File Coverage

blib/lib/AnyEvent/Log.pm
Criterion Covered Total %
statement 62 152 40.7
branch 19 60 31.6
condition 6 32 18.7
subroutine 20 43 46.5
pod 8 8 100.0
total 115 295 38.9


line stmt bran cond sub pod time code
1             =head1 NAME
2              
3             AnyEvent::Log - simple logging "framework"
4              
5             =head1 SYNOPSIS
6              
7             Simple uses:
8              
9             use AnyEvent;
10              
11             AE::log fatal => "No config found, cannot continue!"; # never returns
12             AE::log alert => "The battery died!";
13             AE::log crit => "The battery temperature is too hot!";
14             AE::log error => "Division by zero attempted.";
15             AE::log warn => "Couldn't delete the file.";
16             AE::log note => "Wanted to create config, but config already exists.";
17             AE::log info => "File soandso successfully deleted.";
18             AE::log debug => "the function returned 3";
19             AE::log trace => "going to call function abc";
20              
21             Log level overview:
22              
23             LVL NAME SYSLOG PERL NOTE
24             1 fatal emerg exit system unusable, aborts program!
25             2 alert failure in primary system
26             3 critical crit failure in backup system
27             4 error err die non-urgent program errors, a bug
28             5 warn warning possible problem, not necessarily error
29             6 note notice unusual conditions
30             7 info normal messages, no action required
31             8 debug debugging messages for development
32             9 trace copious tracing output
33              
34             "Complex" uses (for speed sensitive code, e.g. trace/debug messages):
35              
36             use AnyEvent::Log;
37              
38             my $tracer = AnyEvent::Log::logger trace => \my $trace;
39              
40             $tracer->("i am here") if $trace;
41             $tracer->(sub { "lots of data: " . Dumper $self }) if $trace;
42              
43             Configuration (also look at the EXAMPLES section):
44              
45             # set logging for the current package to errors and higher only
46             AnyEvent::Log::ctx->level ("error");
47              
48             # set logging level to suppress anything below "notice"
49             $AnyEvent::Log::FILTER->level ("notice");
50              
51             # send all critical and higher priority messages to syslog,
52             # regardless of (most) other settings
53             $AnyEvent::Log::COLLECT->attach (new AnyEvent::Log::Ctx
54             level => "critical",
55             log_to_syslog => "user",
56             );
57              
58             =head1 DESCRIPTION
59              
60             This module implements a relatively simple "logging framework". It doesn't
61             attempt to be "the" logging solution or even "a" logging solution for
62             AnyEvent - AnyEvent simply creates logging messages internally, and this
63             module more or less exposes the mechanism, with some extra spiff to allow
64             using it from other modules as well.
65              
66             Remember that the default verbosity level is C<4> (C), so only
67             errors and more important messages will be logged, unless you set
68             C to a higher number before starting your program
69             (C is recommended during development), or change the logging
70             level at runtime with something like:
71              
72             use AnyEvent::Log;
73             $AnyEvent::Log::FILTER->level ("info");
74              
75             The design goal behind this module was to keep it simple (and small),
76             but make it powerful enough to be potentially useful for any module,
77             and extensive enough for the most common tasks, such as logging to
78             multiple targets, or being able to log into a database.
79              
80             The module is also usable before AnyEvent itself is initialised, in which
81             case some of the functionality might be reduced.
82              
83             The amount of documentation might indicate otherwise, but the runtime part
84             of the module is still just below 300 lines of code.
85              
86             =head1 LOGGING LEVELS
87              
88             Logging levels in this module range from C<1> (highest priority) to C<9>
89             (lowest priority). Note that the lowest numerical value is the highest
90             priority, so when this document says "higher priority" it means "lower
91             numerical value".
92              
93             Instead of specifying levels by name you can also specify them by aliases:
94              
95             LVL NAME SYSLOG PERL NOTE
96             1 fatal emerg exit system unusable, aborts program!
97             2 alert failure in primary system
98             3 critical crit failure in backup system
99             4 error err die non-urgent program errors, a bug
100             5 warn warning possible problem, not necessarily error
101             6 note notice unusual conditions
102             7 info normal messages, no action required
103             8 debug debugging messages for development
104             9 trace copious tracing output
105              
106             As you can see, some logging levels have multiple aliases - the first one
107             is the "official" name, the second one the "syslog" name (if it differs)
108             and the third one the "perl" name, suggesting (only!) that you log C
109             messages at C priority. The NOTE column tries to provide some
110             rationale on how to chose a logging level.
111              
112             As a rough guideline, levels 1..3 are primarily meant for users of the
113             program (admins, staff), and are the only ones logged to STDERR by
114             default. Levels 4..6 are meant for users and developers alike, while
115             levels 7..9 are usually meant for developers.
116              
117             You can normally only log a message once at highest priority level (C<1>,
118             C), because logging a fatal message will also quit the program - so
119             use it sparingly :)
120              
121             For example, a program that finds an unknown switch on the commandline
122             might well use a fatal logging level to tell users about it - the "system"
123             in this case would be the program, or module.
124              
125             Some methods also offer some extra levels, such as C<0>, C, C
126             or C - these are only valid for the methods that documented them.
127              
128             =head1 LOGGING FUNCTIONS
129              
130             The following functions allow you to log messages. They always use the
131             caller's package as a "logging context". Also, the main logging function,
132             C, is aliased to C and C when the C
133             module is loaded.
134              
135             =over 4
136              
137             =cut
138              
139             package AnyEvent::Log;
140              
141 1     1   7 use Carp ();
  1         2  
  1         21  
142 1     1   4 use POSIX ();
  1         2  
  1         13  
143              
144             # layout of a context
145             # 0 1 2 3 4, 5
146             # [$title, $level, %$slaves, &$logcb, &$fmtcb, $cap]
147              
148 1     1   4 use AnyEvent (); BEGIN { AnyEvent::common_sense }
  1     1   1  
  1         16  
  1         4  
149             #use AnyEvent::Util (); need to load this in a delayed fashion, as it uses AE::log
150              
151             our $VERSION = $AnyEvent::VERSION;
152              
153             our ($COLLECT, $FILTER, $LOG);
154              
155             our ($now_int, $now_str1, $now_str2);
156              
157             # Format Time, not public - yet?
