Re: Re: Re: Memory Use/Garbage Collection: Java vs Perl

You make a very good point! My bad on that bit.

I did say <cite>I think...</cite>

What do you expect at a Perl site? Java expertise :8^)...

</excuses>

Being serious for a moment, if Javac is 'doing the right thing' on that line, that just means that it's memory overhead on recursive subroutines must be even worse than I thought. 4,000 -v- 2,000,000 recursions before blowing the stack is a mind-boggling 500 times less efficient in terms of memory/stack management. I guess I was looking for a rational explanation.

Note: I have made no attempt to verify the numbers

Update:I have confirmed that your assertion is true when using javac from jdk1.3.1 as follows

import java.io.PrintStream;

class dupme
{

    public dupme(int i)
    {
    //    0    0:aload_0         
    //    1    1:invokespecial   #1   <Method void Object()>
    //    2    4:getstatic       #2   <Field PrintStream System.out>
    //    3    7:new             #3   <Class StringBuffer>
    //    4   10:dup             
    //    5   11:invokespecial   #4   <Method void StringBuffer()>
    //    6   14:ldc1            #5   <String "I am '">
    //    7   16:invokevirtual   #6   <Method StringBuffer StringBuffe
+r.append(String)>
    //    8   19:iload_1         
    //    9   20:invokevirtual   #7   <Method StringBuffer StringBuffe
+r.append(int)>
    //   10   23:ldc1            #8   <String "'!">
    //   11   25:invokevirtual   #6   <Method StringBuffer StringBuffe
+r.append(String)>
    //   12   28:invokevirtual   #9   <Method String StringBuffer.toSt
+ring()>
    //   13   31:invokevirtual   #10  <Method void PrintStream.println
+(String)>
    //   14   34:new             #11  <Class dupme>
    //   15   37:dup             
    //   16   38:iload_1         
    //   17   39:iconst_1        
    //   18   40:iadd            
    //   19   41:invokespecial   #12  <Method void dupme(int)>
    //   20   44:astore_2        
    //   21   45:return          
    }
}
[download]

Well It's better than the Abottoire, but Yorkshire!

Comment on Re: Re: Re: Memory Use/Garbage Collection: Java vs Perl Download Code

Replies are listed 'Best First'.
Re: Re: Re: Re: Memory Use/Garbage Collection: Java vs Perl by John M. Dlugosz (Monsignor) on Sep 03, 2002 at 14:53 UTC
The Perl version needs to concatenate strings, too! `perl -MO=Deparse,-q -e"print qq(I am $x\n)"` [download] produces `print 'I am ' . $x . "\n";` [download] not `print ('I am ' , $x , "\n" )`. That is, Perl concatenates the literals and variables together into one string, then calls print with the result. —John	[reply] [d/l] [select]
Re: Re: Re: Re: Re: Memory Use/Garbage Collection: Java vs Perl by BrowserUk (Patriarch) on Sep 03, 2002 at 15:09 UTC
That's interesting, thanks. Am I correct in my (I'm not sure if it's a memory of something I read somewhere, or an assumption I have formed) that Perl will fold string constants? From my (brief and un-expert) look at the byte code produced by javac, it seems to be pushing a new copy of the two constants onto the stack (they could be pointers to a single copy, I can't make up my mind) prior to the call to StringBuffer, at each invokation? Whereas I assume that Perl would push a reference to a single copy of each. Thinking about that, javac is probably pushing a pointer too. Well It's better than the Abottoire, but Yorkshire!	[reply] [d/l]
Re6: Memory Use/Garbage Collection: Java vs Perl by John M. Dlugosz (Monsignor) on Sep 03, 2002 at 15:25 UTC
Am I correct in my (I'm not sure if it's a memory of something I read somewhere, or an assumption I have formed) that Perl will fold string constants? Apparently it does not. `perl -MO=Deparse,-q -e"print qq(I am $x\n) . 'and fold this?'"` [download] it taken as `print(('I am ' . $x . "\n") . 'and fold this?');` [download] not `print('I am ' . $x . "\nand fold this?")`. —John	[reply] [d/l] [select]
Re: Re6: Memory Use/Garbage Collection: Java vs Perl by jsprat (Curate) on Sep 03, 2002 at 20:55 UTC
Re: Re: Re6: Memory Use/Garbage Collection: Java vs Perl by John M. Dlugosz (Monsignor) on Sep 03, 2002 at 21:34 UTC
Re: Re: Re: Re: Memory Use/Garbage Collection: Java vs Perl by hossman (Prior) on Sep 04, 2002 at 00:37 UTC
this whole thread is pretty OT, so i won't let that stop me from pointing out... You aren't garunteed to get the behavior you are seeing from every implimentation of Java -- the JLS only requires that string concatination must be implimented using a StringBuffer, not that multiple string concatenations must be optimized into a single StringBuffer. ie... `this... String foo = "bar" + "baz"; is garunteed to be equivilent to this... StringBuffer tmp = new StringBuffer("bar"); tmp.append("baz"); String foo = tmp.toString(); But this... String wb = "yakko" + "wakko" + "dot"; might be implimented as... StringBuffer tmp1 = new StringBuffer("yakko"); tmp1.append("wakko"); String tmp2 = tmp1.toString(); StringBuffer tmp3 = new StringBuffer(tmp2); tmp3.append("dot"); String wb = tmp3.toString();` [download] You might want to check out JDC TechTip 2002-03-05 particularly it's discussion of "a statement found in the Java Language Specification section 15.18.1.2"	[reply] [d/l]


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