Chapter 10 Storage Management

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Chapter 10 Storage Management

• Implementation details beyond programmers
  control
• Storage/CPU time trade-off
• Binding times to storage

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Storage needed for code

• Code
• User programs
• Library routines
• Storage mgt routines
• Static/automatic/heap allocation
• Garbage collection, storage compaction
• Loaders, interpreters, etc.

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Storage needed for data objects

• programmer variables, constants
• Temps for expression evaluation, functions
  return, parameters
• Other activation record objects
• Static and/or dynamic reference environment
• Return point from subprogram call
• Input/output buffers
• Garbage collection bits, ptrs
• Tables for named heap objects (Snobol4s Central
  Strings Table)

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Routines that call for storage mgt

• Subroutine entry, return
• Prolog, epilog
• Heap object/ class object creation, destruction
• Expression evaluation
• Parameter passing (specifically if expression is
  a parameter)

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Programmer control issues

• Free facility (danger of dangling references)
  versus garbage collection overhead delay in
  knowing when object has lost external path
• Compare to virtual memory
• Efficient allocation of storage in blocks (C)
  rather than according to logical need
• Reuse of freed storage an issue compaction
  problems

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Static storage management

• No run-time storage mgt
• Efficiency of compiler generating location for
  data object as offset from code section
• No table or lists needed
• No overlays of storage
• Problem we have a large tax table that we want
  to hide within a routine that computes taxes
• Where is it defined?
• No recursion

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Stack (automatic) storage management

• Efficient storage mgt stack ptr
• Recursion is possible
• Overlays are system controlled
• Compiler generates location (l-value) as offset
  from start of activation record
• Scope rules
• (Text left this out by error)

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Heap storage mgt

• Allocation from free list typically organized as
  linked list
• Programmer call or creation of object
• Deallocation
• Programmer call or garbage collection
• Is freed object placed at top of list or ordered
  by size?
• Compaction for freed objects of different sizes
• LISP list components are all the same size
• Reuse
• For fixed size elements, free storage is fungible
• For variable size elements, do we allocate from
  best fit, first (random) fit