SedRegex: Cache ircdb.checkIgnored during a request

Benchmarking shows a 2 to 4 seconds improvement for all multiprocessing methods:

| method     | cached | target check        | far  | middle | last |
|  --------- | ------ | ------------------- | ---- | ------ | ---- |
| fork       | no     | before checkIgnored | 17.0 | 17.1 | 13.3 |
| fork       | yes    | before checkIgnored | 12.6 | 13.5 | 11.0 |
| fork       | no     | after checkIgnored  | 16.7 | 17.1 | 13.4 |
| fork       | yes    | after checkIgnored  | 12.6 | 13.4 | 11.2 |
| list fork  | no     | before checkIgnored |
| list fork  | yes    | before checkIgnored | 10.2 | 10.8 | 10.7 |
| list fork  | no     | after checkIgnored  | 14.7 | 15.3 | 14.9 |
| list fork  | yes    | after checkIgnored  | 10.2 | 10.7 | 10.5 |
| forkserver | no     | before checkIgnored | 171.9 | 171.9 | 172.3 |
| forkserver | yes    | before checkIgnored | 168.5 | 167.8 | 169.6 |
| forkserver | no     | after checkIgnored  |
| forkserver | yes    | after checkIgnored  |

```py
    def testPerfLast(self):
        for i in range(10000):
            self.feedMsg(f'xxx {i} yyy')
        self.assertResponse('ping', 'pong')

        before = time.time()
        for _ in range(1000):
            self.feedMsg('s/xxx 9999 yyy/foo/')  # no ^ or $, so it matches itself
        after = time.time()
        print(after - before)
        assert False

    def testPerfMiddle(self):
        for i in range(10000):
            self.feedMsg(f'xxx {i} yyy')
        self.assertResponse('ping', 'pong')

        before = time.time()
        for _ in range(1000):
            self.feedMsg('s/^xxx 1234 yyy$/foo/')  # I meant to use 9876 here. so it's actually the same test as testPerfFar. too bad.
        after = time.time()
        print(after - before)
        assert False

    def testPerfFar(self):
        for i in range(10000):
            self.feedMsg(f'xxx {i} yyy')
        self.assertResponse('ping', 'pong')

        before = time.time()
        for _ in range(1000):
            self.feedMsg('s/^xxx 1234 yyy$/foo/')
        after = time.time()
        print(after - before)
        assert False
```

"pickle fork" means I used fork with this patch:

```diff
diff --git a/plugins/SedRegex/plugin.py b/plugins/SedRegex/plugin.py
@@ -242,8 +246,7 @@ def doPrivmsg(self, irc, msg):
         if self.registryValue('boldReplacementText', msg.channel, irc.network):
             replacement = ircutils.bold(replacement)
         try:
-            if isinstance(world.SUPYPROCESS_MULTIPROCESSING_CONTEXT,
-                          multiprocessing.context.ForkContext):
+            if False:
                 # global state is shared with child processes, so the child
                 # process has access to history and can lazily filter it
                 message = process(self._replacer_process, irc, msg,
```

Author: progval

plugins/SedRegex/plugin.py

@@ -30,6 +30,7 @@
 
 ###
 
+import functools
 import multiprocessing
 from supybot.commands import *
 from supybot.commands import ProcessTimeoutError
@@ -64,6 +65,9 @@ class SearchNotFoundError(Exception):
 def filter_messages(network, msg, target, messages, ignoreRegex, sedRegex):
     """Applies all filters but the user-provided regexp, so it is safe to
     run in the main process."""
+    # short-lived cache for the duration of this request.
+    checkIgnored = functools.cache(ircdb.checkIgnored)
+
     for m in messages:
         if m.command in ('PRIVMSG', 'NOTICE') and \
                 ircutils.strEqual(m.args[0], msg.args[0]) and \