[committed] libstdc++: Simplify std::shared_ptr construction from std::weak_ptr
Jonathan Wakely
jwakely@redhat.com
Wed Oct 21 20:14:00 GMT 2020
The _M_add_ref_lock() and _M_add_ref_lock_nothrow() members of
_Sp_counted_base are very similar, except that the former throws an
exception when the use count is zero and the latter returns false. The
former (and its callers) can be implemented in terms of the latter.
This results in a small reduction in code size, because throwing an
exception now only happens in one place.
libstdc++-v3/ChangeLog:
* include/bits/shared_ptr.h (shared_ptr(const weak_ptr&, nothrow_t)):
Add noexcept.
* include/bits/shared_ptr_base.h (_Sp_counted_base::_M_add_ref_lock):
Remove specializations and just call _M_add_ref_lock_nothrow.
(__shared_count, __shared_ptr): Use nullptr for null pointer
constants.
(__shared_count(const __weak_count&)): Use _M_add_ref_lock_nothrow
instead of _M_add_ref_lock.
(__shared_count(const __weak_count&, nothrow_t)): Add noexcept.
(__shared_ptr::operator bool()): Add noexcept.
(__shared_ptr(const __weak_ptr&, nothrow_t)): Add noexcept.
Tested powerpc64le-linux. Committed to trunk.
-------------- next part --------------
commit 945151b7f14c5d105abd8117f208ae9e3db91fb4
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Wed Oct 21 21:13:41 2020
libstdc++: Simplify std::shared_ptr construction from std::weak_ptr
The _M_add_ref_lock() and _M_add_ref_lock_nothrow() members of
_Sp_counted_base are very similar, except that the former throws an
exception when the use count is zero and the latter returns false. The
former (and its callers) can be implemented in terms of the latter.
This results in a small reduction in code size, because throwing an
exception now only happens in one place.
libstdc++-v3/ChangeLog:
* include/bits/shared_ptr.h (shared_ptr(const weak_ptr&, nothrow_t)):
Add noexcept.
* include/bits/shared_ptr_base.h (_Sp_counted_base::_M_add_ref_lock):
Remove specializations and just call _M_add_ref_lock_nothrow.
(__shared_count, __shared_ptr): Use nullptr for null pointer
constants.
(__shared_count(const __weak_count&)): Use _M_add_ref_lock_nothrow
instead of _M_add_ref_lock.
(__shared_count(const __weak_count&, nothrow_t)): Add noexcept.
(__shared_ptr::operator bool()): Add noexcept.
(__shared_ptr(const __weak_ptr&, nothrow_t)): Add noexcept.
diff --git a/libstdc++-v3/include/bits/shared_ptr.h b/libstdc++-v3/include/bits/shared_ptr.h
index 0c393e23132..0bfb525aae7 100644
--- a/libstdc++-v3/include/bits/shared_ptr.h
+++ b/libstdc++-v3/include/bits/shared_ptr.h
@@ -413,7 +413,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
allocate_shared(const _Alloc& __a, _Args&&... __args);
// This constructor is non-standard, it is used by weak_ptr::lock().
- shared_ptr(const weak_ptr<_Tp>& __r, std::nothrow_t)
+ shared_ptr(const weak_ptr<_Tp>& __r, std::nothrow_t) noexcept
: __shared_ptr<_Tp>(__r, std::nothrow) { }
friend class weak_ptr<_Tp>;
diff --git a/libstdc++-v3/include/bits/shared_ptr_base.h b/libstdc++-v3/include/bits/shared_ptr_base.h
index ff578e66117..ca37f2bebd6 100644
--- a/libstdc++-v3/include/bits/shared_ptr_base.h
+++ b/libstdc++-v3/include/bits/shared_ptr_base.h
@@ -142,10 +142,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
{ __gnu_cxx::__atomic_add_dispatch(&_M_use_count, 1); }
void
- _M_add_ref_lock();
+ _M_add_ref_lock()
+ {
+ if (!_M_add_ref_lock_nothrow())
+ __throw_bad_weak_ptr();
+ }
bool
- _M_add_ref_lock_nothrow();
+ _M_add_ref_lock_nothrow() noexcept;
void
_M_release() noexcept
@@ -214,48 +218,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
_Atomic_word _M_weak_count; // #weak + (#shared != 0)
};
- template<>
- inline void
- _Sp_counted_base<_S_single>::
- _M_add_ref_lock()
- {
- if (_M_use_count == 0)
- __throw_bad_weak_ptr();
- ++_M_use_count;
- }
-
- template<>
- inline void
- _Sp_counted_base<_S_mutex>::
- _M_add_ref_lock()
- {
- __gnu_cxx::__scoped_lock sentry(*this);
- if (__gnu_cxx::__exchange_and_add_dispatch(&_M_use_count, 1) == 0)
- {
- _M_use_count = 0;
- __throw_bad_weak_ptr();
- }
- }
-
- template<>
- inline void
- _Sp_counted_base<_S_atomic>::
- _M_add_ref_lock()
- {
- // Perform lock-free add-if-not-zero operation.
