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annotate doc/v2_planning/plugin_architecture_GD.txt @ 1526:5804e44d7a1b
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| author | Frederic Bastien <nouiz@nouiz.org> |
|---|---|
| date | Fri, 09 Nov 2012 16:58:17 -0500 |
| parents | 9ff2242a817b |
| children |
| rev | line source |
|---|---|
| 1139 | 1 Overview |
| 2 ======== | |
| 3 | |
| 4 The "central authority" (CA) is the glue which takes care of interfacing plugins | |
| 5 with one another. It has 3 basic roles: | |
|
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6 |
| 1139 | 7 * it maintains a list of "registered" or "active" plugins |
| 8 * it receives and queues the various messages sent by the plugins | |
| 9 * dispatches the messages to the recipient, based on various "events" | |
| 10 | |
| 11 Events can take different forms: | |
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Frederic Bastien <nouiz@nouiz.org>
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12 |
| 1139 | 13 * the CA can trigger various events based on running time |
| 14 * can be linked to messages emitted by the various plugins. Events can be | |
| 15 triggered based on the frequency of such messages. | |
| 16 * Once an event is triggered, it is relayed to the appropriate "recipient | |
| 17 plugin(s)" | |
| 18 | |
| 19 It is the responsibility of each plugin to inform the CA of which "events" it | |
| 20 cares about. | |
| 21 | |
| 22 | |
| 23 Generic Pseudo-code | |
| 24 =================== | |
| 25 | |
| 26 I'll try to write this in pseudo-python as best I can. I'll do this in | |
| 27 traditional OOP, as this is what I'm more comfortable with. I'll leave it up to | |
| 28 James and OB to python-ize this :) | |
| 29 | |
| 30 | |
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31 .. code-block:: python |
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parents:
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32 |
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Frederic Bastien <nouiz@nouiz.org>
parents:
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33 class MessageX(Message): |
| 1139 | 34 """ |
| 35 A message is basically a data container. This could very well be replaced by | |
| 36 a generic Python object. | |
| 37 """ | |
| 38 | |
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Frederic Bastien <nouiz@nouiz.org>
parents:
1139
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|
39 class Plugin(object): |
| 1139 | 40 """ |
| 41 The base plugin object doesn't do much. It contains a reference to the CA | |
| 42 (upon plugin being registered with the CA), provides boilerplate code | |
| 43 for storing which "events" this plugin is susceptible to, as well as code | |
| 44 for registering callback functions for the various messages. | |
| 45 """ | |
| 46 | |
| 47 CA = None # to be initialized upon plugin registration | |
| 48 active_msg = {} # dictionary of messages this plugin is susceptible to | |
| 49 callbacks = {} # mapping of message class names --> callback function | |
| 50 | |
| 51 def listen(msg_class, interval): | |
| 52 """ | |
| 53 :param msg_class: reference to the "message" class we are interested in. | |
| 54 These messages will be forwarded to this plugin, when | |
| 55 the trigger condition is met. | |
| 56 :param interval: integer. Forward the message to this plugin every 'interval' | |
| 57 such messages. | |
| 58 """ | |
| 59 self.active_msg[msg_class] = interval | |
| 60 | |
| 61 | |
| 62 def check_trigger(msg_class, time): | |
| 63 """ | |
| 64 Checks whether or not the "trigger" condition associated with message of | |
| 65 class 'msg_class' is satisfied or not. This could be the default | |
| 66 behavior, and be overridden by the various plugins. | |
| 67 """ | |
| 68 return time % self.active_msg[msg_class] == 0 | |
| 69 | |
| 70 | |
| 71 def handler(msg_class, callback): | |
| 72 """ | |
| 73 Decorator which registers a callback function for the given message | |
| 74 type. | |
| 75 | |
| 76 NOTE: I don't think what I wrote would work as a Python decorator. I am | |
| 77 not sure how to handle decoraters with multiple parameters (one | |
