/* Copyright (c) 2005-2017 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_scan_H #define __TBB_parallel_scan_H #include "task.h" #include "aligned_space.h" #include #include "partitioner.h" namespace tbb { //! Used to indicate that the initial scan is being performed. /** @ingroup algorithms */ struct pre_scan_tag { static bool is_final_scan() {return false;} }; //! Used to indicate that the final scan is being performed. /** @ingroup algorithms */ struct final_scan_tag { static bool is_final_scan() {return true;} }; //! @cond INTERNAL namespace internal { //! Performs final scan for a leaf /** @ingroup algorithms */ template class final_sum: public task { public: Body my_body; private: aligned_space my_range; //! Where to put result of last subrange, or NULL if not last subrange. 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: task* execute() __TBB_override { my_body( *my_range.begin(), final_scan_tag() ); if( my_stuff_last ) my_stuff_last->assign(my_body); return NULL; } }; //! Split work to be done in the scan. /** @ingroup algorithms */ template class sum_node: public task { typedef final_sum 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_stuff_last(NULL), 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; } } task* execute() __TBB_override { 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 friend class start_scan; template friend class finish_scan; }; //! Combine partial results /** @ingroup algorithms */ template class finish_scan: public task { typedef sum_node sum_node_type; typedef final_sum 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; task* execute() __TBB_override { __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 ); } }; //! Initial task to split the work /** @ingroup algorithms */ template class start_scan: public task { typedef sum_node sum_node_type; typedef final_sum final_sum_type; final_sum_type* my_body; /** Non-null if caller is requesting total. */ final_sum_type** my_sum; sum_node_type** my_return_slot; /** Null if computing root. */ sum_node_type* my_parent_sum; bool my_is_final; bool my_is_right_child; Range my_range; typename Partitioner::partition_type my_partition; task* execute() __TBB_override ; 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 start_pass1_type; internal::sum_node* root = NULL; typedef internal::final_sum 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_ ); temp_body->my_body.reverse_join(body_); 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 task* start_scan::execute() { typedef internal::finish_scan finish_pass1_type; finish_pass1_type* p = my_parent_sum ? static_cast( 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 //! @endcond // Requirements on Range concept are documented in blocked_range.h /** \page parallel_scan_body_req Requirements on parallel_scan body Class \c Body implementing the concept of parallel_scan body must define: - \code Body::Body( Body&, split ); \endcode Splitting constructor. Split \c b so that \c this and \c b can accumulate separately - \code Body::~Body(); \endcode Destructor - \code void Body::operator()( const Range& r, pre_scan_tag ); \endcode Preprocess iterations for range \c r - \code void Body::operator()( const Range& r, final_scan_tag ); \endcode Do final processing for iterations of range \c r - \code void Body::reverse_join( Body& a ); \endcode Merge preprocessing state of \c a into \c this, where \c a was created earlier from \c b by b's splitting constructor **/ /** \name parallel_scan See also requirements on \ref range_req "Range" and \ref parallel_scan_body_req "parallel_scan Body". **/ //@{ //! Parallel prefix with default partitioner /** @ingroup algorithms **/ template void parallel_scan( const Range& range, Body& body ) { internal::start_scan::run(range,body,__TBB_DEFAULT_PARTITIONER()); } //! Parallel prefix with simple_partitioner /** @ingroup algorithms **/ template void parallel_scan( const Range& range, Body& body, const simple_partitioner& partitioner ) { internal::start_scan::run(range,body,partitioner); } //! Parallel prefix with auto_partitioner /** @ingroup algorithms **/ template void parallel_scan( const Range& range, Body& body, const auto_partitioner& partitioner ) { internal::start_scan::run(range,body,partitioner); } //@} } // namespace tbb #endif /* __TBB_parallel_scan_H */