java.lang.ref.SoftReference: Add a timeout attribute

Name: bk70084 Date: 07/13/98

Let say one have a very big array which can be computed in about 10 seconds
(for example the result of some kind of spectral analysis). Let say one need
this array often (for example each time a component is draw). In my
understanding of the java.lang.ref package, the SoftReference class is perfect
for that, since it is always possible to recompute this array if it as been
garbage collected for memory reasons.

Now there is my problem: Let say the user is working on an other component
which hide the first one. The big array may not be need for one hour. It make
sense to me to keep this array if it is often used. But does it make sense to
keep for many hours an unused array which can be recomputed in 10 seconds? I
know almost nothing about operating system, but it seem to me that some
operation systems may begin to swap memory on the hard drive before the
SoftReference class get a MemoryAdvice. YELLOW advice. In this case, the
unused big array will be really slowing down the system instead of making it
faster.

My suggestion would be to add one method to the SoftReference class:

    setTimeout(int nmillis)

If nmillis seconds are elapsed since the last call to the get method, then
SoftReference may clear this reference. Each time the get method is called, the
count of elapsed time is reset to zero. So if a big object is not use for, say,
one hour, it may be cleared and his memory used for other task.

I see an other advantage: when SoftReference get a MemoryAdvice.YELLOW advice,
it may use this information to choose which references to clear first. For
example if the reference A has a timeout of 3 minutes and the reference B has a
timeout of 1 minute, and if 2 minutes 45 seconds have been elapsed since the
last A.get() call and only 25 seconds since the last B.get() call, then the
SoftReference class will try to clear A before B (because A would timeout in 15
seconds and B in 35 seconds).

Anyway, I don't know if it is reasonable to implement. Thank for listening.


(Review ID: 34962)
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