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/* reducer.h -*- C++ -*-
*
* Copyright (C) 2009-2016, Intel Corporation
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
* * Neither the name of Intel Corporation nor the names of its
* contributors may be used to endorse or promote products derived
* from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY
* WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*
* *********************************************************************
*
* PLEASE NOTE: This file is a downstream copy of a file mainitained in
* a repository at cilkplus.org. Changes made to this file that are not
* submitted through the contribution process detailed at
* http://www.cilkplus.org/submit-cilk-contribution will be lost the next
* time that a new version is released. Changes only submitted to the
* GNU compiler collection or posted to the git repository at
* https://bitbucket.org/intelcilkruntime/intel-cilk-runtime.git are
* not tracked.
*
* We welcome your contributions to this open source project. Thank you
* for your assistance in helping us improve Cilk Plus.
*/
/** @file reducer.h
*
* @brief Defines foundation classes for creating Intel(R) Cilk(TM) Plus reducers.
*
* @ingroup Reducers
*
* @see @ref pagereducers
*
* @defgroup Reducers Reducers
*/
#ifndef REDUCER_H_INCLUDED
#define REDUCER_H_INCLUDED
#include "cilk/hyperobject_base.h"
#include "cilk/metaprogramming.h"
#ifdef __cplusplus
//===================== C++ interfaces ===================================
#include <new>
namespace cilk {
/** Class for provisionally constructed objects.
*
* The monoid_base<T,V>::construct() functions manually construct both a
* monoid and a view. If one of these is constructed successfully, and the
* construction of the other (or some other initialization) fails, then the
* first one must be destroyed to avoid a memory leak. Because the
* construction is explicit, the destruction must be explicit, too.
*
* A provisional_guard object wraps a pointer to a newly constructed
* object. A call to its confirm() function confirms that the object is
* really going to be used. If the guard is destroyed without being
* confirmed, then the pointed-to object is destroyed (but not
* deallocated).
*
* Expected usage:
*
* provisional_guard<T1> x1_provisional( new (x1) T1 );
* … more initialization …
* x1_provisional.confirm();
*
* or
*
* provisional_guard<T1> x1_provisional( new (x1) T1 );
* x1_provisional.confirm_if( new (x2) T2 );
*
* If an exception is thrown in the "more initialization" code in the
* first example, or in the `T2` constructor in the second example, then
* `x1_provisional` will not be confirmed, so when its destructor is
* called during exception unwinding, the `T1` object that was constructed
* in `x1` will be destroyed.
*
* **NOTE**: Do *not* be tempted to chain a `provisional_guard`
* constructor with `confirm_if` as in this example:
*
* // BAD IDEA
* provisional_guard<T1>( new (x1) T1 ).confirm_if( new (x2) T2 );
*
* The code above is problematic because the evaluation of the T2
* constructor is unsequenced with respect to the call to the
* `provisional_guard` constructor (and with respect the T1 constructor).
* Thus, the compiler may choose to evaluate `new (x2) T2` before
* constructing the guard and leak the T1 object if the `T2` constructor
* throws.
*
* @tparam Type The type of the provisionally constructed object.
*/
template <typename Type>
class provisional_guard {
Type* m_ptr;
public:
/** Constructor. Creates a guard for a provisionally constructed object.
*
* @param ptr A pointer to the provisionally constructed object.
*/
provisional_guard(Type* ptr) : m_ptr(ptr) {}
/** Destructor. Destroy the object pointed to by the contained pointer
* if it has not been confirmed.
*/
~provisional_guard() { if (m_ptr) m_ptr->~Type(); }
/** Confirm the provisional construction. Do *not* delete the contained
* pointer when the guard is destroyed.
*/
void confirm() { m_ptr = 0; }
/** Confirm provisional construction if argument is non-null. Note that
* if an exception is thrown during evaluation of the argument
* expression, then this function will not be called, and the
* provisional object will not be confirmed. This allows the usage:
*
* x1_provisional.confirm_if( new (x2) T2() );
*
* @param cond An arbitrary pointer. The provisional object will be
* confirmed if @a cond is not null.
*
* @returns The value of the @a cond argument.
*/
template <typename Cond>
Cond* confirm_if(Cond* cond) { if (cond) m_ptr = 0; return cond; }
};
/** Base class for defining monoids.
*
* The monoid_base class template is useful for creating classes that model
* the monoid concept. It provides the core type and memory management
* functionality. A subclass of monoid_base need only declare and implement
* the `identity` and `reduce` functions.
*
* The monoid_base class also manages the integration between the monoid, the
* reducer class that is based on it, and an optional view class which wraps
* value objects and restricts access to their operations.
*
* @tparam Value The value type for the monoid.
* @tparam View An optional view class that serves as a proxy for the value
* type.
*
* @see monoid_with_view
*/
template <typename Value, typename View = Value>
class monoid_base
{
public:
/** Value type of the monoid.
*/
typedef Value value_type;
/** View type of the monoid. Defaults to be the same as the value type.
* @see monoid_with_view
*/
typedef View view_type;
enum {
/** Should reducers created with this monoid be aligned?
*
* @details
* "Aligned" means that the view is allocated at a cache-line aligned
* offset in the reducer, and the reducer must be cache-line aligned.
* "Unaligned" means that the reducer as a whole is just naturally
* aligned, but it contains a large enough block of uninitialized
* storage for a cache-line aligned view to be allocated in it at
* reducer construction time.
*
* Since the standard heap allocator (new reducer) does not allocate
* cache-line aligned storage, only unaligned reducers can be safely
* allocated on the heap.
*
* Default is false (unaligned) unless overridden in a subclass.
*
* @since 1.02
* (In Intel Cilk Plus library versions 1.0 and 1.01, the default was true.
* In Intel Cilk Plus library versions prior to 1.0, reducers were always
* aligned, and this data member did not exist.)
*/
align_reducer = false
};
/** Destroys a view. Destroys (without deallocating) the @a View object
* pointed to by @a p.
*
* @param p The address of the @a View object to be destroyed.
*/
void destroy(view_type* p) const { p->~view_type(); }
/** Allocates raw memory. Allocate @a s bytes of memory with no
* initialization.
*
* @param s The number of bytes of memory to allocate.
* @return An untyped pointer to the allocated memory.
*/
void* allocate(size_t s) const { return operator new(s); }
/** Deallocates raw memory pointed to by @a p
* without doing any destruction.
*
* @param p Pointer to the memory to be deallocated.
*
* @pre @a p points to a block of memory that was allocated by a
* call to allocate().
*/
void deallocate(void* p) const { operator delete(p); }
/** Creates the identity value. Constructs (without allocating) a @a View
* object representing the default value of the @a Value type.
*
* @param p A pointer to a block of raw memory large enough to hold a
* @a View object.
*
* @post The memory pointed to by @a p contains a @a View object that
* represents the default value of the @a View type.
*
* @deprecated This function constructs the @a View object with its default
* constructor, which will often, but not always, yield the
* appropriate identity value. Monoid classes should declare
* their identity function explicitly, rather than relying on
* this default definition.
*/
void identity(View* p) const { new ((void*) p) View(); }
/** @name Constructs the monoid and the view with arbitrary arguments.
*
* A @ref reducer object contains monoid and view data members, which are
* declared as raw storage (byte arrays), so that they are not implicitly
* constructed when the reducer is constructed. Instead, a reducer
* constructor calls one of the monoid class's static construct()
* functions with the addresses of the monoid and the view, and the
* construct() function uses placement `new` to construct them.
* This allows the monoid to determine the order in which the monoid and
* view are constructed, and to make one of them dependent on the other.
*
* Any arguments to the reducer constructor are just passed on as
* additional arguments to the construct() function (after the monoid
* and view addresses are set).
*
* A monoid whose needs are satisfied by the suite of construct()
* functions below, such as @ref monoid_with_view, can just inherit them
* from monoid_base. Other monoids will need to provide their own versions
* to override the monoid_base functions.
