8259842: Remove Result cache from StringCoding #2102

cl4es · 2021-01-15T14:33:19Z

The StringCoding.resultCached mechanism is used to remove the allocation of a StringCoding.Result object on potentially hot paths used in some String constructors. Using a ThreadLocal has overheads though, and the overhead got a bit worse after JDK-8258596 which addresses a leak by adding a SoftReference.

This patch refactors much of the decode logic back into String and gets rid of not only the Result cache, but the Result class itself along with the StringDecoder class and cache.

Microbenchmark results:

Baseline

Benchmark                                           (charsetName)  Mode  Cnt    Score    Error   Units
decodeCharset                                            US-ASCII  avgt   15  193.043 ±  8.207   ns/op
decodeCharset:·gc.alloc.rate.norm                        US-ASCII  avgt   15  112.009 ±  0.001    B/op
decodeCharset                                          ISO-8859-1  avgt   15  164.580 ±  6.514   ns/op
decodeCharset:·gc.alloc.rate.norm                      ISO-8859-1  avgt   15  112.009 ±  0.001    B/op
decodeCharset                                               UTF-8  avgt   15  328.370 ± 18.420   ns/op
decodeCharset:·gc.alloc.rate.norm                           UTF-8  avgt   15  224.019 ±  0.002    B/op
decodeCharset                                               MS932  avgt   15  328.870 ± 20.056   ns/op
decodeCharset:·gc.alloc.rate.norm                           MS932  avgt   15  232.020 ±  0.002    B/op
decodeCharset                                          ISO-8859-6  avgt   15  193.603 ± 12.305   ns/op
decodeCharset:·gc.alloc.rate.norm                      ISO-8859-6  avgt   15  112.010 ±  0.001    B/op
decodeCharsetName                                        US-ASCII  avgt   15  209.454 ±  9.040   ns/op
decodeCharsetName:·gc.alloc.rate.norm                    US-ASCII  avgt   15  112.009 ±  0.001    B/op
decodeCharsetName                                      ISO-8859-1  avgt   15  188.234 ±  7.533   ns/op
decodeCharsetName:·gc.alloc.rate.norm                  ISO-8859-1  avgt   15  112.009 ±  0.001    B/op
decodeCharsetName                                           UTF-8  avgt   15  399.463 ± 12.437   ns/op
decodeCharsetName:·gc.alloc.rate.norm                       UTF-8  avgt   15  224.019 ±  0.003    B/op
decodeCharsetName                                           MS932  avgt   15  358.839 ± 15.385   ns/op
decodeCharsetName:·gc.alloc.rate.norm                       MS932  avgt   15  208.017 ±  0.003    B/op
decodeCharsetName                                      ISO-8859-6  avgt   15  162.570 ±  7.090   ns/op
decodeCharsetName:·gc.alloc.rate.norm                  ISO-8859-6  avgt   15  112.009 ±  0.001    B/op
decodeDefault                                                 N/A  avgt   15  316.081 ± 11.101   ns/op
decodeDefault:·gc.alloc.rate.norm                             N/A  avgt   15  224.019 ±  0.002    B/op

