NAME
AnyEvent::Log - simple logging "framework"
SYNOPSIS
Simple uses:
use AnyEvent;
AE::log trace => "going to call function abc";
AE::log debug => "the function returned 3";
AE::log info => "file soandso successfully deleted";
AE::log note => "wanted to create config, but config was alraedy created";
AE::log warn => "couldn't delete the file";
AE::log error => "failed to retrieve data";
AE::log crit => "the battery temperature is too hot";
AE::log alert => "the battery died";
AE::log fatal => "no config found, cannot continue"; # never returns
Log level overview:
LVL NAME SYSLOG PERL NOTE
1 fatal emerg exit system unusable, aborts program!
2 alert failure in primary system
3 critical crit failure in backup system
4 error err die non-urgent program errors, a bug
5 warn warning possible problem, not necessarily error
6 note notice unusual conditions
7 info normal messages, no action required
8 debug debugging messages for development
9 trace copious tracing output
"Complex" uses (for speed sensitive code, e.g. trace/debug messages):
use AnyEvent::Log;
my $tracer = AnyEvent::Log::logger trace => \$my $trace;
$tracer->("i am here") if $trace;
$tracer->(sub { "lots of data: " . Dumper $self }) if $trace;
Configuration (also look at the EXAMPLES section):
# set logging for the current package to errors and higher only
AnyEvent::Log::ctx->level ("error");
# set logging level to suppress anything below "notice"
$AnyEvent::Log::FILTER->level ("notice");
# send all critical and higher priority messages to syslog,
# regardless of (most) other settings
$AnyEvent::Log::COLLECT->attach (new AnyEvent::Log::Ctx
level => "critical",
log_to_syslog => "user",
);
DESCRIPTION
This module implements a relatively simple "logging framework". It doesn't attempt to be "the" logging solution or even "a" logging solution for AnyEvent - AnyEvent simply creates logging messages internally, and this module more or less exposes the mechanism, with some extra spiff to allow using it from other modules as well.
Remember that the default verbosity level is 0
(off
), so nothing will be logged, unless you set PERL_ANYEVENT_VERBOSE
to a higher number before starting your program, or change the logging level at runtime with something like:
use AnyEvent::Log;
$AnyEvent::Log::FILTER->level ("info");
The design goal behind this module was to keep it simple (and small), but make it powerful enough to be potentially useful for any module, and extensive enough for the most common tasks, such as logging to multiple targets, or being able to log into a database.
The module is also usable before AnyEvent itself is initialised, in which case some of the functionality might be reduced.
The amount of documentation might indicate otherwise, but the runtime part of the module is still just below 300 lines of code.
LOGGING LEVELS
Logging levels in this module range from 1
(highest priority) to 9
(lowest priority). Note that the lowest numerical value is the highest priority, so when this document says "higher priority" it means "lower numerical value".
Instead of specifying levels by name you can also specify them by aliases:
LVL NAME SYSLOG PERL NOTE
1 fatal emerg exit system unusable, aborts program!
2 alert failure in primary system
3 critical crit failure in backup system
4 error err die non-urgent program errors, a bug
5 warn warning possible problem, not necessarily error
6 note notice unusual conditions
7 info normal messages, no action required
8 debug debugging messages for development
9 trace copious tracing output
As you can see, some logging levels have multiple aliases - the first one is the "official" name, the second one the "syslog" name (if it differs) and the third one the "perl" name, suggesting (only!) that you log die
messages at error
priority. The NOTE column tries to provide some rationale on how to chose a logging level.
As a rough guideline, levels 1..3 are primarily meant for users of the program (admins, staff), and are the only logged to STDERR by default. Levels 4..6 are meant for users and developers alike, while levels 7..9 are usually meant for developers.
You can normally only log a single message at highest priority level (1
, fatal
), because logging a fatal message will also quit the program - so use it sparingly :)
Some methods also offer some extra levels, such as 0
, off
, none
or all
- these are only valid in the methods they are documented for.
LOGGING FUNCTIONS
These functions allow you to log messages. They always use the caller's package as a "logging context". Also, the main logging function log
is callable as AnyEvent::log
or AE::log
when the AnyEvent
module is loaded.
