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8266369: (se) Add wepoll based Selector #3816

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@AlanBateman AlanBateman commented Apr 30, 2021

This PR proposes a new Selector implementation for the Windows platform based on the Bert Belder's "wepoll" library. The wepoll library provides a scalable polling interface to the Ancillary Function Driver for Winsock. The interface that it exposes is close to the Linux epoll interface. The main benefit is that the cost of selection operations are a function of the number of sockets that are ready for I/O rather than the number of channels registered with the Selector. The existing Selector on Windows uses the legacy "select" which scales horribly, partly because it's O(N) on the number of registered channels and partly because it is limited to 1024 sockets and so requires a thread per 1024 sockets.

The patch brings the wepoll sources into the repo, adds a small shim, and the Selector implementation itself. The new implementation needs to handle OOB data in the same way as the old implementation so the method to discard OOB moves to Net.

I've added a microbenchmark to demonstrate the scaling when there is 1, 10, ... 10k connections and one socket ready for I/O. Windows Server 2019 was used for the data here. I've seen improvements with almost everything that I've tried. The only exception is a select after a wakeup where the old implementation skips the selection operation (arguably a long standing bug in the old implementation).

Existing select based Selector where the selection operation is almost 1ms when there are 10,000 channels registered.

Benchmark                (nchannels)  Mode  Cnt       Score       Error  Units
SelectOne.testSelectOne            1  avgt   20    1587.429 ±     4.053  ns/op
SelectOne.testSelectOne           10  avgt   20    2515.324 ±     8.141  ns/op
SelectOne.testSelectOne          100  avgt   20   10903.445 ±    65.508  ns/op
SelectOne.testSelectOne         1000  avgt   20  101651.369 ±   673.781  ns/op
SelectOne.testSelectOne        10000  avgt   20  932032.385 ± 59004.246  ns/op

New wepoll based Selector:

Benchmark                (nchannels)  Mode  Cnt     Score    Error  Units
SelectOne.testSelectOne            1  avgt   20  1428.914 ±  6.648  ns/op
SelectOne.testSelectOne           10  avgt   20  1429.806 ±  5.537  ns/op
SelectOne.testSelectOne          100  avgt   20  1433.371 ±  3.253  ns/op
SelectOne.testSelectOne         1000  avgt   20  1435.007 ± 12.420  ns/op
SelectOne.testSelectOne        10000  avgt   20  1445.201 ±  7.902  ns/op

Replacing the Selector implementation after 19 years of service is a big step. The proposal is to leave the existing implementation until there is confidence with the new implementation. It also serves as a backup in case Windows were to significantly change the AFD interface. The old Selector can be used by running with -Djava.nio.channels.spi.SelectorProvider=sun.nio.ch.WindowsSelectorProvider. A selection of existing tests have been updated to run a second time with the old Selector so that it is continues to be tested.

CSR and Release Note planned.


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@bridgekeeper bridgekeeper bot commented Apr 30, 2021

👋 Welcome back alanb! 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.

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@openjdk openjdk bot commented Apr 30, 2021

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

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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.

@openjdk openjdk bot added the nio label Apr 30, 2021
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@AlanBateman AlanBateman commented Apr 30, 2021

/issue JDK-8266369

@openjdk openjdk bot changed the title 8266369: Add wepoll based Selector 8266369: (se) Add wepoll based Selector Apr 30, 2021
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@openjdk openjdk bot commented Apr 30, 2021

@AlanBateman This issue is referenced in the PR title - it will now be updated.

@AlanBateman AlanBateman marked this pull request as ready for review Apr 30, 2021
@openjdk openjdk bot added the rfr label Apr 30, 2021
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@mlbridge mlbridge bot commented Apr 30, 2021

* Returns event[i];
*/
static long getEvent(long address, int i) {
return address + (SIZEOF_EPOLLEVENT*i);
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@vyommani vyommani May 4, 2021

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space issue (SIZEOF_EPOLLEVENT*i);

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@ChrisHegarty ChrisHegarty left a comment

Overall, this looks like a very nice addition.

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@openjdk openjdk bot commented May 5, 2021

@AlanBateman 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:

8266369: (se) Add wepoll based Selector

Reviewed-by: chegar, michaelm, vtewari, dfuchs, bpb

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 16 new commits pushed to the master branch:

  • 0790e60: 8196743: jstatd doesn't see new Java processes inside Docker container
  • c6aa8f1: 8232644: bugs in serialized-form.html
  • b5b3119: 8266589: (fs) Improve performance of Files.copy() on macOS using copyfile(3)
  • 947d69d: 8265042: javadoc HTML files not generated for types nested in records
  • 946b0fe: 8266645: javac should not check for sealed supertypes in intersection types
  • 74fecc0: 8266503: [UL] Make Decorations safely copy-able and reduce their size
  • 86b8dc9: 8265426: Update java.security to use instanceof pattern variable
  • 3fcdc50: 8266646: Add more diagnostic to java/lang/System/LoggerFinder/modules
  • 9a19a0c: 8264760: JVM crashes when two threads encounter the same resolution error
  • 14f0afe: 8214237: Join parallel phases post evacuation
  • ... and 6 more: https://git.openjdk.java.net/jdk/compare/ebb68d2b8652328b80780f6a39c78ff19f24136a...master

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.

@openjdk openjdk bot added the ready label May 5, 2021
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@vyommani vyommani left a comment

LGTM

dfuch
dfuch approved these changes May 6, 2021
bplb
bplb approved these changes May 7, 2021
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@bplb bplb left a comment

A good improvement. Approved.

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@AlanBateman AlanBateman commented May 8, 2021

/integrate

@openjdk openjdk bot closed this May 8, 2021
@openjdk openjdk bot added integrated and removed ready rfr labels May 8, 2021
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@openjdk openjdk bot commented May 8, 2021

@AlanBateman Since your change was applied there have been 18 commits pushed to the master branch:

  • ff77ca8: 8266675: Optimize IntHashTable for encapsulation and ease of use
  • 04fad70: 8266765: [BACKOUT] JDK-8255493 Support for pre-generated java.lang.invoke classes in CDS dynamic archive
  • 0790e60: 8196743: jstatd doesn't see new Java processes inside Docker container
  • c6aa8f1: 8232644: bugs in serialized-form.html
  • b5b3119: 8266589: (fs) Improve performance of Files.copy() on macOS using copyfile(3)
  • 947d69d: 8265042: javadoc HTML files not generated for types nested in records
  • 946b0fe: 8266645: javac should not check for sealed supertypes in intersection types
  • 74fecc0: 8266503: [UL] Make Decorations safely copy-able and reduce their size
  • 86b8dc9: 8265426: Update java.security to use instanceof pattern variable
  • 3fcdc50: 8266646: Add more diagnostic to java/lang/System/LoggerFinder/modules
  • ... and 8 more: https://git.openjdk.java.net/jdk/compare/ebb68d2b8652328b80780f6a39c78ff19f24136a...master

Your commit was automatically rebased without conflicts.

Pushed as commit be4f25b.

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