Patched:
Benchmark                                           (charsetName)  Mode  Cnt    Score    Error   Units
decodeCharset                                            US-ASCII  avgt   15  159.153 ±  6.082   ns/op
decodeCharset:·gc.alloc.rate.norm                        US-ASCII  avgt   15  112.009 ±  0.001    B/op
decodeCharset                                          ISO-8859-1  avgt   15  134.433 ±  6.203   ns/op
decodeCharset:·gc.alloc.rate.norm                      ISO-8859-1  avgt   15  112.009 ±  0.001    B/op
decodeCharset                                               UTF-8  avgt   15  297.234 ± 21.654   ns/op
decodeCharset:·gc.alloc.rate.norm                           UTF-8  avgt   15  224.019 ±  0.002    B/op
decodeCharset                                               MS932  avgt   15  311.583 ± 16.445   ns/op
decodeCharset:·gc.alloc.rate.norm                           MS932  avgt   15  208.018 ±  0.002    B/op
decodeCharset                                          ISO-8859-6  avgt   15  156.216 ±  6.522   ns/op
decodeCharset:·gc.alloc.rate.norm                      ISO-8859-6  avgt   15  112.010 ±  0.001    B/op
decodeCharsetName                                        US-ASCII  avgt   15  180.752 ±  9.411   ns/op
decodeCharsetName:·gc.alloc.rate.norm                    US-ASCII  avgt   15  112.010 ±  0.001    B/op
decodeCharsetName                                      ISO-8859-1  avgt   15  156.170 ±  8.003   ns/op
decodeCharsetName:·gc.alloc.rate.norm                  ISO-8859-1  avgt   15  112.010 ±  0.001    B/op
decodeCharsetName                                           UTF-8  avgt   15  370.337 ± 22.199   ns/op
decodeCharsetName:·gc.alloc.rate.norm                       UTF-8  avgt   15  224.019 ±  0.001    B/op
decodeCharsetName                                           MS932  avgt   15  312.589 ± 15.067   ns/op
decodeCharsetName:·gc.alloc.rate.norm                       MS932  avgt   15  208.018 ±  0.002    B/op
decodeCharsetName                                      ISO-8859-6  avgt   15  173.205 ±  9.647   ns/op
decodeCharsetName:·gc.alloc.rate.norm                  ISO-8859-6  avgt   15  112.009 ±  0.001    B/op
decodeDefault                                                 N/A  avgt   15  303.459 ± 16.452   ns/op
decodeDefault:·gc.alloc.rate.norm                             N/A  avgt   15  224.019 ±  0.001    B/op

Most variants improve. There's a small added overhead in String charsetName variants for some charsets such as ISO-8859-6 that benefited slightly from the StringDecoder cache due avoiding a lookup, but most variants are not helped by this cache and instead see a significant gain from skipping that step. Charset variants don't need a lookup and improve across the board.

Another drawback is that we need to cram more logic into String to bypass the StringCoding.Result indirection - but getting rid of two commonly used ThreadLocal caches and most cases getting a bit better raw throughput in the process I think more than enough makes up for that.

Testing: tier1-4

Progress

Change must not contain extraneous whitespace
Commit message must refer to an issue
Change must be properly reviewed

Issue

JDK-8259842: Remove Result cache from StringCoding

Reviewers

Naoto Sato (@naotoj - Reviewer) ⚠️ Review applies to 2143cb3
Peter Levart (@plevart - Reviewer) ⚠️ Review applies to ba279a7
Roger Riggs (@RogerRiggs - Reviewer) ⚠️ Review applies to 2143cb3

Download

$ git fetch https://git.openjdk.java.net/jdk pull/2102/head:pull/2102
$ git checkout pull/2102

…ringCoding rather than eagerly initialize on String clinit

…null, foo etc

bridgekeeper · 2021-01-15T14:34:16Z

👋 Welcome back redestad! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

openjdk · 2021-01-15T14:35:02Z

@cl4es The following label will be automatically applied to this pull request:

core-libs

When this pull request is ready to be reviewed, an "RFR" email will be sent to the corresponding mailing list. If you would like to change these labels, use the /label pull request command.

mlbridge · 2021-01-15T15:09:12Z

Webrevs

RogerRiggs · 2021-01-15T16:49:57Z

Interesting, I was/am in the middle of converting Result to be a Valhalla primitive class to reduce the memory pressure and had written some new jmh tests too.
And to reduce the dependency on ThreadLocals.

cl4es · 2021-01-15T18:04:05Z

Interesting, I was/am in the middle of converting Result to be a Valhalla primitive class to reduce the memory pressure and had written some new jmh tests too.
And to reduce the dependency on ThreadLocals.

Ok, I expect that would end up at similar performance while retaining the separation of concerns. But this way we're not dependent on valhalla to get rid of the TLs.

