From: Terry Lee Tucker <terry@esc1.com>
Organization: Enhanced Solutions Computing
To: PostgreSQL Interfaces <pgsql-interfaces@postgresql.org>
Subject: Re: libpq, blocking/nonblocking mechanism
Date: Tue, 31 May 2005 06:51:54 -0400
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=46rom the docs:
PQsetnonblocking

Sets the nonblocking status of the connection.=20

int PQsetnonblocking(PGconn *conn, int arg);


 Sets the state of the connection to nonblocking if arg is 1, or blocking i=
f=20
arg is 0. Returns 0 if OK, -1 if error.=20


In the nonblocking state, calls to PQsendQuery, PQputline, PQputnbytes, and=
=20
PQendcopy will not block but instead return an error if they need to be=20
called again.=20


Note that PQexec does not honor nonblocking mode; if it is called, it will =
act=20
in blocking fashion anyway.=20

A call to PQsetnonblocking only affects PQsendQuery, etc. These commands wi=
ll=20
work without calling PQsetnonblocking, but they will block. Our application=
=20
uses a combination of PQexec and PQsendQuery.

I'm looking at the documentation in:
file:/usr/share/doc/postgresql-7.4.6/html/libpq-async.html
on my machine.

On Saturday 28 May 2005 04:34 pm, Volkan YAZICI saith:
> Hi,
>
> While I'm trying to figure out the point of PQsetnonblocking() call,
> confused so much on blocking/nonblocking mechanism.
>
> Sync. Connect =BB Async. Query
> Async. Connect =BB Sync. Query
>
> Both of above flows work without any PQsetnonblocking() call.
> Therefore sync/async connection and sync/async query execution are not
> dependent to each other. (Right?) If so, what's the point of
> PQsetnonblocking() function? When do we require it and when should we
> use it?
>
> As I saw from src/interfaces/libpq/fe-exec.c, PQsetnonblocking() only
> assigns True or False to conn->nonblocking variable. When I searched
> for "->nonblocking" under libpq directory, I found that it's used
> while creating an empty PGconn and while closing PGconn. This didn't
> help me too.
>
> I'd be so appreciated for a comprehensive "specialized for dummies" answe=
r.
> Regards.
>
> P.S. Documentation pointers will be accepted with pleasure too.
>
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