8351458: (ch) Move preClose to UnixDispatcher #23956

AlanBateman · 2025-03-09T09:10:15Z

Network channels in blocking mode, and the NIO based SocketImpl, have to deal with async close when there are threads blocked on the channel. Virtual threads blocked on the channel need to be unparked. On Unix systems, platform threads blocked on the channel require the file descriptor to be dup'ed to a special file descriptor and the threads signalled.

There is a bit of duplication in the implementation of the 5 channels, and in the SocketImpl. In addition, there is discussion on net-dev about an issue in AIX that will require allowing for signals to be queued (the current implementation does not require OS to support queuing of signals).

We refactor this code so that the "prepare for close" is in one place, UnixDispatcher.

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Issue

JDK-8351458: (ch) Move preClose to UnixDispatcher (Enhancement - P4)

Reviewers

Brian Burkhalter (@bplb - Reviewer)
Jaikiran Pai (@jaikiran - Reviewer)

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Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk.git pull/23956/head:pull/23956
$ git checkout pull/23956

Update a local copy of the PR:
$ git checkout pull/23956
$ git pull https://git.openjdk.org/jdk.git pull/23956/head

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Checkout this PR locally:
$ git pr checkout 23956

View PR using the GUI difftool:
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bridgekeeper · 2025-03-09T09:11:12Z

👋 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 · 2025-03-09T09:11:17Z

@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:

8351458: (ch) Move preClose to UnixDispatcher

Reviewed-by: bpb, jpai

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 28 new commits pushed to the master branch:

4cf6316: 8351414: C2: MergeStores must happen after RangeCheck smearing
8a5ed47: 8350148: Native stack overflow when writing Java heap objects into AOT cache
5928209: 8347405: MergeStores with reverse bytes order value
f984c2b: 8351505: (fs) Typo in the documentation of java.nio.file.spi.FileSystemProvider.getFileSystem()
ffa6340: 8351567: Jar Manifest test ValueUtf8Coding produces misleading diagnostic output
8d8bd0c: 8349492: Update sun/security/pkcs12/KeytoolOpensslInteropTest.java to use a recent Openssl version
73465b9: 8160327: Support for thumbnails present in APP1 marker for JPEG
dbdbbd4: 8348597: Update HarfBuzz to 10.4.0
7999091: 8351555: Help section added in JDK-8350638 uses invalid HTML
8450ae9: 8351440: Link with -reproducible on macOS
... and 18 more: https://git.openjdk.org/jdk/compare/a90f323d05f1c90767823b8729b124de0bead265...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 · 2025-03-09T09:11:41Z

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

nio

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 · 2025-03-10T14:47:28Z

Webrevs

00: Full (cabd1fa3)

bplb

I don't see any problems. This looks like a nice cleanup.

jaikiran · 2025-03-11T04:21:34Z

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

+     */
+    final void preClose(FileDescriptor fd, long reader, long writer) throws IOException {
+        if (NativeThread.isVirtualThread(reader) || NativeThread.isVirtualThread(writer)) {
+            int fdVal = JIOFDA.get(fd);


Hello Alan, previously, in the case of DatagramChannelImpl, the fdVal was a final that was determined when the channel was constructed. Now, that fdVal gets determined as and when needed and I see that FileDescriptor allows this underlying value to be changed/reset. Is there anything practical to consider here in context of a fdVal that has been reset in the FileDescriptor?

repairSocket doesn't change fd/fdVal, instead they will be connected to a new socket if the method succeeds (or the old socket if it fails).

It was the FileDescriptor.set(int fd) method which I had in mind. But I now looked at its references and I see that there aren't any in the code paths that this PR deals with. So I believe the proposed change looks good.

jaikiran · 2025-03-11T04:25:24Z

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

+     * dup'ed to a special fd and the thread signalled so that the syscall fails with EINTR.
+     */
+    final void preClose(FileDescriptor fd, long reader, long writer) throws IOException {
+        if (NativeThread.isVirtualThread(reader) || NativeThread.isVirtualThread(writer)) {


There used to be a if (reader != 0 || writer != 0) {...} check before doing any of this pre-close work, in DatagramChannelImpl. Is that no longer needed?

There used to be a if (reader != 0 || writer != 0) {...} check before doing any of this pre-close work, in DatagramChannelImpl. Is that no longer needed?

Looking at the implementation of NativeThread.isNativeThread() and NativeThread.isVirtualThread(), it already implicitly takes into account the != 0 check, so I guess the previous explicit checks before calling those methods was redundant.

Right, there are a several places where check for != 0 would be redundant.

jaikiran

The changes look good to me.

Michael-Mc-Mahon

So, on Unix, the fd needs to be dup'ed and the native thread signalled. On Windows, the dup() operation does not happen, but the threads were being signalled previously, but not any more. Was that redundant previously?

AlanBateman · 2025-03-11T08:50:36Z

So, on Unix, the fd needs to be dup'ed and the native thread signalled. On Windows, the dup() operation does not happen, but the threads were being signalled previously, but not any more. Was that redundant previously?

