threadsafety in value objects

Question

I am a bit confused with the requirements to synchronize the access the private instance variables in java. I have an applicaion which executes scheduled tasks multithreaded. These tasks (instances of a class) have an instance variable that holds a value object. Further, these tasks have the run methods that execute the task by calling someother classes that hold the execution logic (they in turn use more value objects as part of the processing.)

Now at a high level it looks like all the parallel threads will spawn a chain of these tasks,instance variables , implementation classes and value objects. Do all these need to be made thread safe? all instance variables in all the possible classes and value objects that can be potentially invoked in parallel?

Answer 1

You need to make objects thread safe if multiple threads are going to access them at the same time and if their state is going to change.

It sounds like your task objects are not multi-threaded in that different threads won't access the same task. If that is true you wouldn't need to make your task objects thread safe.

Are the value objects mutable and are they shared in such a way that the same value object instance could be accessed by multiple threads at the same time? If either is yes then you need to make them thread safe.

The easiest way to make an object thread safe is to make it immutable. If its internal state can't change after the object is constructed then it is inherently thread safe. If you can't make your objects immutable then you need to synchronize access to any instance variables whose state could be changed.