- AnyEvent::Log::log $level, $msg[, @args]
-
Requests logging of the given
$msg
with the given log level, and returns true if the message was logged somewhere.For loglevel
fatal
, the program will abort.If only a
$msg
is given, it is logged as-is. With extra@args
, the$msg
is interpreted as an sprintf format string.The
$msg
should not end with\n
, but may if that is convenient for you. Also, multiline messages are handled properly.Last not least,
$msg
might be a code reference, in which case it is supposed to return the message. It will be called only then the message actually gets logged, which is useful if it is costly to create the message in the first place.This function takes care of saving and restoring
$!
and$@
, so you don't have to.Whether the given message will be logged depends on the maximum log level and the caller's package. The return value can be used to ensure that messages or not "lost" - for example, when AnyEvent::Debug detects a runtime error it tries to log it at
die
level, but if that message is lost it simply uses warn.Note that you can (and should) call this function as
AnyEvent::log
orAE::log
, withoutuse
-ing this module if possible (i.e. you don't need any additional functionality), as those functions will load the logging module on demand only. They are also much shorter to write.Also, if you optionally generate a lot of debug messages (such as when tracing some code), you should look into using a logger callback and a boolean enabler (see
logger
, below).Example: log something at error level.
AE::log error => "something";
Example: use printf-formatting.
AE::log info => "%5d %-10.10s %s", $index, $category, $msg;
Example: only generate a costly dump when the message is actually being logged.
AE::log debug => sub { require Data::Dump; Data::Dump::dump \%cache };
- $logger = AnyEvent::Log::logger $level[, \$enabled]
-
Creates a code reference that, when called, acts as if the
AnyEvent::Log::log
function was called at this point with the given level.$logger
is passed a$msg
and optional@args
, just as with theAnyEvent::Log::log
function:my $debug_log = AnyEvent::Log::logger "debug"; $debug_log->("debug here"); $debug_log->("%06d emails processed", 12345); $debug_log->(sub { $obj->as_string });
The idea behind this function is to decide whether to log before actually logging - when the
logger
function is called once, but the returned logger callback often, then this can be a tremendous speed win.Despite this speed advantage, changes in logging configuration will still be reflected by the logger callback, even if configuration changes after it was created.
To further speed up logging, you can bind a scalar variable to the logger, which contains true if the logger should be called or not - if it is false, calling the logger can be safely skipped. This variable will be updated as long as
$logger
is alive.Full example:
# near the init section use AnyEvent::Log; my $debug_log = AnyEvent:Log::logger debug => \my $debug; # and later in your program $debug_log->("yo, stuff here") if $debug; $debug and $debug_log->("123");
- AnyEvent::Log::exact_time $on
-
By default,
AnyEvent::Log
will useAE::now
, i.e. the cached eventloop time, for the log timestamps. After calling this function with a true value it will instead resort toAE::time
, i.e. fetch the current time on each log message. This only makes a difference for event loops that actually cache the time (such as EV or AnyEvent::Loop).This setting can be changed at any time by calling this function.
Since
AnyEvent::Log
has to work even before the AnyEvent has been initialised, this switch will also decide whether to useCORE::time
orTime::HiRes::time
when logging a message before AnyEvent becomes available.
LOGGING CONTEXTS
This module associates every log message with a so-called logging context, based on the package of the caller. Every perl package has its own logging context.
A logging context has three major responsibilities: filtering, logging and propagating the message.
For the first purpose, filtering, each context has a set of logging levels, called the log level mask. Messages not in the set will be ignored by this context (masked).
For logging, the context stores a formatting callback (which takes the timestamp, context, level and string message and formats it in the way it should be logged) and a logging callback (which is responsible for actually logging the formatted message and telling AnyEvent::Log
whether it has consumed the message, or whether it should be propagated).
For propagation, a context can have any number of attached slave contexts. Any message that is neither masked by the logging mask nor masked by the logging callback returning true will be passed to all slave contexts.
Each call to a logging function will log the message at most once per context, so it does not matter (much) if there are cycles or if the message can arrive at the same context via multiple paths.
