Log::Async

Thread-safe asynchronous logging using supplies.

Synopsis

use Log::Async;
logger.send-to($*OUT);

trace 'how';
debug 'now';
warning 'brown';
info 'cow';
fatal 'ow';

(start debug 'one')
  .then({ debug 'two' });
(start debug 'buckle')
  .then({ debug 'my shoe' });
sleep 1;

my $when = now + 1;

for ^100 {
     Promise.at($when)
         .then({ debug "come together"})
         .then({ debug "right now"})
         .then({ debug "over me"});
}

logger.send-to("/var/log/hal.errors", :level(ERROR));
error "I'm sorry Dave, I'm afraid I can't do that";

Description

Log::Async provides asynchronous logging using the supply and tap semantics of Perl 6. Log messages are emitted asynchronously to a supply. Taps are only executed by one thread at a time.

By default a single tap is created which prints the timestamp, level and message to stdout.

Exports

trace, debug, info, warning, error, fatal: each of these asynchronously emits a message at that level.

enum Loglevels: TRACE DEBUG INFO WARNING ERROR FATAL

class Log::Async: Does the real work.

sub logger: return or create a logger singleton.

sub set-logger: set a new logger singleton.

Log::Async Methods

add-tap(Code $code,:$level,:$msg)

my $tap = logger.add-tap({ say $^m<msg> ~ '!!!!!' },  :level(FATAL));
logger.add-tap({ $*ERR.say $^m<msg> },      :level(DEBUG | ERROR));
logger.add-tap({ say "# $^m<msg>"},          :level(* < ERROR) );
logger.add-tap({ say "meow: " ~ $^m<msg> }, :msg(rx/cat/));
logger.add-tap(-> $m { say "thread { $m<THREAD>.id } says $m<msg>" });
logger.add-tap(-> $m { say "$m<when> {$m<frame>.file} {$m<frame>.line} $m<level>: $m<msg>" });
logger.add-tap(-> $m { say "{ $m<when>.utc } ($m<level>) $m<msg>",
    :level(INFO..WARNING) });

Add a tap, optionally filtering by the level or by the message. $code receives a hash with the keys msg (a string), level (a Loglevel), when (a DateTime), THREAD (the caller's $*THREAD), frame (the current callframe), and possibly ctx (the context, see below).

$level and $msg are filters: they will be smartmatched against the level and msg keys respectively.

add-tap returns a tap, which can be sent to remove-tap to turn it off.

remove-tap($tap)

logger.remove-tap($tap)

Closes and removes a tap.

send-to(Str $filename, Code :$formatter, |args)

send-to(IO::Handle $handle)
send-to(IO::Path $path)
logger.send-to('/tmp/out.log');
logger.send-to('/tmp/out.log', :level( * >= ERROR));
logger.send-to('/tmp/out.log', formatter => -> $m, :$fh { $fh.say: "{$m<level>.lc}: $m<msg>" });
logger.send-to($*OUT,
  formatter => -> $m, :$fh {
    $fh.say: "{ $m<frame>.file } { $m<frame>.line } { $m<frame>.code.name }: $m<msg>"
  });

Add a tap that prints timestamp, level and message to a file or filehandle. formatter is a Code argument which takes $m (see above), as well as the named argument :$fh -- an open filehandle for the destination.

Additional args (filters) are sent to add-tap.

close-taps

logger.close-taps

Close all the taps.

done

logger.done

Tell the supplier it is done, then wait for the supply to be done. This is automatically called in the END phase.

untapped-ok

logger.untapped-ok = True

This will suppress warnings about sending a log message before any taps are added.

Context

To display stack trace information, logging can be initialized with add-context. This sends a stack trace with every log request (so may be expensive). Once add-context has been called, a ctx element will be passed which is a Log::Async::Context object. This has a stack method which returns an array of backtrace frames.

logger.add-context;
logger.send-to('/var/log/debug.out',
  formatter => -> $m, :$fh {
    $fh.say: "file { $m<ctx>.file}, line { $m<ctx>.line }, message { $m<msg> }"
    }
  );
logger.send-to('/var/log/trace.out',
  formatter => -> $m, :$fh {
      $fh.say: $m<msg>;
      $fh.say: "file { .file}, line { .line }" for $m<ctx>.stack;
    }
  );

A custom context object can be used as an argument to add-context. This object should have a generate method. generate will be called to generate context whenever a log message is sent.

For instance:

my $context = Log::Async::Context.new but role {
  method generate { ... }
  method custom-method { ... }
  };
logger.add-context($context);

# later
logger.add-tap(-> $m { say $m.ctx.custom-method } )

More Examples

Send debug messages to stdout.

logger.send-to($*OUT,:level(DEBUG));

Send warnings, errors, and fatals to a log file.

logger.send-to('/var/log/error.log',:level(* >= WARNING));

Add a tap that prints the file, line number, message, and utc timestamp.

logger.send-to($*OUT,
  formatter => -> $m, :$fh {
    $fh.say: "{ $m<when>.utc } ({ $m<frame>.file } +{ $m<frame>.line }) $m<level> $m<msg>"
  });
trace 'hi';

# output:
2017-02-20T14:00:00.961447Z (eg/out.raku +10) TRACE hi

Caveats

Because messages are emitted asynchronously, the order in which they are emitted depends on the scheduler. Taps are executed in the same order in which they are emitted. Therefore timestamps in the log might not be in chronological order.

Author

Brian Duggan

Contributors

Bahtiar Gadimov

Curt Tilmes

Marcel Timmerman

Juan Julián Merelo Guervós

Slobodan Mišković