158             sub format_time($) {
159 0     0 1 0 my $i = int $_[0];
160 0         0 my $f = sprintf "%06d", 1e6 * ($_[0] - $i);
161              
162 0 0       0 ($now_int, $now_str1, $now_str2) = ($i, split /\x01/, POSIX::strftime "%Y-%m-%d %H:%M:%S.\x01 %z", localtime $i)
163             if $now_int != $i;
164              
165 0         0 "$now_str1$f$now_str2"
166             }
167              
168             our %CTX; # all package contexts
169              
170             # creates a default package context object for the given package
171             sub _pkg_ctx($) {
172 2     2   8 my $ctx = bless [$_[0], (1 << 10) - 1 - 1, {}], "AnyEvent::Log::Ctx";
173              
174             # link "parent" package
175             my $parent = $_[0] =~ /^(.+)::/
176 2 100 33     24 ? $CTX{$1} ||= &_pkg_ctx ("$1")
177             : $COLLECT;
178              
179 2         7 $ctx->[2]{$parent+0} = $parent;
180              
181 2         6 $ctx
182             }
183              
184             =item AnyEvent::Log::log $level, $msg[, @args]
185              
186             Requests logging of the given C<$msg> with the given log level, and
187             returns true if the message was logged I.
188              
189             For loglevel C, the program will abort.
190              
191             If only a C<$msg> is given, it is logged as-is. With extra C<@args>, the
192             C<$msg> is interpreted as an sprintf format string.
193              
194             The C<$msg> should not end with C<\n>, but may if that is convenient for
195             you. Also, multiline messages are handled properly.
196              
197             Last not least, C<$msg> might be a code reference, in which case it is
198             supposed to return the message. It will be called only then the message
199             actually gets logged, which is useful if it is costly to create the
200             message in the first place.
201              
202             This function takes care of saving and restoring C<$!> and C<$@>, so you
203             don't have to.
204              
205             Whether the given message will be logged depends on the maximum log level
206             and the caller's package. The return value can be used to ensure that
207             messages or not "lost" - for example, when L detects a
208             runtime error it tries to log it at C level, but if that message is
209             lost it simply uses warn.
210              
211             Note that you can (and should) call this function as C or
212             C, without C-ing this module if possible (i.e. you don't
213             need any additional functionality), as those functions will load the
214             logging module on demand only. They are also much shorter to write.
215              
216             Also, if you optionally generate a lot of debug messages (such as when
217             tracing some code), you should look into using a logger callback and a
218             boolean enabler (see C, below).
219              
220             Example: log something at error level.
221              
222             AE::log error => "something";
223              
224             Example: use printf-formatting.
225              
226             AE::log info => "%5d %-10.10s %s", $index, $category, $msg;
227              
228             Example: only generate a costly dump when the message is actually being logged.
229              
230             AE::log debug => sub { require Data::Dump; Data::Dump::dump \%cache };
231              
232             =cut
233              
234             # also allow syslog equivalent names
235             our %STR2LEVEL = (
236             fatal => 1, emerg => 1, exit => 1,
237             alert => 2,
238             critical => 3, crit => 3,
239             error => 4, err => 4, die => 4,
240             warn => 5, warning => 5,
241             note => 6, notice => 6,
242             info => 7,
243             debug => 8,
244             trace => 9,
245             );
246              
247             our $TIME_EXACT;
248              
249             sub exact_time($) {
250 2     2 1 4 $TIME_EXACT = shift;
251             *_ts = $AnyEvent::MODEL
252             ? $TIME_EXACT ? \&AE::now : \&AE::time
253 2 50   0   3501 : sub () { $TIME_EXACT ? do { require Time::HiRes; Time::HiRes::time () } : time };
  0 0       0  
  0 50       0  
  0         0  
254             }
255              
256             BEGIN {
257 1     1   6 exact_time 0;
258             }
259              
260             AnyEvent::post_detect {
261             exact_time $TIME_EXACT;
262             };
263              
264             our @LEVEL2STR = qw(0 fatal alert crit error warn note info debug trace);
265              
266             # time, ctx, level, msg
267             sub default_format($$$$) {
268 0     0 1 0 my $ts = format_time $_[0];
269 0         0 my $ct = " ";
270              
271 0         0 my @res;
272              
273 0         0 for (split /\n/, sprintf "%-5s %s: %s", $LEVEL2STR[$_[2]], $_[1][0], $_[3]) {
274 0         0 push @res, "$ts$ct$_\n";
275 0         0 $ct = " + ";
276             }
277              
278 0         0 join "", @res
279             }
280              
281             sub fatal_exit() {
282 0     0 1 0 exit 1;
283             }
284              
285             sub _log {
286 1     1   4 my ($ctx, $level, $format, @args) = @_;
287              
288             $level = $level > 0 && $level <= 9
289             ? $level+0
290 1 50 33     6 : $STR2LEVEL{$level} || Carp::croak "$level: not a valid logging level, caught";
      0        
291              
292 1         2 my $mask = 1 << $level;
293              
294 1         3 my ($success, %seen, @ctx, $now, @fmt);
295              
296             do
297 1         2 {
298             # if !ref, then it's a level number
299 4 50 66     29 if (!ref $ctx) {
    100          
300 0         0 $level = $ctx;
301             } elsif ($ctx->[1] & $mask and !$seen{$ctx+0}++) {
302             # logging/recursing into this context
303              
304             # level cap
305 3 50       10 if ($ctx->[5] > $level) {
306 0         0 push @ctx, $level; # restore level when going up in tree
307 0         0 $level = $ctx->[5];
308             }
309              
310             # log if log cb
311 3 50       6 if ($ctx->[3]) {
312             # logging target found
313              
314 0         0 local ($!, $@);
315              
316             # now get raw message, unless we have it already
317 0 0       0 unless ($now) {
318 0 0       0 $format = $format->() if ref $format;
319 0 0       0 $format = sprintf $format, @args if @args;
320 0         0 $format =~ s/\n$//;
321 0         0 $now = _ts;
322             };
323              
324             # format msg
325 0 0 0     0 my $str = $ctx->[4]
326             ? $ctx->[4]($now, $_[0], $level, $format)
327             : ($fmt[$level] ||= default_format $now, $_[0], $level, $format);
328              
329 0         0 $success = 1;
330              
331             $ctx->[3]($str)
332 0 0       0 or push @ctx, values %{ $ctx->[2] }; # not consumed - propagate
  0         0  
333             } else {
334 3         5 push @ctx, values %{ $ctx->[2] }; # not masked - propagate
  3         11  
335             }
336             }
337             }
338             while $ctx = pop @ctx;
339              
340 1 50       3 fatal_exit if $level <= 1;
341              
342 1         4 $success
343             }
344              
345             sub log($$;@) {
346             _log
347 1   33 1 1 9 $CTX{ (caller)[0] } ||= _pkg_ctx +(caller)[0],
348             @_;
349             }
350              
351             =item $logger = AnyEvent::Log::logger $level[, \$enabled]
352              
353             Creates a code reference that, when called, acts as if the
354             C function was called at this point with the given
355             level. C<$logger> is passed a C<$msg> and optional C<@args>, just as with
356             the C function:
357              
358             my $debug_log = AnyEvent::Log::logger "debug";
359              
360             $debug_log->("debug here");
361             $debug_log->("%06d emails processed", 12345);
362             $debug_log->(sub { $obj->as_string });
363              
364             The idea behind this function is to decide whether to log before actually
365             logging - when the C function is called once, but the returned
366             logger callback often, then this can be a tremendous speed win.
