| // 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/vlog_is_on.h | |
| // ----------------------------------------------------------------------------- | |
| // | |
| // This header defines the `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 (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. | |
| // `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. | |
| // IWYU pragma: private, include "absl/log/log.h" | |
| // Each 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. | |
| // | |
| // VLOG_IS_ON is not async signal safe, but it is guaranteed not to allocate | |
| // new memory. | |