1 // Copyright 2012 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
15 This module is used by the compiler when emitting output for the logging family
16 of macros. The methods of this module shouldn't necessarily be used directly,
17 but rather through the logging macros defined.
19 There are five macros that the logging subsystem uses:
21 * `log!(level, ...)` - the generic logging macro, takes a level as a u32 and any
22 related `format!` arguments
23 * `debug!(...)` - a macro hard-wired to the log level of `DEBUG`
24 * `info!(...)` - a macro hard-wired to the log level of `INFO`
25 * `warn!(...)` - a macro hard-wired to the log level of `WARN`
26 * `error!(...)` - a macro hard-wired to the log level of `ERROR`
28 All of these macros use the same style of syntax as the `format!` syntax
29 extension. Details about the syntax can be found in the documentation of
30 `std::fmt` along with the Rust tutorial/manual.
32 If you want to check at runtime if a given logging level is enabled (e.g. if the
33 information you would want to log is expensive to produce), you can use the
36 * `log_enabled!(level)` - returns true if logging of the given level is enabled
40 Log levels are controlled on a per-module basis, and by default all logging is
41 disabled except for `error!` (a log level of 1). Logging is controlled via the
42 `RUST_LOG` environment variable. The value of this environment variable is a
43 comma-separated list of logging directives. A logging directive is of the form:
46 path::to::module=log_level
49 The path to the module is rooted in the name of the crate it was compiled for,
50 so if your program is contained in a file `hello.rs`, for example, to turn on
51 logging for this file you would use a value of `RUST_LOG=hello`. Furthermore,
52 this path is a prefix-search, so all modules nested in the specified module will
53 also have logging enabled.
55 The actual `log_level` is optional to specify. If omitted, all logging will be
56 enabled. If specified, the it must be either a numeric in the range of 1-255, or
57 it must be one of the strings `debug`, `error`, `info`, or `warn`. If a numeric
58 is specified, then all logging less than or equal to that numeral is enabled.
59 For example, if logging level 3 is active, error, warn, and info logs will be
60 printed, but debug will be omitted.
62 As the log level for a module is optional, the module to enable logging for is
63 also optional. If only a `log_level` is provided, then the global log level for
64 all modules is set to this value.
66 Some examples of valid values of `RUST_LOG` are:
69 hello // turns on all logging for the 'hello' module
70 info // turns on all info logging
71 hello=debug // turns on debug logging for 'hello'
72 hello=3 // turns on info logging for 'hello'
73 hello,std::hashmap // turns on hello, and std's hashmap logging
74 error,hello=warn // turn on global error logging and also warn for hello
77 ## Performance and Side Effects
79 Each of these macros will expand to code similar to:
82 if log_level <= my_module_log_level() {
83 ::std::logging::log(log_level, format!(...));
87 What this means is that each of these macros are very cheap at runtime if
88 they're turned off (just a load and an integer comparison). This also means that
89 if logging is disabled, none of the components of the log will be executed.
93 For convenience, if a value of `::help` is set for `RUST_LOG`, a program will
94 start, print out all modules registered for logging, and then exit.
100 use rt::local::Local;
101 use rt::logging::{Logger, StdErrLogger};
105 pub static DEBUG: u32 = 4;
107 pub static INFO: u32 = 3;
109 pub static WARN: u32 = 2;
111 pub static ERROR: u32 = 1;
113 /// This function is called directly by the compiler when using the logging
114 /// macros. This function does not take into account whether the log level
115 /// specified is active or not, it will always log something if this method is
118 /// It is not recommended to call this function directly, rather it should be
119 /// invoked through the logging family of macros.
120 pub fn log(_level: u32, args: &fmt::Arguments) {
122 let optional_task: Option<*mut Task> = Local::try_unsafe_borrow();
123 match optional_task {
125 // Lazily initialize the local task's logger
126 match (*local).logger {
127 // Use the available logger if we have one
128 Some(ref mut logger) => { logger.log(args); }
130 let mut logger = StdErrLogger::new();
132 (*local).logger = Some(logger);
136 // If there's no local task, then always log to stderr
138 let mut logger = StdErrLogger::new();