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libstdc++: Use helper type for checking thread ID

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This encapsulates the storing and checking of the thread ID into a class
type, so that the macro _GLIBCXX_HAS_GTHREADS is only checked in one
place. The code doing the checks just calls member functions of the new
type, without caring whether that really does any work or not.

libstdc++-v3/ChangeLog:

	* include/std/stop_token (_Stop_state_t::_M_requester): Define
	new struct with members to store and check the thread ID.
	(_Stop_state_t::_M_request_stop()): Use _M_requester._M_set().
	(_Stop_state_t::_M_remove_callback(_Stop_cb*)): Use
	_M_requester._M_is_current_thread().
This commit is contained in:
Jonathan Wakely 2020-11-11 09:28:50 +00:00
parent ca813880dc
commit 43f9e5aff0
1 changed files with 13 additions and 7 deletions
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20
libstdc++-v3/include/std/stop_token
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@ -162,9 +162,18 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
std::atomic<value_type> _M_owners{1};
std::atomic<value_type> _M_value{_S_ssrc_counter_inc};
_Stop_cb* _M_head = nullptr;
struct
{
#ifdef _GLIBCXX_HAS_GTHREADS
__gthread_t _M_requester;
__gthread_t _M_id;
void _M_set() { _M_id = __gthread_self(); }
bool _M_is_current_thread() const
{ return __gthread_equal(_M_id, __gthread_self()); }
#else
void _M_set() { }
constexpr bool _M_is_current_thread() const { return true; }
#endif
} _M_requester;
_Stop_state_t() = default;
@ -237,9 +246,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
}
while (!_M_try_lock_and_stop(__old));
#ifdef _GLIBCXX_HAS_GTHREADS
_M_requester = __gthread_self();
#endif
_M_requester._M_set();
while (_M_head)
{
@ -343,18 +350,17 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
// Callback is not in the list, so must have been removed by a call to
// _M_request_stop.
#ifdef _GLIBCXX_HAS_GTHREADS
// Despite appearances there is no data race on _M_requester. The only
// write to it happens before the callback is removed from the list,
// and removing it from the list happens before this read.
if (!__gthread_equal(_M_requester, __gthread_self()))
if (!_M_requester._M_is_current_thread())
{
// Synchronize with completion of callback.
__cb->_M_done.acquire();
// Safe for ~stop_callback to destroy *__cb now.
return;
}
#endif
if (__cb->_M_destroyed)
*__cb->_M_destroyed = true;
}