On Thu, 17 Feb 2011, comain chen wrote:

> 1. When using persistent connections, is there a reliable way to detect
> whether the reused connection is still alive?

Yes, and libcurl does it in two ways: first it checks if the socket has turned
writable which would mean that it died. Then, it takes a special precaution in
case the first operation on the re-used socket fails and re-creates the
connection if it does.

> I think there is no way to do so.

Why not?

> Therefore, the transfer over a reused connection can fail at all possible
> stages (i.e. the reused connection is suddenly dad)

No. A persistent connection can only validly get disconnected between two
usages. It cannot disconnect during a request without that being an actual
error.

> 2. If the above is true,  all states in curl_multi_runsingle should
> check for this case and make sure to retry a new fresh connection to
> recover.

But it isn't true so we don't.

> This caused my problem, I am using mutli to connect to several http servers
> which does not favor persistent connection and closed the connection
> immediately after response.

Then it also signals that in the response, and even if doesn't signal it but
simply closes it anyway, closing the connection after a full response
shouldn't cause a problem.

> When a later request comes, it is possible that an old dead connection is
> reused and caused failure in various stages.

No. When a request is started it is in the start stage(s), not "in various
stages", so it can only legitimately fail there and not later on during the
request's life time.

-- 
  / daniel.haxx.se

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Received on 2011-02-17