2.4 Incremental Collection

Incremental GC   

Another way to avoid the appearance that garbage collection is locking up the system is to modify the algorithm so that it can be run one small piece at a time.

• Conceptually, every time a program tries to allocate a new object, we run just a few mark steps or a few sweep steps,
• By dividing the effort into small pieces, we give the illusion that garbage collection is without a major cost.

  There is a difficuty here, though. Because the program might be modifying the heap while we are marking objects, we have to take extra care to be sure that we don’t improperly flag something as garbage just because all the pointers to it have suddenly been moved into some other data structure that we had already swept.

• In languages like Java where parallel processes/threads are built in to the language capabilities, systems can take the incremental approach event further by running the garbage collector in parallel with the main calculation.

  Again, special care has to be taken so that the continuously running garbage collector and the main calculation don’t interfere with one another.