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handler_ptr is move-only:

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It is no longer a reference counted object and now has semantics
close to a std::unique_ptr.

Signed-off-by: Damian Jarek <damian.jarek93@gmail.com>
This commit is contained in:
Damian Jarek
2017-12-02 16:48:05 +01:00
committed by Vinnie Falco
parent 200e898f7e
commit e08132106e
4 changed files with 110 additions and 180 deletions
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1
CHANGELOG.md
View File

@@ -6,6 +6,7 @@ Version 149:
* Protect calls from macros
* pausation always allocates
* Don't copy completion handlers
* handler_ptr is move-only
--------------------------------------------------------------------------------

143
include/boost/beast/core/handler_ptr.hpp
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@@ -10,10 +10,9 @@
#ifndef BOOST_BEAST_HANDLER_PTR_HPP
#define BOOST_BEAST_HANDLER_PTR_HPP
#include <boost/beast/core/detail/allocator.hpp>
#include <boost/beast/core/detail/config.hpp>
#include <boost/beast/core/detail/type_traits.hpp>
#include <atomic>
#include <cstdint>
#include <type_traits>
#include <utility>
@@ -22,73 +21,63 @@ namespace beast {
/** A smart pointer container with associated completion handler.
This is a smart pointer that retains shared ownership of an
object through a pointer. Memory is managed using the allocation
and deallocation functions associated with a completion handler,
which is also stored in the object. The managed object is
destroyed and its memory deallocated when one of the following
happens:
This is a smart pointer that retains unique ownership of an
object through a pointer. Memory is managed using the allocator
associated with a completion handler stored in the object. The
managed object is destroyed and its memory deallocated when one
of the following occurs:
@li The function @ref invoke is called.
@li The function @ref release_handler is called.
@li The last remaining container owning the object is destroyed.
@li The container is destroyed.
Objects of this type are used in the implementation of
composed operations. Typically the composed operation's shared
state is managed by the @ref handler_ptr and an allocator
associated with the final handler is used to create the managed
object.
Objects of this type are used in the implementation of composed
operations with states that are expensive or impossible to move.
This container manages that non-trivial state on behalf of the
composed operation.
@par Thread Safety
@e Distinct @e objects: Safe.@n
@e Shared @e objects: Unsafe.
@note The reference count is stored using a 16 bit unsigned
integer. Making more than 2^16 copies of one object results
in undefined behavior.
@tparam T The type of the owned object.
@tparam T The type of the owned object. Must be noexcept destructible.
@tparam Handler The type of the completion handler.
*/
template<class T, class Handler>
class handler_ptr
{
struct P
{
T* t;
std::atomic<std::uint16_t> n;
T* t_ = nullptr;
Handler h_;
// There's no way to put the handler anywhere else
// without exposing ourselves to race conditions
// and all sorts of ugliness.
// See:
// https://github.com/boostorg/beast/issues/215
Handler handler;
template<class DeducedHandler, class... Args>
P(DeducedHandler&& handler, Args&&... args);
};
P* p_;
void clear();
public:
/// The type of element this object stores
static_assert(std::is_nothrow_destructible<T>::value,
"T must be nothrow destructible");
/// The type of element stored
using element_type = T;
/// The type of handler this object stores
/// The type of handler stored
using handler_type = Handler;
/// Copy assignment (disallowed).
/// Default constructor (deleted).
handler_ptr() = delete;
/// Copy assignment (deleted).
