It appears that D has multiple ways of determining which created
objects are subject to GC.
For class instances, new creates a new class instance, returning
a pointer to it. While "alive", other pointers may also point to
the class instance. Once no pointers are pointing to this class
instance, it may be garbage collected.
OOP languages such as Eiffel can keep track of pointers to class
instances. They then do a generational lookup or do a thorough
mark and sweep.
C, C++ and D can play shenanigans with pointers, such as casting
them to size_t, which hides them from the GC.
In addition, D provides several ways to allocate and free memory.
GC.calloc can allocate memory for a slice of MyClass instances.
The developer may run GC.free to free the allocated memory.
But GC may perform its own garbage collection of GC allocated
memory blocks.
Let's look at each attribute: (confirm if my analysis is right,
otherwise correct)
FINALIZE - just before GC reclaims the memory, such as with
GC.free,
call destructors, aka finalizers.
NO_SCAN - There may be false positives regarding byte values that
look like 'new'
allocated pointers. This can result in 'garbage'
memory not being collected.
If we are CERTAIN that this memory block doesn't
contain any pointers to
'new' SomeClass allocated memory, then mark as NO_SCAN.
Question 1: if GC-calloc has allocated MyClass that has
a string 'name' member,
which may expand in size, would be still properly apply
NO_SCAN.
Question 2: if GC-calloc has allocated MyClass, which
may allocate
new MyStudent(...), would that mean 'don't apply
NO_SCAN'?
NO_MOVE - For GC.realloc, if increasing memory allocated, and
it's not available,
throw 'MEMORY_NOT_AVAILABLE' exception.
APPENDABLE - For D internal runtime use. Don't mark this
yourself.
NO_INTERIOR - This says that only the base address of the block
may be a target address
of other GC allocated pointers.
All other possible pointers are 'false' pointers.
Question 3: How is this different that NO_SCAN.
Perhaps I am missing the fundamentals of various D garbage
collectors.
Are there any articles that expound on this issue?
