// 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.

//

// -----------------------------------------------------------------------------

// vlog_config.h

// -----------------------------------------------------------------------------

//

// This header file defines `VLogSite`, a public primitive that represents

// a callsite for the `VLOG` family of macros and related libraries.

// It also declares and defines multiple internal utilities used to implement

// `VLOG`, such as `VLogSiteManager`.

#ifndef ABSL_LOG_INTERNAL_VLOG_CONFIG_H_

#define ABSL_LOG_INTERNAL_VLOG_CONFIG_H_

// IWYU pragma: private, include "absl/log/log.h"

#include <atomic>

#include <cstdint>

#include <functional>

#include <limits>

#include <type_traits>

#include "absl/base/attributes.h"

#include "absl/base/config.h"

#include "absl/base/optimization.h"

#include "absl/base/thread_annotations.h"

#include "absl/strings/string_view.h"

namespace absl {

ABSL_NAMESPACE_BEGIN

namespace log_internal {

class SyntheticBinary;

class VLogSite;

int RegisterAndInitialize(VLogSite* v);

void UpdateVLogSites();

constexpr int kUseFlag = (std::numeric_limits<int16_t>::min)();

// Represents a unique callsite for a `VLOG()` or `VLOG_IS_ON()` call.

//

// Libraries that provide `VLOG`-like functionality should use this to

// efficiently handle --vmodule.

//

// VLogSite objects must not be destroyed until the program exits. Doing so will

// probably yield nasty segfaults in VLogSiteManager::UpdateLogSites(). The

// recommendation is to make all such objects function-local statics.

class VLogSite final {

 public:

  // `f` must not be destroyed until the program exits.

  explicit constexpr VLogSite(const char* f)

      : file_(f), v_(kUninitialized), next_(nullptr) {}

  VLogSite(const VLogSite&) = delete;

  VLogSite& operator=(const VLogSite&) = delete;

  // Inlining the function yields a ~3x performance improvement at the cost of a

  // 1.5x code size increase at the call site.

  // Takes locks but does not allocate memory.

  ABSL_ATTRIBUTE_ALWAYS_INLINE

  bool IsEnabled(int level) {

    int stale_v = v_.load(std::memory_order_relaxed);

    if (ABSL_PREDICT_TRUE(level > stale_v)) {

      return false;

    }

    // We put everything other than the fast path, i.e. vlogging is initialized

    // but not on, behind an out-of-line function to reduce code size.

    // "level" is almost always a call-site constant, so we can save a bit

    // of code space by special-casing for a few common levels.

#if ABSL_HAVE_BUILTIN(__builtin_constant_p) || defined(__GNUC__)

    if (__builtin_constant_p(level)) {

      if (level == 0) return SlowIsEnabled0(stale_v);

      if (level == 1) return SlowIsEnabled1(stale_v);

      if (level == 2) return SlowIsEnabled2(stale_v);

      if (level == 3) return SlowIsEnabled3(stale_v);

      if (level == 4) return SlowIsEnabled4(stale_v);

      if (level == 5) return SlowIsEnabled5(stale_v);

    }

#endif

    return SlowIsEnabled(stale_v, level);

  }

 private:

  friend int log_internal::RegisterAndInitialize(VLogSite* v);

  friend void log_internal::UpdateVLogSites();

  friend class log_internal::SyntheticBinary;

  static constexpr int kUninitialized = (std::numeric_limits<int>::max)();

  // SlowIsEnabled performs slower checks to determine whether a log site is

  // enabled. Because it is expected to be called somewhat rarely

  // (comparatively), it is not inlined to save on code size.

  //

  // Prerequisites to calling SlowIsEnabled:

  //   1) stale_v is uninitialized OR

  //   2) stale_v is initialized and >= level (meaning we must log).

  // Takes locks but does not allocate memory.

  ABSL_ATTRIBUTE_NOINLINE

  bool SlowIsEnabled(int stale_v, int level);

  ABSL_ATTRIBUTE_NOINLINE bool SlowIsEnabled0(int stale_v);

  ABSL_ATTRIBUTE_NOINLINE bool SlowIsEnabled1(int stale_v);

  ABSL_ATTRIBUTE_NOINLINE bool SlowIsEnabled2(int stale_v);

  ABSL_ATTRIBUTE_NOINLINE bool SlowIsEnabled3(int stale_v);

  ABSL_ATTRIBUTE_NOINLINE bool SlowIsEnabled4(int stale_v);

  ABSL_ATTRIBUTE_NOINLINE bool SlowIsEnabled5(int stale_v);

  // This object is too size-sensitive to use absl::string_view.

  const char* const file_;

  std::atomic<int> v_;

  std::atomic<VLogSite*> next_;

};

static_assert(std::is_trivially_destructible<VLogSite>::value,

              "VLogSite must be trivially destructible");

// Returns the current verbose log level of `file`.

// Does not allocate memory.

int VLogLevel(absl::string_view file);

// Registers a site `v` to get updated as `vmodule` and `v` change.  Also

// initializes the site based on their current values, and returns that result.

// Does not allocate memory.

int RegisterAndInitialize(VLogSite* v);

// Allocates memory.

void UpdateVLogSites();

// Completely overwrites the saved value of `vmodule`.

// Allocates memory.

void UpdateVModule(absl::string_view vmodule);

// Updates the global verbosity level to `v` and returns the prior value.

// Allocates memory.

int UpdateGlobalVLogLevel(int v);

// Atomically prepends `module_pattern=log_level` to the start of vmodule.

// Returns the prior value for `module_pattern` if there was an exact match and

// `global_v` otherwise.

// Allocates memory.

int PrependVModule(absl::string_view module_pattern, int log_level);

// Registers `on_update` to be called whenever `v` or `vmodule` change.

// Allocates memory.

void OnVLogVerbosityUpdate(std::function<void()> cb);

// Does not allocate memory.

VLogSite* SetVModuleListHeadForTestOnly(VLogSite* v);

}  // namespace log_internal

ABSL_NAMESPACE_END

}  // namespace absl

#endif  // ABSL_LOG_INTERNAL_VLOG_CONFIG_H_