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Message:
synchronization in ctrs
Posted by Julia Renouard on 23 Jul 1998, 2:34 PM
> Synchronization works the same in a constructor as it does > in a method, so it would certainly be possible to write > RGBColor's constructor as you suggest. > The one thing to note is that you don't need the synchronization > in the constructor, because only one thread can ever be > executing the code of the constructor at any one time. No > other thread can get a reference to the object until after > the construction of the object completes. Hence, you don't > need to synchronize anything in the constructor. This means > that any synchronization you add to the code executed by > the constructor unecessarily gives you a performance hit. My > philosophy is to avoid unecessary locking of objects, so > I didn't call setColor() from the constructor. > Note that you can write a constructor such that synchronization > becomes important, though this way of writing a constructor > goes against my "Constructors and initializers should just > be about initialization, the whole initialization, and nothing > but initialization" guideline. For example, from a constructor > you could call a method in some other class or object and pass > a reference to this (the object being constructed). That other > method could give the reference to another thread which could > try to invoke a method on the object. I can't imagine any good > reason why someone would want to do this, but I'll bet it has > probably happened somewhere. > bv I've recently been working with an example that has synchronization the constructor - and for good reason. The class has a static thread object that it only wants instantiated once. So the code looks like this
public MyClass { static Thread myThread; public MyClass { synchronized (getClass()) { if (myThread == null) { myThread = new Thread(...); } } }
: } The ctr actually puts a lock on the class so that we won't try and create more than one thread if multiple instances of the object are instantiated at once (i.e. from separate threads).
I hadn't seen any references to the use of getClass() this way, but it will server me well in my static class methods that need protection as well.
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