Asynchronous garbage collection

Details Asynchronous garbage collection Asynchronous garbage collection

1991-07-18

1994-10-11

MacDonald, Allen R.

Boots, shoes, and leggings

395425, 364DIG1, 3642811, 3642813, 3642814, 364282, G06F 1200

Patent

active

053554833

ABSTRACT:
The present invention consists of a new type of garbage collector, one that runs in a different process being scanned. With this method, the process being collected communicates its memory state ("a memory snapshot") to a garbage collecting process (GC), and the GC process scans the memory and sends back the information about garbage. As a result, the present invention permits garbage collection to be performed asynchronously. The process being scanned for garbage is interrupted only briefly, to obtain the memory snapshot. The process then runs without interruption while the garbage collection is being performed. The present invention makes the assumption that if an object is garbage at the time of the memory snapshot it remains garbage any time later, since new pointers to that object cannot be created during asynchronous collection. The method further considers the case where the results of a cache computation is a collectable object itself. The method includes keeping a list while a collection is in progress of all the objects being given away from the cache. When an object is received as garbage from the GC, it is only freed if it is not on the list. The garbage collecting process is performed using a conservative scan. The garbage collector finds out if an object is garbage by scanning the memory address space and comparing the value found in each scanned memory address to see if the value matches the candidate for garbage. If no match is found, this means that the candidate for garbage is not referenced and therefore, is garbage.

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