RFR: 8330940: Impossible to create a socket backlog greater than 200 on Windows 8+
Jaikiran Pai
jpai at openjdk.org
Mon Jun 16 07:00:31 UTC 2025
Can I please get a review of this change which proposes to enhance the implementation of `ServerSocket` and `ServerSocketChannel` to allow for `backlog` values to be greater than 200 on Windows? This addresses https://bugs.openjdk.org/browse/JDK-8330940.
As noted in that enhancement request, right now on Windows, if the backlog is specified to be more than 200, then Windows caps it to a platform internal `SOMAXCONN`. As noted in the documentation here https://learn.microsoft.com/en-us/windows/win32/api/winsock2/nf-winsock2-listen applications can increase that limit by using the `SOMAXCONN_HINT` macro. That macro then adjusts the value to be between 200 and 65535, thus allowing for a higher backlog of connections.
The commit in this PR uses this macro when the specified backlog is 200 or more. A new jtreg test has been introduced to verify this change. This test and other existing tests in tier1, tier2 and tier3 continue to pass.
A similar restriction on the backlog value applies in Linux too https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.rst#tcp-variables. But from what I can see, unlike Windows, it cannot be adjusted when calling `listen()`.
-------------
Commit messages:
- fix typo in code comment in test
- 8330940: Impossible to create a socket backlog greater than 200 on Windows 8+
Changes: https://git.openjdk.org/jdk/pull/25819/files
Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25819&range=00
Issue: https://bugs.openjdk.org/browse/JDK-8330940
Stats: 107 lines in 2 files changed: 107 ins; 0 del; 0 mod
Patch: https://git.openjdk.org/jdk/pull/25819.diff
Fetch: git fetch https://git.openjdk.org/jdk.git pull/25819/head:pull/25819
PR: https://git.openjdk.org/jdk/pull/25819
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