Im writing a scheduler/calendar type application. The user enters some information and that gets stored in a database, then I have a service which polls the database every sixty seconds looking for events and spits them out via a notification.
It used to be working pretty well until I started trying to put progress spinners in which needed to go in a thread to display. (I still can't get them to spin). At this point I started to get loads of errors with database locks. I've done a lot of tidying up, now Im finding a problem between the service and the insert commands. The service utilises "getReadableDatabase" and "rawQuery", while the separate updater function (user controlled) utilises "getWritableDatabase" and "execSQL" to perform inserts. I get errors in the log such as: I/CMT ( 405): Running Scheduler... D/AndroidRuntime( 405): Shutting down VM W/dalvikvm( 405): threadid=1: thread exiting with uncaught exception (group=0x4001d800) E/AndroidRuntime( 405): FATAL EXCEPTION: main E/AndroidRuntime( 405): android.database.sqlite.SQLiteException: error code 5: database is locked E/AndroidRuntime( 405): at android.database.sqlite.SQLiteStatement.native_execute(Native Method) E/AndroidRuntime( 405): at android.database.sqlite.SQLiteStatement.execute(SQLiteStatement.java: 55) E/AndroidRuntime( 405): at android.database.sqlite.SQLiteDatabase.delete(SQLiteDatabase.java: 1598) E/AndroidRuntime( 405): at xxx.xxx.xxx.ProgramLocation:999) I've asked elsewhere and I've looked for solutions such as using synchronized (Im still trying to wrap my head around that at the moment), but ideally what I want to know is why is this error being generated. If I can find why things work instead of what the solutions are, I'll be a better Android programmer. Immediately before the insert, I check to see if the database isLockedByOtherthreads(), but the answer is false. However it seems when I open/read the database in the Service, Android then fails to be able to do the Insert in the Activity and errors that the database is locked. Why does a read lock the database? What is generating the lock? Why does isLockedByOtherThreads() return false and then the Insert fail? Perhaps "database is locked" is an erroneous error and refers to it not being able to generate an exclusive lock for the insert? Is there a way to find out programmatically what locks there are on a database? And finally what are some solutions for this? I presume I can do reads all over the app as I wish, but the problem comes when I try to do a write at the same time a read is being performed. Perhaps I should disable the service while the update is in progress. Or I've heard about synchronized but I really don't have any experience with this and Im looking for some good (android related) theory about what it is, how it works, why you do it, and how you do it? Thanks Simon -- You received this message because you are subscribed to the Google Groups "Android Developers" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/android-developers?hl=en