| 78 explicit, and the other as the reference to the function). I'm pretty | |
| 79 sure James or OB could figure it out though ! | |
| 80 | |
| 81 :params msg_class: reference to the message class for which we are | |
| 82 registering a callback function | |
| 83 :params callback : reference to which function to call for a given message | |
| 84 """ | |
| 85 | |
| 86 self.callbacks[msg_class] = callback | |
| 87 | |
| 88 | |
| 89 def execute(self, message): | |
| 90 """ | |
| 91 Boiler-plate code which executes the right callback function, for the | |
| 92 given message type. | |
| 93 """ | |
| 94 for (msg_class, callback) in self.callbacks.iteritems(): | |
| 95 if message.__class__ == msg_class: | |
| 96 callback(message) | |
| 97 | |
| 98 | |
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Frederic Bastien <nouiz@nouiz.org>
parents:
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99 class ProducerPlugin(Plugin): |
| 1139 | 100 |
| 101 def dostuff(): | |
| 102 """ | |
| 103 A typical "producer" plugin. It basically performs an arbitrary action | |
| 104 and asks the CA to forward the results (in the form of a message) to | |
| 105 other plugins. | |
| 106 """ | |
| 107 | |
| 108 # iteratively do stuff and relay messages to other plugins | |
| 109 while(condition): | |
| 110 | |
| 111 msga = # do something | |
| 112 ca.send(msga) # ask CA to forward to other plugins | |
| 113 | |
| 114 | |
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Frederic Bastien <nouiz@nouiz.org>
parents:
1139
diff
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|
115 class ConsumerPlugin(Plugin): |
| 1139 | 116 |
| 117 @handler(MessageA) | |
| 118 def func(msga): | |
| 119 """ | |
| 120 A consumer or "passive plugin" (eg. logger, etc). This function is | |
| 121 register as being the callback function for Message A objects. | |
| 122 """ | |
| 123 # do something with message A | |
| 124 | |
| 125 | |
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9ff2242a817b
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Frederic Bastien <nouiz@nouiz.org>
parents:
1139
diff
changeset
|
126 class ConsumerProducerPlugin(Plugin): |
| 1139 | 127 |
| 128 @handler(MessageA) | |
| 129 def func(msga): | |
| 130 """ | |
| 131 Example of a consumer / producer plugin. It receives MessageA messages, | |
| 132 processes the data, then asks the CA to send a new message (MessageB) as | |
| 133 the result of its computation. The CA will automatically forward to all | |
| 134 interested parties. | |
| 135 | |
| 136 :param msga: MessageA instance | |
| 137 """ | |
| 138 | |
| 139 data = dostuff(msga) # process message | |
| 140 msgb = MessageB(data) # generate new message for other plugins | |
| 141 ca.send(msgb) # ask CA to forward to other plugins | |
| 142 | |
| 143 | |
| 144 | |
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1190
9ff2242a817b
fix rst syntax errors/warnings
Frederic Bastien <nouiz@nouiz.org>
parents:
1139
diff
changeset
|
145 class CentralAuthority(object): |
| 1139 | 146 |
| 147 active_plugins = [] # contains a list of registered plugins | |
| 148 | |
| 149 mailmain = {} # dictionary which contains, for each message class, a | |
| 150 # list of plugins interested in this message | |
| 151 | |
| 152 event_count = {} # dictionary of "event" counts for various messages | |
| 153 | |
| 154 def register(plugin): | |
| 155 """ | |
| 156 Registers the plugin and adds it as a listener for the various messages | |
| 157 it is interested in. | |
| 158 :param plugin: plugin instance which we want to "activate" | |
| 159 """ | |
| 160 | |
| 161 # each plugin must have a reference to the CA | |
| 162 plugin.ca = self | |
| 163 | |
| 164 # maintain list of active plugins | |
| 165 active_plugins.append(plugin) | |
| 166 | |
| 167 # remember which messages this plugin cares about | |
| 168 for msg in plugin.active_msg.keys(): | |
| 169 self.mailman[msg].append(plugin) | |
| 170 self.event_count[msg] = 0 | |
| 171 | |
| 172 def send(msg): | |
| 173 """ | |
| 174 This function relays the message to the appropriate plugins, based on | |
| 175 their "trigger" condition. It also keeps track of the number of times | |