367              
368             Despite this speed advantage, changes in logging configuration will
369             still be reflected by the logger callback, even if configuration changes
370             I it was created.
371              
372             To further speed up logging, you can bind a scalar variable to the logger,
373             which contains true if the logger should be called or not - if it is
374             false, calling the logger can be safely skipped. This variable will be
375             updated as long as C<$logger> is alive.
376              
377             Full example:
378              
379             # near the init section
380             use AnyEvent::Log;
381              
382             my $debug_log = AnyEvent:Log::logger debug => \my $debug;
383              
384             # and later in your program
385             $debug_log->("yo, stuff here") if $debug;
386              
387             $debug and $debug_log->("123");
388              
389             =cut
390              
391             our %LOGGER;
392              
393             # re-assess logging status for all loggers
394             sub _reassess {
395 2     2   7 local $SIG{__DIE__};
396 2     0   6 my $die = sub { die };
  0         0  
397              
398 2 50       12 for (@_ ? $LOGGER{$_[0]} : values %LOGGER) {
399 0         0 my ($ctx, $level, $renabled) = @$_;
400              
401             # to detect whether a message would be logged, we actually
402             # try to log one and die. this isn't fast, but we can be
403             # sure that the logging decision is correct :)
404              
405 0         0 $$renabled = !eval {
406 0         0 _log $ctx, $level, $die;
407              
408 0         0 1
409             };
410             }
411             }
412              
413             sub _logger {
414 0     0   0 my ($ctx, $level, $renabled) = @_;
415              
416 0         0 $$renabled = 1;
417              
418 0         0 my $logger = [$ctx, $level, $renabled];
419              
420 0         0 $LOGGER{$logger+0} = $logger;
421              
422 0         0 _reassess $logger+0;
423              
424 0 0       0 require AnyEvent::Util unless $AnyEvent::Util::VERSION;
425             my $guard = AnyEvent::Util::guard (sub {
426             # "clean up"
427 0     0   0 delete $LOGGER{$logger+0};
428 0         0 });
429              
430             sub {
431 0     0   0 $guard if 0; # keep guard alive, but don't cause runtime overhead
432              
433 0 0       0 _log $ctx, $level, @_
434             if $$renabled;
435             }
436 0         0 }
437              
438             sub logger($;$) {
439             _logger
440 0   0 0 1 0 $CTX{ (caller)[0] } ||= _pkg_ctx +(caller)[0],
441             @_
442             }
443              
444             =item AnyEvent::Log::exact_time $on
445              
446             By default, C will use C, i.e. the cached
447             eventloop time, for the log timestamps. After calling this function with a
448             true value it will instead resort to C, i.e. fetch the current
449             time on each log message. This only makes a difference for event loops
450             that actually cache the time (such as L or L).
451              
452             This setting can be changed at any time by calling this function.
453              
454             Since C has to work even before the L has been
455             initialised, this switch will also decide whether to use C or
456             C when logging a message before L becomes
457             available.
458              
459             =item AnyEvent::Log::format_time $timestamp
460              
461             Formats a timestamp as returned by C<< AnyEvent->now >> or C<<
462             AnyEvent->time >> or many other functions in the same way as
463             C does.
464              
465             In your main program (as opposed to in your module) you can override
466             the default timestamp display format by loading this module and then
467             redefining this function.
468              
469             Most commonly, this function can be used in formatting callbacks.
470              
471             =item AnyEvent::Log::default_format $time, $ctx, $level, $msg
472              
473             Format a log message using the given timestamp, logging context, log level
474             and log message.
475              
476             This is the formatting function used to format messages when no custom
477             function is provided.
478              
479             In your main program (as opposed to in your module) you can override the
480             default message format by loading this module and then redefining this
481             function.
482              
483             =item AnyEvent::Log::fatal_exit
484              
485             This is the function that is called after logging a C log
486             message. It must not return.
487              
488             The default implementation simply calls C.
489              
490             In your main program (as opposed to in your module) you can override
491             the fatal exit function by loading this module and then redefining this
492             function. Make sure you don't return.
493              
494             =back
495              
496             =head1 LOGGING CONTEXTS
497              
498             This module associates every log message with a so-called I
499             context>, based on the package of the caller. Every perl package has its
500             own logging context.
501              
502             A logging context has three major responsibilities: filtering, logging and
503             propagating the message.
504              
505             For the first purpose, filtering, each context has a set of logging
506             levels, called the log level mask. Messages not in the set will be ignored
507             by this context (masked).
508              
509             For logging, the context stores a formatting callback (which takes the
510             timestamp, context, level and string message and formats it in the way
511             it should be logged) and a logging callback (which is responsible for
512             actually logging the formatted message and telling C
513             whether it has consumed the message, or whether it should be propagated).
514              
515             For propagation, a context can have any number of attached I
516             contexts>. Any message that is neither masked by the logging mask nor
517             masked by the logging callback returning true will be passed to all slave
518             contexts.
519              
520             Each call to a logging function will log the message at most once per
521             context, so it does not matter (much) if there are cycles or if the
522             message can arrive at the same context via multiple paths.
523              
524             =head2 DEFAULTS
525              
526             By default, all logging contexts have an full set of log levels ("all"), a
527             disabled logging callback and the default formatting callback.
528              
529             Package contexts have the package name as logging title by default.
530              
531             They have exactly one slave - the context of the "parent" package. The
532             parent package is simply defined to be the package name without the last
533             component, i.e. C becomes C,
534             and C becomes ... C<$AnyEvent::Log::COLLECT> which is the
535             exception of the rule - just like the "parent" of any single-component
536             package name in Perl is C
, the default slave of any top-level
537             package context is C<$AnyEvent::Log::COLLECT>.
538              
539             Since perl packages form only an approximate hierarchy, this slave
540             context can of course be removed.
541              
542             All other (anonymous) contexts have no slaves and an empty title by
543             default.
544              
545             When the module is loaded it creates the C<$AnyEvent::Log::LOG> logging
546             context that simply logs everything via C, without propagating
547             anything anywhere by default. The purpose of this context is to provide
548             a convenient place to override the global logging target or to attach
549             additional log targets. It's not meant for filtering.
