Fix Crash under high load

[halter73]

#1327

@Eilon

[Eilon]

This patch bug is approved. Please use the normal code review process w/ a PR and make sure the fix is in the correct branch, then close the bug and mark it as done.

[newbie2006]

I'm doing load test using VS2015 for an application that we're developing. The application is behind IIS/Kestrel. After couple mins, the server stopped responding, however, CPU and memory usage are fairly low. The thread count under the Resource Monitor went up to several thousands. I'm assuming this is caused by the similar issues that were discussed here regarding the thread lock on Kestrel. Does anyone have any recommendations on what I should do to resolve the issues? Thanks.