Re: java.nio.CharBuffer
Andreas Delmelle wrote:
On Jul 14, 2008, at 18:15, Andreas Delmelle wrote:
snip /
Just quickly ran Jeremias' test-app myself, and on Apple JVM (1.5), the
difference is +/-300ms for a million iterations, but not very
consistent. Sometimes StringBuffer operates slightly faster, other times
it's CharBuffer that wins. I guess the backing implementations are very
closely related anyway, so it's not all that surprising.
It would most definitely be a huge overkill if it is /only/ used for
simple String concatenation. In the context of catching SAX characters()
events, I think the penalty is bound to be limited (maybe even on the
contrary: see below). That is, I don't think I've ever seen a parser
that reports characters one at a time (which would make the current
implementation using CharBuffer very slow). Most SAX parsers report the
characters in reasonably large chunks (as much as possible).
Just for fun, make it:
...
private static final char[] prefix = {' ', 'm', 'y', 'V', 'a', 'l', 'u',
'e', '='};
...
public String runCharBuffer() {
CharBuffer buf = CharBuffer.allocate(1024);
for (int i = 0; i STEPS; i++) {
buf.put(prefix).put(Integer.toString(i).toCharArray());
}
return buf.rewind().toString();
}
...
On my end, this runs noticeably faster than when passing Strings (almost
20%). When switching StringBuffer.append() to use char[] parameters, it
runs a tiny bit slower than with Strings... No idea if this also holds
for the Sun, IBM or Apache implementations.
Qua flexibility, the API for a CharBuffer (optionally) offers the
possibility to get a reference to the backing array. For StringBuffer,
we'd have to do something like: sb.toString().toCharArray(), and IIC,
this always yields an independent copy of the StringBuffer's array, not
the array itself. (Note that this obviously also has its drawbacks;
sometimes, you just /need/ an independent copy...)
Come 1.5, you get StringBuilder.
--
Peter B. West http://cv.pbw.id.au/
Folio http://defoe.sourceforge.net/folio/
Re: java.nio.CharBuffer
On Jul 15, 2008, at 09:16, Peter B. West wrote: Andreas Delmelle wrote: snip / Come 1.5, you get StringBuilder. Yep, this indeed becomes /the/ weapon of choice for building strings (in single-threaded context), if that's the goal. For FOText, I don't think that is the goal. We're simply buffering accumulating characters there, and in that case, a CharBuffer seems much more appropriate (even in Java 1.5+). Not sure what explains the drop in performance in Sun Java 1.6 though... For Harmony, I guess the implementation has not yet been optimized. Understandable, especially if CharBuffer is not commonly used. Cheers Andreas
java.nio.CharBuffer
I noticed that Andreas used CharBuffer in his initial patch for #45390. I was curious about the performance implications, so I wrote a little micro-benchmark. The results: Sun Java 1.4.2_16: StringBuffer def: 6594 ms StringBuffer 1024: 6609 ms CharBuffer: 5250 ms Sun Java 1.5.0_14: StringBuffer def: 5375 ms StringBuffer 1024: 5375 ms CharBuffer: 5594 ms Sun Java 6.0_03: StringBuffer def: 2750 ms StringBuffer 1024: 2750 ms CharBuffer: 4719 ms Apache Harmony r618795: StringBuffer def: 4687 ms StringBuffer 1024: 4672 ms CharBuffer: 7766 ms So this is a single-threaded test. It might perform differently in a heavy multi-threading environment. Anyway, it looks it doesn't make much sense to use the CharBuffer instead of the more familiar StringBuffer for simple string concatenation. I'm sure there's a benefit in using CharBuffer in scenarios where nio can really show its muscles. Jeremias Maerki CharBufferSpeedTest.java Description: Binary data
Re: java.nio.CharBuffer
On Jul 14, 2008, at 08:44, Jeremias Maerki wrote: I noticed that Andreas used CharBuffer in his initial patch for #45390. I was curious about the performance implications, so I wrote a little micro-benchmark. The results: snip / So this is a single-threaded test. It might perform differently in a heavy multi-threading environment. Anyway, it looks it doesn't make much sense to use the CharBuffer instead of the more familiar StringBuffer for simple string concatenation. I'm sure there's a benefit in using CharBuffer in scenarios where nio can really show its muscles. Yeah, it was OK for FOText, I think, but for the smaller portions, it's probably more overkill... I'll look into replacing what's unnecessary. nio.CharBuffer is very suitable if there's a lot of bulk get() and put () (like when removing leading white-space characters) While implementing it in FOText, I noticed that if you use CharBuffer.wrap(), you actually don't even create a new char array. You get a CharBuffer instance that is literally wrapped around a portion of the parameter char array). Unfortunately, this caused issues when I started shifting characters due to white-space-removal (as the char array was the very same one that the parser was using to store the chars from the source XML) I did a small test myself, before committing the changes, but that was more focused on CharSequence.charAt() and the difference in timing with simple index-based array fetches (for TextLayoutManager). In that case, the difference was really negligeable, even for millions of calls/fetches, I only got a few milliseconds difference in total. Cheers Andreas
Re: java.nio.CharBuffer
On Jul 14, 2008, at 18:15, Andreas Delmelle wrote:
snip /
Just quickly ran Jeremias' test-app myself, and on Apple JVM (1.5),
the difference is +/-300ms for a million iterations, but not very
consistent. Sometimes StringBuffer operates slightly faster, other
times it's CharBuffer that wins. I guess the backing implementations
are very closely related anyway, so it's not all that surprising.
It would most definitely be a huge overkill if it is /only/ used for
simple String concatenation. In the context of catching SAX characters
() events, I think the penalty is bound to be limited (maybe even on
the contrary: see below). That is, I don't think I've ever seen a
parser that reports characters one at a time (which would make the
current implementation using CharBuffer very slow). Most SAX parsers
report the characters in reasonably large chunks (as much as possible).
Just for fun, make it:
...
private static final char[] prefix = {' ', 'm', 'y', 'V', 'a', 'l',
'u', 'e', '='};
...
public String runCharBuffer() {
CharBuffer buf = CharBuffer.allocate(1024);
for (int i = 0; i STEPS; i++) {
buf.put(prefix).put(Integer.toString(i).toCharArray());
}
return buf.rewind().toString();
}
...
On my end, this runs noticeably faster than when passing Strings
(almost 20%). When switching StringBuffer.append() to use char[]
parameters, it runs a tiny bit slower than with Strings... No idea if
this also holds for the Sun, IBM or Apache implementations.
Qua flexibility, the API for a CharBuffer (optionally) offers the
possibility to get a reference to the backing array. For
StringBuffer, we'd have to do something like: sb.toString
().toCharArray(), and IIC, this always yields an independent copy of
the StringBuffer's array, not the array itself. (Note that this
obviously also has its drawbacks; sometimes, you just /need/ an
independent copy...)
Cheers
Andreas
