// 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_