*/
//@{
/** Default-constructs the monoid, identity-constructs the view.
*
* @param monoid Address of uninitialized monoid object.
* @param view Address of uninitialized initial view object.
*/
//@{
template <typename Monoid>
static void construct(Monoid* monoid, View* view)
{
provisional_guard<Monoid> guard( new((void*) monoid) Monoid() );
monoid->identity(view);
guard.confirm();
}
//@}
/** Default-constructs the monoid, and passes one to five const reference
* arguments to the view constructor.
*/
//@{
template <typename Monoid, typename T1>
static void construct(Monoid* monoid, View* view, const T1& x1)
{
provisional_guard<Monoid> guard( new((void*) monoid) Monoid() );
guard.confirm_if( new((void*) view) View(x1) );
}
template <typename Monoid, typename T1, typename T2>
static void construct(Monoid* monoid, View* view,
const T1& x1, const T2& x2)
{
provisional_guard<Monoid> guard( new((void*) monoid) Monoid() );
guard.confirm_if( new((void*) view) View(x1, x2) );
}
template <typename Monoid, typename T1, typename T2, typename T3>
static void construct(Monoid* monoid, View* view,
const T1& x1, const T2& x2, const T3& x3)
{
provisional_guard<Monoid> guard( new((void*) monoid) Monoid() );
guard.confirm_if( new((void*) view) View(x1, x2, x3) );
}
template <typename Monoid, typename T1, typename T2, typename T3,
typename T4>
static void construct(Monoid* monoid, View* view,
const T1& x1, const T2& x2, const T3& x3,
const T4& x4)
{
provisional_guard<Monoid> guard( new((void*) monoid) Monoid() );
guard.confirm_if( new((void*) view) View(x1, x2, x3, x4) );
}
template <typename Monoid, typename T1, typename T2, typename T3,
typename T4, typename T5>
static void construct(Monoid* monoid, View* view,
const T1& x1, const T2& x2, const T3& x3,
const T4& x4, const T5& x5)
{
provisional_guard<Monoid> guard( new((void*) monoid) Monoid() );
guard.confirm_if( new((void*) view) View(x1, x2, x3, x4, x5) );
}
//@}
/** Default-constructs the monoid, and passes one non-const reference
* argument to the view constructor.
*/
//@{
template <typename Monoid, typename T1>
static void construct(Monoid* monoid, View* view, T1& x1)
{
provisional_guard<Monoid> guard( new((void*) monoid) Monoid() );
guard.confirm_if( new((void*) view) View(x1) );
}
//@}
/** Copy-constructs the monoid, and identity-constructs the view
* constructor.
*
* @param monoid Address of uninitialized monoid object.
* @param view Address of uninitialized initial view object.
* @param m Object to be copied into `*monoid`
*/
//@{
template <typename Monoid>
static void construct(Monoid* monoid, View* view, const Monoid& m)
{
provisional_guard<Monoid> guard( new((void*) monoid) Monoid(m) );
monoid->identity(view);
guard.confirm();
}
//@}
/** Copy-constructs the monoid, and passes one to four const reference
* arguments to the view constructor.
*/
//@{
template <typename Monoid, typename T1>
static void construct(Monoid* monoid, View* view, const Monoid& m,
const T1& x1)
{
provisional_guard<Monoid> guard( new((void*) monoid) Monoid(m) );
guard.confirm_if( new((void*) view) View(x1) );
}
template <typename Monoid, typename T1, typename T2>
static void construct(Monoid* monoid, View* view, const Monoid& m,
const T1& x1, const T2& x2)
{
provisional_guard<Monoid> guard( new((void*) monoid) Monoid(m) );
guard.confirm_if( new((void*) view) View(x1, x2) );
}
template <typename Monoid, typename T1, typename T2, typename T3>
static void construct(Monoid* monoid, View* view, const Monoid& m,
const T1& x1, const T2& x2, const T3& x3)
{
provisional_guard<Monoid> guard( new((void*) monoid) Monoid(m) );
guard.confirm_if( new((void*) view) View(x1, x2, x3) );
}
template <typename Monoid, typename T1, typename T2, typename T3,
typename T4>
static void construct(Monoid* monoid, View* view, const Monoid& m,
const T1& x1, const T2& x2, const T3& x3,
const T4& x4)
{
provisional_guard<Monoid> guard( new((void*) monoid) Monoid(m) );
guard.confirm_if( new((void*) view) View(x1, x2, x3, x4) );
}
//@}
//@}
};
/** Monoid class that gets its value type and identity and reduce operations
* from its view.
*
* A simple implementation of the monoid-view-reducer architecture would
* distribute knowledge about the type and operations for the reduction
* between the monoid and the view - the identity and reduction operations are
* specified in the monoid, the reduction operations are implemented in the
* view, and the value type is specified in both the monoid and the view.
* This is inelegant.
*
* monoid_with_view is a subclass of @ref monoid_base that gets its value type
* and its identity and reduction operations from its view class. No
* customization of the monoid_with_view class itself is needed beyond
* instantiating it with an appropriate view class. (Customized subclasses of
* monoid_with_view may be needed for other reasons, such as to keep some
* state for the reducer.) All of the Intel Cilk Plus predefined reducers use
* monoid_with_view or one of its subclasses.
*
* The view class `View` of a monoid_with_view must provide the following
* public definitions:
*
* Definition | Meaning
* ---------------------------------|--------
* `value_type` | a typedef of the value type for the reduction
* `View()` | a default constructor which constructs the identity value for the reduction
* `void reduce(const View* other)` | a member function which applies the reduction operation to the values of `this` view and the `other` view, leaving the result as the value of `this` view, and leaving the value of the `other` view undefined (but valid)
*
* @tparam View The view class for the monoid.
* @tparam Align If true, reducers instantiated on this monoid will be
* cache-aligned. By default, library reducers (unlike legacy
* library reducer _wrappers_) are aligned only as required by
* contents.
*/
template <class View, bool Align = false>
class monoid_with_view : public monoid_base<typename View::value_type, View>
{
public:
/** Should reducers created with this monoid be aligned?
*/
enum { align_reducer = Align };
/** Create the identity value.
*
* Implements the monoid `identity` operation by using the @a View class's
* default constructor.
*
* @param p A pointer to a block of raw memory large enough to hold a
* @p View object.
*/
void identity(View* p) const { new((void*) p) View(); }
/** Reduce the values of two views.
*
* Implements the monoid `reduce` operation by calling the left view's
* `%reduce()` function with the right view as an operand.
*
* @param left The left operand of the reduce operation.
* @param right The right operand of the reduce operation.
* @post The left view contains the result of the reduce
* operation, and the right view is undefined.
*/
void reduce(View* left, View* right) const { left->reduce(right); }
};
/** Base class for simple views with (usually) scalar values.
*
* The scalar_view class is intended as a base class which provides about half
* of the required definitions for simple views. It defines the `value_type`
* required by a @ref monoid_with_view (but not the identity constructor and
* reduce operation, which are inherently specific to a particular kind of
* reduction). It also defines the value access functions which will be called
* by the corresponding @ref reducer functions. (It uses copy semantics for
* the view_move_in() and view_move_out() functions, which is appropriate
* for simple scalar types, but not necessarily for more complex types like
* STL containers.
*
* @tparam Type The type of value wrapped by the view.
*/
template <typename Type>
class scalar_view
{
protected:
Type m_value; ///< The wrapped accumulator variable.
public:
/** Value type definition required by @ref monoid_with_view.
*/
typedef Type value_type;
/** Default constructor.
*/
scalar_view() : m_value() {}
/** Value constructor.
*/
scalar_view(const Type& v) : m_value(v) {}
/** @name Value functions required by the reducer class.
*
* Note that the move in/out functions use simple assignment semantics.
*/
//@{
/** Set the value of the view.
*/
void view_move_in(Type& v) { m_value = v; }
/** Get the value of the view.