I'd be happy to add more JMH tests here. I expected this area to already have some, but it seems all the micros added during the work on compact strings work in JDK 9 are unaccounted for.

naotoj

Nit: copyright year in System.java is 2021.

src/java.base/share/classes/java/lang/String.java

plevart · 2021-01-15T21:39:00Z

Hi Claes,
This is quite an undertaking in re-factoring!
I think that decoding logic that you produced can still be kept in StringCoding class though. The private constructor that you created for UTF-8 decoding is unnecessary. The logic can be kept in a static method and then the String instance constructed in it from the value and coder. The only public constructor that remains is then the one taking a Charset parameter. I took your code and moved it back to StringCoding while for the mentioned constructor I tried the following trick which could work (I haven't tested yet with JMH): if you pass an instance of newly constructed object down to a method that is inlined into the caller and that method does not pass that object to any other methods, JIT will eliminate the heap allocation, so I suspect that you can pass results from the called method back in that object and still avoid allocation...

plevart@691600e

WDYT?

cl4es · 2021-01-15T22:03:31Z

WDYT?

I get that the approach I took got a bit messy, but I've just spent some time cleaning it up. Please have a look at the latest, which outlines much of the logic and consolidates the replace/throw logic in the UTF8 decode paths. I've checked it does not regress on the micro, and I think the overall state of the code now isn't much messier than the original code.

plevart · 2021-01-16T00:25:24Z

Some common logic is now extracted into methods. That's good. But much of the decoding logic still remains in String. I still think all of static methods can be moved to StringCoding directly as they are now while the private UTF-8 decoding constructor can be replaced with static method and moved to StringCoding. The only problem might be the public String constructor taking Charset parameter. But even here, passing a newly constructed mutable object to the method can be used to return multiple values from the method while relying on JIT to eliminate object allocation.
Do you think this code belongs more to String than to StringCoding?

cl4es · 2021-01-16T01:02:20Z

Do you think this code belongs more to String than to StringCoding?

I consider StringCoding an implementation detail of String, so I'm not sure there's (much) value in maintaining the separation of concern if it is cause for a performance loss. While encapsulating and separating concerns is a fine purpose I think the main purpose served by StringCoding is to resolve some bootstrap issues: String is one of the first classes to be loaded and eagerly pulling in dependencies like ThreadLocal and Charsets before bootstrapping leads to all manner of hard to decipher issues (yes - I've tried :-)).

plevart · 2021-01-17T09:21:27Z

When you combine the logic of String.lookupCharset:

    private static Charset lookupCharset(String charsetName)
            throws UnsupportedEncodingException {
        Objects.requireNonNull(charsetName);
        try {
            Charset cs = StringCoding.lookupCharset(charsetName);
            if (cs == null) {
                throw new UnsupportedEncodingException(charsetName);
            }
            return cs;
        } catch (IllegalCharsetNameException ics) {
            throw new UnsupportedEncodingException(charsetName);
        }
    }

... and StringCoding.lookupCharset:

    static Charset lookupCharset(String csn) {
        if (Charset.isSupported(csn)) {
            try {
                return Charset.forName(csn);
            } catch (UnsupportedCharsetException x) {
                throw new Error(x);
            }
        }
        return null;
    }

...you get this:

    private static Charset lookupCharset(String charsetName)
            throws UnsupportedEncodingException {
        Objects.requireNonNull(charsetName);
        try {
            Charset cs;
            inner: {
                if (Charset.isSupported(charsetName)) {
                    try {
                        cs = Charset.forName(charsetName);
                        break inner;
                    } catch (UnsupportedCharsetException x) {
                        throw new Error(x);
                    }
                }
                cs = null;
            }
            if (cs == null) {
                throw new UnsupportedEncodingException(charsetName);
            }
            return cs;
        } catch (IllegalCharsetNameException ics) {
            throw new UnsupportedEncodingException(charsetName);
        }
    }

...and that can be simplified to this:

    static Charset lookupCharset(String csn) throws UnsupportedEncodingException {
        Objects.requireNonNull(csn);
        try {
            return Charset.forName(csn);
        } catch (UnsupportedCharsetException | IllegalCharsetNameException x) {
            throw new UnsupportedEncodingException(csn);
        }
    }

which has an additional benefit that it only performs one lookup (Charset.forName) instead of two (Charset.isSupported & Charset.forName)...

cl4es · 2021-01-17T12:16:00Z

@plevart: I simplified the lookup logic based on your suggestion. Removed some unreachable paths in and simplified StringCoding.encode(String, byte, byte[]) as a result.

