7116990: (spec) Socket.connect(addr,timeout) not clear if IOException because of TCP timeout #25690

jaikiran · 2025-06-09T07:39:02Z

Can I please get a review of this doc-only change which proposes to add a @apiNote to the Socket.connect(SocketAddress endpoint, int timeout) method? This addresses https://bugs.openjdk.org/browse/JDK-7116990.

As noted in that issue, users can find it surprising that when the Socket.connect(...) method is called with a timeout value, then if that timeout value happens to be greater than the connect timeout that operating systems typically impose, then a IOException gets thrown instead of the SocketTimeoutException. The change in this PR proposes to add a @apiNote which explains this current behaviour.

If this requires a CSR, I'll open one once we settle on the proposed text.

Progress

Change must be properly reviewed (1 review required, with at least 1 Reviewer)
Change must not contain extraneous whitespace
Commit message must refer to an issue
Change requires CSR request JDK-8359249 to be approved

Issues

JDK-7116990: (spec) Socket.connect(addr,timeout) not clear if IOException because of TCP timeout (Bug - P3)
JDK-8359249: (spec) Socket.connect(addr,timeout) not clear if IOException because of TCP timeout (CSR)

Reviewers

Alan Bateman (@AlanBateman - Reviewer) Review applies to d6978f0d
Daniel Fuchs (@dfuch - Reviewer)

Reviewing

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Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk.git pull/25690/head:pull/25690
$ git checkout pull/25690

Update a local copy of the PR:
$ git checkout pull/25690
$ git pull https://git.openjdk.org/jdk.git pull/25690/head

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Checkout this PR locally:
$ git pr checkout 25690

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https://git.openjdk.org/jdk/pull/25690.diff

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… because of TCP timeout

bridgekeeper · 2025-06-09T07:39:41Z

👋 Welcome back jpai! 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 · 2025-06-09T07:40:51Z

@jaikiran This change is no longer ready for integration - check the PR body for details.

openjdk · 2025-06-09T07:41:17Z

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

net

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 · 2025-06-09T07:44:32Z

Webrevs

dfuch · 2025-06-09T09:59:22Z

src/java.base/share/classes/java/net/Socket.java

@@ -621,6 +621,12 @@ public void connect(SocketAddress endpoint) throws IOException {
     *        {@code SocketException} with the interrupt status set.
     * </ol>
     *
+     * @apiNote Establishing a TCP/IP connection is subject to connection timeout settings
+     * in the operating system. The typical timeout is 60 seconds. If the operating system


Suggested change

* in the operating system. The typical timeout is 60 seconds. If the operating system

* in the operating system. The typical operating system timeout is 60 seconds. If the operating system

I would suggest repeating "operating system timeout" here too, to remove confusion with the simple API timeout which also appears later in this paragraph.

FWIW:
Stating a typical value of 60 seconds timeout can lead to a misconception or set an expectation ... From from TCP standards and depending on which literature you read (OS docs or unix networking socket programming) then 75 secs should be a more typical default

I think the 60 seconds comes from a perceived setting on linux. For example if a linux config of
net.ipv4.tcp_syn_retries = 6 is set and the RTO == 1 sec, with a backoff policy of doubling the timeout each retry, then the connect timeout would expect to be 63 secs

It would be better to say that, the value is OS dependent, influenced by OS network setting relating to syn receive timeouts and the number of syn retries, and governed by the TCP retransmission timer implementation, rather than stating a particular value.

Hello Mark,
Alan's thought was that it might be OK to have that sentence about the typical 60 second timeout. The primary guidance to developers here is that "The {@code timeout} specified to this method is typically a timeout value that is shorter than the operating system timeout." so that they set a lower value when appropriate.

Alan @AlanBateman, do you suggest we continue with this text or would any update be necessary?

I think it is an unnecessary quantification, is somewhat inaccurate, and set an expectation of a developer that this is gospel or axiomatic. Indicating that it is OS dependent should be sufficient.

"The timeout values noted in that text are mere examples to convey the detail that application developers need to be aware that the timeout they pass to the connect() method may not influence connection establishment failure due to timeout. They aren't exhaustive. I had considered including 21 in that text too. Alan's suggestion was to mention "60 or 75 seconds". "

Right, the objective is to convey to a developer that when specifying a timeout to the connect method, that this timeout may be superseded by an OS's TCP/IP configuration's Connect timeout settings.

This is all that needs to be said. There is no need to state any typical values, but if you do then those values need to be factually correct, and for the currently supported platforms 60 seconds is not typical, it's 21, 75, and 128 seconds

But if a developer takes guidance from the "typically 60 seconds" statement on a Windows environment and set a timeout of 50 seconds, they will get
IOException is a java.net.ConnectException
java.net.ConnectException: Operation timed out

as reported in the original bug and as such, defeats the purpose of the apiNote

This is all that needs to be said. There is no need to state any typical values, but if you do then those values need to be factually correct, and for the currently supported platforms 60 seconds is not typical, it's 21, 75, and 128 seconds

The proposed wording in the current draft looks okay. It explains to the reader that establishing a TCP/IP connection is subject to an operating system timeout. It gives a sense of what that timeout might be, it's not hours or days, it's tens of seconds. I don't think we should attempt to list specific timeouts for specific operating system versions and configurations.

why are you insisting on specifying 60 seconds? It does not exist on any supported OS platform. There is no need to specify any value in the apiNote, all it does is add misinformation

Maybe we could say:

The typical operating system timeout ranges within tens of seconds to minutes.

👍 very good suggestion

AlanBateman

Good

dfuch

Not sure this requires a CSR. It might - if only for the sake of clarifying expectations for JCK too.

jaikiran · 2025-06-11T11:48:10Z

/csr

openjdk · 2025-06-11T11:48:25Z

@jaikiran has indicated that a compatibility and specification (CSR) request is needed for this pull request.

@jaikiran please create a CSR request for issue JDK-7116990 with the correct fix version. This pull request cannot be integrated until the CSR request is approved.

jaikiran · 2025-06-11T17:29:37Z

The CSR is now ready for review https://bugs.openjdk.org/browse/JDK-8359249

AlanBateman · 2025-06-11T18:31:45Z

The CSR is now ready for review https://bugs.openjdk.org/browse/JDK-8359249

It's okay to have a CSR but no usually needed for API notes.

7116990: (spec) Socket.connect(addr,timeout) not clear if IOException…

909d7d2

… because of TCP timeout

openjdk bot added the rfr Pull request is ready for review label Jun 9, 2025

openjdk bot added the net [email protected] label Jun 9, 2025

dfuch reviewed Jun 9, 2025

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Daniel's suggestion

d6978f0

AlanBateman approved these changes Jun 9, 2025

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openjdk bot added the ready Pull request is ready to be integrated label Jun 9, 2025

dfuch approved these changes Jun 9, 2025

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openjdk bot added the csr Pull request needs approved CSR before integration label Jun 11, 2025

openjdk bot removed the ready Pull request is ready to be integrated label Jun 11, 2025

improve text

124e097

dfuch approved these changes Jun 13, 2025

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	* in the operating system. The typical timeout is 60 seconds. If the operating system
	* in the operating system. The typical operating system timeout is 60 seconds. If the operating system

7116990: (spec) Socket.connect(addr,timeout) not clear if IOException because of TCP timeout #25690

Are you sure you want to change the base?

7116990: (spec) Socket.connect(addr,timeout) not clear if IOException because of TCP timeout #25690

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jaikiran commented Jun 9, 2025 •

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