[PATCH] Significantly reduce allocations during startup in XmlObjectParser and PluginListParser

[taylor.smock]

With the Name Suggestion Index preset added to JOSM, the following methods are relatively expensive during startup (mem old -> mem new, cpu old -> cpu new):

• XmlObjectParser$Entry.getField (124 MB -> 8.1 MB, 501ms -> 99ms)
• XmlObjectParser$Entry.getMethod (126 MB -> 452 kB, 292ms -> 45ms)

The gains are almost entirely from getting rid of copy calls to Method and Field (done when calling Class.getMethods() and Class.getFields()). There are further gains in JVM methods (like GC), but those can be a bit ticklish to profile correctly. It does look like a 20% improvement there though (32,653ms -> 26,075ms).

Note: I'm also including a change in PluginListParser to avoid compiling a pattern over and over again. That reduces the cost of PluginListParser.parse from 25.5 mb to 12.1 mb and 217ms to 162ms. Most of the remaining cost is stuff we cannot do anything about.

Additional note: The PluginListParser numbers included the cost of interning the strings. I ended up removing that since code analysis indicated that the strings were not kept long-term.

[taylor.smock]

I might want to add the following to the patch:

src/org/openstreetmap/josm/plugins/ReadLocalPluginInformationTask.java

@@ -13 +13 @@
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
 
 import org.openstreetmap.josm.data.Preferences;
 import org.openstreetmap.josm.gui.PleaseWaitRunnable;
@@ -82 +84 @@
     }
 
     private static File[] listFiles(File pluginsDirectory, final String regex) {
-        return pluginsDirectory.listFiles((FilenameFilter) (dir, name) -> name.matches(regex));
+        final Matcher matcher = Pattern.compile(regex).matcher("");
+        return pluginsDirectory.listFiles((dir, name) -> matcher.reset(name).matches());
     }
 
     protected void scanSiteCacheFiles(ProgressMonitor monitor, File pluginsDirectory) {

This removes 7.2 MB of allocations if all plugins have been downloaded.

[taylor.smock]

In 18796/josm:

Fix #23097: Significantly reduce allocations during startup in XmlObjectParser, PluginListParser, and ReadLocalPluginInformationTask

With the Name Suggestion Index preset added to JOSM, the following methods are
relatively expensive during startup (mem old -> mem new, cpu old -> cpu new):

• XmlObjectParser$Entry.getField (124 MB -> 8.1 MB, 501ms -> 99ms)
• XmlObjectParser$Entry.getMethod (126 MB -> 452 kB, 292ms -> 45ms)

The gains are almost entirely from getting rid of copy calls to Method and Field
(done when calling Class.getMethods() and Class.getFields()). There are
further gains in JVM methods (like GC), but those can be a bit ticklish to
profile correctly. It does look like a 20% improvement there though
(32,653ms -> 26,075ms).

This additionally reduces pattern compilation from PluginListParser.parse and
ReadLocalPluginInformationTask.listFiles.