CS 4448 - Spring 1998
Object-Oriented Programming and Design
Talk 7.2.1
by
Kavita Ravi

• If new were implemented with a different call than malloc (this flexibility should be provided), then compatibility with free will not always be possible.

Destructors:

• Destructors must be executed over all objects being destroyed to free up dynamic memory. If the array were not indicated by [], then the number of objects should be indicated to delete. One solution is to write the size of the object at the beginning of the memory allocated for it. But since delete uses free sometimes (for built-in types), this compatibility will be destroyed by specifying the size.

One Solution:

• Objects that are vectors (arrays) are stored in a table as an (address, size) pair. Scalars are not stored in the table. delete will be interpreted as a scalar being freed. delete [] will be treated as a vector and the table is looked up to find out the number of objects in this array. (The destructor can then be executed over all the objects in this array.

Garbage Collection

• The user doesnt have to take care of destroying created objects.
• Garbage collection is normally done using "use-counts".
• Assuming garbage collection is done, when should destructors be executed? During garbage collection? Memory overhead in storing objects.
• If a destructor allocates some memory, infinite allocation-free looping.
• Problems with initialized pointers. Objects may have spurious pointers to them.
• Garbage Collection has memory overhead.
• Conservative collection - one solution. Hard to quantify the performance standard.