1 package Object::Remote::Logging;
5 use Log::Contextual qw( :log );
6 use Object::Remote::LogRouter;
7 use Object::Remote::LogDestination;
8 use Log::Contextual::SimpleLogger;
11 use base qw(Log::Contextual);
14 return $_[1] if defined $_[1];
17 return $Router_Instance if defined $Router_Instance;
19 $Router_Instance = Object::Remote::LogRouter->new(
31 if ($ENV{OBJECT_REMOTE_LOG_LEVEL}) {
32 $class->init_logging_stderr($ENV{OBJECT_REMOTE_LOG_LEVEL});
36 sub init_logging_stderr {
37 my ($class, $level) = @_;
38 our $Log_Level = $level;
39 chomp(my $hostname = `hostname`);
40 our $Log_Output = Object::Remote::LogDestination->new(
41 logger => Log::Contextual::SimpleLogger->new({
42 levels_upto => $Log_Level,
43 coderef => sub { warn "[$hostname $$] ", @_ },
46 $Log_Output->connect($class->arg_router);
49 sub init_logging_forwarding {
50 my ($class, $remote_parent) = @_;
51 chomp(my $host = `hostname`);
52 $class->arg_router->description("$$ $host");
53 $class->arg_router->parent_router($remote_parent);
54 $remote_parent->add_child_router($class->arg_router);
61 #Hierarchical routed logging concept
65 # Object::Remote and systems built on it would benefit from a standard model
66 # for logging that enables simple and transparent log generation and consumption
67 # that can cross the Perl interpreter instance boundaries transparently. More
68 # generally CPAN would benefit from a common logging framework that allows all
69 # log message generators to play nicely with all log message consumers with out
70 # making the generators or consumers jump through hoops to do what they want to do.
71 # If these two solutions are the same then all modules built using the
72 # logging framework will transparently operate properly when run under Object::Remote.
74 # Such a solution needs to be flexible and have a low performance impact when it is not
75 # actively logging. The hiearchy of log message routers is the way to achieve all of these
76 # goals. The abstracted message router interface introduced to Log::Contextual allows
77 # the hierarchical routing system to be built and tested inside Object::Remote with possible
78 # larger scale deployment in the future.
80 # Hierarchy of log routers
82 # * Each Perl module ideally would use at least a router dedicated
83 # to that module and may have child routers if the module is complex.
84 # * Log messages inserted at low levels in the hierarchy
85 # are available at routers at higher levels in the hierarchy.
86 # * Each running Perl instance has a root router which receives
87 # all log messages generated in the Perl instance.
88 # * The routing hierarchy is available for introspection and connections
89 # from child routers to parent routers have human readable strings
90 # * The entire routing system is dynamic
91 # * Add and remove routers while the system is in operation
92 # * Add and remove taps into routers while the system is in operation
93 # * Auto-solves Object::Remote logging by setting the parent router of the
94 # root router in the remote instance to a router in the local instance the
95 # log messages will flow into the local router via a proxy object
96 # * Should probably be two modes of operation for Object::Remote logging
97 # * forwarding across instances for ease of use during normal operation
98 # * stderr output by default for debugging cases to limit the usage of
105 # * System::Introspector
106 # * Object::Remote [2]
109 # * hostname-1.example.com [5]
111 # * System::Introspector
114 # * hostname-2.example.com
116 # * System::Introspector
120 # [1] This router has all logs generated anywhere
121 # even on remote hosts
122 # [2] Everything related to Object::Remote including
123 # log messages from remote nodes for things other
124 # than Object::Remote
125 # [3] Log messages generated by Object::Remote on the local
127 # [4] All log messages from all remote nodes
128 # [5] This is the connection from a remote instance to the
129 # local instance using a proxy object
131 # As a demonstration of the flexibility of the this system consider a CPAN testers GUI
132 # tool. This hypothetical tool would allow a tester to select a module by name and perform
133 # the automated tests for that package and all dependent packages. Inside the tool is a pane for
134 # the output of the process (STDOUT and STDERR), a pane for log messages, and a pane displaying
135 # the modules that are participating in routed logging. The tester could then click on individual
136 # packages and enable logging for that package dynamically. If neccassary more than one package
137 # could be monitored if neccassary. If the GUI is wrapping a program that runs for long periods of
138 # time or if the application is a daemon then being able to dynamically add and remove logging
139 # becomes very useful.
141 # Log message selection and output
144 # * Modules and packages know how they want to format log messages
145 # * Consumers of log messages want to know
146 # * Which Perl module/package generated that message
147 # * When running with Object::Remote if the log message is from
148 # a remote node and if so which node
149 # * Consuming a log message is something the consumer knows how it wants
150 # to be done; the module/package should not be dictating how to receive
152 # * Most log messages most of the time will be completely ignored and unused
154 # * A consumer of log messages will tap into a router at any arbitrary point
155 # in the router hierarchy even across machines if Object::Remote is involved
156 # * The tap is used to access a stream of log data and is not used to select
157 # which packages/modules should be logged
158 # * For instance Object::Remote has log messages flowing through it that
159 # include logs generated on remote nodes even if those logs were generated
160 # by a module other than Object::Remote
162 # * The module has defined what the log message format is
163 # * The tap has defined the scope of messages that will be
164 # available for selection, ie: all log messages everywhere,
165 # all logs generated on Object::Remote nodes, etc
166 # * Selection defines what log messages are going to be delivered
167 # to a logger object instance
168 # * Selectors act as a gate between a tap and the logger object
169 # * Selectors are closures that perform introspection on the log
170 # message; if the selector returns true the logger will be invoked
171 # to log this message
172 # * The logger still has a log level assigned to it and still will have
173 # the is_$level method invoked to only log at that specific level
175 # * A log destination is an instance of a logger object and the associated
177 # * Consuming logging data from this system is a matter of
178 # * Constructing an instance of a logging destination object which has
179 # the following attributes:
180 # * logger - the logger object, like warnlogger or log4perl instance
181 # * selectors - a list of closures; the first one that returns true
182 # causes the logger to be checked for this log_level and
183 # invoked if neccassary
184 # * Register selectors with the destination by invoking a method and specifying
185 # sub refs as an argument
187 # Technical considerations
188 # * Log contextual likes to have the logger invoked directly inside the exported log
189 # specific methods because it removes a need to muck with logger caller depths to
190 # report back the proper caller information for the logger.
191 # * Because of this the best strategy identified is to return a list of loggers
192 # to those exported methods which then invoke the loggers inside the method
193 # * This means that log message forwarding is a process of querying each parent
194 # router for a list of logger objects that should be invoked. Each router along
195 # the hierarchy adds to this list and the log_* method will invoke all loggers
197 # * The routing hierarchy has cycles where parent routers hold a reference to the child
198 # and the child holds a reference to the parent. The cycles are not a problem if weak
199 # references are used however proxy objects don't seem to currently work with weak
201 # * Once a logger hits a proxy object the caller information is totally blown; this
202 # crossing isn't transparent yet