550              
551             It then creates the C<$AnyEvent::Log::FILTER> context whose
552             purpose is to suppress all messages with priority higher
553             than C<$ENV{PERL_ANYEVENT_VERBOSE}>. It then attached the
554             C<$AnyEvent::Log::LOG> context to it. The purpose of the filter context
555             is to simply provide filtering according to some global log level.
556              
557             Finally it creates the top-level package context C<$AnyEvent::Log::COLLECT>
558             and attaches the C<$AnyEvent::Log::FILTER> context to it, but otherwise
559             leaves it at default config. Its purpose is simply to collect all log
560             messages system-wide.
561              
562             The hierarchy is then:
563              
564             any package, eventually -> $COLLECT -> $FILTER -> $LOG
565              
566             The effect of all this is that log messages, by default, wander up to the
567             C<$AnyEvent::Log::COLLECT> context where all messages normally end up,
568             from there to C<$AnyEvent::Log::FILTER> where log messages with lower
569             priority then C<$ENV{PERL_ANYEVENT_VERBOSE}> will be filtered out and then
570             to the C<$AnyEvent::Log::LOG> context to be passed to C.
571              
572             This makes it easy to set a global logging level (by modifying $FILTER),
573             but still allow other contexts to send, for example, their debug and trace
574             messages to the $LOG target despite the global logging level, or to attach
575             additional log targets that log messages, regardless of the global logging
576             level.
577              
578             It also makes it easy to modify the default warn-logger ($LOG) to
579             something that logs to a file, or to attach additional logging targets
580             (such as loggign to a file) by attaching it to $FILTER.
581              
582             =head2 CREATING/FINDING/DESTROYING CONTEXTS
583              
584             =over 4
585              
586             =item $ctx = AnyEvent::Log::ctx [$pkg]
587              
588             This function creates or returns a logging context (which is an object).
589              
590             If a package name is given, then the context for that packlage is
591             returned. If it is called without any arguments, then the context for the
592             callers package is returned (i.e. the same context as a C call
593             would use).
594              
595             If C is given, then it creates a new anonymous context that is not
596             tied to any package and is destroyed when no longer referenced.
597              
598             =cut
599              
600             sub ctx(;$) {
601 5 50   5 1 11 my $pkg = @_ ? shift : (caller)[0];
602              
603             ref $pkg
604             ? $pkg
605             : defined $pkg
606 5 50 0     27 ? $CTX{$pkg} ||= AnyEvent::Log::_pkg_ctx $pkg
    100          
607             : bless [undef, (1 << 10) - 1 - 1], "AnyEvent::Log::Ctx"
608             }
609              
610             =item AnyEvent::Log::reset
611              
612             Resets all package contexts and recreates the default hierarchy if
613             necessary, i.e. resets the logging subsystem to defaults, as much as
614             possible. This process keeps references to contexts held by other parts of
615             the program intact.
616              
617             This can be used to implement config-file (re-)loading: before loading a
618             configuration, reset all contexts.
619              
620             =cut
621              
622             our $ORIG_VERBOSE = $AnyEvent::VERBOSE;
623             $AnyEvent::VERBOSE = 9;
624              
625             sub reset {
626             # hard to kill complex data structures
627             # we "recreate" all package loggers and reset the hierarchy
628 1     1 1 6 while (my ($k, $v) = each %CTX) {
629 0         0 @$v = ($k, (1 << 10) - 1 - 1, { });
630              
631 0 0       0 $v->attach ($k =~ /^(.+)::/ ? $CTX{$1} : $AnyEvent::Log::COLLECT);
632             }
633              
634             @$_ = ($_->[0], (1 << 10) - 1 - 1)
635 1         11 for $LOG, $FILTER, $COLLECT;
636              
637             #$LOG->slaves;
638 1         4 $LOG->title ('$AnyEvent::Log::LOG');
639 1         3 $LOG->log_to_warn;
640              
641 1         3 $FILTER->slaves ($LOG);
642 1         3 $FILTER->title ('$AnyEvent::Log::FILTER');
643 1         4 $FILTER->level ($ORIG_VERBOSE);
644              
645 1         4 $COLLECT->slaves ($FILTER);
646 1         2 $COLLECT->title ('$AnyEvent::Log::COLLECT');
647              
648 1         2 _reassess;
649             }
650              
651             # override AE::log/logger
652             *AnyEvent::log = *AE::log = \&log;
653             *AnyEvent::logger = *AE::logger = \&logger;
654              
655             # convert AnyEvent loggers to AnyEvent::Log loggers
656             $_->[0] = ctx $_->[0] # convert "pkg" to "ctx"
657             for values %LOGGER;
658              
659             # create the default logger contexts
660             $LOG = ctx undef;
661             $FILTER = ctx undef;
662             $COLLECT = ctx undef;
663              
664             AnyEvent::Log::reset;
665              
666             # hello, CPAN, please catch me
667             package AnyEvent::Log::LOG;
668             package AE::Log::LOG;
669             package AnyEvent::Log::FILTER;
670             package AE::Log::FILTER;
671             package AnyEvent::Log::COLLECT;
672             package AE::Log::COLLECT;
673              
674             package AnyEvent::Log::Ctx;
675              
676             =item $ctx = new AnyEvent::Log::Ctx methodname => param...
677              
678             This is a convenience constructor that makes it simpler to construct
679             anonymous logging contexts.
680              
681             Each key-value pair results in an invocation of the method of the same
682             name as the key with the value as parameter, unless the value is an
683             arrayref, in which case it calls the method with the contents of the
684             array. The methods are called in the same order as specified.
685              
686             Example: create a new logging context and set both the default logging
687             level, some slave contexts and a logging callback.
688              
689             $ctx = new AnyEvent::Log::Ctx
690             title => "dubious messages",
691             level => "error",
692             log_cb => sub { print STDOUT shift; 0 },
693             slaves => [$ctx1, $ctx, $ctx2],
694             ;
695              
696             =back
697              
698             =cut
699              
700             sub new {
701 0     0   0 my $class = shift;
702              
703 0         0 my $ctx = AnyEvent::Log::ctx undef;
704              
705 0         0 while (@_) {
706 0         0 my ($k, $v) = splice @_, 0, 2;
707 0 0       0 $ctx->$k (ref $v eq "ARRAY" ? @$v : $v);
708             }
709              
710 0         0 bless $ctx, $class # do we really support subclassing, hmm?
711             }
712              
713              
714             =head2 CONFIGURING A LOG CONTEXT
715              
716             The following methods can be used to configure the logging context.
717              
718             =over 4
719              
720             =item $ctx->title ([$new_title])
721              
722             Returns the title of the logging context - this is the package name, for
723             package contexts, and a user defined string for all others.
