On 27.05.2015 21:08, Xueming Shen wrote:
targLen = max(1, tagLen); ?
Well, almost :)
With such targLen, (i = j + targLen) would result in i == length() + 1,
which will cause IOOBE in the following append().
I'm sure the algorithms can be adopted to run correctly with empty
target, it just needs some accurate checking.
But why can't we consider the first variant of replace()?
http://cr.openjdk.java.net/~igerasim/8058779/02/webrev/
It's still faster and it can handle larger strings without OOME. I
think this is important.
I haven't heard any critics of it except for its relative complexity,
comparing to the original code.
And we have a backup variant with StringBuilder, if problems are found.
Sincerely yours,
Ivan
On 05/27/2015 10:59 AM, Ivan Gerasimov wrote:
On 27.05.2015 20:40, Xueming Shen wrote:
The .append(srepl) -> append(srep.value)
And I would simply remove the "fastpath" for the target.length() = 0
special case ...
And maybe pick an appropriate initial size (maybe this.length + 16 *
diff) for the sb
to further reduce its internal expanding ...
Sorry, I forgot to comment this. This is not really a fastpath.
This is a special case, which isn't handled by the general algorithm.
We can modify the general algorithm, of course to handle empty
target, but I thought it would be more clear to have a separate branch.
I think your variant below would loop forever in the loop with an
empty target:
i = j + targLen; // targLen == 0
j = indexOf(starget, i) // j == i
Sincerely yours,
Ivan
Personally this code is straightforward and I would be happy with
the 800+ vs 1000+
score diff.
public String replace(CharSequence target, CharSequence
replacement) {
String starget = target.toString();
int targLen = starget.length();
String srepl = replacement.toString();
int j = indexOf(starget);
// special case: nothing to replace
if (j< 0) {
return this;
}
final char[] value = this.value;
StringBuilder sb = new StringBuilder();
int i = 0;
do {
sb.append(value, i, j - i)
.append(srepl.value);
i = j + targLen;
} while ((j = indexOf(starget, i))> 0);
return sb.append(this, i, length()).toString();
}
-Sherman
On 05/27/2015 10:06 AM, Ivan Gerasimov wrote:
On 27.05.2015 18:44, Xueming Shen wrote:
You might want to use directly sb.append.(char[], off, len),
instead of append(str, off, len)/append(str).
Ah, yes sure! It would improve things.
I updated the webrev in place:
http://cr.openjdk.java.net/~igerasim/8058779/03/webrev/
However the general picture is almost the same:
performance:
Baseline: MyBenchmark.test thrpt 40 257'051.948 ±
4537.484 ops/s
StringBuilder: MyBenchmark.test thrpt 40 808'033.808 ±
22152.166 ops/s
Arrays: MyBenchmark.test thrpt 40 1'049'235.602 ±
15501.803 ops/s
Memory efficiency is still less then for array-version:
$ time ~/java9/jdk-build/bin/java -showversion -Xmx1g C
java version "1.9.0-internal"
Java(TM) SE Runtime Environment (build
1.9.0-internal-igerasim_2015_05_27_14_47-b00)
Java HotSpot(TM) 64-Bit Server VM (build
1.9.0-internal-igerasim_2015_05_27_14_47-b00, mixed mode)
25) 100663296
real 0m2.429s
user 0m2.112s
sys 0m0.792s
Sincerely yours,
Ivan
Btw, is the target.lenght==0 the popular use case/scenario? Just
wonder why do we need a special case
here for it.
thanks,
-Sherman
On 5/27/15 8:29 AM, Ivan Gerasimov wrote:
For completeness, here's another webrev, which uses StringBuilder:
http://cr.openjdk.java.net/~igerasim/8058779/03/webrev/
Its performance is somewhere in between the current
implementation and the array-based implementation:
MyBenchmark.test thrpt 40 796'059.192 ± 12455.970 ops/s
Memory efficiency is less then the one of array-based
implementation:
$ time ~/java9/jdk-build/bin/java -showversion -Xmx1g C
java version "1.9.0-internal"
Java(TM) SE Runtime Environment (build
1.9.0-internal-igerasim_2015_05_27_14_47-b00)
Java HotSpot(TM) 64-Bit Server VM (build
1.9.0-internal-igerasim_2015_05_27_14_47-b00, mixed mode)
25) 100663296
real 0m2.585s
user 0m1.875s
sys 0m0.887s
Sincerely yours,
Ivan
On 27.05.2015 2:38, Xueming Shen wrote:
Ivan,
It might be worth trying String.index + StringBuilder, instead
of writing/handling everything yourself.
