Small buffer optimization for Boost.Function

[SVN r32282]
This commit is contained in:
Douglas Gregor
2006-01-10 23:52:35 +00:00
parent 93c691fbdf
commit 78f6b385d5
6 changed files with 347 additions and 283 deletions

View File

@ -1,6 +1,6 @@
// Boost.Function library
// Copyright Douglas Gregor 2001-2004. Use, modification and
// Copyright Douglas Gregor 2001-2006. Use, modification and
// distribution is subject to the Boost Software License, Version
// 1.0. (See accompanying file LICENSE_1_0.txt or copy at
// http://www.boost.org/LICENSE_1_0.txt)
@ -19,10 +19,10 @@
#include <boost/assert.hpp>
#include <boost/type_traits/is_integral.hpp>
#include <boost/type_traits/composite_traits.hpp>
#include <boost/type_traits/is_stateless.hpp>
#include <boost/ref.hpp>
#include <boost/pending/ct_if.hpp>
#include <boost/mpl/if.hpp>
#include <boost/detail/workaround.hpp>
#include <boost/type_traits/alignment_of.hpp>
#ifndef BOOST_NO_SFINAE
# include "boost/utility/enable_if.hpp"
#else
@ -105,42 +105,36 @@ inline void swap(function<Signature, Allocator>& f1,
namespace boost {
namespace detail {
namespace function {
class X;
/**
* A union of a function pointer and a void pointer. This is necessary
* because 5.2.10/6 allows reinterpret_cast<> to safely cast between
* function pointer types and 5.2.9/10 allows static_cast<> to safely
* cast between a void pointer and an object pointer. But it is not legal
* to cast between a function pointer and a void* (in either direction),
* so function requires a union of the two. */
union any_pointer
* A buffer used to store small function objects in
* boost::function. It is a union containing function pointers,
* object pointers, and a structure that resembles a bound
* member function pointer.
*/
union function_buffer
{
// For pointers to function objects
void* obj_ptr;
// For pointers to std::type_info objects
// (get_functor_type_tag, check_functor_type_tag).
const void* const_obj_ptr;
void (*func_ptr)();
char data[1];
// For function pointers of all kinds
mutable void (*func_ptr)();
// For bound member pointers
struct bound_memfunc_ptr_t {
void (X::*memfunc_ptr)(int);
void* obj_ptr;
} bound_memfunc_ptr;
// To relax aliasing constraints
mutable char data;
};
inline any_pointer make_any_pointer(void* o)
{
any_pointer p;
p.obj_ptr = o;
return p;
}
inline any_pointer make_any_pointer(const void* o)
{
any_pointer p;
p.const_obj_ptr = o;
return p;
}
inline any_pointer make_any_pointer(void (*f)())
{
any_pointer p;
p.func_ptr = f;
return p;
}
/**
* The unusable class is a placeholder for unused function arguments
* It is also completely unusable except that it constructable from
@ -169,7 +163,8 @@ namespace boost {
enum functor_manager_operation_type {
clone_functor_tag,
destroy_functor_tag,
check_functor_type_tag
check_functor_type_tag,
get_functor_type_tag
};
// Tags used to decide between different types of functions
@ -177,57 +172,79 @@ namespace boost {
struct function_obj_tag {};
struct member_ptr_tag {};
struct function_obj_ref_tag {};
struct stateless_function_obj_tag {};
template<typename F>
class get_function_tag
{
typedef typename ct_if<(is_pointer<F>::value),
function_ptr_tag,
function_obj_tag>::type ptr_or_obj_tag;
typedef typename mpl::if_c<(is_pointer<F>::value),
function_ptr_tag,
function_obj_tag>::type ptr_or_obj_tag;
typedef typename ct_if<(is_member_pointer<F>::value),
member_ptr_tag,
ptr_or_obj_tag>::type ptr_or_obj_or_mem_tag;
typedef typename mpl::if_c<(is_member_pointer<F>::value),
member_ptr_tag,
ptr_or_obj_tag>::type ptr_or_obj_or_mem_tag;
typedef typename ct_if<(is_reference_wrapper<F>::value),
function_obj_ref_tag,
ptr_or_obj_or_mem_tag>::type or_ref_tag;
typedef typename mpl::if_c<(is_reference_wrapper<F>::value),
function_obj_ref_tag,
ptr_or_obj_or_mem_tag>::type or_ref_tag;
public:
typedef typename ct_if<(is_stateless<F>::value),
stateless_function_obj_tag,
or_ref_tag>::type type;
typedef or_ref_tag type;
};
// The trivial manager does nothing but return the same pointer (if we
// are cloning) or return the null pointer (if we are deleting).
