畢業(yè)設(shè)計(jì)外文文獻(xiàn)翻譯---java垃圾收集器的工作方式-展示頁(yè)
2025-05-26 23:22本頁(yè)面
【正文】 it’s the way some JVMs work, and it means that allocating storage for heap objects in Java can be nearly as fast as creating storage on the stack in other languages. For example, you can think of the C++ heap as a yard where each stakes out its own piece of turf object. This real estate can bee abandoned sometime later and must be reused. In some JVMs, the Java heap is quite different。 it’s more like a conveyor belt that moves forward every time you allocate a new object. This means that object storage allocation is remarkably rapid. The “heap pointer” is simply moved forward into virgin territory, so it’s effectively the same as C++’s stack allocation. (Of course, there’s a little extra overhead for bookkeeping, but it’s nothing like searching for storage.) You might observe that the heap isn’t in fact a conveyor belt, and if you treat it that way, you’ll start paging memory—moving it on and off disk, so that you can appear to have more memory than you actually do. Paging significantly impacts performance. Eventually, after you create enough objects, you’ll run out of memory. The trick is that the garbage collector steps in, and while it collects the garbage it pacts all the objects in the heap so that you’ve effectively moved the “heap pointer” closer to the beginning of the conveyor belt and farther away from a page fault. The garbage collector rearranges things and makes it possible for the highspeed, infinitefreeheap model to be used while allocating storage. To understand garbage collection in Java, it’s helpful learn how garbagecollection schemes work in other systems. A simple but slow garbagecollection technique is 2 called reference counting. This means that each object contains a reference counter, and every time a reference is attached to that object, the reference count is increased. Every time a reference goes out of scope or is set to null, the reference count is decreased. Thus, managing reference counts is a small but constant overhead that happens throughout the lifetime of your program. The garbage collector moves through the entire list of objects, and when it finds one with a reference count of zero it releases that storage (however, reference counting schemes often release an object as soon as the count goes to zero). The one drawback is that if objects circularly refer to each other they can have nonzero reference counts while still being garbage. Locating such selfreferential groups requires significant extra work for the garbage collector. Reference counting is monly used to explain one kind of garbage collection, but it doesn’t seem to be used in any JVM implementations. In faster schemes, garbage collection is not based on reference counting. Instead, it is based on the idea that any n
畢業(yè)設(shè)計(jì)相關(guān)推薦
鄂ICP備17016276號(hào)-1