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Programming Languages Storage Management

Cao Hoaøng Truï

Khoa Coâng Ngheä Thoâng TinÑaïi Hoïc Baùch Khoa TP. HCM

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Storage Management

• Major run-time elements requiring storage

• Major operations requiring storage to be allocated/freed

• Storage management phases

• Storage management techniques

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Run-time elements

• Code segments

• System run-time programs library routines storage management routines

• User-defined data structures

• Subprogram return points

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Run-time elements

• Referencing environments

• Temporaries in expression evaluation

• Temporaries in parameter transmission

• Input-output buffers

• Miscellaneous system data

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Run-time operations

• Subprogram call and return operations

• Data structure creation and destruction operations

• Component insertion and deletion operations

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Storage Management Phases

1. Initial allocation: allocating free storage

2. Recovery: recovering unused storage garbage collection

3. Compaction and reuse: compaction: to construct large blocks reuse: as initial allocation

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Storage Management Techniques

1. Static storage management

2. Stack-based storage management

3. Heap storage management fixed-size elements variable-size elements

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Static Storage Management

Static allocation: allocation that remains fixed through out execution.

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Stack-based Storage Management

• First Allocated - Last Freed.

• Simple storage recovery, compaction and reuse.

• Not applicable if storage needs to be allocated/freed at arbitrary points.

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Heap Storage Management

Heap: a block of storage within which data are allocated/freed in an arbitrary manner.

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heap

head

initial free-space list

heap

head

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heap (storage allocated by NEW)

typical Pascal memory organization

subprogram code segmentsand system run-time routines (statically allocated) stack

bottomactivation records

free space

heap bottom