724              
725             If C<$new_title> is given, then it replaces the package name or title.
726              
727             =cut
728              
729             sub title {
730 3 50   3   10 $_[0][0] = $_[1] if @_ > 1;
731 3         4 $_[0][0]
732             }
733              
734             =back
735              
736             =head3 LOGGING LEVELS
737              
738             The following methods deal with the logging level set associated with the
739             log context.
740              
741             The most common method to use is probably C<< $ctx->level ($level) >>,
742             which configures the specified and any higher priority levels.
743              
744             All functions which accept a list of levels also accept the special string
745             C which expands to all logging levels.
746              
747             =over 4
748              
749             =item $ctx->levels ($level[, $level...)
750              
751             Enables logging for the given levels and disables it for all others.
752              
753             =item $ctx->level ($level)
754              
755             Enables logging for the given level and all lower level (higher priority)
756             ones. In addition to normal logging levels, specifying a level of C<0> or
757             C disables all logging for this level.
758              
759             Example: log warnings, errors and higher priority messages.
760              
761             $ctx->level ("warn");
762             $ctx->level (5); # same thing, just numeric
763              
764             =item $ctx->enable ($level[, $level...])
765              
766             Enables logging for the given levels, leaving all others unchanged.
767              
768             =item $ctx->disable ($level[, $level...])
769              
770             Disables logging for the given levels, leaving all others unchanged.
771              
772             =item $ctx->cap ($level)
773              
774             Caps the maximum priority to the given level, for all messages logged
775             to, or passing through, this context. That is, while this doesn't affect
776             whether a message is logged or passed on, the maximum priority of messages
777             will be limited to the specified level - messages with a higher priority
778             will be set to the specified priority.
779              
780             Another way to view this is that C<< ->level >> filters out messages with
781             a too low priority, while C<< ->cap >> modifies messages with a too high
782             priority.
783              
784             This is useful when different log targets have different interpretations
785             of priority. For example, for a specific command line program, a wrong
786             command line switch might well result in a C log message, while the
787             same message, logged to syslog, is likely I fatal to the system or
788             syslog facility as a whole, but more likely a mere C.
789              
790             This can be modeled by having a stderr logger that logs messages "as-is"
791             and a syslog logger that logs messages with a level cap of, say, C,
792             or, for truly system-critical components, actually C.
793              
794             =cut
795              
796             sub _lvl_lst {
797             map {
798 1     1   2 $_ > 0 && $_ <= 9 ? $_+0
799             : $_ eq "all" ? (1 .. 9)
800 1 0 33     9 : $STR2LEVEL{$_} || Carp::croak "$_: not a valid logging level, caught"
    50 0        
801             } @_
802             }
803              
804             sub _lvl {
805 1 50   1   7 $_[0] =~ /^(?:0|off|none)$/ ? 0 : (_lvl_lst $_[0])[-1]
806             }
807              
808             our $NOP_CB = sub { 0 };
809              
810             sub levels {
811 0     0   0 my $ctx = shift;
812 0         0 $ctx->[1] = 0;
813             $ctx->[1] |= 1 << $_
814 0         0 for &_lvl_lst;
815 0         0 AnyEvent::Log::_reassess;
816             }
817              
818             sub level {
819 1     1   2 my $ctx = shift;
820 1         2 $ctx->[1] = ((1 << &_lvl) - 1) << 1;
821 1         3 AnyEvent::Log::_reassess;
822             }
823              
824             sub enable {
825 0     0   0 my $ctx = shift;
826             $ctx->[1] |= 1 << $_
827 0         0 for &_lvl_lst;
828 0         0 AnyEvent::Log::_reassess;
829             }
830              
831             sub disable {
832 0     0   0 my $ctx = shift;
833             $ctx->[1] &= ~(1 << $_)
834 0         0 for &_lvl_lst;
835 0         0 AnyEvent::Log::_reassess;
836             }
837              
838             sub cap {
839 0     0   0 my $ctx = shift;
840 0         0 $ctx->[5] = &_lvl;
841             }
842              
843             =back
844              
845             =head3 SLAVE CONTEXTS
846              
847             The following methods attach and detach another logging context to a
848             logging context.
849              
850             Log messages are propagated to all slave contexts, unless the logging
851             callback consumes the message.
852              
853             =over 4
854              
855             =item $ctx->attach ($ctx2[, $ctx3...])
856              
857             Attaches the given contexts as slaves to this context. It is not an error
858             to add a context twice (the second add will be ignored).
859              
860             A context can be specified either as package name or as a context object.
861              
862             =item $ctx->detach ($ctx2[, $ctx3...])
863              
864             Removes the given slaves from this context - it's not an error to attempt
865             to remove a context that hasn't been added.
866              
867             A context can be specified either as package name or as a context object.
868              
869             =item $ctx->slaves ($ctx2[, $ctx3...])
870              
871             Replaces all slaves attached to this context by the ones given.
872              
873             =cut
874              
875             sub attach {
876 2     2   3 my $ctx = shift;
877              
878             $ctx->[2]{$_+0} = $_
879 2         90 for map { AnyEvent::Log::ctx $_ } @_;
  2         7  
880             }
881              
882             sub detach {
883 0     0   0 my $ctx = shift;
884              
885             delete $ctx->[2]{$_+0}
886 0         0 for map { AnyEvent::Log::ctx $_ } @_;
  0         0  
887             }
888              
889             sub slaves {
890 2     2   4 undef $_[0][2];
891 2         4 &attach;
892             }
893              
894             =back
895              
896             =head3 LOG TARGETS
897              
898             The following methods configure how the logging context actually does
899             the logging (which consists of formatting the message and printing it or
900             whatever it wants to do with it).
901              
902             =over 4
903              
904             =item $ctx->log_cb ($cb->($str))
905              
906             Replaces the logging callback on the context (C disables the
907             logging callback).
908              
909             The logging callback is responsible for handling formatted log messages
910             (see C below) - normally simple text strings that end with a
911             newline (and are possibly multiline themselves).
912              
913             It also has to return true iff it has consumed the log message, and false
914             if it hasn't. Consuming a message means that it will not be sent to any
915             slave context. When in doubt, return C<0> from your logging callback.
916              
917             Example: a very simple logging callback, simply dump the message to STDOUT
918             and do not consume it.
919              
920             $ctx->log_cb (sub { print STDERR shift; 0 });
921              
922             You can filter messages by having a log callback that simply returns C<1>
923             and does not do anything with the message, but this counts as "message
924             being logged" and might not be very efficient.
925              
926             Example: propagate all messages except for log levels "debug" and
927             "trace". The messages will still be generated, though, which can slow down
928             your program.
929              
930             $ctx->levels ("debug", "trace");
931             $ctx->log_cb (sub { 1 }); # do not log, but eat debug and trace messages
932              
933             =item $ctx->fmt_cb ($fmt_cb->($timestamp, $orig_ctx, $level, $message))
934              
935             Replaces the formatting callback on the context (C restores the
936             default formatter).
