THUAI6/CAPI/cpp/grpc/include/absl/base/internal/spinlock_wait.h

// Copyright 2017 The Abseil Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#ifndef ABSL_BASE_INTERNAL_SPINLOCK_WAIT_H_
#define ABSL_BASE_INTERNAL_SPINLOCK_WAIT_H_

// Operations to make atomic transitions on a word, and to allow
// waiting for those transitions to become possible.

#include <stdint.h>
#include <atomic>

#include "absl/base/internal/scheduling_mode.h"

namespace absl
{
    ABSL_NAMESPACE_BEGIN
    namespace base_internal
    {

        // SpinLockWait() waits until it can perform one of several transitions from
        // "from" to "to".  It returns when it performs a transition where done==true.
        struct SpinLockWaitTransition
        {
            uint32_t from;
            uint32_t to;
            bool done;
        };

        // Wait until *w can transition from trans[i].from to trans[i].to for some i
        // satisfying 0<=i<n && trans[i].done, atomically make the transition,
        // then return the old value of *w.   Make any other atomic transitions
        // where !trans[i].done, but continue waiting.
        //
        // Wakeups for threads blocked on SpinLockWait do not respect priorities.
        uint32_t SpinLockWait(std::atomic<uint32_t>* w, int n, const SpinLockWaitTransition trans[], SchedulingMode scheduling_mode);

        // If possible, wake some thread that has called SpinLockDelay(w, ...). If `all`
        // is true, wake all such threads. On some systems, this may be a no-op; on
        // those systems, threads calling SpinLockDelay() will always wake eventually
        // even if SpinLockWake() is never called.
        void SpinLockWake(std::atomic<uint32_t>* w, bool all);

        // Wait for an appropriate spin delay on iteration "loop" of a
        // spin loop on location *w, whose previously observed value was "value".
        // SpinLockDelay() may do nothing, may yield the CPU, may sleep a clock tick,
        // or may wait for a call to SpinLockWake(w).
        void SpinLockDelay(std::atomic<uint32_t>* w, uint32_t value, int loop, base_internal::SchedulingMode scheduling_mode);

        // Helper used by AbslInternalSpinLockDelay.
        // Returns a suggested delay in nanoseconds for iteration number "loop".
        int SpinLockSuggestedDelayNS(int loop);

    }  // namespace base_internal
    ABSL_NAMESPACE_END
}  // namespace absl

// In some build configurations we pass --detect-odr-violations to the
// gold linker.  This causes it to flag weak symbol overrides as ODR
// violations.  Because ODR only applies to C++ and not C,
// --detect-odr-violations ignores symbols not mangled with C++ names.
// By changing our extension points to be extern "C", we dodge this
// check.
extern "C"
{
    void ABSL_INTERNAL_C_SYMBOL(AbslInternalSpinLockWake)(std::atomic<uint32_t>* w, bool all);
    void ABSL_INTERNAL_C_SYMBOL(AbslInternalSpinLockDelay)(
        std::atomic<uint32_t>* w, uint32_t value, int loop, absl::base_internal::SchedulingMode scheduling_mode
    );
}

inline void absl::base_internal::SpinLockWake(std::atomic<uint32_t>* w, bool all)
{
    ABSL_INTERNAL_C_SYMBOL(AbslInternalSpinLockWake)
    (w, all);
}

inline void absl::base_internal::SpinLockDelay(
    std::atomic<uint32_t>* w, uint32_t value, int loop, absl::base_internal::SchedulingMode scheduling_mode
)
{
    ABSL_INTERNAL_C_SYMBOL(AbslInternalSpinLockDelay)
    (w, value, loop, scheduling_mode);
}

#endif  // ABSL_BASE_INTERNAL_SPINLOCK_WAIT_H_