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 // 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/absl_vlog_is_on.h
 // -----------------------------------------------------------------------------
 //
 // This header defines the `ABSL_VLOG_IS_ON()` macro that controls the
 // variable-verbosity conditional logging.
 //
 // It's used by `VLOG` in log.h, or it can also be used directly like this:
 //
 //   if (ABSL_VLOG_IS_ON(2)) {
 //     foo_server.RecomputeStatisticsExpensive();
 //     LOG(INFO) << foo_server.LastStatisticsAsString();
 //   }
 //
 // Each source file has an effective verbosity level that's a non-negative
 // integer computed from the `--vmodule` and `--v` flags.
 // `ABSL_VLOG_IS_ON(n)` is true, and `VLOG(n)` logs, if that effective verbosity
 // level is greater than or equal to `n`.
 //
 // `--vmodule` takes a comma-delimited list of key=value pairs.  Each key is a
 // pattern matched against filenames, and the values give the effective severity
 // level applied to matching files.  '?' and '*' characters in patterns are
 // interpreted as single-character and zero-or-more-character wildcards.
 // Patterns including a slash character are matched against full pathnames,
 // while those without are matched against basenames only.  One suffix (i.e. the
 // last . and everything after it) is stripped from each filename prior to
 // matching, as is the special suffix "-inl".
 //
 // Files are matched against globs in `--vmodule` in order, and the first match
 // determines the verbosity level.
 //
 // Files which do not match any pattern in `--vmodule` use the value of `--v` as
 // their effective verbosity level.  The default is 0.
 //
 // SetVLogLevel helper function is provided to do limited dynamic control over
 // V-logging by appending to `--vmodule`. Because these go at the beginning of
 // the list, they take priority over any globs previously added.
 //
 // Resetting --vmodule will override all previous modifications to `--vmodule`,
 // including via SetVLogLevel.
 
 #ifndef ABSL_LOG_ABSL_VLOG_IS_ON_H_
 #define ABSL_LOG_ABSL_VLOG_IS_ON_H_
 
 #include "absl/base/attributes.h"
 #include "absl/base/config.h"
 #include "absl/log/internal/vlog_config.h"  // IWYU pragma: export
 #include "absl/strings/string_view.h"
 
 // IWYU pragma: private, include "absl/log/log.h"
 
 // This is expanded at the callsite to allow the compiler to optimize
 // always-false cases out of the build.
 // An ABSL_MAX_VLOG_VERBOSITY of 2 means that VLOG(3) and above should never
 // log.
 #ifdef ABSL_MAX_VLOG_VERBOSITY
 #define ABSL_LOG_INTERNAL_MAX_LOG_VERBOSITY_CHECK(x) \
   ((x) <= ABSL_MAX_VLOG_VERBOSITY)&&
 #else
 #define ABSL_LOG_INTERNAL_MAX_LOG_VERBOSITY_CHECK(x)
 #endif
 
 // Each ABSL_VLOG_IS_ON call site gets its own VLogSite that registers with the
 // global linked list of sites to asynchronously update its verbosity level on
 // changes to --v or --vmodule. The verbosity can also be set by manually
 // calling SetVLogLevel.
 //
 // ABSL_VLOG_IS_ON is not async signal safe, but it is guaranteed not to
 // allocate new memory.
 #define ABSL_VLOG_IS_ON(verbose_level)                                     \
   (ABSL_LOG_INTERNAL_MAX_LOG_VERBOSITY_CHECK(verbose_level)[]()            \
        ->::absl::log_internal::VLogSite *                                  \
    {                                                                       \
      ABSL_CONST_INIT static ::absl::log_internal::VLogSite site(__FILE__); \
      return &site;                                                         \
    }()                                                                     \
        ->IsEnabled(verbose_level))
 
 #endif  // ABSL_LOG_ABSL_VLOG_IS_ON_H_

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