Re: [Vala] shared access to sqlite database

[Jim Nelson <jim yorba org>]

To chime in some agreement, we attempted many strategies to parallelize 
transactions and work around SQLite's locking issues in Geary before 
finally waving the white flag.  Evan's correct, SQLite's built-in busy 
handler is what you want to use.  In fact, we use a single background 
thread to service all calls, as the busy handler isn't entirely fair 
when multiple threads contend for the lock.

-- Jim

On Wed, Aug 7, 2013 at 12:33 AM, Evan Nemerson <evan coeus-group com> 
wrote:
> On Wed, 2013-08-07 at 08:16 +0200, David López González wrote:
> >  Hi everyone,
> >  
> >  I need to access to a single data base with diferent processes, and 
> >  eventually, I  always get an access error "Error: 5, database is 
> > locked".
> >  A simplified code which reproduce the problem it's presented below.
> Take a look at [1].  I know unlock notify isn't what you're after 
> (since
> you have multiple processes, not multiple threads), but IIRC it should
> give you a pretty good feel for sqlite does.
>
> Really, the only option is to just retry the operation.  You can do 
> this
> automatically using sqlite3_busy_timeout ([2]).  It is bound as
> Sqlite.Database.busy_timeout.
>
> There is also sqlite3_busy_handler ([3])...  I don't think it's bound 
> in
> Vala at the moment, but it would be trivial to add it to the bindings
> (or just use the extern keyword).  Theoretically you could use it to
> iterate through the main loop or something while you wait, but it's a
> lot simpler to just use busy_timeout and interact with sqlite in a
> thread if you really need to.
>
>
> -E
>
> [1] https://sqlite.org/unlock_notify.html
> [2] https://sqlite.org/c3ref/busy_timeout.html
> [3] https://sqlite.org/c3ref/busy_handler.html
>
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