DEFAULTS
By default, all logging contexts have an full set of log levels ("all"), a disabled logging callback and the default formatting callback.
Package contexts have the package name as logging title by default.
They have exactly one slave - the context of the "parent" package. The parent package is simply defined to be the package name without the last component, i.e. AnyEvent::Debug::Wrapped
becomes AnyEvent::Debug
, and AnyEvent
becomes ... $AnyEvent::Log::COLLECT
which is the exception of the rule - just like the "parent" of any single-component package name in Perl is main
, the default slave of any top-level package context is $AnyEvent::Log::COLLECT
.
Since perl packages form only an approximate hierarchy, this slave context can of course be removed.
All other (anonymous) contexts have no slaves and an empty title by default.
When the module is loaded it creates the $AnyEvent::Log::LOG
logging context that simply logs everything via warn
, without propagating anything anywhere by default. The purpose of this context is to provide a convenient place to override the global logging target or to attach additional log targets. It's not meant for filtering.
It then creates the $AnyEvent::Log::FILTER
context whose purpose is to suppress all messages with priority higher than $ENV{PERL_ANYEVENT_VERBOSE}
. It then attached the $AnyEvent::Log::LOG
context to it. The purpose of the filter context is to simply provide filtering according to some global log level.
Finally it creates the top-level package context $AnyEvent::Log::COLLECT
and attaches the $AnyEvent::Log::FILTER
context to it, but otherwise leaves it at default config. Its purpose is simply to collect all log messages system-wide.
The hierarchy is then:
any package, eventually -> $COLLECT -> $FILTER -> $LOG
The effect of all this is that log messages, by default, wander up to the $AnyEvent::Log::COLLECT
context where all messages normally end up, from there to $AnyEvent::Log::FILTER
where log messages with lower priority then $ENV{PERL_ANYEVENT_VERBOSE}
will be filtered out and then to the $AnyEvent::Log::LOG
context to be passed to warn
.
This makes it easy to set a global logging level (by modifying $FILTER), but still allow other contexts to send, for example, their debug and trace messages to the $LOG target despite the global logging level, or to attach additional log targets that log messages, regardless of the global logging level.
It also makes it easy to modify the default warn-logger ($LOG) to something that logs to a file, or to attach additional logging targets (such as loggign to a file) by attaching it to $FILTER.
CREATING/FINDING/DESTROYING CONTEXTS
- $ctx = AnyEvent::Log::ctx [$pkg]
-
This function creates or returns a logging context (which is an object).
If a package name is given, then the context for that packlage is returned. If it is called without any arguments, then the context for the callers package is returned (i.e. the same context as a
AE::log
call would use).If
undef
is given, then it creates a new anonymous context that is not tied to any package and is destroyed when no longer referenced. - AnyEvent::Log::reset
-
Resets all package contexts and recreates the default hierarchy if necessary, i.e. resets the logging subsystem to defaults, as much as possible. This process keeps references to contexts held by other parts of the program intact.
This can be used to implement config-file (re-)loading: before loading a configuration, reset all contexts.
- $ctx = new AnyEvent::Log::Ctx methodname => param...
-
This is a convenience constructor that makes it simpler to construct anonymous logging contexts.
Each key-value pair results in an invocation of the method of the same name as the key with the value as parameter, unless the value is an arrayref, in which case it calls the method with the contents of the array. The methods are called in the same order as specified.
Example: create a new logging context and set both the default logging level, some slave contexts and a logging callback.
$ctx = new AnyEvent::Log::Ctx title => "dubious messages", level => "error", log_cb => sub { print STDOUT shift; 0 }, slaves => [$ctx1, $ctx, $ctx2], ;
CONFIGURING A LOG CONTEXT
The following methods can be used to configure the logging context.
- $ctx->title ([$new_title])
-
Returns the title of the logging context - this is the package name, for package contexts, and a user defined string for all others.
If
$new_title
is given, then it replaces the package name or title.
LOGGING LEVELS
The following methods deal with the logging level set associated with the log context.
The most common method to use is probably $ctx->level ($level)
, which configures the specified and any higher priority levels.
All functions which accept a list of levels also accept the special string all
which expands to all logging levels.
