RFR: 8308593: Add Keepalive Extended Socket Options Support for Windows

[Alan Bateman]

On Tue, 30 May 2023 22:46:05 GMT, Terry Chow <duke at openjdk.org> wrote:

> The PR adds support for setting the keepalive extended socket options on Windows. The implemented native code uses the SIO_KEEPALIVE_VALS control code, which is how keepalive values are set on Windows and so there are a few caveats.
> 
> 1. The keepalive time and keepalive interval must both be set at the same time. In the implementation, a new SioKeepAlive class and ExtendedSocketOptions is created to capture this behaviour for Windows only. Keepalive enablement must also be configured when using SIO_KEEPALIVE_VALS, and so by default when setting keepalive time and keepalive interval,
> keepalive will automatically be enabled.
> 
> [SIO_KEEPALIVE_VALS doc](https://learn.microsoft.com/en-us/windows/win32/winsock/sio-keepalive-vals)
> 
> 2. It doesn't seem possible to acquire the Keepalive time and keepalive interval values on Windows. So, the implementation doesn't support acquiring the values.
> 
> https://stackoverflow.com/questions/14197347/how-to-query-socket-keep-alive-values-using-winsock/14198462#14198462
> https://stackoverflow.com/questions/18391341/reading-sio-keepalive-vals-fields-on-a-windows-socket-for-keepalive-idle-and-in
> 
> 3. Keepalive probes are not supported. On Windows Vista and later, the number of keep-alive probes is set to 10 and cannot be changed.
> 
> [SIO_KEEPALIVE_VALS Remarks](https://learn.microsoft.com/en-us/windows/win32/winsock/sio-keepalive-vals#remarks)
> 
> For testing, I've updated the existing keepalive tests. But, since it's not possible to acquire the keepalive values on Windows to verify, I've indirectly tested setting the keepalive values by confirming keepalive is enabled where possible (since keepalive is enabled also when keepalive values are set).

In the discussion on net-dev/nio-dev, Daniel Jeliński pointed out that Windows does have TCP_KEEPIDLE and TCP_KEEPINTVL since Windows 10 version 1709. So I assume this PR can be returned to closed or re-returned to draft while the implementation changes are developed to make use of these socket options.

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PR Comment: https://git.openjdk.org/jdk/pull/14232#issuecomment-1588700452