Here's a bit more locking info that I found useful to help understand it
all out of the archives:
http://www.mail-archive.com/sqlite-users@sqlite.org/msg02845.html
If you are writing a Windows app, you can use a named mutex which can be
shared across processes.
I have need for a blocking (as opposed to SQLITE_BUSY) mechanism as
well. As the referenced thread points out, it is not straightforward.
Still working something out...
Lee Crain wrote:
Ken, Igor,
I read the article you referenced. Much appreciated.
http://sqlite.org/lockingv3.html
I didn't want to complicate my original questions with the intricate
details of the application requirements which involve not allowing any
database access while certain other operations are executing. I think a
MUTEX, even with its inherent performance limitations, is the best
solution.
Thanks for your replies,
Lee Crain
P.S. Ken, I'm pretty certain that a MUTEX is both an intra- and
inter-process mutual exclusion object.
________________________
-----Original Message-----
From: Ken [mailto:[EMAIL PROTECTED]
Sent: Wednesday, October 24, 2007 2:22 PM
To: sqlite-users@sqlite.org
Subject: RE: [sqlite] Re: Some Questions Regarding Access To a SQLite
Database By More Than One Process
If you are using seperate processes then a mutex will not help since it is
local to a process. A semaphore could be used however.
You can use a begin immediate around all statements that perform DML
(ins/upd/sel)
Then loop on the busy at the begin immediate command. This is a fairly
simple thing to do.
Then for selects you'll need only test the prepare/ and first step After
the first step you should not get a sqlite busy.
Lee Crain <[EMAIL PROTECTED]> wrote: Igor,
I did say "controlled" concurrency.
I'll rephrase question 3.
3) Would use of a MUTEX to avoid the dreaded "SQLite busy" condition be a
good solution? Or is some other method of avoiding a busy condition
recommended?
Lee Crain
__________________
-----Original Message-----
From: Igor Tandetnik [mailto:[EMAIL PROTECTED]
Sent: Wednesday, October 24, 2007 1:36 PM
To: SQLite
Subject: [sqlite] Re: Some Questions Regarding Access To a SQLite Database
By More Than One Process
Lee Crain wrote:
1. Can multiple processes "concurrently" access the same SQLite
database?
Yes.
2. If so, can multiple processes maintain an open connection to the
database? Or must the connection be opened and closed, before and
after,
respectively, each database access?
You can have multiple open connections, from the same or different
processes, at any given time. You can keep a connection open as long as
necessary.
3. Would the use of a MUTEX as access protection be adequate to
successfully implement controlled "concurrency"?
I'm not sure I understand this question. Mutexes are all about _not_
allowing concurrency.
Igor Tandetnik
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