Simplifying to one lookup speeds up decodeCharsetName cases a notch:

before:
decodeCharsetName          UTF-8  avgt   15  370.337 ± 22.199  ns/op
after:
decodeCharsetName          UTF-8  avgt   15  335.971 ± 15.894  ns/op

plevart

This looks good.
Are you planning to do similar things for encoding too?

openjdk · 2021-01-17T14:57:40Z

@cl4es This change now passes all automated pre-integration checks.

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

After integration, the commit message for the final commit will be:

8259842: Remove Result cache from StringCoding

Reviewed-by: naoto, plevart, rriggs

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been 8 new commits pushed to the master branch:

2f47c39: 8259943: FileDescriptor.close0 does not handle EINTR
a8073ef: 8253478: (se) epoll Selector should use eventfd for wakeup instead of pipe
34eb8b3: 8255765: Shenandoah: Isolate concurrent, degenerated and full GC
c3c6662: 8259954: gc/shenandoah/mxbeans tests fail with -Xcomp
6ce0799: 8259851: Use boolean type for tasks in SubTasksDone
4bcffeb: 8260029: aarch64: fix typo in verify_oop_array
e1de0bf: 8260043: Reduce allocation in sun.net.www.protocol.jar.Handler.parseURL
4dfd8cc: 8259897: gtest os.dll_address_to_function_and_library_name_vm fails on AIX

Please see this link for an up-to-date comparison between the source branch of this pull request and the master branch.
As there are no conflicts, your changes will automatically be rebased on top of these commits when integrating. If you prefer to avoid this automatic rebasing, please check the documentation for the /integrate command for further details.

➡️ To integrate this PR with the above commit message to the master branch, type /integrate in a new comment.

plevart · 2021-01-17T15:51:58Z

I already approved the changes and they are OK. Maybe for a followup: just noticing after the fact that logic for newStringUTF8NoRepl(....) vs. new String(...., StringCoding.UTF_8) differ in handling unmappabale characters, which is by the spec, but also the constructor contains special handling of input that only contains non-negative bytes:

        if (charset == UTF_8) {
            if (COMPACT_STRINGS && !StringCoding.hasNegatives(bytes, offset, length)) {
                this.value = Arrays.copyOfRange(bytes, offset, offset + length);
                this.coder = LATIN1;
                return;

...while newStringUTF8NoRepl(....) does not contain this optimization. I guess ZipCoder could benefit from that optimization too since paths are mostly ASCII only. So WDYT of this additional simplification/consolidation of UTF-8 decoding:

plevart@0b8b12c

cl4es · 2021-01-17T22:36:56Z

newStringUTF8NoRepl(....) does not contain this optimization.

Good catch: this optimization was in the original code for newStringNoRepl but not newStringUTF8NoRepl. I'll put it back to avoid a regression, but this time into newStringUTF8NoRepl so that both paths get the optimization.

plevart

This looks good, Claes.

RogerRiggs

The large number of package exposed methods in StringCoding is ugly and makes the code harder to maintain.
Can the code duplication of UTF8 in the String constructors be reduced?
It would be cleaner to move all of the remaining StringCoding methods into String and make them private again. Reading the code now requires quite a bit of cross referencing and the invariants are hard to verify.

RogerRiggs · 2021-01-19T16:46:10Z

src/java.base/share/classes/java/lang/StringCoding.java

-        while (sp < sl) {
-            int b1 = src[sp++];
+    static int decodeUTF8_UTF16(byte[] bytes, int offset, int sl, byte[] dst, int dp, boolean doReplace) {
+        while (offset < sl) {


The renaming of sp -> offset seems unmotivated and breaks the symmetry with dp.

…nd the ThreadLocal encoder facility.

RogerRiggs

This looks very good. Thanks for the extra refactoring and consolidating of code.

RogerRiggs · 2021-01-21T22:23:49Z

src/java.base/share/classes/java/lang/StringCoding.java

-    }
+    static final Charset ISO_8859_1 = sun.nio.cs.ISO_8859_1.INSTANCE;
+    static final Charset US_ASCII = sun.nio.cs.US_ASCII.INSTANCE;
+    static final Charset UTF_8 = sun.nio.cs.UTF_8.INSTANCE;


These could move to String also, if there is a benefit them being local.
Otherwise, the uses in String could refer directly to the INSTANCEs in the sun.nio.cs... classes.

