Memory allocation: Difference between revisions

=={{header|Smalltalk}}==

Smalltalk does automatic memory management and garbage collection.

So in normal use, all you do is allocate by instantiating objects.

However, to support passing data in and out to external functions (typically: C-functions or data for a GPU or similar),

a number of additional APIs are present (which may differ slightly among Smalltalk dialects):

{{works with|Smalltalk/X}}

To allocate a non-movable, non garbage collected block of memory; (eg. to hand out a block of memory on which an external C-function keeps a reference). The memory must be explicitly freed by the programmer:

<lang smalltalk>handle := ExternalBytes new:size

...

handle free</lang>

To allocate a non-movable block of memory, which is garbage collected as soon as the reference is no longer reachable by Smalltalk (useful to hand out a block of memory to an external function which does NOT keep a reference on it:

<lang smalltalk>handle := ExternalBytes unprotectedNew:size

...

handle := nil "or no longer reachable"

...

block will be freed by the garbage collector eventually</lang>

Of course, both are to be used with great care, as memory leaks are possible. Thus, it is only used by core parts of the system, eg. for async I/O buffers, shared memory, mapped I/O devices etc. Normal programs would not use them.