handler_ptr& operator=(handler_ptr const&) = delete;
/** Destructs the owned object if no more @ref handler_ptr link to it.
/// Move assignment (deleted).
handler_ptr& operator=(handler_ptr &&) = delete;
If `*this` owns an object and it is the last @ref handler_ptr
owning it, the object is destroyed and the memory deallocated
using the associated deallocator.
/** Destructor
If `*this` owns an object the object is destroyed and
the memory deallocated using the allocator associated
with the handler.
*/
~handler_ptr();
@@ -99,54 +88,42 @@ public:
*/
handler_ptr(handler_ptr&& other);
/// Copy constructor
handler_ptr(handler_ptr const& other);
/// Copy constructor (deleted).
handler_ptr(handler_ptr const& other) = delete;
/** Construct a new @ref handler_ptr
/** Constructor
This creates a new @ref handler_ptr with an owned object
of type `T`. The allocator associated with the handler will
be used to allocate memory for the owned object. The constructor
for the owned object will be called thusly:
This creates a new container with an owned object of
type `T`. The allocator associated with the handler will
be used to allocate memory for the owned object. The
constructor for the owned object will be called with the
following equivalent signature:
@code
T(handler, std::forward<Args>(args)...)
T::T(Handler&, Args&&...)
@endcode
@param handler The handler to associate with the owned
object. The argument will be moved.
object. The argument will be moved if it is an xvalue.
@param args Optional arguments forwarded to
the owned object's constructor.
*/
template<class... Args>
handler_ptr(Handler&& handler, Args&&... args);
template<class DeducedHandler, class... Args>
explicit handler_ptr(DeducedHandler&& handler, Args&&... args);
/** Construct a new @ref handler_ptr
This creates a new @ref handler_ptr with an owned object
of type `T`. The allocator associated with the handler will
be used to allocate memory for the owned object. The constructor
for the owned object will be called thusly:
@code
T(handler, std::forward<Args>(args)...)
@endcode
@param handler The handler to associate with the owned
object. The argument will be copied.
@param args Optional arguments forwarded to
the owned object's constructor.
*/
template<class... Args>
handler_ptr(Handler const& handler, Args&&... args);
/// Returns a const reference to the handler
handler_type const&
handler() const
{
return h_;
}
/// Returns a reference to the handler
handler_type&
handler() const
handler()
{
return p_->handler;
return h_;
}
/** Returns a pointer to the owned object.
@@ -154,32 +131,30 @@ public:
T*
get() const
{
return p_->t;
return t_;
}
/// Return a reference to the owned object.
T&
operator*() const
{
return *p_->t;
return *t_;
}
/// Return a pointer to the owned object.
T*
operator->() const
{
return p_->t;
return t_;
}
/** Release ownership of the handler
Requires: `*this` owns an object
Before this function returns,
the owned object is destroyed, satisfying the
deallocation-before-invocation Asio guarantee. All
instances of @ref handler_ptr which refer to the
same owned object will be reset, including this instance.
Before this function returns, the owned object is
destroyed, satisfying the deallocation-before-invocation
Asio guarantee.
@return The released handler.
*/
@@ -191,9 +166,7 @@ public:
This function invokes the handler in the owned object
with a forwarded argument list. Before the invocation,
the owned object is destroyed, satisfying the
deallocation-before-invocation Asio guarantee. All
instances of @ref handler_ptr which refer to the
same owned object will be reset, including this instance.
deallocation-before-invocation Asio guarantee.
@note Care must be taken when the arguments are themselves
stored in the owned object. Such arguments must first be

