Improve TCP backpressure handling on Windows #4252
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Our prior setting of backpressure for TCP writes on Windows was naive. It was based purely on the number of buffers currently outstanding on an IOCP socket. The amount of data didn't matter at all. Whether more data could be accepted or not, also wasn't taken into consideration. This commit greatly improves the situation by only applying backpressure when Windows tells us that it is applying backpressure. No more guessing. Two runtime API methods have been updated on Windows. The Windows version of `pony_os_writev` will now return the number of buffers accepted or zero if backpressure is encountered. All other errors still cause an error that must be handled on the Pony side of the API via a `try` block. The Windows version of `pony_os_send` will now return the number of bytes accepted or zero if backpressure is encountered. All other errors still cause an error that must be handled on the Pony side of the API via a `try` block. I consider these changes non-breaking as previously, the return values from both functions had no meaning. Closes #4081
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Our prior setting of backpressure for TCP writes on Windows was naive. It was based purely on the number of buffers currently outstanding on an IOCP socket. The amount of data didn't matter at all. Whether more data could be accepted or not, also wasn't taken into consideration. This commit greatly improves the situation by only applying backpressure when Windows tells us that it is applying backpressure.
No more guessing.
Two runtime API methods have been updated on Windows.
The Windows version of
pony_os_writevwill now return the number of buffers accepted or zero if backpressure is encountered. All other errors still cause an error that must be handled on the Pony side of the API via atryblock.The Windows version of
pony_os_sendwill now return the number of bytes accepted or zero if backpressure is encountered. All other errors still cause an error that must be handled on the Pony side of the API via atryblock.I consider these changes non-breaking as previously, the return values from both functions had no meaning.
Closes #4081