Library
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Parameter
Class
Class type
Logging infrastructure inspired by the Python logging module. The aim of this module is to provide a quick and easy to use logging infrastructure.
It has the following features :
string
or string lazy_t
messageMakeLogging
functor.open Easy_logging
logger = Logging.make_logger "my_logger" (Some Debug) [Cli Debug];;
logger#info "log_message";;
will output to the stdout a message of the form
1.306 my_logger Info log_message
The logging infrastructure is based on four concepts:
loggers, handlers, log items and logging tree.
A call to logger will create a log item, which it will pass to its handlers. Each handler will treats the item (e.g. transform it to a string, and then outputs to stdout or to a file).
___________ | handler 1 | _______________ |-----------| | logger | ==> | ( * ) | |---------------| |___________| (message) ==> | -> log item | ___________ [_______________| ==> | handler 2 | | ... |
Loggers are stored in a tree structure, with the following properties :
set_propagate
method).A (Info, Cli Debug) / \ A.B A.C / \ A.B.D (Warning) A.C.E (Debug, (File "f", Debug), propagate=false)
For example, with the above logging tree
A
, A.B
or A.C
of level Info or more are written to the stdout.A.B.D
of level Warning
or above are written the stdout.A.C.E
are only written to the file "f"
To each logger and log message are associated a level, which will be used to filter the messages going through the logging infrastructure.
The predefined levels are, in increasing order of precedence :
A log item has type
type log_item = {
level : level;
logger_name : string;
msg : string;
tags : tag list
}
where the tag
type is defined by the Handlers
module.
By default, two handlers are provided. They are instantiated with a level of their own to filter messages :
Cli handler: outputs colored messages to stdout.
let h = Default_handlers.make (Cli Debug)
File handler : outputs messages to a given file.
let h = Default_handlers.make (File ("filename", Debug))
Note that file handlers will write to files in the logs
folder in the current path, creating it if it doesn't exist. See more about default handlers at Easy_logging__Default_handlers
.
See complete class documentation at Easy_logging.Logging.logger
A logger object can be created directly (in which case it will not be part of the logging tree)
let logger1 = new Logging.logger "my_logger1"
or through helper functions of the The Logging module module.
A logger object has three methods for each of the log levels:
one that takes a formatting string and parameters (printf like)
logger1#debug "Myvar : %s" (to_string myvar);
one that takes a string lazy_t
logger1#ldebug (lazy (heavy_calculation ()));
one that takes a string
logger1#sdebug (to_string myvar);
The Easy_logging.Logging
module is that application of MakeLogging
over DefaultHandlers
. It provides two functions :
val make_logger :
?propagate:bool -> string -> log_level -> Default_handlers.desc list
Instantiates a logger with some paramters, and adds it to the logging tree.
val get_logger : string -> logger
Returns a registered logger, or creates a new one if it doesn't exist.
The MakeLogging functor takes a Easy_logging__.Easy_logging_types.HandlersT
typed module, and creates a Logging module.
When declaring your Handlers module, do not coerce it the type HandlersT
, because then its internal types t
and desc
won't be accessible.
Here is a very simple example :
module MyHandlers =
struct
type t = string -> unit
type desc = string list ref
let set_formatter _ _ = ()
let set_level _ _ = ()
let apply h (item : log_item) = h item.msg
let make (_internal : desc) =
fun s -> _internal := s::!_internal
end
module MyLogging = MakeLogging(MyHandlers)
let l = ref [];;
let mylogger = MyLogging.make_logger "mylogger" Debug [l];;
mylogger#info "this is a message";