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From "Alexei Fedotov (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HARMONY-4569) [classlib][performance] Ineffecient manifest parsing results in slowdown when debugging java code
Date Sat, 29 Mar 2008 18:07:24 GMT

    [ https://issues.apache.org/jira/browse/HARMONY-4569?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12583346#action_12583346
] 

Alexei Fedotov commented on HARMONY-4569:
-----------------------------------------

Nathan,
Thank you for your answer. I'm sorry, it's hard for me to accept that anything we have in
the code is conventional. Sometimes something that existed in the code, eg a bug or a duplicate
function,  was being changed if there was a sufficient reason for that change. I accept that
sometimes things are kept in the bad shape intentionally, for example, due to insufficient
resources. If we would set a clear goal to migrate to symbolic names, then any step would
be good. But it seems that for some reason we might not want that goal. I'm missing something,
and cannot understand what is it.

I may guess few reasons of having the numeric localization entries:
 * one has localization tables for other languages which stick to this format
 * one has a tool which operates with these numeric entries, making it them maintainable
 * this is just a bad style we all don't like but bear since the migration would hardly be
completed one day

It would be enough for me to specify explicitly that we don't want symbolic names even due
to some unnamed reason, and I would be happy.


> [classlib][performance] Ineffecient manifest parsing results in slowdown when debugging
java code
> -------------------------------------------------------------------------------------------------
>
>                 Key: HARMONY-4569
>                 URL: https://issues.apache.org/jira/browse/HARMONY-4569
>             Project: Harmony
>          Issue Type: Bug
>          Components: Classlib
>            Reporter: Gregory Shimansky
>            Assignee: Tim Ellison
>         Attachments: ByteBuffer.java, ExposedByteArrayInputStream.java, methodee-stack.cpp,
methodee.cpp, remove_writes.patch, remove_writes_25032008.patch, remove_writes_todo.patch,
remove_writes_todo_1.patch, remove_writes_todo_completed.patch, ThreadLocalCache.java
>
>
> I've reported this already some time ago [1], but since it wasn't noticed I decided to
create a bug report.
> To run a hello world class which contains only 1 method takes 319046 method calls on
Harmony. Out of them 291637 method calls are the calls that happen when Java class loader
tries to find Hello.class and 27409 are what it takes for classlib to startup.
> I've found these numbers using two simple JVMTI agents that I wrote some time ago. First
one [2] counts all MethodEnter events and outputs method names to log file. Second one [3]
monitors a particular method and writes down a stack trace to the log file. It should be noted
that MethodEnter event according to specification is sent by VM only in LIVE phase, that is
after classlib startup, so to find out the overall number of method calls I've used debug
version of DRLVM with an additional argument -Xtrace:jvmti.event.method.entry:log which wrote
down *all* of the calls to Java method while executing the application.
> Parsing the logs for statistics can be done with the following command:
> cat method_entry.log | sort | uniq -c | sort -nr > method_entry.log-sorted
> It creates a file with the number that each method was called. The absolute champion
since my post in [1] still remains the method Ljava/io/ByteArrayOutputStream;.write(I)V, it
is called 131114 times. Using second agent [3] I've found out that the most popular stack
trace for calling ByteArrayOutputStream;.write looks like this (please note that numbers at
the ends of the lines are not line numbers, these are the bytecode numbers):
> Ljava/io/ByteArrayOutputStream;.write(I)V:0
> Ljava/util/jar/InitManifest;.nextChunk(Ljava/io/InputStream;Ljava/util/List;)[B:308
> Ljava/util/jar/InitManifest;.<init>(Ljava/io/InputStream;Ljava/util/jar/Attributes;Ljava/util/Map;Ljava/util/Map;Ljava/lang/String;)V:385
> Ljava/util/jar/Manifest;.read(Ljava/io/InputStream;)V:18
> Ljava/util/jar/Manifest;.<init>(Ljava/io/InputStream;Z)V:43
> Ljava/util/jar/JarFile;.getManifest()Ljava/util/jar/Manifest;:90
> Ljava/net/URLClassLoader;.createURLJarHandler(Ljava/net/URL;)Ljava/net/URLClassLoader$URLHandler;:141
> Ljava/net/URLClassLoader;.makeNewHandler()V:64
> Ljava/net/URLClassLoader;.getHandler(I)Ljava/net/URLClassLoader$URLHandler;:24
> Ljava/net/URLClassLoader;.findClassImpl(Ljava/lang/String;)Ljava/lang/Class;:82
> Ljava/net/URLClassLoader$4;.run()Ljava/lang/Class;:8
> Ljava/net/URLClassLoader$4;.run()Ljava/lang/Object;:1
> Ljava/security/AccessController;.doPrivilegedImpl(Ljava/security/PrivilegedAction;Ljava/security/AccessControlContext;)Ljava/lang/Object;:79
> Ljava/security/AccessController;.doPrivileged(Ljava/security/PrivilegedAction;Ljava/security/AccessControlContext;)Ljava/lang/Object;:16
> Ljava/net/URLClassLoader;.findClass(Ljava/lang/String;)Ljava/lang/Class;:13
> Ljava/lang/ClassLoader;.loadClass(Ljava/lang/String;Z)Ljava/lang/Class;:80
> Ljava/lang/ClassLoader$SystemClassLoader;.loadClass(Ljava/lang/String;Z)Ljava/lang/Class;:65
> Ljava/lang/ClassLoader;.loadClass(Ljava/lang/String;)Ljava/lang/Class;:3
> This stack trace occurs 123029 number of times, about 8000 times ByteArrayOutputStream;.write
is called from InitManifest class with a bit different stack trace, but all of the calls to
write occur from this class. It seems that InitManifest code copies memory by bytes and there
is quite a lot of the memory that is copied. This may not be a big problem in the normal execution
of Java application because JIT usually inlines such hot methods. Although it is still inefficient,
it may be not a big performance hit (actually this should be checked).
> But when trying to debug Java code, DRLVM uses JET, which doesn't inline any methods.
It has to execute all of them and all of those calls to ByteArrayOutputStream;.write are executed
on startup of the application. It takes several minutes to get to the point of executing the
actual user program.
> [1] http://thread.gmane.org/gmane.comp.java.harmony.devel/21104/focus=21133 see also
messages posted in this subthread by me
> [2] http://people.apache.org/~gshimansky/methodee.cpp
> [3] http://people.apache.org/~gshimansky/methodee-stack.cpp

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