Bug 39315 - Mono.Security.Protocol.Tls.SslStreamBase blocks on asynchronous operations
Summary: Mono.Security.Protocol.Tls.SslStreamBase blocks on asynchronous operations
Alias: None
Product: Class Libraries
Classification: Mono
Component: Mono.Security ()
Version: 4.2.0 (C6)
Hardware: PC Linux
: --- normal
Target Milestone: Untriaged
Assignee: Martin Baulig
Depends on:
Reported: 2016-03-03 09:42 UTC by Dr. John Wason
Modified: 2017-09-13 19:29 UTC (History)
2 users (show)

Is this bug a regression?: ---
Last known good build:

Notice (2018-05-24): bugzilla.xamarin.com is now in read-only mode.

Please join us on Visual Studio Developer Community and in the Xamarin and Mono organizations on GitHub to continue tracking issues. Bugzilla will remain available for reference in read-only mode. We will continue to work on open Bugzilla bugs, copy them to the new locations as needed for follow-up, and add the new items under Related Links.

Our sincere thanks to everyone who has contributed on this bug tracker over the years. Thanks also for your understanding as we make these adjustments and improvements for the future.

Please create a new report on GitHub or Developer Community with your current version information, steps to reproduce, and relevant error messages or log files if you are hitting an issue that looks similar to this resolved bug and you do not yet see a matching new report.

Related Links:

Description Dr. John Wason 2016-03-03 09:42:36 UTC
The class Mono.Security.Tls.SslStreamBase provides asynchronous stream functions including BeginRead, EndRead, BeginWrite, and EndWrite. Unfortunately these asynchronous functions are blocking in situations where both BeginRead and BeginWrite are called at the same time, as is very common in threaded networking design.  An example of the offending code in BeginRead is:

                        if (this.MightNeedHandshake)
				if (! BeginNegotiateHandshake(asyncResult))
					//we made it down here so the handshake was not started.
					//another thread must have started it in the mean time.
					//wait for it to complete and then perform our original operation


The "this.negotiationComplete.WaitOne();" causes a deadlock that is very difficult if not impossible to avoid.  The class needs to either expose the handshaking as a separate function like SslStream does, or it needs to not have a hard block in the asynchronous functions.