I'm not sure what the preferred behaviour would be. Maybe it would help me with a further explanation of the use case. Why do you turn on and off pipelining dynamically?

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** [bugs:#1411] Disabling pipelining on multi handle with in-progress pipelined requests leads to heap corruption and crash**
**Status:** open
**Labels:** pipelining 
**Created:** Thu Aug 14, 2014 03:38 AM UTC by Monty Brandenberg
**Last Updated:** Sat Aug 23, 2014 11:55 AM UTC
**Owner:** Linus Nielsen
With 7.38.0 closing, I thought I'd get this report in now such as it is.
This is 7.37.0 on Win7/64-bit in a large application.  A multi-handle is being used with a per-host connection limit of 8.  Multi-handle may have up to 100 HTTP GET requests queued or in-progress.  Pipelining is a dynamic setting in the application and can be toggled on and off at will.  Dynamic change is implemented by communicating the change to the thread associated with the multi-handle which then enables or disables pipelining on the multi handle, no cross-thread issue should be involved.
Observed:  with requests active on the multi handle, a transition from pipelining to non-pipelining is frequently followed by a sequence of errors.  First will be an error from the library about missing server status (thought the error code was 9, not certain).  That's followed shortly by a hard crash:  typically calloc() throwing a runtime exception.
Suspected the library fails to honor in-progress/queued requests once pipelining is turned off so I did an application mod.  When settings are changed, the multi handle is allowed to run until no requests are active then the multi options are set (enabling/disabling pipelining, etc.).  This mod appears stable and reliable.
I imagine there's an easy fix which would simply be to continue processing the side request queues regardless of pipelining setting.  Haven't checked that this is, in fact, the needed fix.
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