General Public License.
*/

#ifndef __TBB_parallel_scan_H
#define __TBB_parallel_scan_H

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

namespace tbb {


struct pre_scan_tag {
    static bool is_final_scan() {return false;}
};


struct final_scan_tag {
    static bool is_final_scan() {return true;}
};

namespace internal {


    template<typename Range, typename Body>
    class final_sum: public task {
    public:
        Body my_body;
    private:
        aligned_space<Range> my_range;
        Body* my_stuff_last;
    public:
        final_sum( Body& body_ ) :
            my_body(body_,split())
        {
            poison_pointer(my_stuff_last);
        }
        ~final_sum() {
            my_range.begin()->~Range();
        }
        void finish_construction( const Range& range_, Body* stuff_last_ ) {
            new( my_range.begin() ) Range(range_);
            my_stuff_last = stuff_last_;
        }
    private:
        /*override*/ task* execute() {
            my_body( *my_range.begin(), final_scan_tag() );
            if( my_stuff_last )
                my_stuff_last->assign(my_body);
            return NULL;
        }
    };


    template<typename Range, typename Body>
    class sum_node: public task {
        typedef final_sum<Range,Body> final_sum_type;
    public:
        final_sum_type *my_incoming;
        final_sum_type *my_body;
        Body *my_stuff_last;
    private:
        final_sum_type *my_left_sum;
        sum_node *my_left;
        sum_node *my_right;
        bool my_left_is_final;
        Range my_range;
        sum_node( const Range range_, bool left_is_final_ ) :
            my_left_sum(NULL),
            my_left(NULL),
            my_right(NULL),
            my_left_is_final(left_is_final_),
            my_range(range_)
        {
            // Poison fields that will be set by second pass.
            poison_pointer(my_body);
            poison_pointer(my_incoming);
        }
        task* create_child( const Range& range_, final_sum_type& f, sum_node* n, final_sum_type* incoming_, Body* stuff_last_ ) {
            if( !n ) {
                f.recycle_as_child_of( *this );
                f.finish_construction( range_, stuff_last_ );
                return &f;
            } else {
                n->my_body = &f;
                n->my_incoming = incoming_;
                n->my_stuff_last = stuff_last_;
                return n;
            }
        }
        /*override*/ task* execute() {
            if( my_body ) {
                if( my_incoming )
                    my_left_sum->my_body.reverse_join( my_incoming->my_body );
                recycle_as_continuation();
                sum_node& c = *this;
                task* b = c.create_child(Range(my_range,split()),*my_left_sum,my_right,my_left_sum,my_stuff_last);
                task* a = my_left_is_final ? NULL : c.create_child(my_range,*my_body,my_left,my_incoming,NULL);
                set_ref_count( (a!=NULL)+(b!=NULL) );
                my_body = NULL;
                if( a ) spawn(*b);
                else a = b;
                return a;
            } else {
                return NULL;
            }
        }
        template<typename Range_,typename Body_,typename Partitioner_>
        friend class start_scan;

        template<typename Range_,typename Body_>
        friend class finish_scan;
    };


    template<typename Range, typename Body>
    class finish_scan: public task {
        typedef sum_node<Range,Body> sum_node_type;
        typedef final_sum<Range,Body> final_sum_type;
        final_sum_type** const my_sum;
        sum_node_type*& my_return_slot;
    public:
        final_sum_type* my_right_zombie;
        sum_node_type& my_result;

        /*override*/ task* execute() {
            __TBB_ASSERT( my_result.ref_count()==(my_result.my_left!=NULL)+(my_result.my_right!=NULL), NULL );
            if( my_result.my_left )
                my_result.my_left_is_final = false;
            if( my_right_zombie && my_sum )
                ((*my_sum)->my_body).reverse_join(my_result.my_left_sum->my_body);
            __TBB_ASSERT( !my_return_slot, NULL );
            if( my_right_zombie || my_result.my_right ) {
                my_return_slot = &my_result;
            } else {
                destroy( my_result );
            }
            if( my_right_zombie && !my_sum && !my_result.my_right ) {
                destroy(*my_right_zombie);
                my_right_zombie = NULL;
            }
            return NULL;
        }

        finish_scan( sum_node_type*& return_slot_, final_sum_type** sum_, sum_node_type& result_ ) :
            my_sum(sum_),
            my_return_slot(return_slot_),
            my_right_zombie(NULL),
            my_result(result_)
        {
            __TBB_ASSERT( !my_return_slot, NULL );
        }
    };


    template<typename Range, typename Body, typename Partitioner=simple_partitioner>
    class start_scan: public task {
        typedef sum_node<Range,Body> sum_node_type;
        typedef final_sum<Range,Body> final_sum_type;
        final_sum_type* my_body;
        final_sum_type** my_sum;
        sum_node_type** my_return_slot;
        sum_node_type* my_parent_sum;
        bool my_is_final;
        bool my_is_right_child;
        Range my_range;
        typename Partitioner::partition_type my_partition;
        /*override*/ task* execute();
    public:
        start_scan( sum_node_type*& return_slot_, start_scan& parent_, sum_node_type* parent_sum_ ) :
            my_body(parent_.my_body),
            my_sum(parent_.my_sum),
            my_return_slot(&return_slot_),
            my_parent_sum(parent_sum_),
            my_is_final(parent_.my_is_final),
            my_is_right_child(false),
            my_range(parent_.my_range,split()),
            my_partition(parent_.my_partition,split())
        {
            __TBB_ASSERT( !*my_return_slot, NULL );
        }