*/
void view_move_out(Type& v) { v = m_value; }
/** Set the value of the view.
*/
void view_set_value(const Type& v) { m_value = v; }
/** Get the value of the view.
*/
Type const& view_get_value() const { return m_value; }
/** Type returned by view_get_value.
*/
typedef Type const& return_type_for_get_value;
/** Get a reference to the value contained in the view. For legacy
* reducer support only.
*/
Type & view_get_reference() { return m_value; }
/** Get a reference to the value contained in the view. For legacy
* reducer support only.
*/
Type const& view_get_reference() const { return m_value; }
//@}
};
/** Wrapper class for move-in construction.
*
* Some types allow their values to be _moved_ as an alternative to copying.
* Moving a value may be much faster than copying it, but may leave the value
* of the move's source undefined. Consider the `swap` operation provided by
* many STL container classes:
*
* list<T> x, y;
* x = y; // Copy
* x.swap(y); // Move
*
* The assignment _copies_ the value of `y` into `x` in time linear in the
* size of `y`, leaving `y` unchanged. The `swap` _moves_ the value of `y`
* into `x` in constant time, but it also moves the value of `x` into `y`,
* potentially leaving `y` undefined.
*
* A move_in_wrapper simply wraps a pointer to an object. It is created by a
* call to cilk::move_in(). Passing a move_in_wrapper to a view constructor
* (actually, passing it to a reducer constructor, which passes it to the
* monoid `construct()` function, which passes it to the view constructor)
* allows, but does not require, the value pointed to by the wrapper to be
* moved into the view instead of copied.
*
* A view class exercises this option by defining a _move-in constructor_,
* i.e., a constructor with a move_in_wrapper parameter. The constructor calls
* the wrapper's `value()` function to get a reference to its pointed-to
* value, and can then use that reference in a move operation.
*
* A move_in_wrapper also has an implicit conversion to its pointed-to value,
* so if a view class does not define a move-in constructor, its ordinary
* value constructor will be called with the wrapped value. For example, an
* @ref ReducersAdd "op_add" view does not have a move-in constructor, so
*
* int x;
* reducer< op_add<int> > xr(move_in(x));
*
* will simply call the `op_add_view(const int &)` constructor. But an
* @ref ReducersList "op_list_append" view does have a move-in constructor,
* so
*
* list<int> x;
* reducer< op_list_append<int> > xr(move_in(x));
*
* will call the `op_list_append_view(move_in_wrapper<int>)` constructor,
* which can `swap` the value of `x` into the view.
*
* @note Remember that passing the value of a variable to a reducer
* constructor using a move_in_wrapper leaves the variable undefined.
* You cannot assume that the constructor either will or will not copy
* or move the value.
*
* @tparam Type The type of the wrapped value.
*
* @see cilk::move_in()
*/
template <typename Type>
class move_in_wrapper
{
Type *m_pointer;
public:
/** Constructor that captures the address of its argument. This is almost
* always called from the @ref move_in function.
*/
explicit move_in_wrapper(Type& ref) : m_pointer(&ref) { }
/** Implicit conversion to the wrapped value. This allows a move_in_wrapper
* to be used where a value of the wrapped type is expected, in which case
* the wrapper is completely transparent.
*/
operator Type&() const { return *m_pointer; }
/** Get a reference to the pointed-to value. This has the same effect as
* the implicit conversion, but makes the intent clearer in a move-in
* constructor.
*/
Type& value() const { return *m_pointer; }
};
/** Function to create a move_in_wrapper for a value.
*
* @tparam Type The type of the argument, which will be the `type` of the
* created wrapper.
*
* @see move_in_wrapper
*/
template <typename Type>
inline
move_in_wrapper<Type> move_in(Type& ref)
{ return move_in_wrapper<Type>(ref); }
/** @copydoc move_in(Type&)
*
* @note Applying a function that is explicitly specified as modifying its
* argument to a const argument is obviously an irrational thing to
* do. This move_in() variant is just provided to allow calling a
* move-in constructor with a function return value, which the
* language treats as a const. Using it for any other purpose will
* probably end in tears.
*/
template <typename Type>
inline
move_in_wrapper<Type> move_in(const Type& ref)
{ return move_in_wrapper<Type>(ref); }
/** Wrapper class to allow implicit downcasts to reducer subclasses.
*
* The Intel Cilk Plus library contains a collection of reducer wrapper classes which
* were created before the `cilk::reducer<Monoid>` style was developed. For
* example, `cilk::reducer_opadd<Type>` provided essentially the same
* functionality that is now provided by
* `cilk::reducer< cilk::op_add<Type> >`. These legacy reducer classes are
* deprecated, but still supported, and they have been reimplemented as
* subclasses of the corresponding `cilk::reducer` classes. For example:
*
* template <class T>
* reducer_opadd<T> : public reducer< op_add<T> > { ... };
*
* This reimplementation allows transparent conversion between legacy and
* new reducers. That is, a `reducer<op_add>*` or `reducer<op_add>&` can be
* used anywhere that a `reducer_opadd*` or `reducer_opadd&` is expected,
* and vice versa.
*
* The conversion from the legacy reducer to the new reducer is just an
* up-cast, which is provided for free by C++. The conversion from the new
* reducer to the legacy reducer is a down-cast, though, which requires an
* explicit conversion member function in the `reducer` class. The challenge
* is to define a function in the reducer template class which will convert
* each cilk::reducer specialization to the corresponding legacy reducer,
* if there is one.
*
* The trick is in the legacy_reducer_downcast template class, which provides
* a mapping from `cilk::reducer` specializations to legacy reducer classes.
* `reducer<Monoid>` has a conversion function to convert itself to
* `legacy_reducer_downcast< reducer<Monoid> >::%type`. By default,
* `legacy_reducer_downcast<Reducer>::%type` is just a trivial subclass of
* `Reducer`, which is uninteresting, but a reducer with a legacy counterpart
* will have a specialization of `legacy_reducer_downcast` whose `type` is
* the corresponding legacy reducer. For example:
*
* template <typename Type>
* struct legacy_reducer_downcast< reducer< op_add<Type> > >
* {
* typedef reducer_opadd<Type> type;
* };
*
*
* @tparam Reducer The new-style reducer class whose corresponding legacy
* reducer class is `type`, if there is such a legacy reducer
* class.
*/
template <typename Reducer>
struct legacy_reducer_downcast
{
/** The related legacy reducer class.
*
* By default, this is just a trivial subclass of Reducer, but it can be
* overridden in the specialization of legacy_reducer_downcast for
* a reducer that has a corresponding legacy reducers.
*/
struct type : Reducer { };
};
namespace internal {
/// @cond internal
template <typename Value, typename View>
struct reducer_set_get
{
// sizeof(notchar) != sizeof(char)
struct notchar { char x[2]; };
// `does_view_define_return_type_for_get_value(View*)` returns `char` if
// `View` defines `return_type_for_get_value`, and `notchar` if it doesn't.
template <typename T>
struct using_type {};
template <typename T>
static char does_view_define_return_type_for_get_value(
using_type<typename T::return_type_for_get_value>*);
template <typename T>
static notchar does_view_define_return_type_for_get_value(...);
// `VIEW_DOES_DEFINE_RETURN_TYPE_FOR_GET_VALUE` is true if `View` defines
// `return_type_for_get_value`.
enum { VIEW_DOES_DEFINE_RETURN_TYPE_FOR_GET_VALUE =
sizeof( does_view_define_return_type_for_get_value<View>(0) )
== sizeof(char) } ;
// `return_type_for_get_value` is `View::return_type_for_get_value`
// if it is defined, and just `Value` otherwise.
template <typename InnerView, bool ViewDoesDefineReturnTypeForGetValue>
struct return_type_for_view_get_value {
typedef Value type;
};
template <typename InnerView>
struct return_type_for_view_get_value<InnerView, true> {
typedef typename InnerView::return_type_for_get_value type;
};
public:
typedef
typename
return_type_for_view_get_value<
View,
VIEW_DOES_DEFINE_RETURN_TYPE_FOR_GET_VALUE
>::type
return_type_for_get_value;
static void move_in(View& view, Value& v) { view.view_move_in(v); }
static void move_out(View& view, Value& v) { view.view_move_out(v); }
static void set_value(View& view, const Value& v)
{ view.view_set_value(v); }
static return_type_for_get_value get_value(const View& view)
{ return view.view_get_value(); }
};
template <typename Value>
struct reducer_set_get<Value, Value>
{
typedef const Value& return_type_for_get_value;
static void move_in(Value& view, Value& v) { view = v; }
static void move_out(Value& view, Value& v) { v = view; }
static void set_value(Value& view, const Value& v)
{ view = v; }
static return_type_for_get_value get_value(const Value& view)
{ return view; }
};
/// @endcond
/** Base class defining the data layout that is common to all reducers.
