Since commit fd90eec6 (2 months ago), the Synchronet Web Server on
my Windows systems has occasionally gone into a state where every HTTP session
thread was causing 100% CPU utilization and each new HTTP session thread
would just exacerbate the problem eventually leading to complete system
instability/unresponsiveness until the sbbs instance was terminated. This was
more readily reproducible on a Win7-32 VM, but would occasionally, though
much less frequently, happen in a native instance on Win10-64 as well.

Using the VisualStudio debugger, I was able to narrow it down to this:

Each new HTTP thread (eventually, hundreds of such threads) would get stuck
in this loop in http_output_thread():

    while(session->socket!=INVALID_SOCKET) {

		/* Wait for something to output in the RingBuffer */
		if((avail=RingBufFull(obuf))==0) {	/* empty */
			if(WaitForEvent(obuf->data_event, 1000) != WAIT_OBJECT_0)
				continue;
			/* Check...