Closing the database in a ContentProvider

Question

This week I've been learning all about ContentProvider and using the SQLiteOpenHelper class to manage the creation and upgrading of the database inside of a provider. Specifically, I've been reading through the NotePad example from the sdk's samples directory.

Now, I can see that SQLiteOpenHelper has a close() method. I'm aware that leaving idle databases open is bad practice and can cause memory leaks and whatnot (unless this discussion is headed in the right direction). If I were using the class in an Activity, then I would simply call close() in the onDestroy() method, but as far as I know, ContentProvider does not have the same life cycle that activities do. The code for NotePad never seems to call close(), so I would like to assume that it is handled by SQLiteOpenHelper or some other piece of the puzzle, but I'd really like to know for sure. I don't really trust the sample code that much, either...

Question summary: When should we close the database in a provider, if at all?

Answer 1

According to Dianne Hackborn (Android framework engineer) there is no need to close the database in a content provider.

A content provider is created when its hosting process is created, and remains around for as long as the process does, so there is no need to close the database -- it will get closed as part of the kernel cleaning up the process's resources when the process is killed.

Thanks @bigstones for pointing this out.

Answer 2

This question is a bit old but is still quite relevant. Note that if you're doing things the 'modern' way (e.g. using LoaderManager and creating CursorLoaders to query a ContentProvider in a background thread), make sure that you do NOT call db.close() in your ContentProvider implementation. I was getting all sorts of crashes relating to CursorLoader/AsyncTaskLoader when it tried to access the ContentProvider in a background thread, which were resolved by removing the db.close() calls.

So if you're running into crashes that look like this (Jelly Bean 4.1.1):

Caused by: java.lang.IllegalStateException: Cannot perform this operation because the connection pool has been closed.     at android.database.sqlite.SQLiteConnectionPool.throwIfClosedLocked(SQLiteConnectionPool.java:962)     at android.database.sqlite.SQLiteConnectionPool.waitForConnection(SQLiteConnectionPool.java:677)     at android.database.sqlite.SQLiteConnectionPool.acquireConnection(SQLiteConnectionPool.java:348)     at android.database.sqlite.SQLiteSession.acquireConnection(SQLiteSession.java:894)     at android.database.sqlite.SQLiteSession.executeForCursorWindow(SQLiteSession.java:834)     at android.database.sqlite.SQLiteQuery.fillWindow(SQLiteQuery.java:62)     at android.database.sqlite.SQLiteCursor.fillWindow(SQLiteCursor.java:143)     at android.database.sqlite.SQLiteCursor.getCount(SQLiteCursor.java:133)     at android.content.ContentResolver.query(ContentResolver.java:388)     at android.content.ContentResolver.query(ContentResolver.java:313)     at com.hindsightlabs.paprika.loaders.GroceryListLoader.loadInBackground(GroceryListLoader.java:147)     at com.hindsightlabs.paprika.loaders.GroceryListLoader.loadInBackground(GroceryListLoader.java:1)     at android.support.v4.content.AsyncTaskLoader.onLoadInBackground(AsyncTaskLoader.java:240)     at android.support.v4.content.AsyncTaskLoader$LoadTask.doInBackground(AsyncTaskLoader.java:51)     at android.support.v4.content.AsyncTaskLoader$LoadTask.doInBackground(AsyncTaskLoader.java:40)     at android.support.v4.content.ModernAsyncTask$2.call(ModernAsyncTask.java:123)     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)     ... 4 more 

Or this (ICS 4.0.4):

Caused by: java.lang.IllegalStateException: database /data/data/com.hindsightlabs.paprika/databases/Paprika.db (conn# 0) already closed     at android.database.sqlite.SQLiteDatabase.verifyDbIsOpen(SQLiteDatabase.java:2215)     at android.database.sqlite.SQLiteDatabase.lock(SQLiteDatabase.java:436)     at android.database.sqlite.SQLiteDatabase.lock(SQLiteDatabase.java:422)     at android.database.sqlite.SQLiteQuery.fillWindow(SQLiteQuery.java:79)     at android.database.sqlite.SQLiteCursor.fillWindow(SQLiteCursor.java:164)     at android.database.sqlite.SQLiteCursor.getCount(SQLiteCursor.java:156)     at android.content.ContentResolver.query(ContentResolver.java:318)     at android.support.v4.content.CursorLoader.loadInBackground(CursorLoader.java:49)     at android.support.v4.content.CursorLoader.loadInBackground(CursorLoader.java:35)     at android.support.v4.content.AsyncTaskLoader.onLoadInBackground(AsyncTaskLoader.java:240)     at android.support.v4.content.AsyncTaskLoader$LoadTask.doInBackground(AsyncTaskLoader.java:51)     at android.support.v4.content.AsyncTaskLoader$LoadTask.doInBackground(AsyncTaskLoader.java:40)     at android.support.v4.content.ModernAsyncTask$2.call(ModernAsyncTask.java:123)     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)     ... 4 more 

Or if you're seeing error messages in LogCat that look like this:

Cursor: invalid statement in fillWindow() 

Then check your ContentProvider implementation and make sure you're not closing the database prematurely. According to this, the ContentProvider will get cleaned up automatically when the process is killed anyway, so you don't need to close its database ahead of time.

That said, make sure you are still correctly:

1. Closing your Cursors that are returned from ContentProvider.query(). (CursorLoader/LoaderManager does this automatically for you, but if you're doing direct queries outside of the LoaderManager framework, or you've implemented a custom CursorLoader/AsyncTaskLoader subclass, you'll have to make sure you're cleaning up your cursors properly.)
2. Implementing your ContentProvider in a thread-safe way. (The easiest way to do this is to make sure your database access methods are wrapped in a synchronized block.)