*/
template <typename Monoid>
class reducer_base {
typedef typename Monoid::view_type view_type;
// This makes the reducer a hyper-object. (Partially initialized in
// the derived reducer_content class.)
//
__cilkrts_hyperobject_base m_base;
// The monoid is allocated here as raw bytes, and is constructed explicitly
// by a call to the monoid_type::construct() function in the constructor of
// the `reducer` subclass.
//
storage_for_object<Monoid> m_monoid;
// Used for sanity checking at destruction.
//
void* m_initialThis;
// The leftmost view comes next. It is defined in the derived
// reducer_content class.
/** @name C-callable wrappers for the C++-coded monoid dispatch functions.
*/
//@{
static void reduce_wrapper(void* r, void* lhs, void* rhs);
static void identity_wrapper(void* r, void* view);
static void destroy_wrapper(void* r, void* view);
static void* allocate_wrapper(void* r, __STDNS size_t bytes);
static void deallocate_wrapper(void* r, void* view);
//@}
protected:
/** Constructor.
*
* @param leftmost The address of the leftmost view in the reducer.
*/
reducer_base(char* leftmost)
{
static const cilk_c_monoid c_monoid_initializer = {
(cilk_c_reducer_reduce_fn_t) &reduce_wrapper,
(cilk_c_reducer_identity_fn_t) &identity_wrapper,
(cilk_c_reducer_destroy_fn_t) &destroy_wrapper,
(cilk_c_reducer_allocate_fn_t) &allocate_wrapper,
(cilk_c_reducer_deallocate_fn_t) &deallocate_wrapper
};
m_base.__c_monoid = c_monoid_initializer;
m_base.__flags = 0;
m_base.__view_offset = (char*)leftmost - (char*)this;
m_base.__view_size = sizeof(view_type);
m_initialThis = this;
__cilkrts_hyper_create(&m_base);
}
/** Destructor.
*/
__CILKRTS_STRAND_STALE(~reducer_base())
{
// Make sure we haven't been memcopy'd or corrupted
__CILKRTS_ASSERT(
this == m_initialThis ||
// Allow for a layout bug that may put the initialThis field one
// word later in 1.0 reducers than in 0.9 and 1.1 reducers.
this == *(&m_initialThis + 1)
);
__cilkrts_hyper_destroy(&m_base);
}
/** Monoid data member.
*
* @return A pointer to the reducer's monoid data member.
*/
Monoid* monoid_ptr() { return &m_monoid.object(); }
/** Leftmost view data member.
*
* @return A pointer to the reducer's leftmost view data member.
*
* @note This function returns the address of the *leftmost* view,
* which is unique for the lifetime of the reducer. It is
* intended to be used in constructors and destructors.
* Use the reducer::view() function to access the per-strand
* view instance.
*/
view_type* leftmost_ptr()
{
char* view_addr = (char*)this + m_base.__view_offset;
return reinterpret_cast<view_type*>(view_addr);
}
public:
/** @name Access the current view.
*
* These functions return a reference to the instance of the reducer's
* view that was created for the current strand of a parallel computation
* (and create it if it doesn't already exist). Note the difference from
* the (private) leftmost_ptr() function, which returns a pointer to the
* _leftmost_ view, which is the same in all strands.
*/
//@{
/** Per-strand view instance.
*
* @return A reference to the per-strand view instance.
*/
view_type& view()
{
return *static_cast<view_type *>(__cilkrts_hyper_lookup(&m_base));
}
/** @copydoc view()
*/
const view_type& view() const
{
return const_cast<reducer_base*>(this)->view();
}
//@}
/** Initial view pointer field.
*
* @internal
*
* @return a reference to the m_initialThis field.
*
* @note This function is provided for "white-box" testing of the
* reducer layout code. There is never any reason for user code
* to call it.
*/
const void* const & initial_this() const { return m_initialThis; }
};
template <typename Monoid>
void reducer_base<Monoid>::reduce_wrapper(void* r, void* lhs, void* rhs)
{
Monoid* monoid = static_cast<reducer_base*>(r)->monoid_ptr();
monoid->reduce(static_cast<view_type*>(lhs),
static_cast<view_type*>(rhs));
}
template <typename Monoid>
void reducer_base<Monoid>::identity_wrapper(void* r, void* view)
{
Monoid* monoid = static_cast<reducer_base*>(r)->monoid_ptr();
monoid->identity(static_cast<view_type*>(view));
}
template <typename Monoid>
void reducer_base<Monoid>::destroy_wrapper(void* r, void* view)
{
Monoid* monoid = static_cast<reducer_base*>(r)->monoid_ptr();
monoid->destroy(static_cast<view_type*>(view));
}
template <typename Monoid>
void* reducer_base<Monoid>::allocate_wrapper(void* r, __STDNS size_t bytes)
{
Monoid* monoid = static_cast<reducer_base*>(r)->monoid_ptr();
return monoid->allocate(bytes);
}
template <typename Monoid>
void reducer_base<Monoid>::deallocate_wrapper(void* r, void* view)
{
Monoid* monoid = static_cast<reducer_base*>(r)->monoid_ptr();
monoid->deallocate(static_cast<view_type*>(view));
}
/** Base class defining the data members of a reducer.
*
* @tparam Aligned The `m_view` data member, and therefore the entire
* structure, are cache-line aligned if this parameter
* is `true'.
*/
template <typename Monoid, bool Aligned = Monoid::align_reducer>
class reducer_content;
/** Base class defining the data members of an aligned reducer.
*/
template <typename Monoid>
class reducer_content<Monoid, true> : public reducer_base<Monoid>
{
typedef typename Monoid::view_type view_type;
// The leftmost view is defined as raw bytes. It will be constructed
// by the monoid `construct` function. It is cache-aligned, which
// will push it into a new cache line. Furthermore, its alignment causes
// the reducer as a whole to be cache-aligned, which makes the reducer
// size a multiple of a cache line. Since there is nothing in the reducer
// after the view, all this means that the leftmost view gets one or more
// cache lines all to itself, which prevents false sharing.
//
__CILKRTS_CACHE_ALIGN
char m_leftmost[sizeof(view_type)];
/** Test if the reducer is cache-line-aligned.
*
* Used in assertions.
*/
bool reducer_is_cache_aligned() const
{ return 0 == ((std::size_t) this & (__CILKRTS_CACHE_LINE__ - 1)); }
protected:
/** Constructor.
*/
reducer_content() : reducer_base<Monoid>((char*)&m_leftmost)
{
#ifndef CILK_IGNORE_REDUCER_ALIGNMENT
assert(reducer_is_cache_aligned() &&
"Reducer should be cache aligned. Please see comments following "
"this assertion for explanation and fixes.");
#endif
/* "REDUCER SHOULD BE CACHE ALIGNED" ASSERTION.
*
* This Reducer class instantiation specifies cache-line alignment of the
* leftmost view field (and, implicitly, of the reducer itself). You got
* this assertion because a reducer with this class was allocated at a
* non-cache-aligned address, probably because it was allocated on the
* heap with `new`. This can be a problem for two reasons:
*
* 1. If the leftmost view is not on a cache line by itself, there might
* be a slowdown resulting from accesses to the same cache line from
* different threads.
