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| author | Jonathan Wakely <jwakely@redhat.com> | 2022-01-16 20:47:09 +0000 |
|---|---|---|
| committer | Jonathan Wakely <jwakely@redhat.com> | 2022-01-17 00:06:28 +0000 |
| commit | 2ac0649d7bf3eacbf92add1ec2b54045c401a4c2 (patch) | |
| tree | c858f264e67f6e875b9a122ebe865ed95bc6f154 /libstdc++-v3/include/std/version | |
| parent | 86e3b476d5defaa79c94d40b76cbeec21cd02e5f (diff) | |
| download | gcc-2ac0649d7bf3eacbf92add1ec2b54045c401a4c2.zip gcc-2ac0649d7bf3eacbf92add1ec2b54045c401a4c2.tar.gz gcc-2ac0649d7bf3eacbf92add1ec2b54045c401a4c2.tar.bz2 | |
libstdc++: Implement C++20 atomic<shared_ptr> and atomic<weak_ptr>
This adds another piece of C++20, the std::atomic specializations for
std::shared_ptr and std::weak_ptr.
The new _Sp_atomic type mimics the structure of shared_ptr<T> and
weak_ptr<T>, holding a T* pointer (the one returned by get() on a
shared_ptr/weak ptr) and a _Sp_counted_base<>* pointer to the
ref-counted control block. For _Sp_atomic the low bit of the control
block pointer is used as a lock bit, to ensure only one thread will
access the object at a time. The pointer is actually stored as a
uintptr_t to avoid accidental dereferences of the pointer when unlocked
(which would be a race) or when locked (which would dereference the
wrong pointer value due to the low bit being set). To get a raw pointer
to the control block, the lock must be acquired. Converting between a
_Sp_atomic and a shared_ptr or weak_ptr requires manually adjusting the
T* and _Sp_counted_base<>* members of the shared/weak ptr, instead of
going through the public API. This must be done carefully to ensure that
any change in the number of owners is reflected in a ref-count update.
Co-authored-by: Thomas Rodgers <trodgers@redhat.com>
Signed-off-by: Thomas Rodgers <trodgers@redhat.com>
libstdc++-v3/ChangeLog:
* include/bits/shared_ptr_atomic.h (__cpp_lib_atomic_shared_ptr):
New macro.
(_Sp_atomic): New class template.
(atomic<shared_ptr<T>>, atomic<weak_ptr<T>>): New partial
specializations.
* include/bits/shared_ptr_base.h (__shared_count, __weak_count)
(__shared_ptr, __weak_ptr): Declare _Sp_atomic as a friend.
* include/std/version (__cpp_lib_atomic_shared_ptr): New macro.
* testsuite/20_util/shared_ptr/atomic/atomic_shared_ptr.cc: New
test.
* testsuite/20_util/weak_ptr/atomic_weak_ptr.cc: New test.
Diffstat (limited to 'libstdc++-v3/include/std/version')
| -rw-r--r-- | libstdc++-v3/include/std/version | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/libstdc++-v3/include/std/version b/libstdc++-v3/include/std/version index a8b792e..7bd32f6 100644 --- a/libstdc++-v3/include/std/version +++ b/libstdc++-v3/include/std/version @@ -215,6 +215,7 @@ #if _GLIBCXX_HOSTED #define __cpp_lib_array_constexpr 201811L #define __cpp_lib_assume_aligned 201811L +#define __cpp_lib_atomic_shared_ptr 201711L #if defined _GLIBCXX_HAS_GTHREADS || defined _GLIBCXX_HAVE_LINUX_FUTEX # define __cpp_lib_atomic_wait 201907L # if __cpp_aligned_new |