Appel, A. W. Garbage collection. In Topics in Advanced Language Implementation, P. Lee, Ed. MIT Press, Cambridge, MA, 1991. ch. 4.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....ts in main memory, and an even greater advantage as the heap gets paged to disk. 1 1 Introduction Garbage collection is an important component of many modern programming languages. Since McCarthy s original work in 1960 [12] many di erent garbage collection algorithms have been developed [6, 2, 19]. Among the basic garbage collection techniques are mark sweep [12, 20] mark compact [7] and copying garbage collection [4, 8] In the last decade or so, generational garbage collection (GGC) 11, 17, 13] has become one of the most important garbage collection techniques. 1.1 Generational ....

Andrew W. Appel. Garbage collection. In Peter Lee, editor, Topics in Advanced language Implementation, pages 89-100. MIT Press, Cambridge, Massachusetts, 1991.

....into three main classes: reference counting, mark and sweep, and copying collectors. This chapter examines each of these in turn, providing background for the rest of the thesis. Cohen [Cohen 81] provides a survey of garbage collection techniques known prior to the 1980 s in greater depth. Appel [Appel 90] surveys more recent techniques. As we consider each collection technique, we also evaluate its applicability to languages such as C and C . 2.1. Reference Counting Collection An object is garbage if and only if there are no references to it. A reference counting collector detects unreferenced ....

Appel, Andrew W. Garbage collection. In Peter Lee (editor), Topics in Advanced Language Implementation. MIT Press, Cambridge, MA, 1990. To appear.

.... and Modula 3 [7] Garbage collectors have also been implemented for languages that were not originally designed to support garbage collection, such as Modula 2 [8] C [9] and even C [10] Recent implementations tend to use copying collection algorithms instead of mark and sweep algorithms [11, 12]. Copying algorithms take time that is proportional to the amount of accessible data and identify and compact accessible data in one pass. Mark and sweep algorithms take time that is proportional to the amount of accessible and inaccessible data and the compacting variants require another pass to ....

....into two semi spaces. Allocation proceeds as in the existing collector from old space until a request cannot be satisfied. During collection, accessible data is copied from old space to new space, which also compacts the data, the roles of the spaces are reversed, and execution continues [11]. When a block is copied, a forwarding pointer is left in the original so that other descriptors pointing to the block can be re aimed at its location in new space. The second alternative, string, eliminates the separate string region and allocates strings and blocks in a single region and ....

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Andrew W. Appel. Garbage collection. In Peter Lee, editor, Topics in Advanced Language Implementation Techniques, pages 89--100. MIT Press, Cambridge, MA, 1991.

....of forward is treated as a mark bit. If it points into the range of to space, we say mark is set ; if it has any other value including a pointer into from space then it is clear. This convention is consistent with the role of marking in all garbage collectors. The stop and copy collector [8, 2] is a two finger algorithm, whose effect is to move all nodes out of the from semispace, compacting them into the to semispace. Initially, all root nodes are copied into one end of the to space, without changing any content; rooting is discussed in detail in the next section. Thereafter, one ....

....in the next section. Thereafter, one finger, called next, always points to the first unused address in to space. The other, called scan, starts at the beginning of to space and updates every pointer in sequence until it catches up with next. For a complete description and figure, see Appel [2]. Next and scan are denoted N fl and S fl in the figures; this description focuses on scan. Figure 1 illustrates the effects of scanning the first and then later sticky references to a binary node at address A. Blank entries there indicate don t care. Figure 1.1 is the situation before ....

A. Appel. Garbage collection. In P. Lee (ed.), Topics in Advanced Language Implementation, Cambridge MA, M.I.T. Press (1991) 89-100.

....handle cyclical references, which makes them unsuitable for EZ , where cycles abound. Copying collectors have the potential to be much more efficient than reference counting and markand sweep collectors; especially when the total available memory is much larger than the amount of active objects [1]. These collectors avoid touching the garbage and their work is proportional to the number of accessible pages; they do, however, split the memory into two semi spaces halving the memory available for objects. However, objects in EZ s virtual address space do not move; this restriction greatly ....

Andrew W. Appel. 1991. Garbage collection. In Peter Lee, editor, Topics in Advanced Language Implementation Techniques, chapter 4. MIT Press.