*
* 2. The compiler thinks that reducer is cache-line aligned, but it
* really isn't. If the reducer is contained in a structure, then the
* compiler will believe that the containing structure, and other
* fields contained in it, are also more aligned than they really
* are. In particular, if the structure contains a numeric array that
* is used in a vectorizable loop, then the compiler might generate
* invalid vector instructions, resulting in a runtime error.
*
* The compiler will always allocate reducer variables, and structure
* variables containing reducers, with their required alignment.
* Reducers, and structures containing a reducer, which are allocated
* on the heap with `new` will _not_ be properly aligned.
*
* There are three ways that you can fix this assertion failure.
*
* A. Rewrite your code to use the new-style `reducer< op_XXX<Type> >`
* instead of the legacy `reducer_XXX<type>`. The new-style reducers
* are not declared to be cache-aligned, and will work properly if
* they are not cache-aligned.
*
* B. If you must allocate an old-style reducer or a structure containing
* a reducer on the heap, figure out how to align it correctly. The
* suggested fix is to use `cilk::aligned_new()` and
* `cilk::aligned_delete()` instead of `new` and `delete`, as follows:
*
* Type* ptr = cilk::aligned_new<Type>(constructor-arguments);
* cilk::aligned_delete(ptr);
*
* C. Define the macro CILK_IGNORE_REDUCER_ALIGNMENT, which will suppress
* the assertion check. Do this only if you are comfortable that
* problem (2) above will not occur.
*/
}
};
/** Base class defining the data members of an unaligned reducer.
*/
template <typename Monoid>
class reducer_content<Monoid, false> : public reducer_base<Monoid>
{
typedef typename Monoid::view_type view_type; ///< The view type.
// Reserve space for the leftmost view. The view will be allocated at an
// aligned offset in this space at runtime, to guarantee that the view
// will get one or more cache lines all to itself, to prevent false
// sharing.
//
// The number of bytes to reserve is determined as follows:
// * Start with the view size.
// * Round up to a multiple of the cache line size, to get the total size
// of the cache lines that will be dedicated to the view.
// * Add (cache line size - 1) filler bytes to guarantee that the reserved
// area will contain a cache-aligned block of the required cache lines,
// no matter where the reserved area starts.
//
char m_leftmost[
// View size rounded up to multiple cache lines
( (sizeof(view_type) + __CILKRTS_CACHE_LINE__ - 1)
& ~ (__CILKRTS_CACHE_LINE__ - 1)
)
// plus filler to allow alignment.
+ __CILKRTS_CACHE_LINE__ - 1
];
protected:
/** Constructor. Find the first cache-aligned position in the reserved
* area, and pass it to the base constructor as the leftmost view
* address.
*/
reducer_content() :
reducer_base<Monoid>(
(char*)( ((std::size_t)&m_leftmost + __CILKRTS_CACHE_LINE__ - 1)
& ~ (__CILKRTS_CACHE_LINE__ - 1) ) )
{}
};
} // namespace internal
// The __cilkrts_hyperobject_ functions are defined differently depending on
// whether a file is compiled with or without the CILK_STUB option. Therefore,
// reducers compiled in the two modes should be link-time incompatible, so that
// object files compiled with stubbed reducers won't be linked into an
// unstubbed program, or vice versa. We achieve this by putting the reducer
// class definition into the cilk::stub namespace in a stubbed compilation.
#ifdef CILK_STUB
namespace stub {
#endif
/** Reducer class.
*
* A reducer is instantiated on a Monoid. The Monoid provides the value
* type, associative reduce function, and identity for the reducer.
*
* @tparam Monoid The monoid class that the reducer is instantiated on. It
* must model the @ref reducers_monoid_concept "monoid
* concept".
*
* @see @ref pagereducers
*/
template <class Monoid>
class reducer : public internal::reducer_content<Monoid>
{
typedef internal::reducer_content<Monoid> base;
using base::monoid_ptr;
using base::leftmost_ptr;
public:
typedef Monoid monoid_type; ///< The monoid type.
typedef typename Monoid::value_type value_type; ///< The value type.
typedef typename Monoid::view_type view_type; ///< The view type.
private:
typedef internal::reducer_set_get<value_type, view_type> set_get;
reducer(const reducer&); ///< Disallow copying.
reducer& operator=(const reducer&); ///< Disallow assignment.
public:
/** @name Constructors
*
* All reducer constructors call the static `construct()` function of the
* monoid class to construct the reducer's monoid and leftmost view.
*
* The reducer constructor arguments are simply passed through to the
* construct() function. Thus, the constructor parameters accepted by a
* particular reducer class are determined by its monoid class.
*/
//@{
/** 0 – 6 const reference parameters.
*/
//@{
reducer()
{
monoid_type::construct(monoid_ptr(), leftmost_ptr());
}
template <typename T1>
reducer(const T1& x1)
{
monoid_type::construct(monoid_ptr(), leftmost_ptr(), x1);
}
template <typename T1, typename T2>
reducer(const T1& x1, const T2& x2)
{
monoid_type::construct(monoid_ptr(), leftmost_ptr(), x1, x2);
}
template <typename T1, typename T2, typename T3>
reducer(const T1& x1, const T2& x2, const T3& x3)
{
monoid_type::construct(monoid_ptr(), leftmost_ptr(), x1, x2, x3);
}
template <typename T1, typename T2, typename T3, typename T4>
reducer(const T1& x1, const T2& x2, const T3& x3, const T4& x4)
{
monoid_type::construct(monoid_ptr(), leftmost_ptr(), x1, x2, x3, x4);
}
template <typename T1, typename T2, typename T3, typename T4, typename T5>
reducer(const T1& x1, const T2& x2, const T3& x3, const T4& x4,
const T5& x5)
{
monoid_type::construct(monoid_ptr(), leftmost_ptr(),
x1, x2, x3, x4, x5);
}
template <typename T1, typename T2, typename T3, typename T4,
typename T5, typename T6>
reducer(const T1& x1, const T2& x2, const T3& x3, const T4& x4,
const T5& x5, const T6& x6)
{
monoid_type::construct(monoid_ptr(), leftmost_ptr(),
x1, x2, x3, x4, x5, x6);
}
//@}
/** 1 non-const reference parameter.
*/
//@{
template <typename T1>
reducer(T1& x1)
{
monoid_type::construct(monoid_ptr(), leftmost_ptr(), x1);
}
//@}
/** Destructor.
*/
__CILKRTS_STRAND_STALE(~reducer())
{
leftmost_ptr()->~view_type();
monoid_ptr()->~monoid_type();
}
//@{
/** Get the monoid.
*
* @return A reference to the monoid object belonging to this reducer.
*/
Monoid& monoid() { return *monoid_ptr(); }
const Monoid& monoid() const
{ return const_cast<reducer*>(this)->monoid(); }
//@}
//@{
/** Access the current view.
*
* Return a reference to the instance of the reducer's view that was
* created for the current strand of a parallel computation (and create
* it if it doesn't already exist).
*/
view_type& view() { return base::view(); }
const view_type& view() const { return base::view(); }
//@}
/** @name Dereference the reducer to get the view.
*
* "Dereferencing" a reducer yields the view for the current strand. The
* view, in turn, acts as a proxy for its contained value, exposing only
* those operations which are consistent with the reducer's monoid. Thus,
* all modifications of the reducer's accumulator variable are written as
*
* *reducer OP ...
*
* or
*
* reducer->func(...)
*
* (The permitted operations on a reducer's accumulator are listed in the
* documentation for that particular kind of reducer.)
*
* @note `*r` is a synonym for `r.view()`. Recommended style is to use
* `*r` (or `r->`) in the common case where code is simply
* updating the accumulator variable wrapped in the view, and to
* use `r.view()` in the unusual case where it is desirable to
* call attention to the view itself.
