parallel_scan.h

/*
    Copyright 2005-2009 Intel Corporation.  All Rights Reserved.

    The source code contained or described herein and all documents related
    to the source code ("Material") are owned by Intel Corporation or its
    suppliers or licensors.  Title to the Material remains with Intel
    Corporation or its suppliers and licensors.  The Material is protected
    by worldwide copyright laws and treaty provisions.  No part of the
    Material may be used, copied, reproduced, modified, published, uploaded,
    posted, transmitted, distributed, or disclosed in any way without
    Intel's prior express written permission.

    No license under any patent, copyright, trade secret or other
    intellectual property right is granted to or conferred upon you by
    disclosure or delivery of the Materials, either expressly, by
    implication, inducement, estoppel or otherwise.  Any license under such
    intellectual property rights must be express and approved by Intel in
    writing.
*/

#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 body;
    private:
        aligned_space<Range,1> range;
        Body* stuff_last;
    public:
        final_sum( Body& body_ ) :
            body(body_,split())
        {
            poison_pointer(stuff_last);
        }
        ~final_sum() {
            range.begin()->~Range();
        }     
        void finish_construction( const Range& range_, Body* stuff_last_ ) {
            new( range.begin() ) Range(range_);
            stuff_last = stuff_last_;
        }
    private:
        /*override*/ task* execute() {
            body( *range.begin(), final_scan_tag() );
            if( stuff_last )
                stuff_last->assign(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 *incoming; 
        final_sum_type *body;
        Body *stuff_last;
    private:
        final_sum_type *left_sum;
        sum_node *left;
        sum_node *right;     
        bool left_is_final;
        Range range;
        sum_node( const Range range_, bool left_is_final_ ) : 
            left_sum(NULL), 
            left(NULL), 
            right(NULL), 
            left_is_final(left_is_final_), 
            range(range_)
        {
            // Poison fields that will be set by second pass.
            poison_pointer(body);
            poison_pointer(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->body = &f;
                n->incoming = incoming;
                n->stuff_last = stuff_last;
                return n;
            }
        }
        /*override*/ task* execute() {
            if( body ) {
                if( incoming )
                    left_sum->body.reverse_join( incoming->body );
                recycle_as_continuation();
                sum_node& c = *this;
                task* b = c.create_child(Range(range,split()),*left_sum,right,left_sum,stuff_last);
                task* a = left_is_final ? NULL : c.create_child(range,*body,left,incoming,NULL);
                set_ref_count( (a!=NULL)+(b!=NULL) );
                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 sum;
        sum_node_type*& return_slot;
    public:
        final_sum_type* right_zombie;
        sum_node_type& result;

        /*override*/ task* execute() {
            __TBB_ASSERT( result.ref_count()==(result.left!=NULL)+(result.right!=NULL), NULL );
            if( result.left )
                result.left_is_final = false;
            if( right_zombie && sum ) 
                ((*sum)->body).reverse_join(result.left_sum->body);
            __TBB_ASSERT( !return_slot, NULL );
            if( right_zombie || result.right ) {
                return_slot = &result;
            } else {
                destroy( result );
            }
            if( right_zombie && !sum && !result.right ) destroy(*right_zombie);
            return NULL;
        }

        finish_scan( sum_node_type*& return_slot_, final_sum_type** sum_, sum_node_type& result_ ) : 
            sum(sum_),
            return_slot(return_slot_), 
            right_zombie(NULL),
            result(result_)
        {
            __TBB_ASSERT( !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* body;
        final_sum_type** sum; 
        sum_node_type** return_slot;
        sum_node_type* parent_sum;
        bool is_final;
        bool is_right_child;
        Range range;
        typename Partitioner::partition_type partition;
        /*override*/ task* execute();
    public:
        start_scan( sum_node_type*& return_slot_, start_scan& parent, sum_node_type* parent_sum_ ) :
            body(parent.body),
            sum(parent.sum),
            return_slot(&return_slot_),
            parent_sum(parent_sum_),
            is_final(parent.is_final),
            is_right_child(false),
            range(parent.range,split()),
            partition(parent.partition,split())
        {
            __TBB_ASSERT( !*return_slot, NULL );
        }

        start_scan( sum_node_type*& return_slot_, const Range& range_, final_sum_type& body_, const Partitioner& partitioner_) :
            body(&body_),
            sum(NULL),
            return_slot(&return_slot_),
            parent_sum(NULL),
            is_final(true),
            is_right_child(false),
            range(range_),
            partition(partitioner_)
        {
            __TBB_ASSERT( !*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(
                    /*return_slot=*/root,
                    range,
                    *temp_body,
                    partitioner );
                task::spawn_root_and_wait( pass1 );
                if( root ) {
                    root->body = temp_body;
                    root->incoming = NULL;
                    root->stuff_last = &body;
                    task::spawn_root_and_wait( *root );
                } else {
                    body.assign(temp_body->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 = 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 = is_right_child && (is_stolen_task() || body!=p->result.left_sum);
        if( treat_as_stolen ) {
            // Invocation is for right child that has been really stolen or needs to be virtually stolen
            p->right_zombie = body = new( allocate_root() ) final_sum_type(body->body);
            is_final = false;
        }
        task* next_task = NULL;
        if( (is_right_child && !treat_as_stolen) || !range.is_divisible() || partition.should_execute_range(*this) ) {
            if( is_final )
                (body->body)( range, final_scan_tag() );
            else if( sum )
                (body->body)( range, pre_scan_tag() );
            if( sum ) 
                *sum = body;
            __TBB_ASSERT( !*return_slot, NULL );
        } else {
            sum_node_type* result;
            if( parent_sum ) 
                result = new(allocate_additional_child_of(*parent_sum)) sum_node_type(range,/*left_is_final=*/is_final);
            else
                result = new(task::allocate_root()) sum_node_type(range,/*left_is_final=*/is_final);
            finish_pass1_type& c = *new( allocate_continuation()) finish_pass1_type(*return_slot,sum,*result);
            // Split off right child
            start_scan& b = *new( c.allocate_child() ) start_scan( /*return_slot=*/result->right, *this, result );
            b.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);
            sum = &result->left_sum;
            return_slot = &result->left;
            is_right_child = false;
            next_task = this;
            parent_sum = result; 
            __TBB_ASSERT( !*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 */

---

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