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5d180d1f99
(...and ASSERT_NOT_REACHED => VERIFY_NOT_REACHED) Since all of these checks are done in release builds as well, let's rename them to VERIFY to prevent confusion, as everyone is used to assertions being compiled out in release. We can introduce a new ASSERT macro that is specifically for debug checks, but I'm doing this wholesale conversion first since we've accumulated thousands of these already, and it's not immediately obvious which ones are suitable for ASSERT.
107 lines
4.4 KiB
C++
107 lines
4.4 KiB
C++
/*
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* Copyright (c) 2020, Sergey Bugaev <bugaevc@serenityos.org>
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are met:
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*
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* 1. Redistributions of source code must retain the above copyright notice, this
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* list of conditions and the following disclaimer.
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*
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* 2. Redistributions in binary form must reproduce the above copyright notice,
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* this list of conditions and the following disclaimer in the documentation
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* and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#include <AK/Assertions.h>
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#include <AK/Atomic.h>
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#include <AK/Types.h>
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#include <pthread.h>
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#include <serenity.h>
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enum State : i32 {
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INITIAL = PTHREAD_ONCE_INIT,
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DONE,
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PERFORMING_NO_WAITERS,
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PERFORMING_WITH_WAITERS,
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};
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int pthread_once(pthread_once_t* self, void (*callback)(void))
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{
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auto& state = reinterpret_cast<Atomic<State>&>(*self);
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// See what the current state is, and at the same time grab the lock if we
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// got here first. We need acquire ordering here because if we see
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// State::DONE, everything we do after that should "happen after" everything
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// the other thread has done before writing the State::DONE.
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State state2 = State::INITIAL;
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bool have_exchanged = state.compare_exchange_strong(
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state2, State::PERFORMING_NO_WAITERS, AK::memory_order_acquire);
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if (have_exchanged) {
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// We observed State::INITIAL and we've changed it to
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// State::PERFORMING_NO_WAITERS, so it's us who should perform the
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// operation.
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callback();
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// Now, record that we're done.
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state2 = state.exchange(State::DONE, AK::memory_order_release);
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switch (state2) {
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case State::INITIAL:
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case State::DONE:
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VERIFY_NOT_REACHED();
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case State::PERFORMING_NO_WAITERS:
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// The fast path: there's no contention, so we don't have to wake
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// anyone.
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break;
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case State::PERFORMING_WITH_WAITERS:
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futex(self, FUTEX_WAKE, INT_MAX, nullptr, nullptr, 0);
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break;
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}
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return 0;
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}
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// We did not get there first. Let's see if we have to wait.
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// state2 contains the observed state.
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while (true) {
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switch (state2) {
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case State::INITIAL:
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VERIFY_NOT_REACHED();
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case State::DONE:
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// Awesome, nothing to do then.
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return 0;
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case State::PERFORMING_NO_WAITERS:
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// We're going to wait for it, but we have to record that we're
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// waiting and the other thread should wake us up. We need acquire
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// ordering here for the same reason as above.
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have_exchanged = state.compare_exchange_strong(
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state2, State::PERFORMING_WITH_WAITERS, AK::memory_order_acquire);
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if (!have_exchanged) {
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// Something has changed already, reevaluate without waiting.
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continue;
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}
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state2 = State::PERFORMING_WITH_WAITERS;
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[[fallthrough]];
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case State::PERFORMING_WITH_WAITERS:
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// Let's wait for it.
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futex(self, FUTEX_WAIT, state2, nullptr, nullptr, 0);
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// We have been woken up, but that might have been due to a signal
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// or something, so we have to reevaluate. We need acquire ordering
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// here for the same reason as above. Hopefully we'll just see
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// State::DONE this time, but who knows.
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state2 = state.load(AK::memory_order_acquire);
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continue;
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}
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}
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}
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