*/
//@{
//@{
/** Dereference operator.
*
* @return A reference to the per-strand view instance.
*/
view_type& operator*() { return view(); }
view_type const& operator*() const { return view(); }
//@}
//@{
/** Pointer operator.
*
* @return A pointer to the per-strand view instance.
*/
view_type* operator->() { return &view(); }
view_type const* operator->() const { return &view(); }
//@}
//@{
/** Deprecated view access.
*
* `r()` is a synonym for `*r` which was used with early versions of
* Intel Cilk Plus reducers. `*r` is now the preferred usage.
*
* @deprecated Use operator*() instead of operator()().
*
* @return A reference to the per-strand view instance.
*/
view_type& operator()() { return view(); }
view_type const& operator()() const { return view(); }
//@}
//@}
/** @name Set and get the value.
*
* These functions are used to set an initial value for the reducer before
* starting the reduction, or to get the final value after the reduction
* is complete.
*
* @note These functions are completely different from the view
* operations that are made available via operator*() and
* operator->(), which are used to _modify_ the reducer's value
* _during_ the reduction.
*
* @warning These functions _can_ be called at any time, and in
* general, they will refer to the value contained in the view
* for the current strand. However, using them other than to
* set the reduction's initial value or get its final value
* will almost always result in undefined behavior.
*/
//@{
/** Move a value into the reducer.
*
* This function is used to set the initial value of the reducer's
* accumulator variable by either copying or _moving_ the value of @a obj
* into it. Moving a value can often be performed in constant time, even
* for large container objects, but has the side effect of leaving the
* value of @a obj undefined. (See the description of the
* @ref move_in_wrapper class for a discussion of moving values.)
*
* @par Usage
* A move_in() call to initialize a reducer is often paired with a
* move_out() call to get its final value:
*
* reducer<Type> xr;
* xr.move_in(x);
* … do the reduction …
* xr.move_out(x);
*
* @par Assumptions
* - You cannot assume either that this will function will copy its
* value or that it will move it.
* - You must assume that the value of @a obj will be undefined
* after the call to move_in().
* - You can assume that move_in() will be at least as efficient as
* set_value(), and you should therefore prefer move_in() unless
* you need the value of @a obj to be unchanged after the call.
* (But you should usually prefer the move-in constructor over a
* move_in() call - see the note below.)
*
* @note The behavior of a default constructor followed by move-in
* initialization:
*
* reducer<Type> xr;
* xr.move_in(x);
*
* @note is not necessarily the same as a move-in constructor:
*
* reducer<Type> xr(move_in(x));
*
* @note In particular, when @a Type is a container type with a
* non-empty allocator, the move-in constructor will create the
* accumulator variable with the same allocator as the input
* argument @a x, while the default constructor will create the
* accumulator variable with a default allocator. The mismatch of
* allocators in the latter case means that the input argument
* @a x may have to be copied in linear time instead of being
* moved in constant time.
*
* @note Best practice is to prefer the move-in constructor over the
* move-in function unless the move-in function is required for
* some specific reason.
*
* @warning Calling this function other than to set the initial value
* for a reduction will almost always result in undefined
* behavior.
*
* @param obj The object containing the value that will be moved into the
* reducer.
*
* @post The reducer contains the value that was initially in @a obj.
* @post The value of @a obj is undefined.
*
* @see set_value()
*/
void move_in(value_type& obj) { set_get::move_in(view(), obj);}
/** Move the value out of the reducer.
*
* This function is used to retrieve the final value of the reducer's
* accumulator variable by either copying or _moving_ the value of @a obj
* into it. Moving a value can often be performed in constant time, even
* for large container objects, but has the side effect of leaving the
* value of the reducer's accumulator variable undefined. (See the
* description of the @ref move_in_wrapper class for a discussion of
* moving values.)
*
* @par Usage
* A move_in() call to initialize a reducer is often paired with a
* move_out() call to get its final value:
*
* reducer<Type> xr;
* xr.move_in(x);
* … do the reduction …
* xr.move_out(x);
*
* @par Assumptions
* - You cannot assume either that this will function will copy its
* value or that it will move it.
* - You must assume that the value of the reducer's accumulator
* variable will be undefined after the call to move_out().
* - You can assume that move_out() will be at least as efficient as
* get_value(), and you should therefore prefer move_out() unless
* you need the accumulator variable to be preserved after the
* call.
*
* @warning Calling this function other than to retrieve the final
* value of a reduction will almost always result in undefined
* behavior.
*
* @param obj The object that the value of the reducer will be moved into.
*
* @post @a obj contains the value that was initially in the reducer.
* @post The value of the reducer is undefined.
*
* @see get_value()
*/
void move_out(value_type& obj) { set_get::move_out(view(), obj); }
/** Set the value of the reducer.
*
* This function sets the initial value of the reducer's accumulator
* variable to the value of @a obj.
*
* @note The behavior of a default constructor followed by
* initialization:
*
* reducer<Type> xr;
* xr.set_value(x);
*
* @note is not necessarily the same as a value constructor:
*
* reducer<Type> xr(x);
*
* @note In particular, when @a Type is a container type with a
* non-empty allocator, the value constructor will create the
* accumulator variable with the same allocator as the input
* argument @a x, while the default constructor will create the
* accumulator variable with a default allocator.
*
* @warning Calling this function other than to set the initial value
* for a reduction will almost always result in undefined
* behavior.
*
* @param obj The object containing the value that will be copied into
* the reducer.
*
* @post The reducer contains a copy of the value in @a obj.
*
* @see move_in()
*/
void set_value(const value_type& obj) { set_get::set_value(view(), obj); }
/** Get the value of the reducer.
*
* This function gets the final value of the reducer's accumulator
* variable.
*
* @warning Calling this function other than to retrieve the final
* value of a reduction will almost always result in undefined
* behavior.
*
* @return A reference to the value contained in the reducer.
*
* @see move_out()
*/
typename set_get::return_type_for_get_value get_value() const
{ return set_get::get_value(view()); }
//@}
/** Implicit downcast to legacy reducer wrapper, if any.
*
* @see legacy_reducer_downcast
*/
operator typename legacy_reducer_downcast<reducer>::type& ()
{
typedef typename legacy_reducer_downcast<reducer>::type downcast_type;
return *reinterpret_cast<downcast_type*>(this);
}
/** Implicit downcast to legacy reducer wrapper, if any.
*
* @see legacy_reducer_downcast
*/
operator const typename legacy_reducer_downcast<reducer>::type& () const
{
typedef typename legacy_reducer_downcast<reducer>::type downcast_type;
return *reinterpret_cast<const downcast_type*>(this);
}
};
#ifdef CILK_STUB
} // namespace stub
using stub::reducer;
#endif
} // end namespace cilk
#endif /* __cplusplus */
/** @page page_reducers_in_c Creating and Using Reducers in C
*
* @tableofcontents
*
* The Intel Cilk Plus runtime supports reducers written in C as well as in C++. The
* basic logic is the same, but the implementation details are very
* different. The C++ reducer implementation uses templates heavily to create
* very generic components. The C reducer implementation uses macros, which
* are a much blunter instrument. The most immediate consequence is that the
* monoid/view/reducer architecture is mostly implicit rather than explicit
* in C reducers.
*
* @section reducers_c_overview Overview of Using Reducers in C
*
* The basic usage pattern for C reducers is:
*
* 1. Create and initialize a reducer object.
* 2. Tell the Intel Cilk Plus runtime about the reducer.
* 3. Update the value contained in the reducer in a parallel computation.
* 4. Tell the Intel Cilk Plus runtime that you are done with the reducer.
* 5. Retrieve the value from the reducer.
