absl/base/internal/tracing.h

// Copyright 2024 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_TRACING_H_
#define ABSL_BASE_INTERNAL_TRACING_H_

#include "absl/base/config.h"

namespace absl {
ABSL_NAMESPACE_BEGIN
namespace base_internal {

// Well known Abseil object types that have causality.
enum class ObjectKind { kUnknown, kBlockingCounter, kNotification };

// `TraceWait` and `TraceContinue` record the start and end of a potentially
// blocking wait operation on `object`. `object` typically represents a higher
// level synchronization object such as `absl::Notification`.
void TraceWait(const void* object, ObjectKind kind);
void TraceContinue(const void* object, ObjectKind kind);

// `TraceSignal` records a signal on `object`.
void TraceSignal(const void* object, ObjectKind kind);

// `TraceObserved` records the non-blocking observation of a signaled object.
void TraceObserved(const void* object, ObjectKind kind);

// ---------------------------------------------------------------------------
// Weak implementation detail:
//
// We define the weak API as extern "C": 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(AbslInternalTraceWait)(const void* object,
                                                     ObjectKind kind);
  void ABSL_INTERNAL_C_SYMBOL(AbslInternalTraceContinue)(const void* object,
                                                         ObjectKind kind);
  void ABSL_INTERNAL_C_SYMBOL(AbslInternalTraceSignal)(const void* object,
                                                       ObjectKind kind);
  void ABSL_INTERNAL_C_SYMBOL(AbslInternalTraceObserved)(const void* object,
                                                         ObjectKind kind);

}  // extern "C"

inline void TraceWait(const void* object, ObjectKind kind) {
  ABSL_INTERNAL_C_SYMBOL(AbslInternalTraceWait)(object, kind);
}

inline void TraceContinue(const void* object, ObjectKind kind) {
  ABSL_INTERNAL_C_SYMBOL(AbslInternalTraceContinue)(object, kind);
}

inline void TraceSignal(const void* object, ObjectKind kind) {
  ABSL_INTERNAL_C_SYMBOL(AbslInternalTraceSignal)(object, kind);
}

inline void TraceObserved(const void* object, ObjectKind kind) {
  ABSL_INTERNAL_C_SYMBOL(AbslInternalTraceObserved)(object, kind);
}

}  // namespace base_internal
ABSL_NAMESPACE_END
}  // namespace absl

#endif  // ABSL_BASE_INTERNAL_TRACING_H_