On 11/05/20 08:43 -0700, Thomas Rodgers wrote:
Jonathan Wakely writes:
On 09/05/20 17:01 -0700, Thomas Rodgers via Libstdc++ wrote:
<snip>
+#include <iostream>
<iostream> shouldn't be here (it adds runtime cost, as well as
compile-time).
Oversight, not removed after debugging it.
<snip>
Can't this just be __old instead of *std::__addressof(__old) ?
Copypasta from elsewhere in the same class, I believe. I'll change it.
<snip>
Isn't alignas(64) already implied by the first data member?
Yes
+ {
+ int32_t alignas(64) _M_ver = 0;
+ int32_t alignas(64) _M_wait = 0;
+
+ // TODO make this used only where we don't have futexes
Don't we always need these even with futexes, for the types that don't
use a futex?
If we have futexes, we can use the address of _M_ver to wake
_M_do_wait() instead of using a condvar for types that don't use a
futex directly.
+ using __lock_t = std::unique_lock<std::mutex>;
+ mutable __lock_t::mutex_type _M_mtx;
+
+#ifdef __GTHREAD_COND_INIT
+ mutable __gthread_cond_t _M_cv = __GTHREAD_COND_INIT;
+ __waiters() noexcept = default;
If we moved std::condition_variable into its own header (or
<bits/std_mutex.h>, could we reuse that here instead of using
__gthread_cond_t directly?
Yes, I started down that route initially, I could revisit it in a future
patch as part of also making it's use only necessary when the platform
doesn't support futex.
+ __atomic_notify(const _Tp* __addr, bool __all) noexcept
+ {
+ using namespace __detail;
+ auto& __w = __waiters::_S_for((void*)__addr);
+ if (!__w._M_waiting())
When __platform_wait_uses_type<_Tp> is true, will __w._M_waiting()
ever be true? Won't this always return before notifying?
Is there meant to be a __waiter constructed here?
__waiter (an RAII type) is constructed in the __atomic_wait(), that
increments the _M_wait count on the way into the wait, and decrements it
on the way out, __atomic_notify checks to see if that count is non-zero
before invoking the platform/semaphore notify because it is cheaper
to do the atomic load than it is to make the syscall() when there are no
waiters.
Doh, yes of course.