*
* @subsection reducers_c_creation Creating and Initializing a C Reducer
*
* The basic pattern for creating and initializing a reducer object in C is
*
* CILK_C_DECLARE_REDUCER(value-type) reducer-name =
* CILK_C_INIT_REDUCER(value-type,
* reduce-function,
* identity-function,
* destroy-function,
* initial-value);
*
* This is simply an initialized definition of a variable named
* _reducer-name_. The @ref CILK_C_DECLARE_REDUCER macro expands to an
* anonymous `struct` declaration for a reducer object containing a view of
* type _value-type_, and the @ref CILK_C_INIT_REDUCER macro expands to a
* struct initializer.
*
* @subsection reducers_c_reduce_func Reduce Functions
*
* The reduce function for a reducer is called when a parallel execution
* strand terminates, to combine the values computed by the terminating
* strand and the strand to its left. It takes three arguments:
*
* - `void* reducer` - the address of the reducer.
* - `void* left` - the address of the value for the left strand.
* - `void* right` - the address of the value for the right (terminating)
* strand.
*
* It must apply the reducer's reduction operation to the `left` and `right`
* values, leaving the result in the `left` value. The `right` value is
* undefined after the reduce function call.
*
* @subsection reducers_c_identity_func Identity Functions
*
* The identity function for a reducer is called when a parallel execution
* strand begins, to initialize its value to the reducer's identity value. It
* takes two arguments:
*
* - `void* reducer` - the address of the reducer.
* - `void* v` - the address of a freshly allocated block of memory of size
* `sizeof(value-type)`.
*
* It must initialize the memory pointed to by `v` so that it contains the
* reducer's identity value.
*
* @subsection reducers_c_destroy_func Destroy Functions
*
* The destroy function for a reducer is called when a parallel execution
* strand terminates, to do any necessary cleanup before its value is
* deallocated. It takes two arguments:
*
* - `void* reducer` - the address of the reducer.
* - `void* p` - the address of the value for the terminating strand.
*
* It must release any resources belonging to the value pointed to by `p`, to
* avoid a resource leak when the memory containing the value is deallocated.
*
* The runtime function `__cilkrts_hyperobject_noop_destroy` can be used for
* the destructor function if the reducer's values do not need any cleanup.
*
* @subsection reducers_c_register Tell the Intel Cilk Plus Runtime About the
* Reducer
*
* Call the @ref CILK_C_REGISTER_REDUCER macro to register the reducer with
* the Intel Cilk Plus runtime:
*
* CILK_C_REGISTER_REDUCER(reducer-name);
*
* The runtime will manage reducer values for all registered reducers when
* parallel execution strands begin and end.
*
* @subsection reducers_c_update Update the Value Contained in the Reducer
*
* The @ref REDUCER_VIEW macro returns a reference to the reducer's value for
* the current parallel strand:
*
* REDUCER_VIEW(reducer-name) = REDUCER_VIEW(reducer-name) OP x;
*
* C++ reducer views restrict access to the wrapped value so that it can only
* be modified in ways consistent with the reducer's operation. No such
* protection is provided for C reducers. It is entirely the responsibility
* of the user to avoid modifying the value in any inappropriate way.
*
* @subsection c_reducers_unregister Tell the Intel Cilk Plus Runtime That You Are
* Done with the Reducer
*
* When the parallel computation is complete, call the @ref
* CILK_C_UNREGISTER_REDUCER macro to unregister the reducer with the
* Intel Cilk Plus runtime:
*
* CILK_C_UNREGISTER_REDUCER(reducer-name);
*
* The runtime will stop managing reducer values for the reducer.
*
* @subsection c_reducers_retrieve Retrieve the Value from the Reducer
*
* When the parallel computation is complete, use the @ref REDUCER_VIEW macro
* to retrieve the final value computed by the reducer.
*
* @subsection reducers_c_example_custom Example - Creating and Using a
* Custom C Reducer
*
* The `IntList` type represents a simple list of integers.
*
* struct _intListNode {
* int value;
* _intListNode* next;
* } IntListNode;
* typedef struct { IntListNode* head; IntListNode* tail; } IntList;
*
* // Initialize a list to be empty
* void IntList_init(IntList* list) { list->head = list->tail = 0; }
*
* // Append an integer to the list
* void IntList_append(IntList* list, int x)
* {
* IntListNode* node = (IntListNode*) malloc(sizeof(IntListNode));
* if (list->tail) list->tail->next = node; else list->head = node;
* list->tail = node;
* }
*
* // Append the right list to the left list, and leave the right list
* // empty
* void IntList_concat(IntList* left, IntList* right)
* {
* if (left->head) {
* left->tail->next = right->head;
* if (right->tail) left->tail = right->tail;
* }
* else {
* *left = *right;
* }
* IntList_init(*right);
* }
*
* This code creates a reducer that supports creating an `IntList` by
* appending values to it.
*
* void identity_IntList(void* reducer, void* list)
* {
* IntList_init((IntList*)list);
* }
*
* void reduce_IntList(void* reducer, void* left, void* right)
* {
* IntList_concat((IntList*)left, (IntList*)right);
* }
*
* CILK_C_DECLARE_REDUCER(IntList) my_list_int_reducer =
* CILK_C_INIT_REDUCER(IntList,
* reduce_int_list,
* identity_int_list,
* __cilkrts_hyperobject_noop_destroy);
* // Initial value omitted //
* ListInt_init(&REDUCER_VIEW(my_int_list_reducer));
*
* CILK_C_REGISTER_REDUCER(my_int_list_reducer);
* cilk_for (int i = 0; i != n; ++i) {
* IntList_append(&REDUCER_VIEW(my_int_list_reducer), a[i]);
* }
* CILK_C_UNREGISTER_REDUCER(my_int_list_reducer);
*
* IntList result = REDUCER_VIEW(my_int_list_reducer);
*
* @section reducers_c_predefined Predefined C Reducers
*
* Some of the predefined reducer classes in the Intel Cilk Plus library come with
* a set of predefined macros to provide the same capabilities in C.
* In general, two macros are provided for each predefined reducer family:
*
* - `CILK_C_REDUCER_operation(reducer-name, type-name, initial-value)` -
* Declares a reducer object named _reducer-name_ with initial value
* _initial-value_ to perform a reduction using the _operation_ on values
* of the type specified by _type-name_. This is the equivalent of the
* general code described in @ref reducers_c_creation :
*
* CILK_C_DECLARE_REDUCER(type) reducer-name =
* CILK_C_INIT_REDUCER(type, ..., initial-value);
*
* where _type_ is the C type corresponding to _type_name_. See @ref
* reducers_c_type_names below for the _type-names_ that you can use.
*
* - `CILK_C_REDUCER_operation_TYPE(type-name)` - Expands to the `typedef`
* name for the type of the reducer object declared by
* `CILK_C_REDUCER_operation(reducer-name, type-name, initial-value)`.
*
* See @ref reducers_c_example_predefined.
*
* The predefined C reducers are:
*
* | Operation | Name | Documentation |
* |-------------------|---------------|-------------------------------|
* | addition | `OPADD` | @ref ReducersAdd |
* | bitwise AND | `OPAND` | @ref ReducersAnd |
* | bitwise OR | `OPOR` | @ref ReducersOr |
* | bitwise XOR | `OPXOR` | @ref ReducersXor |
* | multiplication | `OPMUL` | @ref ReducersMul |
* | minimum | `MIN` | @ref ReducersMinMax |
* | minimum & index | `MIN_INDEX` | @ref ReducersMinMax |
* | maximum | `MAX` | @ref ReducersMinMax |
* | maximum & index | `MAX_INDEX` | @ref ReducersMinMax |
*
* @subsection reducers_c_type_names Numeric Type Names
*
* The type and function names created by the C reducer definition macros
* incorporate both the reducer kind (`opadd`, `opxor`, etc.) and the value
* type of the reducer (`int`, `double`, etc.). The value type is represented
* by a _numeric type name_ string. The types supported in C reducers, and
* their corresponding numeric type names, are given in the following table:
*
* | Type | Numeric Type Name |
* |-----------------------|-------------------------------|
* | `char` | `char` |
* | `unsigned char` | `uchar` |
* | `signed char` | `schar` |
* | `wchar_t` | `wchar_t` |
* | `short` | `short` |
* | `unsigned short` | `ushort` |
* | `int` | `int` |
* | `unsigned int` | `uint` |
* | `unsigned int` | `unsigned` (alternate name) |
* | `long` | `long` |
* | `unsigned long` | `ulong` |
* | `long long` | `longlong` |
* | `unsigned long long` | `ulonglong` |
* | `float` | `float` |
* | `double` | `double` |
* | `long double` | `longdouble` |
*
* @subsection reducers_c_example_predefined Example - Using a Predefined C
* Reducer
*
* To compute the sum of all the values in an array of `unsigned int`:
*
* CILK_C_REDUCER_OPADD(sum, uint, 0);
* CILK_C_REGISTER_REDUCER(sum);
* cilk_for(int i = 0; i != n; ++i) {
* REDUCER_VIEW(sum) += a[i];
* }
* CILK_C_UNREGISTER_REDUCER(sum);
* printf("The sum is %u\n", REDUCER_VIEW(sum));
*/
/** @name C language reducer macros
*
* These macros are used to declare and work with reducers in C code.