        start_scan( sum_node_type*& return_slot_, const Range& range_, final_sum_type& body_, const Partitioner& partitioner_) :
            my_body(&body_),
            my_sum(NULL),
            my_return_slot(&return_slot_),
            my_parent_sum(NULL),
            my_is_final(true),
            my_is_right_child(false),
            my_range(range_),
            my_partition(partitioner_)
        {
            __TBB_ASSERT( !*my_return_slot, NULL );
        }

        static void run( const Range& range_, Body& body_, const Partitioner& partitioner_ ) {
            if( !range_.empty() ) {
                typedef internal::start_scan<Range,Body,Partitioner> start_pass1_type;
                internal::sum_node<Range,Body>* root = NULL;
                typedef internal::final_sum<Range,Body> final_sum_type;
                final_sum_type* temp_body = new(task::allocate_root()) final_sum_type( body_ );
                start_pass1_type& pass1 = *new(task::allocate_root()) start_pass1_type(
                    /*my_return_slot=*/root,
                    range_,
                    *temp_body,
                    partitioner_ );
                task::spawn_root_and_wait( pass1 );
                if( root ) {
                    root->my_body = temp_body;
                    root->my_incoming = NULL;
                    root->my_stuff_last = &body_;
                    task::spawn_root_and_wait( *root );
                } else {
                    body_.assign(temp_body->my_body);
                    temp_body->finish_construction( range_, NULL );
                    temp_body->destroy(*temp_body);
                }
            }
        }
    };

    template<typename Range, typename Body, typename Partitioner>
    task* start_scan<Range,Body,Partitioner>::execute() {
        typedef internal::finish_scan<Range,Body> finish_pass1_type;
        finish_pass1_type* p = my_parent_sum ? static_cast<finish_pass1_type*>( parent() ) : NULL;
        // Inspecting p->result.left_sum would ordinarily be a race condition.
        // But we inspect it only if we are not a stolen task, in which case we
        // know that task assigning to p->result.left_sum has completed.
        bool treat_as_stolen = my_is_right_child && (is_stolen_task() || my_body!=p->my_result.my_left_sum);
        if( treat_as_stolen ) {
            // Invocation is for right child that has been really stolen or needs to be virtually stolen
            p->my_right_zombie = my_body = new( allocate_root() ) final_sum_type(my_body->my_body);
            my_is_final = false;
        }
        task* next_task = NULL;
        if( (my_is_right_child && !treat_as_stolen) || !my_range.is_divisible() || my_partition.should_execute_range(*this) ) {
            if( my_is_final )
                (my_body->my_body)( my_range, final_scan_tag() );
            else if( my_sum )
                (my_body->my_body)( my_range, pre_scan_tag() );
            if( my_sum )
                *my_sum = my_body;
            __TBB_ASSERT( !*my_return_slot, NULL );
        } else {
            sum_node_type* result;
            if( my_parent_sum )
                result = new(allocate_additional_child_of(*my_parent_sum)) sum_node_type(my_range,/*my_left_is_final=*/my_is_final);
            else
                result = new(task::allocate_root()) sum_node_type(my_range,/*my_left_is_final=*/my_is_final);
            finish_pass1_type& c = *new( allocate_continuation()) finish_pass1_type(*my_return_slot,my_sum,*result);
            // Split off right child
            start_scan& b = *new( c.allocate_child() ) start_scan( /*my_return_slot=*/result->my_right, *this, result );
            b.my_is_right_child = true;
            // Left child is recycling of *this.  Must recycle this before spawning b,
            // otherwise b might complete and decrement c.ref_count() to zero, which
            // would cause c.execute() to run prematurely.
            recycle_as_child_of(c);
            c.set_ref_count(2);
            c.spawn(b);
            my_sum = &result->my_left_sum;
            my_return_slot = &result->my_left;
            my_is_right_child = false;
            next_task = this;
            my_parent_sum = result;
            __TBB_ASSERT( !*my_return_slot, NULL );
        }
        return next_task;
    }
} // namespace internal

// Requirements on Range concept are documented in blocked_range.h



template<typename Range, typename Body>
void parallel_scan( const Range& range, Body& body ) {
    internal::start_scan<Range,Body,__TBB_DEFAULT_PARTITIONER>::run(range,body,__TBB_DEFAULT_PARTITIONER());
}


template<typename Range, typename Body>
void parallel_scan( const Range& range, Body& body, const simple_partitioner& partitioner ) {
    internal::start_scan<Range,Body,simple_partitioner>::run(range,body,partitioner);
}


template<typename Range, typename Body>
void parallel_scan( const Range& range, Body& body, const auto_partitioner& partitioner ) {
    internal::start_scan<Range,Body,auto_partitioner>::run(range,body,partitioner);
}

} // namespace tbb

#endif /* __TBB_parallel_scan_H */