RogerRiggs · 2021-01-21T22:23:49Z

src/java.base/share/classes/java/lang/StringCoding.java

@@ -522,85 +48,18 @@ final String requestedCharsetName() {
     */
    private static native void err(String msg);


A separate cleanup could remove this unused method and the corresponding native code in StringCoding.c.

RogerRiggs · 2021-01-21T22:23:49Z

src/java.base/share/classes/java/lang/StringCoding.java

    }

    @IntrinsicCandidate
-    private static int implEncodeISOArray(byte[] sa, int sp,
+    public static int implEncodeISOArray(byte[] sa, int sp,
                                          byte[] da, int dp, int len) {
        int i = 0;


As a separate cleanup...
If there isn't any value to these intrinsics being in StringCoder, they could also move to String
with the corresponding intrinsic references.

cl4es · 2021-01-22T11:26:29Z

Passed testing tiers 1-4

/integrate

openjdk · 2021-01-22T11:27:37Z

@cl4es Since your change was applied there have been 14 commits pushed to the master branch:

d066f2b: 8260030: Improve stringStream buffer handling
1452280: 8164484: Unity, JTable cell editor, javax/swing/JComboBox/6559152/bug6559152.java
a70acf2: 8259928: compiler/jvmci tests fail with -Xint
ba38661: 8259882: Reduce the inclusion of perfData.hpp
92c2f08: 8259869: [macOS] Remove desktop module dependencies on JNF Reference APIs
a7c2ebc: 8239894: Xserver crashes when the wrong high refresh rate is used
2f47c39: 8259943: FileDescriptor.close0 does not handle EINTR
a8073ef: 8253478: (se) epoll Selector should use eventfd for wakeup instead of pipe
34eb8b3: 8255765: Shenandoah: Isolate concurrent, degenerated and full GC
c3c6662: 8259954: gc/shenandoah/mxbeans tests fail with -Xcomp
... and 4 more: https://git.openjdk.java.net/jdk/compare/7f7166dbc8822afaa39382cf9cb42be8458b0e4b...master

Your commit was automatically rebased without conflicts.

Pushed as commit 58ceb25.

💡 You may see a message that your pull request was closed with unmerged commits. This can be safely ignored.

cl4es added 11 commits Jan 14, 2021

First stab

80ef37b

Cleanups and small fixes

67067db

Break bootstrap order issues by statically importing Charsets from St…

6335b3b

…ringCoding rather than eagerly initialize on String clinit

Add simple StringDecode micro

a99079a

Fix micro

1a9797c

resolve merge

f2d8700

More micro fixes

f3b7f74

Cleanups, minor improvements

14b142b

Cleanup includes etc

d336ac4

Refactor charset lookups to ensure expected exceptions are thrown on …

a5f610e

…null, foo etc

Fix charset names in micro settings

dfce627

openjdk bot added the core-libs label Jan 15, 2021

cl4es added 2 commits Jan 15, 2021

Merge branch 'master' into sc_tl_exp

5f9068c

Remove unused imports

f14826b

cl4es marked this pull request as ready for review Jan 15, 2021

openjdk bot added the rfr label Jan 15, 2021

naotoj reviewed Jan 15, 2021

View changes

src/java.base/share/classes/java/lang/String.java Outdated Show resolved Hide resolved

Outline much of the decode logic back into StringCoding

c8899e1

cl4es added 2 commits Jan 15, 2021

Merge branch 'master' into sc_tl_exp

e75b914

Copyrights

f328f45

Further simplifications

eb9c850

Simplify lookupCharset

790e746

plevart approved these changes Jan 17, 2021

View changes

openjdk bot added the ready label Jan 17, 2021

cl4es added 2 commits Jan 17, 2021

ASCII fast-path missing for UTF-8 NoRepl methods

e870b3b

Harmonize empty string checking in newString methods

ba279a7

plevart approved these changes Jan 18, 2021

View changes

RogerRiggs reviewed Jan 19, 2021

View changes

cl4es added 6 commits Jan 19, 2021

More privates

c37aa60

Merge branch 'master' into sc_tl_exp

261b00e

More cleanups, make all things private that can be

869bc10

Move most of the encode/decode code to String, remove StringEncoder a…

a45b761

…nd the ThreadLocal encoder facility.