*
* @see @ref page_reducers_in_c
*/
//@{
/// @cond internal
/** @name Compound identifier macros.
*
* These macros are used to construct an identifier by concatenating two or
* three identifiers.
*/
//@{
/** Expand to an identifier formed by concatenating two identifiers.
*/
#define __CILKRTS_MKIDENT(a,b) __CILKRTS_MKIDENT_IMP(a,b,)
/** Expand to an identifier formed by concatenating three identifiers.
*/
#define __CILKRTS_MKIDENT3(a,b,c) __CILKRTS_MKIDENT_IMP(a,b,c)
/** Helper macro to do the concatenation.
*/
#define __CILKRTS_MKIDENT_IMP(a,b,c) a ## b ## c
//@}
/** Compiler-specific keyword for the "type of" operator.
*/
#if defined(__GNUC__) && !defined(__INTEL_COMPILER)
# define _Typeof __typeof__
#endif
/** @name Predefined reducer function declaration macros.
*
* These macros are used to create the function headers for the identity,
* reduction, and destructor functions for a builtin reducer family. The
* macro can be followed by a semicolon to create a declaration, or by a
* brace-enclosed body to create a definition.
*/
//@{
/** Create an identity function header.
*
* @note The name of the function's value pointer parameter will always be `v`.
*
* @param name The reducer family name.
* @param tn The type name.
*/
#define __CILKRTS_DECLARE_REDUCER_IDENTITY(name,tn) CILK_EXPORT \
void __CILKRTS_MKIDENT3(name,_identity_,tn)(void* key, void* v)
/** Create a reduction function header.
*
* @param name The reducer family name.
* @param tn The type name.
* @param l The name to use for the function's left value pointer parameter.
* @param r The name to use for the function's right value pointer
* parameter.
*/
#define __CILKRTS_DECLARE_REDUCER_REDUCE(name,tn,l,r) CILK_EXPORT \
void __CILKRTS_MKIDENT3(name,_reduce_,tn)(void* key, void* l, void* r)
/** Create a destructor function header.
*
* @param name The reducer family name.
* @param tn The type name.
* @param p The name to use for the function's value pointer parameter.
*/
#define __CILKRTS_DECLARE_REDUCER_DESTROY(name,tn,p) CILK_EXPORT \
void __CILKRTS_MKIDENT3(name,_destroy_,tn)(void* key, void* p)
//@}
/// @endcond
/***************************************************************************
* Real implementation
***************************************************************************/
/** Declaration of a C reducer structure type.
*
* This macro expands into an anonymous structure declaration for a C reducer
* structure which contains a @a Type value. For example:
*
* CILK_C_DECLARE_REDUCER(int) my_add_int_reducer =
* CILK_C_INIT_REDUCER(int, …);
*
* @param Type The type of the value contained in the reducer object.
*
* @see @ref reducers_c_creation
*/
#define CILK_C_DECLARE_REDUCER(Type) struct { \
__cilkrts_hyperobject_base __cilkrts_hyperbase; \
__CILKRTS_CACHE_ALIGN Type value; \
}
/** Initializer for a C reducer structure.
*
* This macro expands into a brace-enclosed structure initializer for a C
* reducer structure that was declared with
* `CILK_C_DECLARE_REDUCER(Type)`. For example:
*
* CILK_C_DECLARE_REDUCER(int) my_add_int_reducer =
* CILK_C_INIT_REDUCER(int,
* add_int_reduce,
* add_int_identity,
* __cilkrts_hyperobject_noop_destroy,
* 0);
*
* @param Type The type of the value contained in the reducer object. Must
* be the same as the @a Type argument of the
* CILK_C_DECLARE_REDUCER macro call that created the
* reducer.
* @param Reduce The address of the @ref reducers_c_reduce_func
* "reduce function" for the reducer.
* @param Identity The address of the @ref reducers_c_identity_func
* "identity function" for the reducer.
* @param Destroy The address of the @ref reducers_c_destroy_func
* "destroy function" for the reducer.
* @param ... The initial value for the reducer. (A single expression if
* @a Type is a scalar type; a list of values if @a Type is a
* struct or array type.)
*
* @see @ref reducers_c_creation
*/
#define CILK_C_INIT_REDUCER(Type, Reduce, Identity, Destroy, ...) \
{ { { Reduce \
, Identity \
, Destroy \
, __cilkrts_hyperobject_alloc \
, __cilkrts_hyperobject_dealloc \
} \
, 0 \
, __CILKRTS_CACHE_LINE__ \
, sizeof(Type) \
} \
, __VA_ARGS__ \
}
/** Register a reducer with the Intel Cilk Plus runtime.
*
* The runtime will manage reducer values for all registered reducers when
* parallel execution strands begin and end. For example:
*
* CILK_C_REGISTER_REDUCER(my_add_int_reducer);
* cilk_for (int i = 0; i != n; ++i) {
* …
* }
*
* @param Expr The reducer to be registered.
*
* @see @ref page_reducers_in_c
*/
#define CILK_C_REGISTER_REDUCER(Expr) \
__cilkrts_hyper_create(&(Expr).__cilkrts_hyperbase)
/** Unregister a reducer with the Intel Cilk Plus runtime.
*
* The runtime will stop managing reducer values for a reducer after it is
* unregistered. For example:
*
* cilk_for (int i = 0; i != n; ++i) {
* …
* }
* CILK_C_UNREGISTER_REDUCER(my_add_int_reducer);
*
* @param Expr The reducer to be unregistered.
*
* @see @ref page_reducers_in_c
*/
#define CILK_C_UNREGISTER_REDUCER(Expr) \
__cilkrts_hyper_destroy(&(Expr).__cilkrts_hyperbase)
/** Get the current view for a reducer.
*
* The `REDUCER_VIEW(reducer-name)` returns a reference to the reducer's
* value for the current parallel strand. This can be used to initialize the
* value of the reducer before it is used, to modify the value of the reducer
* on the current parallel strand, or to retrieve the final value of the
* reducer at the end of the parallel computation.
*
* REDUCER_VIEW(my_add_int_reducer) = REDUCER_VIEW(my_add_int_reducer) + x;
*
* @note C++ reducer views restrict access to the wrapped value so that it
* can only be modified in ways consistent with the reducer's operation. No
* such protection is provided for C reducers. It is entirely the
* responsibility of the user to refrain from modifying the value in any
* inappropriate way.
*
* @param Expr The reducer whose value is to be returned.
*
* @see @ref page_reducers_in_c
*/
#define REDUCER_VIEW(Expr) (*(_Typeof((Expr).value)*) \
__cilkrts_hyper_lookup(&(Expr).__cilkrts_hyperbase))
//@} C language reducer macros
#endif // CILK_REDUCER_H_INCLUDED