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From "Nathan Beyer (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 18:25:24 GMT

    [ https://issues.apache.org/jira/browse/HARMONY-4569?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12583349#action_12583349

Nathan Beyer commented on HARMONY-4569:

> Thank you for your answer. I'm sorry, it's hard for me to accept that anything we have
in the code is conventional.
I'm not sure if I should take that as an insult or not.

> 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.

Again, I'm not sure how to take this either. Even though you may not like it, it doesn't make
it a bug, incorrect, inappropriate or bad.

If you really want to discuss this farther, then please pull it onto the mailing list.

> [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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