- $ctx->levels ($level[, $level...)
-
Enables logging for the given levels and disables it for all others.
- $ctx->level ($level)
-
Enables logging for the given level and all lower level (higher priority) ones. In addition to normal logging levels, specifying a level of
0
oroff
disables all logging for this level.Example: log warnings, errors and higher priority messages.
$ctx->level ("warn"); $ctx->level (5); # same thing, just numeric
- $ctx->enable ($level[, $level...])
-
Enables logging for the given levels, leaving all others unchanged.
- $ctx->disable ($level[, $level...])
-
Disables logging for the given levels, leaving all others unchanged.
- $ctx->cap ($level)
-
Caps the maximum priority to the given level, for all messages logged to, or passing through, this context. That is, while this doesn't affect whether a message is logged or passed on, the maximum priority of messages will be limited to the specified level - messages with a higher priority will be set to the specified priority.
Another way to view this is that
->level
filters out messages with a too low priority, while->cap
modifies messages with a too high priority.This is useful when different log targets have different interpretations of priority. For example, for a specific command line program, a wrong command line switch might well result in a
fatal
log message, while the same message, logged to syslog, is likely not fatal to the system or syslog facility as a whole, but more likely a mereerror
.This can be modeled by having a stderr logger that logs messages "as-is" and a syslog logger that logs messages with a level cap of, say,
error
, or, for truly system-critical components, actuallycritical
.
SLAVE CONTEXTS
The following methods attach and detach another logging context to a logging context.
Log messages are propagated to all slave contexts, unless the logging callback consumes the message.
- $ctx->attach ($ctx2[, $ctx3...])
-
Attaches the given contexts as slaves to this context. It is not an error to add a context twice (the second add will be ignored).
A context can be specified either as package name or as a context object.
- $ctx->detach ($ctx2[, $ctx3...])
-
Removes the given slaves from this context - it's not an error to attempt to remove a context that hasn't been added.
A context can be specified either as package name or as a context object.
- $ctx->slaves ($ctx2[, $ctx3...])
-
Replaces all slaves attached to this context by the ones given.
LOG TARGETS
The following methods configure how the logging context actually does the logging (which consists of formatting the message and printing it or whatever it wants to do with it).
- $ctx->log_cb ($cb->($str)
-
Replaces the logging callback on the context (
undef
disables the logging callback).The logging callback is responsible for handling formatted log messages (see
fmt_cb
below) - normally simple text strings that end with a newline (and are possibly multiline themselves).It also has to return true iff it has consumed the log message, and false if it hasn't. Consuming a message means that it will not be sent to any slave context. When in doubt, return
0
from your logging callback.Example: a very simple logging callback, simply dump the message to STDOUT and do not consume it.
$ctx->log_cb (sub { print STDERR shift; 0 });
You can filter messages by having a log callback that simply returns
1
and does not do anything with the message, but this counts as "message being logged" and might not be very efficient.Example: propagate all messages except for log levels "debug" and "trace". The messages will still be generated, though, which can slow down your program.
$ctx->levels ("debug", "trace"); $ctx->log_cb (sub { 1 }); # do not log, but eat debug and trace messages
- $ctx->fmt_cb ($fmt_cb->($timestamp, $orig_ctx, $level, $message))
-
Replaces the formatting callback on the context (
undef
restores the default formatter).The callback is passed the (possibly fractional) timestamp, the original logging context, the (numeric) logging level and the raw message string and needs to return a formatted log message. In most cases this will be a string, but it could just as well be an array reference that just stores the values.
If, for some reason, you want to use
caller
to find out more baout the logger then you should walk up the call stack until you are no longer inside theAnyEvent::Log
package.Example: format just the raw message, with numeric log level in angle brackets.
