Run-Time Storage Organization

1. Run-Time Storage Organization

2. Introduction • We need to relate the static source text of a program to the actions that must occur at run time • We need to allocate and manage the memory used by the program (static and dynamic)

3. Memory Allocation Techniques • Static Allocation • Stack Allocation • Heap Allocation Code Static Data Stack Heap

4. Static Allocation • The number and size of all objects to be allocated is known at compile time • It is used for: • Global variables that are fixed in size and accessible throughout program execution • Program literals (constants) • Program code

5. Stack Allocation • Information needed by a single execution of a routine (a procedure, function or method) is managed using an activation record or frame • An activation record contains local variables, parameters, return address, etc. • Activation records are pushed and popped as functions calls begin and end

6. Parameter Passing • Call-by-value can be implemented as follows: • A formal parameter is treated like a local variable, so the storage for the formal is in the activation record of the called routine • The caller evaluates the actual parameters and places their values in the storage for the formals • Call-by-reference • The caller passes to the called procedure a reference to the storage address of each actual parameter

7. Heap Allocation • The heap is used to store data which can be allocated and freed at any time and in any order • Deallocation is either manual or automatic (garbage collection) • The heap typically becomes fragmented during use