Keep APM and sync UploadFile/DownloadFile callbacks on the threadpool#1805
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Rob-Hague wants to merge 2 commits into
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Keep APM and sync UploadFile/DownloadFile callbacks on the threadpool#1805Rob-Hague wants to merge 2 commits into
Rob-Hague wants to merge 2 commits into
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Changes to support IProgress<> callback on UploadAsync/DownloadAsync meant wrapping the Action<> callback on existing methods in a Progress<>, which posts the callback onto the current synchronisation context rather than the threadpool. For the legacy APM methods (Begin[..]), let's just preserve their old behaviour. For the synchronous methods, posting to the synchronisation context is probably the worst choice (because if there is one, the method itself is running there). We can either revert to the threadpool as well, or take the opportunity to invoke the callback synchronously, which is a behavioural change but probably the least surprising behaviour for a synchronous method.
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Pull request overview
Adjusts how SftpClient routes progress callbacks so that legacy APM (Begin*) methods keep their historical “thread pool regardless of SynchronizationContext” behavior, while sync UploadFile/DownloadFile no longer post progress back onto the current synchronization context.
Changes:
- Replaced
Progress<T>wrappers for APM methods with a customThreadPoolProgress<T>to avoidSynchronizationContextcapture. - Changed sync
UploadFile/DownloadFilecallback wrapping to use a customSynchronousProgress<T>. - Simplified progress reporting sites to report inline via
?.Report(...)with a freshly constructed progress report value.
We could call the Download callback synchronously easily enough, but the Upload progress reports are being made on the message listener thread upon request ack. A more involved scheme could drain callbacks to fire during the read loop. For now just make it all the same behaviour as in 2025.1.0.
Rob-Hague
changed the title
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Changes to support IProgress<> callback on UploadAsync/DownloadAsync meant wrapping the Action<> callback on existing methods in a Progress<>, which posts the callback onto the current synchronisation context rather than the threadpool. For the legacy APM methods (Begin[..]), let's just preserve their old behaviour.
For the synchronous methods, posting to the synchronisation context is probably the worst choice (because if there is one, the method itself is running there). We can either revert to the threadpool as well,
or take the opportunity to invoke the callback synchronously, which is a behavioural change but probably the least surprising behaviour for a synchronous method.edit: after a nudging from copilot, I remembered that the UploadFile callbacks fire upon receiving sftp status response and on the receiving listener thread, so invoking them synchronously does not have the desired effect. For now just keep the behaviour as in prior releases for all methods.