template<typename F>
struct trivial_manager
struct reference_manager
{
static inline any_pointer
get(any_pointer f, functor_manager_operation_type op)
static inline void
get(const function_buffer& in_buffer, function_buffer& out_buffer,
functor_manager_operation_type op)
{
switch (op) {
case clone_functor_tag: return f;
case clone_functor_tag:
out_buffer.obj_ptr = in_buffer.obj_ptr;
return;
case destroy_functor_tag:
return make_any_pointer(reinterpret_cast<void*>(0));
out_buffer.obj_ptr = 0;
return;
case check_functor_type_tag:
{
std::type_info* t = static_cast<std::type_info*>(f.obj_ptr);
return BOOST_FUNCTION_COMPARE_TYPE_ID(typeid(F), *t)?
f
: make_any_pointer(reinterpret_cast<void*>(0));
// DPG TBD: Since we're only storing a pointer, it's
// possible that the user could ask for a base class or
// derived class. Is that okay?
const std::type_info& check_type =
*static_cast<const std::type_info*>(out_buffer.const_obj_ptr);
if (BOOST_FUNCTION_COMPARE_TYPE_ID(check_type, typeid(F)))
out_buffer.obj_ptr = in_buffer.obj_ptr;
else
out_buffer.obj_ptr = 0;
}
}
return;
// Clears up a warning with GCC 3.2.3
return make_any_pointer(reinterpret_cast<void*>(0));
case get_functor_type_tag:
out_buffer.const_obj_ptr = &typeid(F);
return;
}
}
};
/**
* Determine if boost::function can use the small-object
* optimization with the function object type F.
*/
template<typename F>
struct function_allows_small_object_optimization
{
BOOST_STATIC_CONSTANT
(bool,
value = ((sizeof(F) <= sizeof(function_buffer) &&
(alignment_of<function_buffer>::value
% alignment_of<F>::value == 0))));
};
/**
* The functor_manager class contains a static function "manage" which
* can clone or destroy the given function/function object pointer.
@ -239,30 +256,58 @@ namespace boost {
typedef Functor functor_type;
// For function pointers, the manager is trivial
static inline any_pointer
manager(any_pointer function_ptr,
functor_manager_operation_type op,
function_ptr_tag)
static inline void
manager(const function_buffer& in_buffer, function_buffer& out_buffer,
functor_manager_operation_type op, function_ptr_tag)
{
if (op == clone_functor_tag)
return function_ptr;
else
return make_any_pointer(static_cast<void (*)()>(0));
out_buffer.func_ptr = in_buffer.func_ptr;
else if (op == destroy_functor_tag)
out_buffer.func_ptr = 0;
else /* op == check_functor_type_tag */ {
const std::type_info& check_type =
*static_cast<const std::type_info*>(out_buffer.const_obj_ptr);
if (BOOST_FUNCTION_COMPARE_TYPE_ID(check_type, typeid(Functor)))
out_buffer.obj_ptr = &in_buffer.func_ptr;
else
out_buffer.obj_ptr = 0;
}
}
// For function object pointers, we clone the pointer to each
// function has its own version.
static inline any_pointer
manager(any_pointer function_obj_ptr,
functor_manager_operation_type op,
function_obj_tag)
// Function objects that fit in the small-object buffer.
