Attempt to invoke virtual method '....RetrievalAdapter.getModelClass()' on a null object reference

[jchristof]

DBFlow Version: 4.2.4

Bug or Feature Request: Attempt to invoke virtual method '....RetrievalAdapter.getModelClass()' on a null object reference

Description:
I'm getting the exception occasionally in production. Not sure why this fails only occasionally. Anyone have an idea?

Fatal Exception: java.lang.NullPointerException
Attempt to invoke virtual method 'java.lang.Class com.raizlabs.android.dbflow.structure.RetrievalAdapter.getModelClass()' on a null object reference

com.raizlabs.android.dbflow.sql.saveable.ModelSaver.getWritableDatabase (ModelSaver.java:169)
com.raizlabs.android.dbflow.sql.saveable.ModelSaver.save (ModelSaver.java:29)
com.raizlabs.android.dbflow.structure.ModelAdapter.save (ModelAdapter.java:186)
com.raizlabs.android.dbflow.structure.BaseModel.save (BaseModel.java:62)

[jschools]

I am also getting this error occasionally. I think it is a race condition in ModelAdapter.getModelSaver(). The ModelAdapter lazily initializes an instance of ModelSaver without synchronization here:

DBFlow/dbflow/src/main/java/com/raizlabs/android/dbflow/structure/ModelAdapter.java

Line 429 in 0e06ea8

public ModelSaver<TModel> getModelSaver() {

If multiple threads call getModelSaver() concurrently, it is possible for one thread to get (and attempt to use) the modelSaver instance before setModelAdapter(this) has been called on it, leading to the NPE.

This seems to have been (kind of) fixed in 5.0.0-alpha2. It could result in multiple instances of ModelSaver being used, which would solve this crash but introduce the possibility of synchronization errors, since ModelSaver has several @Synchronized functions:

DBFlow/lib/src/main/kotlin/com/dbflow5/adapter/ModelAdapter.kt

Line 178 in 8c86eaa

var modelSaver: ModelSaver<T>

It is not trivial to upgrade to the new library, and it is also risky to upgrade to a new major "dot zero alpha" version.

As a workaround, you could call .getModelSaver() on each ModelAdapter immediately after initializing DbFlow, as long as you can ensure no other threads are calling save() while this is happening.

[loquitowen]

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