| 176 this event was raised. | |
| 177 | |
| 178 :param msg: message instance | |
| 179 """ | |
| 180 | |
| 181 event_count[msg.__class__] += 1 | |
| 182 | |
| 183 # for all plugins interested in this message ... | |
| 184 for plugin in self.mailman[msg.__class__]: | |
| 185 | |
| 186 # check if trigger condition is met | |
| 187 if plugin.check_trigger(msg, self.event_count[msg.__class__]): | |
| 188 | |
| 189 # have the plugin execute the message | |
| 190 plugin.execute(msg) | |
| 191 | |
| 192 | |
| 193 def run(self): | |
| 194 """ | |
| 195 This would be the main loop of the program. I won't go into details | |
| 196 because its still somewhat blurry in my head :) But basically, the CA | |
| 197 could be configured to send out its own messages, independently from all | |
| 198 other plugins. | |
| 199 | |
| 200 These could be "synchronous" messages such as: "5 seconds have passed", | |
| 201 or others such as "save state we are about to get killed". | |
| 202 | |
| 203 NOTE: seems like this would almost have to live in its own thread ... | |
| 204 """ | |
| 205 | |
| 206 # the following would be parametrized obviously | |
| 207 while(True): | |
| 208 msg = ElapsedTimeMessage(5) | |
| 209 self.send(msg) | |
| 210 sleep(5) | |
| 211 | |
| 212 | |
| 213 | |
| 214 Putting it all-together | |
| 215 ======================= | |
| 216 | |
| 217 | |
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1190
9ff2242a817b
fix rst syntax errors/warnings
Frederic Bastien <nouiz@nouiz.org>
parents:
1139
diff
changeset
|
218 .. code-block:: python |
|
9ff2242a817b
fix rst syntax errors/warnings
Frederic Bastien <nouiz@nouiz.org>
parents:
1139
diff
changeset
|
219 |
|
9ff2242a817b
fix rst syntax errors/warnings
Frederic Bastien <nouiz@nouiz.org>
parents:
1139
diff
changeset
|
220 def main(): |
| 1139 | 221 |
| 222 ca = CentralAuthority() | |
| 223 | |
| 224 producer = ProducerPlugin() | |
| 225 ca.register(producer) | |
| 226 | |
| 227 consumer = ConsumerPlugin() | |
| 228 consumer.listen(MessageB, 1) | |
| 229 ca.register(consumer)) | |
| 230 | |
| 231 other = ConsumerProducerPlugin() | |
| 232 other.listen(MessageB, 10) | |
| 233 ca.register(other) | |
| 234 | |
| 235 # this is the function call which gets the ball rolling | |
| 236 producer.dostuff() | |
| 237 | |
| 238 | |
| 239 DISCUSSION: blocking vs. non-blocking | |
| 240 ===================================== | |
| 241 | |
| 242 In the above example, I used "blocking" sends. However it is not-clear that this | |
| 243 is the best option. | |
| 244 | |
| 245 In the example, the producer basically acts as the main loop. It relinquishes | |
| 246 control of the main loop when the CA decides to forward the message to other | |
| 247 plugins. Control will only be returned once the cascade of send/receives | |
| 248 initiated with MessageA is complete (all subplugins have processed MessageA and | |
| 249 any messages sent as a side-effect have also been processed). | |
| 250 | |
| 251 This definitely imposes constraints on what the plugins can do, and how they do | |
| 252 it. For the type of single-processor / linear jobs we tend to run, this might be | |
| 253 enough (??). | |
| 254 | |
| 255 The good news is that going forward, the above plugin architecture can also | |
| 256 scale to distributed systems, by changing the sends to be non-blocking. Plugins | |
| 257 could then live on different machines and process data as they see fit. | |
| 258 Synchronization would be enforced by way of messages. In the above, the "main | |
| 259 producer" would thus become a consumer/producer who listens for "done processing | |
| 260 MessageA" messages and produces a new MessageA as a result. | |
| 261 | |
| 262 On single-processor systems, the synchronization overhead might be too costly | |
| 263 however. That is something we would have to investigate. On the plus side | |
| 264 however, our plugins would be "future proof" and lend themselves well to the | |
| 265 type of "massively parallel jobs" we wish to run (i.e. meta-learners, etc.) | |
| 266 | |
| 267 | |
| 268 | |
| 269 Logistic Regression | |
| 270 =================== | |
| 271 | |
| 272 | |
| 273 TO COME SOON (?) |