....7.2 Finalization : 57 7. 3 Multiple Differently Managed Heaps : 57 8 Overall Cost of Garbage Collection 58 9 Conclusions and Areas for Research 58 1 Automatic Storage Reclamation Garbage collection is the automatic reclamation of computer storage [Knu69, Coh81, App91] While in many systems programmers must explicitly reclaim heap memory 1 at some point in the program, by using a free or dispose statement; garbage collected systems free the programmer from this burden. The garbage collector s function is to find data objects 2 that are no longer in ....

Andrew W. Appel. Garbage collection. In Peter Lee, editor, Topics in Advanced Language Implementation, pages 89--100. MIT Press, Cambridge, Massachusetts, 1991.

....parallel implementations. Nested parallelism is achieved through the ability to apply functions in parallel to each element of a sequence. NESL s apply to each form is specified using a set like notation similar to set formers in SETL [52] For example, the NESL expression negate(a) a in [3, 4, 9,5] a 4 is read as in parallel, for each a in the sequence [3, 4, 9, 5] such that a is less than 4, negate a . The expression returns [ 3, 4, 9] Parallelism is available both in the evaluation of the expression to the left of the colon ( and in the subselection to the right of the pipe ....

....ability to apply functions in parallel to each element of a sequence. NESL s apply to each form is specified using a set like notation similar to set formers in SETL [52] For example, the NESL expression negate(a) a in [3, 4, 9,5] a 4 is read as in parallel, for each a in the sequence [3, 4, 9, 5] such that a is less than 4, negate a . The expression returns [ 3, 4, 9] Parallelism is available both in the evaluation of the expression to the left of the colon ( and in the subselection to the right of the pipe ( This parallel subselection can be implemented with packing techniques ....

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Andrew W. Appel. Garbage collection. In Peter Lee, editor, Topics in Advanced Language Implementation. MIT Press, Cambridge, MA, 1991. ch. 4.

....with low score hypotheses. We call this time based garbage collection (TBGC) Garbage collection 11 is a technique used in dynamic memory management schemes to reclaim used but provably inaccessible storage space and recycle it into the unused memory pool. For an overview of such techniques see [3]. 11 Ecologically speaking, the term garbage collection is a misnomer, since the garbage is not only collected but also recycled with a 100 efficiency. This mechanism is an extension of the time frame based filtering proposed by Pyka in [20] Adaptive behavior of channels can be implemented ....

Andrew W. Appel. Garbage Collection, pages 89--100. MIT Press, Cambridge, Massachusetts, 1991.

....form of a context free grammar. 2 Safety: As each filter is specified as an LR grammar, the operation of an associated parser for such filters can be proven safe, if stack over and under flow can be prevented. In systems with virtual memory hardware, the cost of maintaining safety is minimal [App91] especially where safety is not violated. Specification generality: The specification language, LR grammars, is powerful enough to allow easy specification of different kinds of filters. For example, no special treatment is needed for packets with varying length fields. Variable length ....

Andrew W. Appel. Garbage collection. In Peter Lee, editor, Topics in Advanced Language Implementation, chapter 4. The MIT Press, 1991.

....of memory and reclaim those data structures for which there are no pointers. Operating system kernels cannot use this type of stop and scan technique due to its performance characteristics (the operating system stops completely during the scan) but more recently developed incremental techniques [1] are amenable to use in kernels. The Mach kernel uses a reference counting technique for existence coordination, in part because garbage collection was not viable for the C language when implementation began. Hardware implementations of multiprocessor locking (e.g. test and set) are the basis for ....

Andrew W. Appel, "Garbage Collection," Topics in Advanced Language Implementation, Peter Lee, ed, MIT Press, (1990).

....improve efficiency and locality by garbage collecting a smaller area more often, while exploiting typical lifetime characteristics to avoid undue overhead from long lived objects. 1 Automatic Storage Reclamation Garbage collection is the automatic reclamation of computer storage [Knu69, Coh81, App91] While in many systems programmers must explicitly reclaim heap memory at some point in the program, by using a free or dispose statement, garbage collected systems free the programmer from this burden. The garbage collector s function is to find data objects 2 that are no longer in use ....

Andrew W. Appel. Garbage collection. In Peter Lee, editor, Topics in Advanced Language Implementation, pages 89--100. MIT Press, Cambridge, Massachusetts, 1991.

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Appel, A. W. Garbage collection. In Topics in Advanced Language Implementation, P. Lee, Ed. MIT Press, Cambridge, MA, 1991. ch. 4.

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