$ctx->fmt_cb (sub { my ($time, $ctx, $lvl, $msg) = @_; "<$lvl>$msg\n" });
Example: return an array reference with just the log values, and use
PApp::SQL::sql_exec
to store the emssage in a database.$ctx->fmt_cb (sub { \@_ }); $ctx->log_cb (sub { my ($msg) = @_; sql_exec "insert into log (when, subsys, prio, msg) values (?, ?, ?, ?)", $msg->[0] + 0, "$msg->[1]", $msg->[2] + 0, "$msg->[3]"; 0 });
- $ctx->log_to_warn
-
Sets the
log_cb
to simply useCORE::warn
to report any messages (usually this logs to STDERR). - $ctx->log_to_file ($path)
-
Sets the
log_cb
to log to a file (by appending), unbuffered. - $ctx->log_to_path ($path)
-
Same as
->log_to_file
, but opens the file for each message. This is much slower, but allows you to change/move/rename/delete the file at basically any time.Needless(?) to say, if you do not want to be bitten by some evil person calling
chdir
, the path should be absolute. Doesn't help withchroot
, but hey... - $ctx->log_to_syslog ([$facility])
-
Logs all messages via Sys::Syslog, mapping
trace
todebug
and all the others in the obvious way. If specified, then the$facility
is used as the facility (user
,auth
,local0
and so on). The default facility isuser
.Note that this function also sets a
fmt_cb
- the logging part requires an array reference with [$level, $str] as input.
MESSAGE LOGGING
These methods allow you to log messages directly to a context, without going via your package context.
- $ctx->log ($level, $msg[, @params])
-
Same as
AnyEvent::Log::log
, but uses the given context as log context. - $logger = $ctx->logger ($level[, \$enabled])
-
Same as
AnyEvent::Log::logger
, but uses the given context as log context.
CONFIGURATION VIA $ENV{PERL_ANYEVENT_LOG}
Logging can also be configured by setting the environment variable PERL_ANYEVENT_LOG
(or AE_LOG
).
The value consists of one or more logging context specifications separated by :
or whitespace. Each logging specification in turn starts with a context name, followed by =
, followed by zero or more comma-separated configuration directives, here are some examples:
# set default logging level
filter=warn
# log to file instead of to stderr
log=file=/tmp/mylog
# log to file in addition to stderr
log=+%file:%file=file=/tmp/mylog
# enable debug log messages, log warnings and above to syslog
filter=debug:log=+%warnings:%warnings=warn,syslog=LOG_LOCAL0
# log trace messages (only) from AnyEvent::Debug to file
AnyEvent::Debug=+%trace:%trace=only,trace,file=/tmp/tracelog
A context name in the log specification can be any of the following:
collect
,filter
,log
-
Correspond to the three predefined
$AnyEvent::Log::COLLECT
,AnyEvent::Log::FILTER
and$AnyEvent::Log::LOG
contexts. %name
-
Context names starting with a
%
are anonymous contexts created when the name is first mentioned. The difference to package contexts is that by default they have no attached slaves. - a perl package name
-
Any other string references the logging context associated with the given Perl
package
. In the unlikely case where you want to specify a package context that matches on of the other context name forms, you can add a::
to the package name to force interpretation as a package.
The configuration specifications can be any number of the following:
stderr
-
Configures the context to use Perl's
warn
function (which typically logs toSTDERR
). Works likelog_to_warn
. file=
path-
Configures the context to log to a file with the given path. Works like
log_to_file
. path=
path-
Configures the context to log to a file with the given path. Works like
log_to_path
. syslog
orsyslog=
expr-
Configures the context to log to syslog. If expr is given, then it is evaluated in the Sys::Syslog package, so you could use:
log=syslog=LOG_LOCAL0
nolog
-
Configures the context to not log anything by itself, which is the default. Same as
$ctx->log_cb (undef)
. cap=
level-
Caps logging messages entering this context at the given level, i.e. reduces the priority of messages with higher priority than this level. The default is
0
(oroff
), meaning the priority will not be touched. 0
oroff
-
Sets the logging level of the context to
0
, i.e. all messages will be filtered out. all
-
Enables all logging levels, i.e. filtering will effectively be switched off (the default).
only
-
Disables all logging levels, and changes the interpretation of following level specifications to enable the specified level only.
Example: only enable debug messages for a context.
context=only,debug
except
-
Enables all logging levels, and changes the interpretation of following level specifications to disable that level. Rarely used.
Example: enable all logging levels except fatal and trace (this is rather nonsensical).
filter=exept,fatal,trace
level
-
Enables all logging levels, and changes the interpretation of following level specifications to be "that level or any higher priority message". This is the default.