937              
938             The callback is passed the (possibly fractional) timestamp, the original
939             logging context (object, not title), the (numeric) logging level and
940             the raw message string and needs to return a formatted log message. In
941             most cases this will be a string, but it could just as well be an array
942             reference that just stores the values.
943              
944             If, for some reason, you want to use C to find out more about the
945             logger then you should walk up the call stack until you are no longer
946             inside the C package.
947              
948             To implement your own logging callback, you might find the
949             C and C
950             functions useful.
951              
952             Example: format the message just as AnyEvent::Log would, by letting
953             AnyEvent::Log do the work. This is a good basis to design a formatting
954             callback that only changes minor aspects of the formatting.
955              
956             $ctx->fmt_cb (sub {
957             my ($time, $ctx, $lvl, $msg) = @_;
958              
959             AnyEvent::Log::default_format $time, $ctx, $lvl, $msg
960             });
961              
962             Example: format just the raw message, with numeric log level in angle
963             brackets.
964              
965             $ctx->fmt_cb (sub {
966             my ($time, $ctx, $lvl, $msg) = @_;
967              
968             "<$lvl>$msg\n"
969             });
970              
971             Example: return an array reference with just the log values, and use
972             C to store the message in a database.
973              
974             $ctx->fmt_cb (sub { \@_ });
975             $ctx->log_cb (sub {
976             my ($msg) = @_;
977              
978             sql_exec "insert into log (when, subsys, prio, msg) values (?, ?, ?, ?)",
979             $msg->[0] + 0,
980             "$msg->[1]",
981             $msg->[2] + 0,
982             "$msg->[3]";
983              
984             0
985             });
986              
987             =item $ctx->log_to_warn
988              
989             Sets the C to simply use C to report any messages
990             (usually this logs to STDERR).
991              
992             =item $ctx->log_to_file ($path)
993              
994             Sets the C to log to a file (by appending), unbuffered. The
995             function might return before the log file has been opened or created.
996              
997             =item $ctx->log_to_path ($path)
998              
999             Same as C<< ->log_to_file >>, but opens the file for each message. This
1000             is much slower, but allows you to change/move/rename/delete the file at
1001             basically any time.
1002              
1003             Needless(?) to say, if you do not want to be bitten by some evil person
1004             calling C, the path should be absolute. Doesn't help with
1005             C, but hey...
1006              
1007             =item $ctx->log_to_syslog ([$facility])
1008              
1009             Logs all messages via L, mapping C to C and
1010             all the others in the obvious way. If specified, then the C<$facility> is
1011             used as the facility (C, C, C and so on). The default
1012             facility is C.
1013              
1014             Note that this function also sets a C - the logging part requires
1015             an array reference with [$level, $str] as input.
1016              
1017             =cut
1018              
1019             sub log_cb {
1020 1     1   2 my ($ctx, $cb) = @_;
1021              
1022 1         3 $ctx->[3] = $cb;
1023             }
1024              
1025             sub fmt_cb {
1026 0     0   0 my ($ctx, $cb) = @_;
1027              
1028 0         0 $ctx->[4] = $cb;
1029             }
1030              
1031             sub log_to_warn {
1032 1     1   2 my ($ctx, $path) = @_;
1033              
1034             $ctx->log_cb (sub {
1035 0     0     warn shift;
1036 0           0
1037 1         4 });
1038             }
1039              
1040             # this function is a good example of why threads are a must,
1041             # simply for priority inversion.
1042             sub _log_to_disk {
1043             # eval'uating this at runtime saves 220kb rss - perl has become
1044             # an insane memory waster.
1045 0     0     eval q{ # poor man's autoloading {}
1046             sub _log_to_disk {
1047             my ($ctx, $path, $keepopen) = @_;
1048              
1049             my $fh;
1050             my @queue;
1051             my $delay;
1052             my $disable;
1053              
1054             use AnyEvent::IO ();
1055              
1056             my $kick = sub {
1057             undef $delay;
1058             return unless @queue;
1059             $delay = 1;
1060              
1061             # we pass $kick to $kick, so $kick itself doesn't keep a reference to $kick.
1062             my $kick = shift;
1063              
1064             # write one or more messages
1065             my $write = sub {
1066             # we write as many messages as have been queued
1067             my $data = join "", @queue;
1068             @queue = ();
1069              
1070             AnyEvent::IO::aio_write $fh, $data, sub {
1071             $disable = 1;
1072             @_
1073             ? ($_[0] == length $data or AE::log 4 => "unable to write to logfile '$path': short write")
1074             : AE::log 4 => "unable to write to logfile '$path': $!";
1075             undef $disable;
1076              
1077             if ($keepopen) {
1078             $kick->($kick);
1079             } else {
1080             AnyEvent::IO::aio_close ($fh, sub {
1081             undef $fh;
1082             $kick->($kick);
1083             });
1084             }
1085             };
1086             };
1087              
1088             if ($fh) {
1089             $write->();
1090             } else {
1091             AnyEvent::IO::aio_open
1092             $path,
1093             AnyEvent::IO::O_CREAT | AnyEvent::IO::O_WRONLY | AnyEvent::IO::O_APPEND,
1094             0666,
1095             sub {
1096             $fh = shift
1097             or do {
1098             $disable = 1;
1099             AE::log 4 => "unable to open logfile '$path': $!";
1100             undef $disable;
1101             return;
1102             };
1103              
1104             $write->();
1105             }
1106             ;
1107             }
1108             };
1109              
1110             $ctx->log_cb (sub {
1111             return if $disable;
1112             push @queue, shift;
1113             $kick->($kick) unless $delay;
1114             0
1115             });
1116              
1117             $kick->($kick) if $keepopen; # initial open
1118             };
1119             };
1120 0 0         die if $@;
1121 0           &_log_to_disk
1122             }
1123              
1124             sub log_to_file {
1125 0     0     my ($ctx, $path) = @_;
1126              
1127 0           _log_to_disk $ctx, $path, 1;
1128             }
1129              
1130             sub log_to_path {
1131 0     0     my ($ctx, $path) = @_;
1132              
1133 0           _log_to_disk $ctx, $path, 0;
1134             }
1135              
1136             sub log_to_syslog {
1137 0     0     my ($ctx, $facility) = @_;
1138              
1139 0           require Sys::Syslog;
1140              
1141             $ctx->fmt_cb (sub {
1142 0     0     my $str = $_[3];
1143 0           $str =~ s/\n(?=.)/\n+ /g;
1144              
1145 0           [$_[2], "($_[1][0]) $str"]
1146 0           });
1147              
1148 0   0       $facility ||= "user";
1149              
1150             $ctx->log_cb (sub {
1151 0 0   0     my $lvl = $_[0][0] < 9 ? $_[0][0] : 8;
1152              
1153             Sys::Syslog::syslog ("$facility|" . ($lvl - 1), $_)
1154 0           for split /\n/, $_[0][1];
1155              
1156 0           0
1157 0           });
1158             }
1159              
1160             =back
1161              
1162             =head3 MESSAGE LOGGING
1163              
1164             These methods allow you to log messages directly to a context, without
1165             going via your package context.
