Taking Out the Garbage
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Collecting the Garbage
One of the huge problems with languages like JavaScript is garbage
collection. Garbage collection just refers to the problem of using memory and
being done with the memory but the computer not being able to reuse the memory
because it doesn't know if you still need it. Got that?
If not, here's how it works: Suppose I create a Rectangle object. I use that
in a calculation. Then I'm done with the object. In a language like C++, you
write a line of code that tells the run-time library that you're done with the
object. The run-time library will then delete the object and allow the part of
memory where the object was stored to be used again for other objects.
But in languages like JavaScript, you don't explicitly tell the run-time
you're done with the object. The run-time does, however, have ways of figuring
out that you're done with the object. Typically, if a function creates an object,
when the function is finished the object can be cleaned up too. But not always:
The function might pass the object on to three more functions to use, for
example, and only after the run-time system figures out that all four
functions-the original and the three others-are finished can it figure out that
the object isn't needed anymore and free the memory.
But the problem is the
object might get saved away as a member within yet another object. Then the run-time
can't delete the first object until this other object is no longer needed! Can
you say, big mess? Yes, there is more than one reason it's called
"garbage collection," and I'm sure some people would like to include
other choice words instead of garbage, as well as directives about other people
cleaning up their own, uh, messes.
Garbage collection is always a problem with languages, because often the
actual garbage collector (the code that does the cleaning) only runs
occasionally, and when it does, the program slows waaaaaaay down.
Google describes in its developer documentation a sophisticated garbage
collector that Chrome uses. This collector stops everything and does its job
very quickly while only collecting what's necessary, and then allowing everything
else to resume. Personally, that sounds suspicious to me; however, I can
understand how that could be better than having the garbage collector slowly
churn away for minutes on end while you're continuing to do your work, albeit
slowly, due to the garbage collector slowing everything down-and, with the work
you're doing slowing the garbage collector down, causing it to run even longer.
So perhaps this new method is better.
