Much thanks for all your thoughts.
-Ulf
Am 08.09.2014 um 20:53 schrieb Jonathan Gibbons:
Sergey,
Many of the suggestions in the webrev change the semantics of the code, and so would not be
appropriate for javac to perform automagically.
For example, in the first few lines of the patch, I found this:
diff -r dde9f5cfde5f
src/share/classes/sun/tools/jconsole/inspector/XArrayDataViewer.java
--- a/src/share/classes/sun/tools/jconsole/inspector/XArrayDataViewer.java Tue Aug 05 19:29:00
2014 -0700
+++ b/src/share/classes/sun/tools/jconsole/inspector/XArrayDataViewer.java Sun Aug 10 18:02:01
2014 -0300
@@ -79,25 +79,24 @@
String textColor = String.format("%06x",
foreground.getRGB() & 0xFFFFFF);
StringBuilder sb = new StringBuilder();
- sb.append("<html><body text=#"+textColor+"><table
width=\"100%\">");
+ sb.append("<html><body text=#").append(textColor).append("><table
width=\"100%\">");
for (int i = 0; i < arr.length; i++) {
if (i % 2 == 0) {
- sb.append("<tr style=\"background-color: " +
- evenRowColorStr + "\"><td><pre>" +
- (arr[i] == null ?
- arr[i] : htmlize(arr[i].toString())) +
- "</pre></td></tr>");
+ sb.append("<tr style=\"background-color: ")
+ .append(evenRowColorStr).append("\"><td><pre>")
+ .append(arr[i] == null ?
+ arr[i] : htmlize(arr[i].toString()))
+ .append("</pre></td></tr>");
Analyzing the flow to determine it is safe to mutate sb in the face of possible exceptions coming
out of methods like htmlize is more than it would be reasonable to do in javac. For example, what
if the for loop were in a try block and the try block referenced sb?
Also, consider the serviceability implications, if a user is stepping through the code with a
debugger.
-- Jon
On 09/08/2014 11:39 AM, Sergey Bylokhov wrote:
On 08.09.2014 21:50, Jonathan Gibbons wrote:
Yes, but is this really a big enough performance and footprint pain point to be worth addressing
in javac itself?
We're now talking about some specific code construction like
new StringBuilder().append(a + b + c)
Any other case where the string builder can be observed externally cannot be subject to the
proposed optimization. The use case is now really getting pretty specific.
Not so specific at least in jdk code:
http://mail.openjdk.java.net/pipermail/core-libs-dev/2014-August/028142.html
-- Jon
On 09/08/2014 10:41 AM, Guy Steele wrote:
Good point, but counterpoint: it might be acceptable to have modified the string buffer in
situations where throwing an exception would always cause the string buffer to become
inaccessible.
—Guy
On Sep 8, 2014, at 1:30 PM, Jonathan Gibbons <jonathan.gibb...@oracle.com>
wrote:
It would be inappropriate/incorrect to apply the optimization as described.
The JLS requires that the argument to a method call should be computed before invoking the
method.
Consider the case when one of the expressions in the series of string concatenations throws an
exception. It would be incorrect to have already partially modified the string buffer.
-- Jon
On 08/29/2014 01:53 PM, Ulf Zibis wrote:
Hi compiler people,
is there some chance that javac could be enhanced to optimize better as discussed in this
thread? Than refactoring of up to now better readable code to ugly StringBuilder@append()
code would be superfluous.
I really like the String concatenation syntax, but unfortunately it often causes slower code
and bigger footprint.
Optimally javac would optimize mixed use of StringBuilder, StringJoiner, concatenation,
toString(), append(String), append(Collection) etc. to a single StringBuilder instance, so
that the resulting code, JITed or not, will have better performance.
Additionally javac could guess a reasonable initial capacity from the given
source code.
Am 29.08.2014 um 10:01 schrieb Wang Weijun:
So it's not that the optimization fails but there is no optimization on them
yet.
I do see the .append("x") case will be easy to deal with, but it looks like historically
javac has not been a place to do many optimizations. It mostly converts the java source to
byte codes in a 1-to-1 mapping and let VM do whatever it wants (to optimize). When you
talked about compiling multiple concatenation into using a single StringBuilder, it's more
like choosing the correct implementation rather than an optimization.
I don't expect to see big change on this in the near future, so shall we go on with the
current enhancement?
Thanks
Max
On Aug 29, 2014, at 2:17, Ulf Zibis <ulf.zi...@cosoco.de> wrote:
I mean:
It does not output byte code that only uses a single char array to compose the entire
String in question.
With "optimization fails", I also mean, there is used an additional "StringComposer" e.g.
another StringBuilder or a StringJoiner in addition to the 1st StringBuilder.
-Ulf
Am 27.08.2014 um 14:02 schrieb Pavel Rappo:
Could you please explain what you mean by "javac optimization fails" here?
-Pavel
On 27 Aug 2014, at 10:41, Ulf Zibis <ulf.zi...@cosoco.de> wrote:
4.) Now we see, that javac optimization fails again if StringBuilder, concatenation,
toString(), append(String), append(Collection) etc. and StringJoiner use is mixed.