1166              
1167             =over 4
1168              
1169             =item $ctx->log ($level, $msg[, @params])
1170              
1171             Same as C, but uses the given context as log context.
1172              
1173             Example: log a message in the context of another package.
1174              
1175             (AnyEvent::Log::ctx "Other::Package")->log (warn => "heely bo");
1176              
1177             =item $logger = $ctx->logger ($level[, \$enabled])
1178              
1179             Same as C, but uses the given context as log
1180             context.
1181              
1182             =cut
1183              
1184             *log = \&AnyEvent::Log::_log;
1185             *logger = \&AnyEvent::Log::_logger;
1186              
1187             =back
1188              
1189             =cut
1190              
1191             package AnyEvent::Log;
1192              
1193             =head1 CONFIGURATION VIA $ENV{PERL_ANYEVENT_LOG}
1194              
1195             Logging can also be configured by setting the environment variable
1196             C (or C).
1197              
1198             The value consists of one or more logging context specifications separated
1199             by C<:> or whitespace. Each logging specification in turn starts with a
1200             context name, followed by C<=>, followed by zero or more comma-separated
1201             configuration directives, here are some examples:
1202              
1203             # set default logging level
1204             filter=warn
1205              
1206             # log to file instead of to stderr
1207             log=file=/tmp/mylog
1208              
1209             # log to file in addition to stderr
1210             log=+%file:%file=file=/tmp/mylog
1211              
1212             # enable debug log messages, log warnings and above to syslog
1213             filter=debug:log=+%warnings:%warnings=warn,syslog=LOG_LOCAL0
1214              
1215             # log trace messages (only) from AnyEvent::Debug to file
1216             AnyEvent::Debug=+%trace:%trace=only,trace,file=/tmp/tracelog
1217              
1218             A context name in the log specification can be any of the following:
1219              
1220             =over 4
1221              
1222             =item C, C, C
1223              
1224             Correspond to the three predefined C<$AnyEvent::Log::COLLECT>,
1225             C and C<$AnyEvent::Log::LOG> contexts.
1226              
1227             =item C<%name>
1228              
1229             Context names starting with a C<%> are anonymous contexts created when the
1230             name is first mentioned. The difference to package contexts is that by
1231             default they have no attached slaves.
1232              
1233             This makes it possible to create new log contexts that can be refered to
1234             multiple times by name within the same log specification.
1235              
1236             =item a perl package name
1237              
1238             Any other string references the logging context associated with the given
1239             Perl C. In the unlikely case where you want to specify a package
1240             context that matches on of the other context name forms, you can add a
1241             C<::> to the package name to force interpretation as a package.
1242              
1243             =back
1244              
1245             The configuration specifications can be any number of the following:
1246              
1247             =over 4
1248              
1249             =item C
1250              
1251             Configures the context to use Perl's C function (which typically
1252             logs to C). Works like C.
1253              
1254             =item CI
1255              
1256             Configures the context to log to a file with the given path. Works like
1257             C.
1258              
1259             =item CI
1260              
1261             Configures the context to log to a file with the given path. Works like
1262             C.
1263              
1264             =item C or CI
1265              
1266             Configures the context to log to syslog. If I is given, then it is
1267             evaluated in the L package, so you could use:
1268              
1269             log=syslog=LOG_LOCAL0
1270              
1271             =item C
1272              
1273             Configures the context to not log anything by itself, which is the
1274             default. Same as C<< $ctx->log_cb (undef) >>.
1275              
1276             =item CI
1277              
1278             Caps logging messages entering this context at the given level, i.e.
1279             reduces the priority of messages with higher priority than this level. The
1280             default is C<0> (or C), meaning the priority will not be touched.
1281              
1282             =item C<0> or C
1283              
1284             Sets the logging level of the context to C<0>, i.e. all messages will be
1285             filtered out.
1286              
1287             =item C
1288              
1289             Enables all logging levels, i.e. filtering will effectively be switched
1290             off (the default).
1291              
1292             =item C
1293              
1294             Disables all logging levels, and changes the interpretation of following
1295             level specifications to enable the specified level only.
1296              
1297             Example: only enable debug messages for a context.
1298              
1299             context=only,debug
1300              
1301             =item C
1302              
1303             Enables all logging levels, and changes the interpretation of following
1304             level specifications to disable that level. Rarely used.
1305              
1306             Example: enable all logging levels except fatal and trace (this is rather
1307             nonsensical).
1308              
1309             filter=exept,fatal,trace
1310              
1311             =item C
1312              
1313             Enables all logging levels, and changes the interpretation of following
1314             level specifications to be "that level or any higher priority
1315             message". This is the default.
1316              
1317             Example: log anything at or above warn level.
1318              
1319             filter=warn
1320              
1321             # or, more verbose
1322             filter=only,level,warn
1323              
1324             =item C<1>..C<9> or a logging level name (C, C etc.)
1325              
1326             A numeric loglevel or the name of a loglevel will be interpreted according
1327             to the most recent C, C or C directive. By default,
1328             specifying a logging level enables that and any higher priority messages.
1329              
1330             =item C<+>I
1331              
1332             Attaches the named context as slave to the context.
1333              
1334             =item C<+>
1335              
1336             A lone C<+> detaches all contexts, i.e. clears the slave list from the
1337             context. Anonymous (C<%name>) contexts have no attached slaves by default,
1338             but package contexts have the parent context as slave by default.
1339              
1340             Example: log messages from My::Module to a file, do not send them to the
1341             default log collector.
