In my applications, I run multiple queries using libdbi/mysql with each query
on it's own thread. Here is what I had to do to make it work:
1. Use a mutex lock around ALL libdbi connect and disconnect calls - you can
see why if you look at the libdbi driver code.
2. Modify the dbd_mysql.c source file, changing dbd_disconnect as follows:
int dbd_disconnect(dbi_conn_t *conn) {
if (conn->connection) mysql_close((MYSQL *)conn->connection);
// added the next three lines to resolve memory leak in threadsafe
mysqlclient library: assumes each thread has it's own connection
if(mysql_thread_safe())
mysql_thread_end();
return 0;
}
3. build and link the dbd_mysql driver. It MUST be linked agains the _r
version of the mysqlclientlib. This was really tricky on OS X.
Now I can have any number of queries running, each in it's own thread. Of
course you only initialize libdbi once in the main thread.
Prior to these steps, I would get crashes from failing to do #1, and "MySQL
server has gone away" errors from not doing #3. Step #2 is a mysql client
library memory leak bug work-around.
Ethan...
On Aug 19, 2010, at 3:28 AM, Kjell Irgens wrote:
> On 08/19/2010 10:24 AM, Markus Hoenicka wrote:
>
>> I'm not familiar with thread-safe programming, so I have no idea if
>> libdbi is currently thread-safe. Someone more familiar with this issue
>> should speak up.
>
> I don't know if it is thread safe, I haven't really looked into that
> really. I just assumed that it was not, and lock a mutex around all
> dbi_conn_query() and dbi_comm_ping() calls.
>
> This has worked perfectly in operational systems for years, with
> extensive use of threads (postgresql only).
>
> --
> --Kjell
>
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