Preserve Invariant
We may be tempted to start threads from constructors to get background tasks running as soon as an object is instantiated. That’s a good intention with undesirable side effects. The call to start forces a memory barrier, exposing the partially created object to other threads. Also, the thread we started may invoke methods on the instance before its construction is complete.
An object should preserve its invariant, and therefore starting threads from within constructors is forbidden.
EnergySource is clearly in violation on this count. We could move the thread-starting code from the constructor to a separate instance method. However, that creates a new set of problems. We have to deal with method calls that may arrive before ...
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