Example: log anything at or above warn level.
filter=warn # or, more verbose filter=only,level,warn
1
..9
or a logging level name (error
,debug
etc.)-
A numeric loglevel or the name of a loglevel will be interpreted according to the most recent
only
,except
orlevel
directive. By default, specifying a logging level enables that and any higher priority messages. +
context-
Attaches the named context as slave to the context.
+
-
A line
+
detaches all contexts, i.e. clears the slave list from the context. Anonymous (%name
) contexts have no attached slaves by default, but package contexts have the parent context as slave by default.Example: log messages from My::Module to a file, do not send them to the default log collector.
My::Module=+,file=/tmp/mymodulelog
Any character can be escaped by prefixing it with a \
(backslash), as usual, so to log to a file containing a comma, colon, backslash and some spaces in the filename, you would do this:
PERL_ANYEVENT_LOG='log=file=/some\ \:file\ with\,\ \\-escapes'
Since whitespace (which includes newlines) is allowed, it is fine to specify multiple lines in PERL_ANYEVENT_LOG
, e.g.:
PERL_ANYEVENT_LOG="
filter=warn
AnyEvent::Debug=+%trace
%trace=only,trace,+log
" myprog
Also, in the unlikely case when you want to concatenate specifications, use whitespace as separator, as ::
will be interpreted as part of a module name, an empty spec with two separators:
PERL_ANYEVENT_LOG="$PERL_ANYEVENT_LOG MyMod=debug"
EXAMPLES
This section shows some common configurations, both as code, and as PERL_ANYEVENT_LOG
string.
- Setting the global logging level.
-
Either put
PERL_ANYEVENT_VERBOSE=
<number> into your environment before running your program, usePERL_ANYEVENT_LOG
or modify the log level of the root context at runtime:PERL_ANYEVENT_VERBOSE=5 ./myprog PERL_ANYEVENT_LOG=log=warn $AnyEvent::Log::FILTER->level ("warn");
- Append all messages to a file instead of sending them to STDERR.
-
This is affected by the global logging level.
$AnyEvent::Log::LOG->log_to_file ($path); PERL_ANYEVENT_LOG=log=file=/some/path
- Write all messages with priority
error
and higher to a file. -
This writes them only when the global logging level allows it, because it is attached to the default context which is invoked after global filtering.
$AnyEvent::Log::FILTER->attach ( new AnyEvent::Log::Ctx log_to_file => $path); PERL_ANYEVENT_LOG=filter=+%filelogger:%filelogger=file=/some/path
This writes them regardless of the global logging level, because it is attached to the toplevel context, which receives all messages before the global filtering.
$AnyEvent::Log::COLLECT->attach ( new AnyEvent::Log::Ctx log_to_file => $path); PERL_ANYEVENT_LOG=%filelogger=file=/some/path:collect=+%filelogger
In both cases, messages are still written to STDERR.
- Additionally log all messages with
warn
and higher priority tosyslog
, but cap aterror
. -
This logs all messages to the default log target, but also logs messages with priority
warn
or higher (and not filtered otherwise) to syslog facilityuser
. Messages with priority higher thanerror
will be logged with levelerror
.$AnyEvent::Log::LOG->attach ( new AnyEvent::Log::Ctx level => "warn", cap => "error", syslog => "user", ); PERL_ANYEVENT_LOG=log=+%syslog:%syslog=warn,cap=error,syslog
- Write trace messages (only) from AnyEvent::Debug to the default logging target(s).
-
Attach the
$AnyEvent::Log::LOG
context to theAnyEvent::Debug
context - this simply circumvents the global filtering for trace messages.my $debug = AnyEvent::Debug->AnyEvent::Log::ctx; $debug->attach ($AnyEvent::Log::LOG); PERL_ANYEVENT_LOG=AnyEvent::Debug=+log
This of course works for any package, not just AnyEvent::Debug, but assumes the log level for AnyEvent::Debug hasn't been changed from the default.
AUTHOR
Marc Lehmann <schmorp@schmorp.de>
http://home.schmorp.de/