Re: [Ruby-DBI-devel] Locking problem

[Michael N. <uu...@rz...>]

Matthew Bloch wrote:
> Hello;
> 
> I've just noticed an undesirable interaction between multithreaded Ruby 
> applications and the MySQL C API (if not other DB APIs); my web spider 
> application was running along fine but suddenly after an unpredictable number 
> of minutes, hours etc. it would stop dead.  I think the problem is that I use 
> a "lock tables" statement which, if used with Ruby threads, blocks the whole 
> Ruby process until the table is unlocked.  Trouble is if the 'thread' holding 
> the lock is an internal Ruby thread in the same process it'll never get run 
> to unlock it :-/
> 
> Is there a general way around this problem with the mysql_ API?  My 
> impression is no, since I can't find any way of telling mysql to use 
> non-blocking semantics through its C API.  Anyhow even if we leave it like 
> this it's probably worth adding a note about this pitfall to the docs.

If only your Ruby application accesses the Mysql database and you want
to lock a table only for one thread, use a Mutex instead of locking the
whole table. But if you lock a table because other processes (outside the Ruby world) 
should not modify the table while one Ruby thread modifies it, I see no other
chance than using processes (start new Ruby interpreter) instead of threads. 

Or have you tried to use an own connection (DBI.connect) for each thread?

Regards,

  Michael