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[orbis-kernel] Hopefully fix shared_cv

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This commit is contained in:
Ivan Chikish 2023-07-07 13:49:59 +03:00
parent 99f520491c
commit 3d78443496
4 changed files with 62 additions and 29 deletions
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40
orbis-kernel/src/utils/SharedCV.cpp
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@ -19,19 +19,29 @@ void shared_cv::impl_wait(shared_mutex &mutex, unsigned _old,
// Cleanup
const auto old = atomic_fetch_op(m_value, [](unsigned &value) {
// Remove waiter (c_waiter_mask)
value -= 1;
// Remove waiter if no signals
if (!(value & ~c_waiter_mask))
value -= 1;
// Try to remove signal
if (value & c_signal_mask)
value -= c_signal_mask & (0 - c_signal_mask);
value -= c_signal_one;
if (value | c_locked_mask)
value -= c_locked_mask;
});
// Lock is already acquired
if (old & c_signal_mask) {
if (old & c_locked_mask) {
return;
}
// Wait directly (waiter has been added)
if (old & c_signal_mask) {
mutex.impl_wait();
return;
}
// Possibly spurious wakeup
mutex.lock();
}
@ -45,34 +55,38 @@ void shared_cv::impl_wake(shared_mutex &mutex, int _count) noexcept {
return;
// Try to lock the mutex
unsigned _m_locks = mutex.lock_forced();
const bool locked = mutex.lock_forced(_count);
const int max_sig = atomic_op(m_value, [&](unsigned &value) {
// Verify the number of waiters
int max_sig = std::min<int>(_count, value & c_waiter_mask);
// Add lock signal (mutex was immediately locked)
if (_m_locks == 0)
value += c_signal_mask & (0 - c_signal_mask);
if (locked && max_sig)
value |= c_locked_mask;
// Add normal signals
value += c_signal_one * max_sig;
// Remove waiters
value -= max_sig;
_old = value;
return max_sig;
});
if (max_sig < _count) {
// Fixup mutex
mutex.lock_forced(max_sig - _count);
_count = max_sig;
}
if (_count) {
// Wake up one thread + requeue remaining waiters
unsigned do_wake = _m_locks == 0;
if (auto r = syscall(SYS_futex, &m_value, FUTEX_CMP_REQUEUE, do_wake,
&mutex, _count - do_wake, _old);
if (auto r = syscall(SYS_futex, &m_value, FUTEX_CMP_REQUEUE, +locked,
&mutex, _count - +locked, _old);
r < _count) {
// Keep awaking waiters
return impl_wake(mutex, is_one ? 1 : INT_MAX);
} else if (mutex.is_free()) {
// Avoid deadlock (TODO: proper fix?)
syscall(SYS_futex, &mutex, FUTEX_WAKE, 1, nullptr, 0, 0);
}
}
}