Simplify getBytes -> encode

6808d4d

Reduce code duplication in getBytes/getBytesNoRepl

2143cb3

RogerRiggs approved these changes Jan 21, 2021

View changes

naotoj approved these changes Jan 21, 2021

View changes

cl4es added 2 commits Jan 21, 2021

Remove StringCoding Charset constants

feb8201

Logic error in exception handling in encodeWithEncoder

14928bf

openjdk bot closed this Jan 22, 2021

openjdk bot added integrated and removed ready rfr labels Jan 22, 2021

mrserb mentioned this pull request Aug 10, 2021

8272120: Avoid looking for standard encodings in "java." modules #5063

Closed

3 tasks

stsypanov mentioned this pull request Sep 3, 2021

8273329: Remove redundant null check from String.getBytes(String charsetName) #5361

Closed

3 tasks

8259842: Remove Result cache from StringCoding #2102

8259842: Remove Result cache from StringCoding #2102

cl4es commented Jan 15, 2021 •

edited by openjdk[bot] bot

bridgekeeper bot commented Jan 15, 2021

openjdk bot commented Jan 15, 2021

mlbridge bot commented Jan 15, 2021 •

edited

RogerRiggs commented Jan 15, 2021 •

edited

cl4es commented Jan 15, 2021

naotoj left a comment

plevart commented Jan 15, 2021

cl4es commented Jan 15, 2021

plevart commented Jan 16, 2021

cl4es commented Jan 16, 2021

plevart commented Jan 17, 2021

cl4es commented Jan 17, 2021

plevart left a comment

openjdk bot commented Jan 17, 2021 •

edited

plevart commented Jan 17, 2021

cl4es commented Jan 17, 2021

plevart left a comment

RogerRiggs left a comment

RogerRiggs Jan 19, 2021

RogerRiggs left a comment

RogerRiggs Jan 21, 2021

RogerRiggs Jan 21, 2021

RogerRiggs Jan 21, 2021

cl4es commented Jan 22, 2021

openjdk bot commented Jan 22, 2021

		@@ -522,85 +48,18 @@ final String requestedCharsetName() {
		*/
		private static native void err(String msg);

8259842: Remove Result cache from StringCoding #2102

8259842: Remove Result cache from StringCoding #2102

Conversation

cl4es commented Jan 15, 2021 • edited by openjdk[bot] bot

Progress

Issue

Reviewers

Download

bridgekeeper bot commented Jan 15, 2021

openjdk bot commented Jan 15, 2021

mlbridge bot commented Jan 15, 2021 • edited

Webrevs

RogerRiggs commented Jan 15, 2021 • edited

cl4es commented Jan 15, 2021

naotoj left a comment

plevart commented Jan 15, 2021

cl4es commented Jan 15, 2021

plevart commented Jan 16, 2021

cl4es commented Jan 16, 2021

plevart commented Jan 17, 2021

cl4es commented Jan 17, 2021

plevart left a comment

openjdk bot commented Jan 17, 2021 • edited

plevart commented Jan 17, 2021

cl4es commented Jan 17, 2021

plevart left a comment

RogerRiggs left a comment

RogerRiggs Jan 19, 2021

Choose a reason for hiding this comment

RogerRiggs left a comment

RogerRiggs Jan 21, 2021

Choose a reason for hiding this comment

RogerRiggs Jan 21, 2021

Choose a reason for hiding this comment

RogerRiggs Jan 21, 2021

Choose a reason for hiding this comment

cl4es commented Jan 22, 2021

openjdk bot commented Jan 22, 2021

cl4es commented Jan 15, 2021 •

edited by openjdk[bot] bot

mlbridge bot commented Jan 15, 2021 •

edited

RogerRiggs commented Jan 15, 2021 •

edited

openjdk bot commented Jan 17, 2021 •

edited