1342              
1343             My::Module=+,file=/tmp/mymodulelog
1344              
1345             =back
1346              
1347             Any character can be escaped by prefixing it with a C<\> (backslash), as
1348             usual, so to log to a file containing a comma, colon, backslash and some
1349             spaces in the filename, you would do this:
1350              
1351             PERL_ANYEVENT_LOG='log=file=/some\ \:file\ with\,\ \\-escapes'
1352              
1353             Since whitespace (which includes newlines) is allowed, it is fine to
1354             specify multiple lines in C, e.g.:
1355              
1356             PERL_ANYEVENT_LOG="
1357             filter=warn
1358             AnyEvent::Debug=+%trace
1359             %trace=only,trace,+log
1360             " myprog
1361              
1362             Also, in the unlikely case when you want to concatenate specifications,
1363             use whitespace as separator, as C<::> will be interpreted as part of a
1364             module name, an empty spec with two separators:
1365              
1366             PERL_ANYEVENT_LOG="$PERL_ANYEVENT_LOG MyMod=debug"
1367              
1368             =cut
1369              
1370             for (my $spec = $ENV{PERL_ANYEVENT_LOG}) {
1371             my %anon;
1372              
1373             my $pkg = sub {
1374             $_[0] eq "log" ? $LOG
1375             : $_[0] eq "filter" ? $FILTER
1376             : $_[0] eq "collect" ? $COLLECT
1377             : $_[0] =~ /^%(.+)$/ ? ($anon{$1} ||= do { my $ctx = ctx undef; $ctx->[0] = $_[0]; $ctx })
1378             : $_[0] =~ /^(.*?)(?:::)?$/ ? ctx "$1" # egad :/
1379             : die # never reached?
1380             };
1381              
1382             /\G[[:space:]]+/gc; # skip initial whitespace
1383              
1384             while (/\G((?:[^:=[:space:]]+|::|\\.)+)=/gc) {
1385             my $ctx = $pkg->($1);
1386             my $level = "level";
1387              
1388             while (/\G((?:[^,:[:space:]]+|::|\\.)+)/gc) {
1389             for ("$1") {
1390             if ($_ eq "stderr" ) { $ctx->log_to_warn;
1391             } elsif (/^file=(.+)/ ) { $ctx->log_to_file ("$1");
1392             } elsif (/^path=(.+)/ ) { $ctx->log_to_path ("$1");
1393             } elsif (/^syslog(?:=(.*))?/ ) { require Sys::Syslog; $ctx->log_to_syslog ("$1");
1394             } elsif ($_ eq "nolog" ) { $ctx->log_cb (undef);
1395             } elsif (/^cap=(.+)/ ) { $ctx->cap ("$1");
1396             } elsif (/^\+(.+)$/ ) { $ctx->attach ($pkg->("$1"));
1397             } elsif ($_ eq "+" ) { $ctx->slaves;
1398             } elsif ($_ eq "off" or $_ eq "0") { $ctx->level (0);
1399             } elsif ($_ eq "all" ) { $ctx->level ("all");
1400             } elsif ($_ eq "level" ) { $ctx->level ("all"); $level = "level";
1401             } elsif ($_ eq "only" ) { $ctx->level ("off"); $level = "enable";
1402             } elsif ($_ eq "except" ) { $ctx->level ("all"); $level = "disable";
1403             } elsif (/^\d$/ ) { $ctx->$level ($_);
1404             } elsif (exists $STR2LEVEL{$_} ) { $ctx->$level ($_);
1405             } else { die "PERL_ANYEVENT_LOG ($spec): parse error at '$_'\n";
1406             }
1407             }
1408              
1409             /\G,/gc or last;
1410             }
1411              
1412             /\G[:[:space:]]+/gc or last;
1413             }
1414              
1415             /\G[[:space:]]+/gc; # skip trailing whitespace
1416              
1417             if (/\G(.+)/g) {
1418             die "PERL_ANYEVENT_LOG ($spec): parse error at '$1'\n";
1419             }
1420             }
1421              
1422             =head1 EXAMPLES
1423              
1424             This section shows some common configurations, both as code, and as
1425             C string.
1426              
1427             =over 4
1428              
1429             =item Setting the global logging level.
1430              
1431             Either put C into your environment before
1432             running your program, use C or modify the log level of
1433             the root context at runtime:
1434              
1435             PERL_ANYEVENT_VERBOSE=5 ./myprog
1436              
1437             PERL_ANYEVENT_LOG=log=warn
1438              
1439             $AnyEvent::Log::FILTER->level ("warn");
1440              
1441             =item Append all messages to a file instead of sending them to STDERR.
1442              
1443             This is affected by the global logging level.
1444              
1445             $AnyEvent::Log::LOG->log_to_file ($path);
1446              
1447             PERL_ANYEVENT_LOG=log=file=/some/path
1448              
1449             =item Write all messages with priority C and higher to a file.
1450              
1451             This writes them only when the global logging level allows it, because
1452             it is attached to the default context which is invoked I global
1453             filtering.
1454              
1455             $AnyEvent::Log::FILTER->attach (
1456             new AnyEvent::Log::Ctx log_to_file => $path);
1457              
1458             PERL_ANYEVENT_LOG=filter=+%filelogger:%filelogger=file=/some/path
1459              
1460             This writes them regardless of the global logging level, because it is
1461             attached to the toplevel context, which receives all messages I
1462             the global filtering.
1463              
1464             $AnyEvent::Log::COLLECT->attach (
1465             new AnyEvent::Log::Ctx log_to_file => $path);
1466              
1467             PERL_ANYEVENT_LOG=%filelogger=file=/some/path:collect=+%filelogger
1468              
1469             In both cases, messages are still written to STDERR.
1470              
1471             =item Additionally log all messages with C and higher priority to
1472             C, but cap at C.
1473              
1474             This logs all messages to the default log target, but also logs messages
1475             with priority C or higher (and not filtered otherwise) to syslog
1476             facility C. Messages with priority higher than C will be
1477             logged with level C.
1478              
1479             $AnyEvent::Log::LOG->attach (
1480             new AnyEvent::Log::Ctx
1481             level => "warn",
1482             cap => "error",
1483             syslog => "user",
1484             );
1485              
1486             PERL_ANYEVENT_LOG=log=+%syslog:%syslog=warn,cap=error,syslog
1487              
1488             =item Write trace messages (only) from L to the default logging target(s).
1489              
1490             Attach the C<$AnyEvent::Log::LOG> context to the C
1491             context - this simply circumvents the global filtering for trace messages.
1492              
1493             my $debug = AnyEvent::Debug->AnyEvent::Log::ctx;
1494             $debug->attach ($AnyEvent::Log::LOG);
1495              
1496             PERL_ANYEVENT_LOG=AnyEvent::Debug=+log
1497              
1498             This of course works for any package, not just L, but
1499             assumes the log level for AnyEvent::Debug hasn't been changed from the
1500             default.
1501              
1502             =back
1503              
1504             =head1 ASYNCHRONOUS DISK I/O
1505              
1506             This module uses L to actually write log messages (in
1507             C and C), so it doesn't block your program when
1508             the disk is busy and a non-blocking L backend is available.
1509              
1510             =head1 AUTHOR
1511              
1512             Marc Lehmann
1513             http://anyevent.schmorp.de
1514              
1515             =cut
1516              
1517             1
1518