Re: PQcancel may hang in the recv call

Hi all,

this is somewhat involved so please bear with me.

We've found a situation where canceling a query may cause the client to
hang, possibly indefinitely. This can happen if the network connection
fails in a specific way.

The reason for this lies in the way the PQcancel function (which
eventually gets called from the higher level interface's cancel
function) is implemented. It works by opening a second connection to
the postmaster (on the same host/port as the existing connection),
send()-ing a cancellation message via the newly opened connection, then
calling recv() to receive an indication that the message was processed.

However, if the network fails in a way that the connection appears to
have been established but subsequent packages are dropped silently,
this recv() call will block.

My questions:

Is this known?
Is this a bug?
What can be done to fix or work around it, apart from applying a
timeout wrapper the cancel operation as well?