8318422: Allow poller threads be virtual threads #16243

AlanBateman · 2023-10-18T10:31:32Z

Virtual threads doing blocking I/O rely on poller threads to unpark virtual threads when sockets are ready for I/O. Right now, the poller threads are dedicated platform threads that block waiting for I/O events. In some environments it would be better to have the poller thread be virtual threads so that handling of I/O events integrates better with the virtual thread scheduler and doesn't steal cycles from the carrier threads.

The changes to support this are straight forward but it has required refactoring the internal Poller class so the changes might look more than they actually are. The changes mean the Poller implementation supports two modes. The default is changed on Linux to use the "virtual thread poller" mode. The default on other platforms is to use platform threads as before. As part of the refactor, the so-called "indirect" mode with updater threads is removed. This mode came from experimenting in the loom repo a long time ago and probably should have been removed before integration.

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Issue

JDK-8318422: Allow poller threads be virtual threads (Enhancement - P3)

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Michael McMahon (@Michael-Mc-Mahon - Reviewer)

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bridgekeeper · 2023-10-18T10:32:53Z

👋 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.

openjdk · 2023-10-18T10:35:16Z

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

net
nio

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

AlanBateman · 2023-10-18T10:41:43Z

/label remove net

openjdk · 2023-10-18T10:42:32Z

@AlanBateman
The net label was successfully removed.

src/java.base/share/classes/sun/nio/ch/Poller.java

mlbridge · 2023-11-02T15:02:11Z

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01: Full - Incremental (87136dde)
00: Full (9588be88)

Michael-Mc-Mahon · 2023-11-02T15:37:41Z

src/java.base/share/classes/sun/nio/ch/Poller.java

-     * Returns true if this poller is for read (POLLIN) events.
+     * Returns the poller's file descriptor, used when the read and write poller threads
+     * are virtual threads.
+     *


Would it be useful to add some more explanation here like: "When there is no activity on any of a subpoller's descriptors, the descriptor of the subpoller is registered with the master poller" ?

Would it be useful to add some more explanation here like: "When there is no activity on any of a subpoller's descriptors, the descriptor of the subpoller is registered with the master poller" ?

The big comment on Mode.VTHREAD_POLLERS explains this. It also links to the Karsten/Barghi paper where a similar scheme is presented. Do you think that's enough?

Michael-Mc-Mahon

Looks good to me.

openjdk · 2023-11-03T12:22:56Z

@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:

8318422: Allow poller threads be virtual threads

Reviewed-by: michaelm

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 3 new commits pushed to the master branch:

008ca2a: 8317620: Build JDK tools with ModuleMainClass attribute
1a21c1a: 8318736: com/sun/jdi/JdwpOnThrowTest.java failed with "transport error 202: bind failed: Address already in use"
81db172: 8318955: Add ReleaseIntArrayElements in Java_sun_awt_X11_XlibWrapper_SetBitmapShape XlbWrapper.c to early return

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.

AlanBateman · 2023-11-03T13:58:25Z

Looks good to me.

Thanks. I've had to one additional update to ProblemList-Virtual.txt to excludevmTestbase/nsk/jdi/VMOutOfMemoryException/VMOutOfMemoryException001/VMOutOfMemoryException001.java on all platforms. It had been excluded on Windows only but it's quite fragile and we tickle it to fail on Linux with these changes. I had a brief exchange with @plummercj in JDK-8285417 about this a few days ago. It's excluded on all platforms in the loom repo already so I should have remembered to include it in this update.

Michael-Mc-Mahon

Latest change is good.

AlanBateman · 2023-11-04T06:50:30Z

/integrate

openjdk · 2023-11-04T06:52:20Z

Going to push as commit c099cf5.
Since your change was applied there have been 6 commits pushed to the master branch:

29cf2c4: 8319053: Segment dump files remain after parallel heap dump on Windows
ea6a88a: 8318466: Improve spec of NumberFormat's methods with unsupported operations
de6667c: 8225377: type annotations are not visible to javac plugins across compilation boundaries
008ca2a: 8317620: Build JDK tools with ModuleMainClass attribute
1a21c1a: 8318736: com/sun/jdi/JdwpOnThrowTest.java failed with "transport error 202: bind failed: Address already in use"
81db172: 8318955: Add ReleaseIntArrayElements in Java_sun_awt_X11_XlibWrapper_SetBitmapShape XlbWrapper.c to early return

Your commit was automatically rebased without conflicts.

openjdk · 2023-11-04T06:52:27Z

@AlanBateman Pushed as commit c099cf5.

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

Initial commit

a7eca12

openjdk bot added nio nio-dev@openjdk.org net net-dev@openjdk.org labels Oct 18, 2023

openjdk bot removed the net net-dev@openjdk.org label Oct 18, 2023

Merge

57a6410

Michael-Mc-Mahon reviewed Nov 1, 2023

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src/java.base/share/classes/sun/nio/ch/Poller.java Outdated Show resolved Hide resolved

AlanBateman added 2 commits November 2, 2023 13:15

Merge

201a187

Sync up changes from loom repo

9588be8

AlanBateman marked this pull request as ready for review November 2, 2023 14:58

openjdk bot added the rfr Pull request is ready for review label Nov 2, 2023

Michael-Mc-Mahon reviewed Nov 2, 2023

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Michael-Mc-Mahon approved these changes Nov 3, 2023

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openjdk bot added the ready Pull request is ready to be integrated label Nov 3, 2023

AlanBateman added 2 commits November 3, 2023 12:29

Merge

16bae1c

VMOutOfMemoryException001.java should be excluded on all platforms

87136dd

Michael-Mc-Mahon approved these changes Nov 3, 2023

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openjdk bot closed this Nov 4, 2023

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8318422: Allow poller threads be virtual threads #16243

8318422: Allow poller threads be virtual threads #16243

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8318422: Allow poller threads be virtual threads #16243

8318422: Allow poller threads be virtual threads #16243

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