Joe Wilson <[EMAIL PROTECTED]> wrote: > --- John Stanton <[EMAIL PROTECTED]> wrote: > > Using a single Sqlite connection for each database and holding the > > connection open means that maximum effect is obtained from Sqlite's > > cache. As far as we can ascertain avoiding fcntl removes any issues > > regarding multiple threads accessing a single connection. > > I did not know that a single sqlite3 connection could be used > concurrently by readers from multiple threads. > > Previous postings on this list suggested that although an sqlite3 > connection could be passed from thread to thread (as is common in > a connection pool scenario), only one thread may use that connection > at a given time. > > Can the SQLite authors confirm that simultaneous use of a single > connection by multiple reader threads is supported without external > mutexes? >
A single connection can only be used by a single thread at a time. If you have multiple threads running at the same time, they each need to have their own connection. If you are not running on a Linux 2.4 kernel, then you can pass connections from one thread to another. So thread A can do a little work, then hand the connection of to thread B to continue. But thread A and thread B should not try to use the same connection at the same time. The reason for this should be obvious. A "connection" is a structure, with various fields holding state information. Each SQLite API call expects the connection to be in a consistent state when it is first invoked and each API call leaves the connection in a consistent state when it returns. But while the API is running, the structure can be in various transient states that are not strictly "consistent". We cannot, after all, make multiple changes to a structure atomically on real hardware. If two threads try to modify the same structure at the same time, they will be seeing each others inconsistent transient state and chaos will ensue. -- D. Richard Hipp <[EMAIL PROTECTED]> ----------------------------------------------------------------------------- To unsubscribe, send email to [EMAIL PROTECTED] -----------------------------------------------------------------------------