- _Atomic_word __count = _M_get_use_count();
- do
- {
- if (__count == 0)
- __throw_bad_weak_ptr();
- // Replace the current counter value with the old value + 1, as
- // long as it's not changed meanwhile.
- }
- while (!__atomic_compare_exchange_n(&_M_use_count, &__count, __count + 1,
- true, __ATOMIC_ACQ_REL,
- __ATOMIC_RELAXED));
- }
-
template<>
inline bool
_Sp_counted_base<_S_single>::
@@ -736,7 +698,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
__shared_count(const __shared_count& __r) noexcept
: _M_pi(__r._M_pi)
{
- if (_M_pi != 0)
+ if (_M_pi != nullptr)
_M_pi->_M_add_ref_copy();
}
@@ -746,9 +708,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
_Sp_counted_base<_Lp>* __tmp = __r._M_pi;
if (__tmp != _M_pi)
{
- if (__tmp != 0)
+ if (__tmp != nullptr)
__tmp->_M_add_ref_copy();
- if (_M_pi != 0)
+ if (_M_pi != nullptr)
_M_pi->_M_release();
_M_pi = __tmp;
}
@@ -765,7 +727,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
long
_M_get_use_count() const noexcept
- { return _M_pi != 0 ? _M_pi->_M_get_use_count() : 0; }
+ { return _M_pi ? _M_pi->_M_get_use_count() : 0; }
bool
_M_unique() const noexcept
@@ -897,9 +859,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
__shared_count<_Lp>::__shared_count(const __weak_count<_Lp>& __r)
: _M_pi(__r._M_pi)
{
- if (_M_pi != nullptr)
- _M_pi->_M_add_ref_lock();
- else
+ if (_M_pi == nullptr || !_M_pi->_M_add_ref_lock_nothrow())
__throw_bad_weak_ptr();
}
@@ -907,12 +867,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
template<_Lock_policy _Lp>
inline
__shared_count<_Lp>::
- __shared_count(const __weak_count<_Lp>& __r, std::nothrow_t)
+ __shared_count(const __weak_count<_Lp>& __r, std::nothrow_t) noexcept
: _M_pi(__r._M_pi)
{
- if (_M_pi != nullptr)
- if (!_M_pi->_M_add_ref_lock_nothrow())
- _M_pi = nullptr;
+ if (_M_pi && !_M_pi->_M_add_ref_lock_nothrow())
+ _M_pi = nullptr;
}
#define __cpp_lib_shared_ptr_arrays 201611L
@@ -1175,7 +1134,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
: _M_ptr(__p), _M_refcount()
{
_M_refcount._M_swap(__r._M_refcount);
- __r._M_ptr = 0;
+ __r._M_ptr = nullptr;
}
__shared_ptr(const __shared_ptr&) noexcept = default;
@@ -1191,7 +1150,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
: _M_ptr(__r._M_ptr), _M_refcount()
{
_M_refcount._M_swap(__r._M_refcount);
- __r._M_ptr = 0;
+ __r._M_ptr = nullptr;
}
template<typename _Yp, typename = _Compatible<_Yp>>
@@ -1199,7 +1158,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
: _M_ptr(__r._M_ptr), _M_refcount()
{
_M_refcount._M_swap(__r._M_refcount);
- __r._M_ptr = 0;
+ __r._M_ptr = nullptr;
}
template<typename _Yp, typename = _Compatible<_Yp>>
@@ -1305,7 +1264,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
reset(_Yp* __p) // _Yp must be complete.
{
// Catch self-reset errors.
- __glibcxx_assert(__p == 0 || __p != _M_ptr);
+ __glibcxx_assert(__p == nullptr || __p != _M_ptr);
__shared_ptr(__p).swap(*this);
}
@@ -1325,8 +1284,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
{ return _M_ptr; }
/// Return true if the stored pointer is not null.
- explicit operator bool() const // never throws
- { return _M_ptr == 0 ? false : true; }
+ explicit operator bool() const noexcept
+ { return _M_ptr != nullptr; }
/// Return true if use_count() == 1.
bool
@@ -1378,7 +1337,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
// This constructor is used by __weak_ptr::lock() and
// shared_ptr::shared_ptr(const weak_ptr&, std::nothrow_t).
- __shared_ptr(const __weak_ptr<_Tp, _Lp>& __r, std::nothrow_t)
+ __shared_ptr(const __weak_ptr<_Tp, _Lp>& __r, std::nothrow_t) noexcept
: _M_refcount(__r._M_refcount, std::nothrow)
{
_M_ptr = _M_refcount._M_get_use_count() ? __r._M_ptr : nullptr;
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