Type-safe languages such as ML or Java offer extraordinary software
engineering advantages over "uncivilized" languages like C. The
compile-time
checking provided by these languages allows programmers to detect their
errors much earlier in the software development cycle and can lead to
tremendous
gains in productivity.
Then why do so many programmers continue to work in the stone age?
One technical reason for preferring a programming language like C over ML is
that it
gives programmers much more control over memory management. In C, you can
explicitly "free" an object, returning the memory used to store the object
to the system so it can be reused. Unfortunately, type-safe languages like
ML and Java do not allow explicit deallocation of memory; they typically
rely on a garbage collector, which *implicitly* recycles memory locations
when it is safe to so.
In this talk, I will introduce you to region-based memory management, which
has been developed by Mads Tofte, Jean-Pierre Talpin, and others at DIKU. In
this memory management scheme, all values are placed into one of many
regions (storage areas). Regions are allocated and explicitly deallocated.
When a region is deallocated, all the storage used for that region is
reclaimed (and the values stored there can no longer be used). It has
several advantages over other forms of memory management. Here are two:
- allocation and deallocation of objects is explicit in a region-annotated
program. Because the lifetimes of objects are represented explicitly in
programs, there is some hope that users (Nuprl?) may be able to reason about
the space complexity of programs.
- there is a sound region-based type system that ensures programs will not
deallocate regions too early. Therefore, programmers do not have to worry
about dereferencing dangling pointers. Programmers have all of software
engineering advantages of type-safe languages with (some) of the control of
languages that allow explicit allocation and deallocation.
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