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0001 // Copyright 2022 The Abseil Authors.
0002 //
0003 // Licensed under the Apache License, Version 2.0 (the "License");
0004 // you may not use this file except in compliance with the License.
0005 // You may obtain a copy of the License at
0006 //
0007 //      https://www.apache.org/licenses/LICENSE-2.0
0008 //
0009 // Unless required by applicable law or agreed to in writing, software
0010 // distributed under the License is distributed on an "AS IS" BASIS,
0011 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
0012 // See the License for the specific language governing permissions and
0013 // limitations under the License.
0014 //
0015 // -----------------------------------------------------------------------------
0016 // File: log/vlog_is_on.h
0017 // -----------------------------------------------------------------------------
0018 //
0019 // This header defines the `VLOG_IS_ON()` macro that controls the
0020 // variable-verbosity conditional logging.
0021 //
0022 // It's used by `VLOG` in log.h, or it can also be used directly like this:
0023 //
0024 //   if (VLOG_IS_ON(2)) {
0025 //     foo_server.RecomputeStatisticsExpensive();
0026 //     LOG(INFO) << foo_server.LastStatisticsAsString();
0027 //   }
0028 //
0029 // Each source file has an effective verbosity level that's a non-negative
0030 // integer computed from the `--vmodule` and `--v` flags.
0031 // `VLOG_IS_ON(n)` is true, and `VLOG(n)` logs, if that effective verbosity
0032 // level is greater than or equal to `n`.
0033 //
0034 // `--vmodule` takes a comma-delimited list of key=value pairs.  Each key is a
0035 // pattern matched against filenames, and the values give the effective severity
0036 // level applied to matching files.  '?' and '*' characters in patterns are
0037 // interpreted as single-character and zero-or-more-character wildcards.
0038 // Patterns including a slash character are matched against full pathnames,
0039 // while those without are matched against basenames only.  One suffix (i.e. the
0040 // last . and everything after it) is stripped from each filename prior to
0041 // matching, as is the special suffix "-inl".
0042 //
0043 // Files are matched against globs in `--vmodule` in order, and the first match
0044 // determines the verbosity level.
0045 //
0046 // Files which do not match any pattern in `--vmodule` use the value of `--v` as
0047 // their effective verbosity level.  The default is 0.
0048 //
0049 // SetVLogLevel helper function is provided to do limited dynamic control over
0050 // V-logging by appending to `--vmodule`. Because these go at the beginning of
0051 // the list, they take priority over any globs previously added.
0052 //
0053 // Resetting --vmodule will override all previous modifications to `--vmodule`,
0054 // including via SetVLogLevel.
0055 
0056 #ifndef ABSL_LOG_VLOG_IS_ON_H_
0057 #define ABSL_LOG_VLOG_IS_ON_H_
0058 
0059 #include "absl/log/absl_vlog_is_on.h"  // IWYU pragma: export
0060 
0061 // IWYU pragma: private, include "absl/log/log.h"
0062 
0063 // Each VLOG_IS_ON call site gets its own VLogSite that registers with the
0064 // global linked list of sites to asynchronously update its verbosity level on
0065 // changes to --v or --vmodule. The verbosity can also be set by manually
0066 // calling SetVLogLevel.
0067 //
0068 // VLOG_IS_ON is not async signal safe, but it is guaranteed not to allocate
0069 // new memory.
0070 #define VLOG_IS_ON(verbose_level) ABSL_VLOG_IS_ON(verbose_level)
0071 
0072 #endif  // ABSL_LOG_VLOG_IS_ON_H_