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List:       sqlite-users
Subject:    Re: [sqlite] vfs implementation question
From:       Richard Klein <Richard.Klein () schange ! com>
Date:       2008-08-19 21:45:19
Message-ID: 48AB3EEF.80600 () schange ! com
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D. Richard Hipp wrote:
> On Aug 19, 2008, at 9:02 AM, Jeffrey Becker wrote:
>
>   
>> Should the xLock member of sqlite3_io_methods object block until the
>> lock can be acquired?
>
> xLock does not block on any of the built-in VFSes.  But if you want to  
> make your own custom VFS that blocks on locks, I don't  know of any  
> reason why that wouldn't work.
I wrote a custom VFS that blocks on locks, and it works just fine.

I also implemented a subset of the five locking levels of SQLite:
just UNLOCKED and EXCLUSIVE.  This means that as soon as a transaction
asks for a SHARED lock, it actually gets an EXCLUSIVE lock, which
locks out all other transactions until the first one commits.

This works fine in an embedded application where there are only a
few threads, whose transactions execute quickly.

- Richard Klein

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