Yes, it inevitably adds an arraycopy at the end to convert the
StrinbBuilder to String, but it might have
better balance between performance and code complexity. The
regex is probably a little heavy for
literal string replacement, but StringBuilder should not be that
bad ...
-Sherman
On 5/26/15 4:11 PM, Ivan Gerasimov wrote:
I updated the webrev:
http://cr.openjdk.java.net/~igerasim/8058779/02/webrev/
In the check at 2300-2301 and 2351-2352 I replaced
MAX_ARRAY_SIZE with Integer.MAX_VALUE, which seems to be more
accurate here.
And I want to add that this proposed implementation is not
only faster, but also more memory efficient.
The following simple stress-test shows that the proposed
version is able to handle twice larger strings, comparing to
the current implementation.
----------------------------------------
public class C {
public static void main(String[] args) throws Throwable {
String s = "string";
for (int i = 1; i < Integer.MAX_VALUE; ++i) {
try {
s = s.replace("string", "stringstring");
} catch (OutOfMemoryError o) {
System.out.println(i + ") " + s.length());
break;
}
}
}
}
----------------------------------------
$ time ~/java9/jdk/bin/java -showversion -Xmx1g C
java version "1.9.0-ea"
Java(TM) SE Runtime Environment (build 1.9.0-ea-b63)
Java HotSpot(TM) 64-Bit Server VM (build 1.9.0-ea-b63, mixed mode)
25) 100663296
real 0m4.525s
user 0m4.402s
sys 0m1.189s
$ time ~/java9/jdk-build/bin/java -showversion -Xmx1g C
java version "1.9.0-internal"
Java(TM) SE Runtime Environment (build
1.9.0-internal-igerasim_2015_05_23_19_25-b00)
Java HotSpot(TM) 64-Bit Server VM (build
1.9.0-internal-igerasim_2015_05_23_19_25-b00, mixed mode)
26) 201326592
real 0m2.139s
user 0m1.960s
sys 0m0.461s
Sincerely yours,
Ivan
On 24.05.2015 23:17, Ivan Gerasimov wrote:
Hello everybody!
I know many people here like it when the performance is
getting better.
It was suggested to make the literal variant of
String.replace() faster.
Currently, this method is implemented as a few calls to regexp
API, so that the whole implementation takes only two lines of
code.
I've created two versions of the fix.
In the first one, we scan the string and store indices of the
found substrings in an array.
Then, we allocate the precisely sized char array and fill it it.
The case with the empty target has to be handled separately.
BUGURL: https://bugs.openjdk.java.net/browse/JDK-8058779
WEBREV: http://cr.openjdk.java.net/~igerasim/8058779/00/webrev/
The second variant is much less verbose, however it's less
efficient too.
Here the StringJoiner is used as an intermediate storage.
WEBREV: http://cr.openjdk.java.net/~igerasim/8058779/01/webrev/
Here are the micro-benchmark results (in a string of ~300
chars do ~15 replacements).
0) Baseline
MyBenchmark.test thrpt 40 257'051.948 ± 4537.484 ops/s
1) Heavy-duty +308%
MyBenchmark.test thrpt 40 1'049'235.602 ± 15501.803 ops/s
2) StringJoiner +190%
MyBenchmark.test thrpt 40 746'000.629 ± 15387.036 ops/s
Personally, I like my first variant better, even though it
adds almost 300 lines of code.
But I'd like to hear what people think of it.
Sincerely yours,
Ivan
