77 lines
2.1 KiB
C
77 lines
2.1 KiB
C
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/*
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* Copyright (C) 2019 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#ifndef TNT_UTILS_SPINLOCK_H
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#define TNT_UTILS_SPINLOCK_H
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#include <utils/compiler.h>
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#include <atomic>
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#include <type_traits>
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#include <assert.h>
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#include <stddef.h>
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namespace utils {
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class SpinLock {
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std::atomic_flag mLock = ATOMIC_FLAG_INIT;
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public:
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void lock() noexcept {
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UTILS_PREFETCHW(&mLock);
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#ifdef __ARM_ACLE
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// we signal an event on this CPU, so that the first yield() will be a no-op,
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// and falls through the test_and_set(). This is more efficient than a while { }
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// construct.
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UTILS_SIGNAL_EVENT();
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do {
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yield();
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} while (mLock.test_and_set(std::memory_order_acquire));
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#else
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goto start;
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do {
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yield();
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start: ;
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} while (mLock.test_and_set(std::memory_order_acquire));
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#endif
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}
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void unlock() noexcept {
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mLock.clear(std::memory_order_release);
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#ifdef __ARM_ARCH_7A__
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// on ARMv7a SEL is needed
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UTILS_SIGNAL_EVENT();
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// as well as a memory barrier is needed
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__dsb(0xA); // ISHST = 0xA (b1010)
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#else
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// on ARMv8 we could avoid the call to SE, but we'd need to write the
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// test_and_set() above by hand, so the WFE only happens without a STRX first.
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UTILS_BROADCAST_EVENT();
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#endif
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}
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private:
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inline void yield() noexcept {
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// on x86 call pause instruction, on ARM call WFE
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UTILS_WAIT_FOR_EVENT();
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}
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};
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} // namespace utils
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#endif //TNT_UTILS_SPINLOCK_H
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