128
include/boost/beast/core/impl/handler_ptr.ipp
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@@ -18,87 +18,63 @@ namespace boost {
namespace beast {
template<class T, class Handler>
template<class DeducedHandler, class... Args>
inline
handler_ptr<T, Handler>::P::
P(DeducedHandler&& h, Args&&... args)
: n(1)
, handler(std::forward<DeducedHandler>(h))
void
handler_ptr<T, Handler>::
clear()
{
typename std::allocator_traits<
boost::asio::associated_allocator_t<Handler>>::
template rebind_alloc<T> alloc{
boost::asio::get_associated_allocator(handler)};
t = std::allocator_traits<decltype(alloc)>::allocate(alloc, 1);
try
{
t = new(t) T{handler,
std::forward<Args>(args)...};
}
catch(...)
{
std::allocator_traits<
decltype(alloc)>::deallocate(alloc, t, 1);
throw;
}
typename beast::detail::allocator_traits<
boost::asio::associated_allocator_t<
Handler>>::template rebind_alloc<T> alloc{
boost::asio::get_associated_allocator(h_)};
beast::detail::allocator_traits<
decltype(alloc)>::destroy(alloc, t_);
beast::detail::allocator_traits<
decltype(alloc)>::deallocate(alloc, t_, 1);
t_ = nullptr;
}
template<class T, class Handler>
handler_ptr<T, Handler>::
~handler_ptr()
{
if(! p_)
return;
if(--p_->n)
return;
if(p_->t)
{
p_->t->~T();
typename std::allocator_traits<
boost::asio::associated_allocator_t<Handler>>::
template rebind_alloc<T> alloc{
boost::asio::get_associated_allocator(
p_->handler)};
std::allocator_traits<
decltype(alloc)>::deallocate(alloc, p_->t, 1);
}
delete p_;
if(t_)
clear();
}
template<class T, class Handler>
handler_ptr<T, Handler>::
handler_ptr(handler_ptr&& other)
: p_(other.p_)
: t_(other.t_)
, h_(std::move(other.h_))
{
other.p_ = nullptr;
other.t_ = nullptr;
}
template<class T, class Handler>
template<class DeducedHandler, class... Args>
handler_ptr<T, Handler>::
handler_ptr(handler_ptr const& other)
: p_(other.p_)
{
if(p_)
++p_->n;
}
template<class T, class Handler>
template<class... Args>
handler_ptr<T, Handler>::
handler_ptr(Handler&& handler, Args&&... args)
: p_(new P{std::move(handler),
std::forward<Args>(args)...})
handler_ptr(DeducedHandler&& handler, Args&&... args)
: t_([&]
{
BOOST_STATIC_ASSERT(! std::is_array<T>::value);
}
template<class T, class Handler>
template<class... Args>
handler_ptr<T, Handler>::
handler_ptr(Handler const& handler, Args&&... args)
: p_(new P{handler, std::forward<Args>(args)...})
typename beast::detail::allocator_traits<
boost::asio::associated_allocator_t<
Handler>>::template rebind_alloc<T> alloc{
boost::asio::get_associated_allocator(handler)};
using A = decltype(alloc);
auto const d =
[&alloc](T* p)
{
beast::detail::allocator_traits<A>::deallocate(alloc, p, 1);
};
std::unique_ptr<T, decltype(d)> p{
beast::detail::allocator_traits<A>::allocate(alloc, 1), d};
beast::detail::allocator_traits<A>::construct(
alloc, p.get(), handler, std::forward<Args>(args)...);
return p.release();
}())
, h_(std::forward<DeducedHandler>(handler))
{
BOOST_STATIC_ASSERT(! std::is_array<T>::value);
}
template<class T, class Handler>
@@ -107,18 +83,9 @@ handler_ptr<T, Handler>::
release_handler() ->
handler_type
{
BOOST_ASSERT(p_);
BOOST_ASSERT(p_->t);
p_->t->~T();
typename std::allocator_traits<
boost::asio::associated_allocator_t<Handler>>::
template rebind_alloc<T> alloc{
boost::asio::get_associated_allocator(
p_->handler)};
std::allocator_traits<
decltype(alloc)>::deallocate(alloc, p_->t, 1);
p_->t = nullptr;
return std::move(p_->handler);
BOOST_ASSERT(t_);
clear();
return std::move(h_);
}
template<class T, class Handler>
@@ -127,18 +94,9 @@ void
handler_ptr<T, Handler>::
invoke(Args&&... args)
{
BOOST_ASSERT(p_);
BOOST_ASSERT(p_->t);
p_->t->~T();
typename std::allocator_traits<
boost::asio::associated_allocator_t<Handler>>::
template rebind_alloc<T> alloc{
boost::asio::get_associated_allocator(
p_->handler)};
std::allocator_traits<
decltype(alloc)>::deallocate(alloc, p_->t, 1);
p_->t = nullptr;
p_->handler(std::forward<Args>(args)...);
BOOST_ASSERT(t_);
clear();
h_(std::forward<Args>(args)...);
}
} // beast

14
test/beast/core/handler_ptr.cpp
View File

@@ -12,6 +12,7 @@
#include <boost/beast/unit_test/suite.hpp>
#include <exception>
#include <memory>
#include <utility>
namespace boost {
@@ -22,8 +23,7 @@ class handler_ptr_test : public beast::unit_test::suite
public:
struct handler
{
handler() = default;
handler(handler const&) = default;
std::unique_ptr<int> ptr;
void
operator()(bool& b) const
@@ -54,12 +54,10 @@ public:
void
run() override
{
handler h;
handler_ptr<T, handler> p1{h};
handler_ptr<T, handler> p2{p1};
handler_ptr<T, handler> p1{handler{}};
try
{
handler_ptr<U, handler> p3{h};
handler_ptr<U, handler> p2{handler{}};
fail();
}
catch(std::exception const&)
@@ -70,9 +68,9 @@ public:
{
fail();
}
handler_ptr<T, handler> p4{std::move(h)};
handler_ptr<T, handler> p3{handler{}};
bool b = false;
p4.invoke(std::ref(b));
p3.invoke(std::ref(b));
BEAST_EXPECT(b);
}
};