static inline void
manager(const function_buffer& in_buffer, function_buffer& out_buffer,
functor_manager_operation_type op, mpl::true_)
{
if (op == clone_functor_tag) {
const functor_type* in_functor =
reinterpret_cast<const functor_type*>(&in_buffer.data);
new ((void*)&out_buffer.data) functor_type(*in_functor);
} else if (op == destroy_functor_tag) {
functor_type* out_functor =
reinterpret_cast<functor_type*>(&out_buffer.data);
out_functor->~functor_type();
} else /* op == check_functor_type_tag */ {
const std::type_info& check_type =
*static_cast<const std::type_info*>(out_buffer.const_obj_ptr);
if (BOOST_FUNCTION_COMPARE_TYPE_ID(check_type, typeid(Functor)))
out_buffer.obj_ptr = &in_buffer.data;
else
out_buffer.obj_ptr = 0;
}
}
// Function objects that require heap allocation
static inline void
manager(const function_buffer& in_buffer, function_buffer& out_buffer,
functor_manager_operation_type op, mpl::false_)
{
#ifndef BOOST_NO_STD_ALLOCATOR
typedef typename Allocator::template rebind<functor_type>::other
allocator_type;
typedef typename allocator_type::pointer pointer_type;
typedef typename Allocator::template rebind<functor_type>::other
allocator_type;
typedef typename allocator_type::pointer pointer_type;
#else
typedef functor_type* pointer_type;
typedef functor_type* pointer_type;
#endif // BOOST_NO_STD_ALLOCATOR
# ifndef BOOST_NO_STD_ALLOCATOR
@ -270,8 +315,8 @@ namespace boost {
# endif // BOOST_NO_STD_ALLOCATOR
if (op == clone_functor_tag) {
functor_type* f =
static_cast<functor_type*>(function_obj_ptr.obj_ptr);
const functor_type* f =
static_cast<const functor_type*>(in_buffer.obj_ptr);
// Clone the functor
# ifndef BOOST_NO_STD_ALLOCATOR
@ -283,12 +328,11 @@ namespace boost {
# else
functor_type* new_f = new functor_type(*f);
# endif // BOOST_NO_STD_ALLOCATOR
return make_any_pointer(static_cast<void*>(new_f));
}
else {
out_buffer.obj_ptr = new_f;
} else if (op == destroy_functor_tag) {
/* Cast from the void pointer to the functor pointer type */
functor_type* f =
reinterpret_cast<functor_type*>(function_obj_ptr.obj_ptr);
static_cast<functor_type*>(out_buffer.obj_ptr);
# ifndef BOOST_NO_STD_ALLOCATOR
/* Cast from the functor pointer type to the allocator's pointer
@ -301,26 +345,43 @@ namespace boost {
# else
delete f;
# endif // BOOST_NO_STD_ALLOCATOR
return make_any_pointer(static_cast<void*>(0));
out_buffer.obj_ptr = 0;
} else /* op == check_functor_type_tag */ {
const std::type_info& check_type =
*static_cast<const std::type_info*>(out_buffer.const_obj_ptr);
if (BOOST_FUNCTION_COMPARE_TYPE_ID(check_type, typeid(Functor)))
out_buffer.obj_ptr = in_buffer.obj_ptr;
else
out_buffer.obj_ptr = 0;
}
}
// For function objects, we determine whether the function
// object can use the small-object optimization buffer or
// whether we need to allocate it on the heap.
static inline void
manager(const function_buffer& in_buffer, function_buffer& out_buffer,
functor_manager_operation_type op, function_obj_tag)
{
manager(in_buffer, out_buffer, op,
mpl::bool_<(function_allows_small_object_optimization<functor_type>::value)>());
}
public:
/* Dispatch to an appropriate manager based on whether we have a
function pointer or a function object pointer. */
static any_pointer
manage(any_pointer functor_ptr, functor_manager_operation_type op)
static inline void
manage(const function_buffer& in_buffer, function_buffer& out_buffer,
functor_manager_operation_type op)
{
if (op == check_functor_type_tag) {
std::type_info* type =
static_cast<std::type_info*>(functor_ptr.obj_ptr);
return (BOOST_FUNCTION_COMPARE_TYPE_ID(typeid(Functor), *type)?
functor_ptr
: make_any_pointer(reinterpret_cast<void*>(0)));
}
else {
typedef typename get_function_tag<functor_type>::type tag_type;
return manager(functor_ptr, op, tag_type());
typedef typename get_function_tag<functor_type>::type tag_type;
switch (op) {
case get_functor_type_tag:
out_buffer.const_obj_ptr = &typeid(functor_type);
return;
default:
return manager(in_buffer, out_buffer, op, tag_type());
}
}
};
@ -394,7 +455,9 @@ namespace boost {
struct vtable_base
{
vtable_base() : manager(0) { }
any_pointer (*manager)(any_pointer, functor_manager_operation_type);
void (*manager)(const function_buffer& in_buffer,
function_buffer& out_buffer,
functor_manager_operation_type op);
};
} // end namespace function
} // end namespace detail
@ -408,27 +471,32 @@ namespace boost {
class function_base
{
public:
function_base() : vtable(0)
{
functor.obj_ptr = 0;
}
function_base() : vtable(0) { }
// Is this function empty?
