96 lines
3.8 KiB
C++
96 lines
3.8 KiB
C++
// Copyright 2017 The Abseil Authors.
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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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// https://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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#ifndef ABSL_BASE_INTERNAL_SPINLOCK_WAIT_H_
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#define ABSL_BASE_INTERNAL_SPINLOCK_WAIT_H_
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// Operations to make atomic transitions on a word, and to allow
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// waiting for those transitions to become possible.
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#include <stdint.h>
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#include <atomic>
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#include "absl/base/internal/scheduling_mode.h"
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namespace absl {
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ABSL_NAMESPACE_BEGIN
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namespace base_internal {
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// SpinLockWait() waits until it can perform one of several transitions from
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// "from" to "to". It returns when it performs a transition where done==true.
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struct SpinLockWaitTransition {
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uint32_t from;
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uint32_t to;
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bool done;
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};
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// Wait until *w can transition from trans[i].from to trans[i].to for some i
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// satisfying 0<=i<n && trans[i].done, atomically make the transition,
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// then return the old value of *w. Make any other atomic transitions
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// where !trans[i].done, but continue waiting.
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//
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// Wakeups for threads blocked on SpinLockWait do not respect priorities.
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uint32_t SpinLockWait(std::atomic<uint32_t> *w, int n,
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const SpinLockWaitTransition trans[],
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SchedulingMode scheduling_mode);
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// If possible, wake some thread that has called SpinLockDelay(w, ...). If `all`
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// is true, wake all such threads. On some systems, this may be a no-op; on
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// those systems, threads calling SpinLockDelay() will always wake eventually
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// even if SpinLockWake() is never called.
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void SpinLockWake(std::atomic<uint32_t> *w, bool all);
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// Wait for an appropriate spin delay on iteration "loop" of a
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// spin loop on location *w, whose previously observed value was "value".
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// SpinLockDelay() may do nothing, may yield the CPU, may sleep a clock tick,
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// or may wait for a call to SpinLockWake(w).
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void SpinLockDelay(std::atomic<uint32_t> *w, uint32_t value, int loop,
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base_internal::SchedulingMode scheduling_mode);
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// Helper used by AbslInternalSpinLockDelay.
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// Returns a suggested delay in nanoseconds for iteration number "loop".
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int SpinLockSuggestedDelayNS(int loop);
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} // namespace base_internal
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ABSL_NAMESPACE_END
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} // namespace absl
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// In some build configurations we pass --detect-odr-violations to the
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// gold linker. This causes it to flag weak symbol overrides as ODR
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// violations. Because ODR only applies to C++ and not C,
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// --detect-odr-violations ignores symbols not mangled with C++ names.
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// By changing our extension points to be extern "C", we dodge this
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// check.
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extern "C" {
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void ABSL_INTERNAL_C_SYMBOL(AbslInternalSpinLockWake)(std::atomic<uint32_t> *w,
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bool all);
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void ABSL_INTERNAL_C_SYMBOL(AbslInternalSpinLockDelay)(
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std::atomic<uint32_t> *w, uint32_t value, int loop,
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absl::base_internal::SchedulingMode scheduling_mode);
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}
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inline void absl::base_internal::SpinLockWake(std::atomic<uint32_t> *w,
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bool all) {
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ABSL_INTERNAL_C_SYMBOL(AbslInternalSpinLockWake)(w, all);
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}
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inline void absl::base_internal::SpinLockDelay(
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std::atomic<uint32_t> *w, uint32_t value, int loop,
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absl::base_internal::SchedulingMode scheduling_mode) {
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ABSL_INTERNAL_C_SYMBOL(AbslInternalSpinLockDelay)
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(w, value, loop, scheduling_mode);
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}
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#endif // ABSL_BASE_INTERNAL_SPINLOCK_WAIT_H_
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