Storage Allocation
Strategies:
There are three different storage allocation strategies
based on runtime storage. They are:
- Static Allocation
- Stack Allocation
- Heap Allocation
Static Allocation:
- Storage is allocated at compile time
- Static storage has fixed allocation that does not change during program execution
- As bindings do not change at runtime, no runtime support is required
- At compile time, compiler can fill the address at which the target code can find the data it operates on
- FORTRAN uses the static allocation strategy
Limitations
- Size of data objects should be known at compile time
- Recursion is not supported
- Data structures cannot be created at runtime
Stack Allocation
- Stack allocation manages the runtime storage as a stack, i.e., control stack
- Activation records are pushed and popped as activation begins and end respectively
- Locals are always bound to fresh storage in each activation, because a new activation is onto a stack when a call is made
- Values of locals are deleted as activation ends
- The data structure can be created dynamically for stack allocation
Limitations
- Values of locals cannot be retained once activation ends
- The memory addressing can be done using pointers and indexed registers
- This type of allocation is slower than static allocation
Heap allocation
- Storage can be allocated and deallocated in any order
- If the values of non-local variables must be retained even after the activation record then such a retaining is not possible by stack allocation
- It is used for retaining of local variables
- The heap allocation allocates the continuous block of memory when required for storage of activation records. This allocated memory can be deallocated when activation ends
- Free space can be further reused by heap manager
- It supports for recursion and data structures can be created at runtime
Limitation
- Heap manages overhead.
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