On 2016-01-02 18:40:38 +0530, Amit Kapila wrote:
> What I wanted to say is that the handling of socket closure is not
> same in WaitLatchOrSocket() and pgwin32_waitforsinglesocket()
> due to which this problem can arise and it seems that is the
> right line of direction to pursue.  I have found that
> in WaitLatchOrSocket(),
> even when the socket is closed, we remember the result as
> WL_SOCKET_READABLE and again tries to wait whereas the
> same is handled properly in pgwin32_waitforsinglesocket().

That's actually intentional, and part of the design:
 * When waiting on a socket, EOF and error conditions are reported by
 * returning the socket as readable/writable or both, depending on

The way this is supposed to work, and does on unixoid systems, is that
WaitLatchOS returns, the recv is retried and signals an error.

> If we
> remember the closed socket event and then take appropriate action,
> then this problem won't happen.  Attached patch which by no-means
> a complete fix shows what I wanted to say and after this the problem
> mentioned by Shay doesn't happen, although I get LOG message
> which is due to the reason that proper handling for socket closure
> needs to be done in this path.  This patch is based on the code
> after commit 387da18874afa17156ee3af63766f17efb53c4b9.  I
> will do testing and refine the fix based on HEAD later as I am done
> for the today.

It's weird that this fixes the problem. As we were previously, according
to Shay, not busy looping, this seems to indicate that FD_CLOSE is only
reported once or somesuch?

It'd be very interesting to add a debug elog() into the
                        if (resEvents.lNetworkEvents & FD_CLOSE)
                                if (wakeEvents & WL_SOCKET_READABLE)
                                        result |= WL_SOCKET_READABLE;
                                if (wakeEvents & WL_SOCKET_WRITEABLE)
                                        result |= WL_SOCKET_WRITEABLE;

path in WaitLatchOrSocket. If it actually returns with the current code,
we have a better idea where to look for problems.


Andres Freund

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