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explained in some detail during our discussion of object serialization (Chapter 21). For now, just

understand that object graphs are used to document all reachable objects. As well, be aware that

the garbage collector will never graph the same object twice, thus avoiding the nasty circular refer-

ence count found in COM programming.

Assume the managed heap contains a set of objects named A, B, C, D, E, F, and G. During a

garbage collection, these objects (as well as any internal object references they may contain) are

examined for active roots. Once the graph has been constructed, unreachable objects (which we

will assume are objects C and F) are marked as garbage. Figure 8-3 diagrams a possible object graph

for the scenario just described (you can read the directional arrows using the phrase 

depends on or

requires, for example, “E depends on G and indirectly B,” “A depends on nothing,” and so on).

Figure 8-3.

Object graphs are constructed to determine which objects are reachable by application

roots.

Once an object has been marked for termination (C and F in this case—as they are not

accounted for in the object graph), they are swept from memory. At this point, the remaining space

on the heap is compacted, which in turn will cause the CLR to modify the set of active application

roots (and the underlying pointers) to refer to the correct memory location (this is done automati-

cally and transparently). Last but not least, the next object pointer is readjusted to point to the next

available slot. Figure 8-4 illustrates the resulting readjustment.