Question

I have an AsyncTask that queries a content provider and does some additional processing in the onPostExecute() of that task. I have a stack trace for an exception that is very hard to reproduce, but I would like to guard against the condition or fix the code. The code is below:

int i = 0;
mIds = new long[cursor.getCount()];
while (cursor.moveToNext()) {
    mIds[i++] = cursor.getLong(COLUMN_ID);
}

The crash is happening on the line in the loop. The way I see it, the only way this could happen
is if:

1. cursor.getCount() is returning an incorrect count.
2. cursor is changed while this loop is executing, but I don’t think that’s possible
   because cursor is a local variable. Perhaps something underlying the cursor has changed that I’m not aware of.
3. mIds has changed. This shouldn’t be possible because we are running
   on the UI thread and this is the only place in which that variable is assigned
   a new value. By the nature of onPostExecute running on the UI thread, it shouldn’t be possible for this code to be running somewhere else at the same time, right?

Am I missing something?

Answer 1

It’s difficult to see what is wrong with that loop without seeing the full code but I note from the docs:

Cursor implementations are not required to be synchronized so code using a Cursor from multiple threads should perform its own synchronization when using the Cursor.