There's never been any signalling of threads on Windows, NativeThread::isNativeThread always returns false. So no change on Windows.

AlanBateman · 2025-03-11T11:26:23Z

Thanks for the reviews/comments.

AlanBateman · 2025-03-11T11:26:28Z

/integrate

openjdk · 2025-03-11T11:26:49Z

Going to push as commit 0de2cdd.
Since your change was applied there have been 29 commits pushed to the master branch:

cd9f1d3: 8286204: [Accessibility,macOS,VoiceOver] VoiceOver reads the spinner value 10 as 1 when user iterates to 10 for the first time on macOS
4cf6316: 8351414: C2: MergeStores must happen after RangeCheck smearing
8a5ed47: 8350148: Native stack overflow when writing Java heap objects into AOT cache
5928209: 8347405: MergeStores with reverse bytes order value
f984c2b: 8351505: (fs) Typo in the documentation of java.nio.file.spi.FileSystemProvider.getFileSystem()
ffa6340: 8351567: Jar Manifest test ValueUtf8Coding produces misleading diagnostic output
8d8bd0c: 8349492: Update sun/security/pkcs12/KeytoolOpensslInteropTest.java to use a recent Openssl version
73465b9: 8160327: Support for thumbnails present in APP1 marker for JPEG
dbdbbd4: 8348597: Update HarfBuzz to 10.4.0
7999091: 8351555: Help section added in JDK-8350638 uses invalid HTML
... and 19 more: https://git.openjdk.org/jdk/compare/a90f323d05f1c90767823b8729b124de0bead265...master

Your commit was automatically rebased without conflicts.

openjdk · 2025-03-11T11:27:03Z

@AlanBateman Pushed as commit 0de2cdd.

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

shruacha1234 · 2025-07-29T03:53:54Z

/backport jdk21u-dev

openjdk · 2025-07-29T03:55:18Z

@shruacha1234 Could not automatically backport 0de2cddf to openjdk/jdk21u-dev due to conflicts in the following files:

src/java.base/share/classes/sun/nio/ch/DatagramChannelImpl.java
src/java.base/share/classes/sun/nio/ch/NioSocketImpl.java
src/java.base/share/classes/sun/nio/ch/ServerSocketChannelImpl.java
src/java.base/share/classes/sun/nio/ch/SocketChannelImpl.java

Please fetch the appropriate branch/commit and manually resolve these conflicts by using the following commands in your personal fork of openjdk/jdk21u-dev. Note: these commands are just some suggestions and you can use other equivalent commands you know.

# Fetch the up-to-date version of the target branch
$ git fetch --no-tags https://git.openjdk.org/jdk21u-dev.git master:master

# Check out the target branch and create your own branch to backport
$ git checkout master
$ git checkout -b backport-shruacha1234-0de2cddf-master

# Fetch the commit you want to backport
$ git fetch --no-tags https://git.openjdk.org/jdk.git 0de2cddf3a7be23f67af93972875af1235f3107e

# Backport the commit
$ git cherry-pick --no-commit 0de2cddf3a7be23f67af93972875af1235f3107e
# Resolve conflicts now

# Commit the files you have modified
$ git add files/with/resolved/conflicts
$ git commit -m 'Backport 0de2cddf3a7be23f67af93972875af1235f3107e'

Once you have resolved the conflicts as explained above continue with creating a pull request towards the openjdk/jdk21u-dev with the title Backport 0de2cddf3a7be23f67af93972875af1235f3107e.

Below you can find a suggestion for the pull request body:

Hi all,

This pull request contains a backport of commit 0de2cddf from the openjdk/jdk repository.

The commit being backported was authored by Alan Bateman on 11 Mar 2025 and was reviewed by Brian Burkhalter and Jaikiran Pai.

Thanks!

Initial commit

cabd1fa

openjdk bot added the nio [email protected] label Mar 9, 2025

AlanBateman changed the title ~~8351458: (ch) Move preclose to UnixDispatcher~~ 8351458: (ch) Move preClose to UnixDispatcher Mar 10, 2025

AlanBateman marked this pull request as ready for review March 10, 2025 14:43

openjdk bot added the rfr Pull request is ready for review label Mar 10, 2025

bplb approved these changes Mar 10, 2025

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jaikiran reviewed Mar 11, 2025

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jaikiran approved these changes Mar 11, 2025

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Michael-Mc-Mahon reviewed Mar 11, 2025

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openjdk bot added the integrated Pull request has been integrated label Mar 11, 2025

openjdk bot closed this Mar 11, 2025

openjdk bot removed ready Pull request is ready to be integrated rfr Pull request is ready for review labels Mar 11, 2025

shruacha1234 mentioned this pull request Jul 20, 2025

8294399: (ch) Refactor some methods out of sun.nio.ch.UnixFileDispatcherImpl openjdk/jdk17u-dev#3631

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shruacha1234 mentioned this pull request Aug 5, 2025

8351458: (ch) Move preClose to UnixDispatcher openjdk/jdk21u-dev#2051

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8351458: (ch) Move preClose to UnixDispatcher #23956

8351458: (ch) Move preClose to UnixDispatcher #23956

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