chromium/third_party/abseil-cpp/absl/log/internal/conditions.h

// Copyright 2022 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.
//
// -----------------------------------------------------------------------------
// File: log/internal/conditions.h
// -----------------------------------------------------------------------------
//
// This file contains implementation of conditional log statements, like LOG_IF
// including all the ABSL_LOG_INTERNAL_..._CONDITION_... macros and
// various condition classes like LogEveryNState.

#ifndef ABSL_LOG_INTERNAL_CONDITIONS_H_
#define ABSL_LOG_INTERNAL_CONDITIONS_H_

#if defined(_WIN32) || defined(__hexagon__)
#include <cstdlib>
#else
#include <unistd.h>
#endif
#include <stdlib.h>

#include <atomic>
#include <cstdint>

#include "absl/base/attributes.h"
#include "absl/base/config.h"
#include "absl/log/internal/voidify.h"

// `ABSL_LOG_INTERNAL_CONDITION` prefixes another macro that expands to a
// temporary `LogMessage` instantiation followed by zero or more streamed
// expressions.  This definition is tricky to read correctly.  It evaluates to
// either
//
//   (void)0;
//
// or
//
//   ::absl::log_internal::Voidify() &&
//       ::absl::log_internal::LogMessage(...) << "the user's message";
//
// If the condition is evaluable at compile time, as is often the case, it
// compiles away to just one side or the other.
//
// Although this is not used anywhere a statement (e.g. `if`) could not go,
// the ternary expression does a better job avoiding spurious diagnostics
// (dangling else, missing switch case) and preserving noreturn semantics (e.g.
// on `LOG(FATAL)`) without requiring braces.
//
// The `switch` ensures that this expansion is the beginning of a statement (as
// opposed to an expression) and prevents shenanigans like
// `AFunction(LOG(INFO))` and `decltype(LOG(INFO))`.  The apparently-redundant
// `default` case makes the condition more amenable to Clang dataflow analysis.
#define ABSL_LOG_INTERNAL_STATELESS_CONDITION(condition) …

// `ABSL_LOG_INTERNAL_STATEFUL_CONDITION` applies a condition like
// `ABSL_LOG_INTERNAL_STATELESS_CONDITION` but adds to that a series of variable
// declarations, including a local static object which stores the state needed
// to implement the stateful macros like `LOG_EVERY_N`.
//
// `for`-loops are used to declare scoped variables without braces (to permit
// streaming into the macro's expansion) and without the dangling-`else`
// problems/diagnostics that come with `if`.
//
// Two more variables are declared in separate `for`-loops:
//
// * `COUNTER` implements a streamable token whose value when streamed is the
//   number of times execution has passed through the macro.
// * A boolean flag is used to prevent any of the `for`-loops from ever actually
//   looping.
#define ABSL_LOG_INTERNAL_STATEFUL_CONDITION(condition) …
#define ABSL_LOG_INTERNAL_STATEFUL_CONDITION_IMPL(kind, ...) …

// `ABSL_LOG_INTERNAL_CONDITION_*` serve to combine any conditions from the
// macro (e.g. `LOG_IF` or `VLOG`) with inherent conditions (e.g.
// `ABSL_MIN_LOG_LEVEL`) into a single boolean expression.  We could chain
// ternary operators instead, however some versions of Clang sometimes issue
// spurious diagnostics after such expressions due to a control flow analysis
// bug.
#ifdef ABSL_MIN_LOG_LEVEL
#define ABSL_LOG_INTERNAL_CONDITION_INFO …
#define ABSL_LOG_INTERNAL_CONDITION_WARNING …
#define ABSL_LOG_INTERNAL_CONDITION_ERROR …
// NOTE: Use ternary operators instead of short-circuiting to mitigate
// https://bugs.llvm.org/show_bug.cgi?id=51928.
#define ABSL_LOG_INTERNAL_CONDITION_FATAL …
// NOTE: Use ternary operators instead of short-circuiting to mitigate
// https://bugs.llvm.org/show_bug.cgi?id=51928.
#define ABSL_LOG_INTERNAL_CONDITION_QFATAL …
#define ABSL_LOG_INTERNAL_CONDITION_DFATAL …

#define ABSL_LOG_INTERNAL_CONDITION_LEVEL …
#define ABSL_LOG_INTERNAL_CONDITION_LEVEL_IMPL …
#else  // ndef ABSL_MIN_LOG_LEVEL
#define ABSL_LOG_INTERNAL_CONDITION_INFO(type, condition) …
#define ABSL_LOG_INTERNAL_CONDITION_WARNING(type, condition) …
#define ABSL_LOG_INTERNAL_CONDITION_ERROR(type, condition) …
#define ABSL_LOG_INTERNAL_CONDITION_FATAL(type, condition) …
#define ABSL_LOG_INTERNAL_CONDITION_QFATAL(type, condition) …
#define ABSL_LOG_INTERNAL_CONDITION_DFATAL(type, condition) …
#define ABSL_LOG_INTERNAL_CONDITION_LEVEL(severity) …
#define ABSL_LOG_INTERNAL_CONDITION_LEVEL_IMPL(type, condition) …
#endif  // ndef ABSL_MIN_LOG_LEVEL

namespace absl {
ABSL_NAMESPACE_BEGIN
namespace log_internal {

// Stateful condition class name should be "Log" + name + "State".
class LogEveryNState final { … };

class LogFirstNState final { … };

class LogEveryPow2State final { … };

class LogEveryNSecState final { … };

// Helper routines to abort the application quietly

[[noreturn]] inline void AbortQuietly() { … }
[[noreturn]] inline void ExitQuietly() { … }
}  // namespace log_internal
ABSL_NAMESPACE_END
}  // namespace absl

#endif  // ABSL_LOG_INTERNAL_CONDITIONS_H_