/** Determine if the function is empty (i.e., has no target). */
bool empty() const { return !vtable; }
/** Retrieve the type of the stored function object, or typeid(void)
if this is empty. */
const std::type_info& target_type() const
{
if (!vtable) return typeid(void);
detail::function::function_buffer type;
vtable->manager(functor, type, detail::function::get_functor_type_tag);
return *static_cast<const std::type_info*>(type.const_obj_ptr);
}
template<typename Functor>
Functor* target()
{
if (!vtable) return 0;
detail::function::any_pointer result =
vtable->manager(detail::function::make_any_pointer(&typeid(Functor)),
detail::function::check_functor_type_tag);
if (!result.obj_ptr) return 0;
else {
typedef typename detail::function::get_function_tag<Functor>::type tag;
return get_functor_pointer<Functor>(tag(), 0);
}
detail::function::function_buffer type_result;
type_result.const_obj_ptr = &typeid(Functor);
vtable->manager(functor, type_result,
detail::function::check_functor_type_tag);
return static_cast<Functor*>(type_result.obj_ptr);
}
template<typename Functor>
@ -440,19 +508,11 @@ public:
{
if (!vtable) return 0;
detail::function::any_pointer result =
vtable->manager(detail::function::make_any_pointer(&typeid(Functor)),
detail::function::check_functor_type_tag);
if (!result.obj_ptr) return 0;
else {
typedef typename detail::function::get_function_tag<Functor>::type tag;
#if defined(BOOST_MSVC) && BOOST_WORKAROUND(BOOST_MSVC, < 1300)
return get_functor_pointer(tag(), 0, (Functor*)0);
#else
return get_functor_pointer<Functor>(tag(), 0);
#endif
}
detail::function::function_buffer type_result;
type_result.const_obj_ptr = &typeid(Functor);
vtable->manager(functor, type_result,
detail::function::check_functor_type_tag);
return static_cast<const Functor*>(type_result.obj_ptr);
}
template<typename F>
@ -495,41 +555,7 @@ public:
public: // should be protected, but GCC 2.95.3 will fail to allow access
detail::function::vtable_base* vtable;
detail::function::any_pointer functor;
private:
template<typename Functor>
#if defined(BOOST_MSVC) && BOOST_WORKAROUND(BOOST_MSVC, < 1300)
Functor* get_functor_pointer(detail::function::function_ptr_tag, int, Functor * = 0)
#else
Functor* get_functor_pointer(detail::function::function_ptr_tag, int)
#endif
{ return reinterpret_cast<Functor*>(&functor.func_ptr); }
template<typename Functor, typename Tag>
#if defined(BOOST_MSVC) && BOOST_WORKAROUND(BOOST_MSVC, < 1300)
Functor* get_functor_pointer(Tag, long, Functor * = 0)
#else
Functor* get_functor_pointer(Tag, long)
#endif
{ return static_cast<Functor*>(functor.obj_ptr); }
template<typename Functor>
const Functor*
#if defined(BOOST_MSVC) && BOOST_WORKAROUND(BOOST_MSVC, < 1300)
get_functor_pointer(detail::function::function_ptr_tag, int, Functor * = 0) const
#else
get_functor_pointer(detail::function::function_ptr_tag, int) const
#endif
{ return reinterpret_cast<const Functor*>(&functor.func_ptr); }
template<typename Functor, typename Tag>
#if defined(BOOST_MSVC) && BOOST_WORKAROUND(BOOST_MSVC, < 1300)
const Functor* get_functor_pointer(Tag, long, Functor * = 0) const
#else
const Functor* get_functor_pointer(Tag, long) const
#endif
{ return static_cast<const Functor*>(functor.const_obj_ptr); }
mutable detail::function::function_buffer functor;
};
/**