8058779: Faster implementation of String.replace(CharSequence, CharSequence) (original) (raw)

Xueming Shen xueming.shen at oracle.com
Wed May 27 17:40:16 UTC 2015

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 ...

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-igerasim201505271447-b00) Java HotSpot(TM) 64-Bit Server VM (build 1.9.0-internal-igerasim201505271447-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-igerasim201505271447-b00) Java HotSpot(TM) 64-Bit Server VM (build 1.9.0-internal-igerasim201505271447-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 MAXARRAYSIZE with Integer.MAXVALUE, 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.MAXVALUE; ++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-igerasim201505231925-b00) Java HotSpot(TM) 64-Bit Server VM (build 1.9.0-internal-igerasim201505231925-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

More information about the core-libs-dev mailing list