maria-developers team mailing list archive

[Kristian Nielsen <knielsen@xxxxxxxxxxxxxxx>]

Gonzalo Diethelm <gonzalo.diethelm@xxxxxxxxx> writes:

> $ brew info mariadb-connector-c
> mariadb-connector-c: stable 2.2.2 (bottled)
> MariaDB database connector for C applications
> https://downloads.mariadb.org/connector-c/

Ok, so this is the separate client library, not the one in the server.

> Notice that in the code snippet you sent, the comparison is greater than
> *or equal to* zero; this could in fact add a zero timeout, right?
>
>     if (vio_timeout >= 0)
>     {
>       b->timeout_value= vio_timeout;
>       b->events_to_wait_for|= MYSQL_WAIT_TIMEOUT;
>     }

Yes, you are right of course. But now I see it: For the application, zero
means no timeout. Internally in the code, this is converted to -1 meaning no
timeout.

And while this looks correct in the server library, the connector-c
standalone library seems to do this incorrectly:

  void vio_read_timeout(Vio *vio, uint timeout)
  {
    vio->read_timeout= (timeout >= 0) ? timeout * 1000 : -1;
  }


  int vio_timeout= (mysql->options.connect_timeout >= 0) ? 
                   mysql->options.connect_timeout * 1000 : -1;

This code is comparing an unsigned value >= 0; the comparison should be >0
(an unsigned value is always >= 0, so this is obviously wrong).

So I was able to reproduce your problem with version 2.2.2 of the standalone
library. However, recent changes seem to have fixed it, I could no longer
reproduce. In particular it seems fixed after these three commits which seem
to rewrite the I/O part of the library:

-----------------------------------------------------------------------
commit a349bee53d38ee133b949b20f84ccc29d3aa4465 (refs/bisect/bad)
Author: Georg Richter <georg@xxxxxxxxxxx>
Date:   Thu Aug 6 15:10:34 2015 +0200

    Added more files

commit cc85e256666a826d3247e72ea39c5332bff721bf (refs/bisect/skip-cc85e256666a826d3247e72ea39c5332bff721bf)
Author: Georg Richter <georg@xxxxxxxxxxx>
Date:   Thu Aug 6 15:08:25 2015 +0200

    Added missing cio components

commit f886562fb2c411bc7ff870d75a872d906674015b (refs/bisect/skip-f886562fb2c411bc7ff870d75a872d906674015b)
Author: Georg Richter <georg@xxxxxxxxxxx>
Date:   Thu Aug 6 13:06:54 2015 +0200

    Initial cio implementation
-----------------------------------------------------------------------

Wlad, Georg, what are the plans for Connector-C? Will the current master
branch be released as an update for the stand-alone client library? Or only
as part of 10.2?

In the latter case, do you agree that a bugfix like the below patch is
needed for existing stable releases of Connector-C? Since it seems that
without it, timeout for non-blocking connects (and read/writes?) is
completely broken?

Gonzola, thanks for bringing this to attention! If possible, you could try
checking the latest git source code if your problem is indeed solved.

Otherwise, one workaround until a fix is released is to use the
libmysqlclient supplied as part of the MariaDB server release.

Alternatively, change your code to interpret MYSQL_WAIT_TIMEOUT with a zero
value from mysql_get_timeout_value() the same as no MYSQL_WAIT_TIMEOUT. This
change will still be correct (though redundant) after the library is fixed,
as MYSQL_WAIT_TIMEOUT can never legally have a zero timeout.

Thanks,

 - Kristian.

diff --git a/libmariadb/libmariadb.c b/libmariadb/libmariadb.c
index 8fd87ba..23aa407 100644
--- a/libmariadb/libmariadb.c
+++ b/libmariadb/libmariadb.c
@@ -254,7 +254,7 @@ static int
 connect_sync_or_async(MYSQL *mysql, NET *net, my_socket fd,
                       const struct sockaddr *name, uint namelen)
 {
-  int vio_timeout= (mysql->options.connect_timeout >= 0) ? 
+  int vio_timeout= (mysql->options.connect_timeout > 0) ? 
                    mysql->options.connect_timeout * 1000 : -1;
 
   if (mysql->options.extension && mysql->options.extension->async_context &&
@@ -1767,7 +1767,7 @@ MYSQL *mthd_my_real_connect(MYSQL *mysql, const char *host, const char *user,
     vio_write_timeout(net->vio, mysql->options.read_timeout);
   /* Get version info */
   mysql->protocol_version= PROTOCOL_VERSION;	/* Assume this */
-  if (mysql->options.connect_timeout >= 0 &&
+  if (mysql->options.connect_timeout > 0 &&
       vio_wait_or_timeout(net->vio, FALSE, mysql->options.connect_timeout * 1000) < 1)
   {
     my_set_error(mysql, CR_SERVER_LOST, SQLSTATE_UNKNOWN,
diff --git a/libmariadb/violite.c b/libmariadb/violite.c
index 1fbdcc3..722724f 100644
--- a/libmariadb/violite.c
+++ b/libmariadb/violite.c
@@ -127,13 +127,13 @@ void vio_timeout(Vio *vio, int type, uint timeval)
 
 void vio_read_timeout(Vio *vio, uint timeout)
 {
-  vio->read_timeout= (timeout >= 0) ? timeout * 1000 : -1;
+  vio->read_timeout= (timeout > 0) ? timeout * 1000 : -1;
   vio_timeout(vio, SO_RCVTIMEO, vio->read_timeout);
 }
 
 void vio_write_timeout(Vio *vio, uint timeout)
 {
-  vio->write_timeout= (timeout >= 0) ? timeout * 1000 : -1;
+  vio->write_timeout= (timeout > 0) ? timeout * 1000 : -1;
   vio_timeout(vio, SO_SNDTIMEO, vio->write_timeout);
 }