Lesson plan
Stale pointer bug
A stale pointer bug, otherwise known as an aliasing bug, is a class of subtle programming errors that can arise in code that does dynamic memory allocation, especially via the malloc function or equivalent. If several pointers address (are aliases for) a given chunk of storage, it may happen that the storage is freed or reallocated (and thus moved) through one alias and then referenced through another, which may lead to subtle (and possibly intermittent) errors depending on the state and the allocation history of the malloc arena. This bug can be avoided by never creating aliases for allocated memory, by controlling the dynamic scope of references to the storage so that none can remain when it is freed, or by use of a garbage collector, in the form of an intelligent memory-allocation library or as provided by higher-level languages, such as Lisp. The term aliasing bug is nowadays associated with C programming, but it was already in use in a very similar sense in the ALGOL 60 and Fortran programming language communities in the 1960s.
Article summary
A stale pointer bug, otherwise known as an aliasing bug, is a class of subtle programming errors that can arise in code that does dynamic memory allocation, especially via the malloc function or equivalent. If several pointers address (are aliases for) a given chunk of storage, it may happen that the storage is freed or reallocated (and thus moved) through one alias and then referenced through another, which may lead to subtle (and possibly intermittent) errors depending on the state and the allocation history of the malloc arena. This bug can be avoided by never creating aliases for allocated memory, by controlling the dynamic scope of references to the storage so that none can remain when it is freed, or by use of a garbage collector, in the form of an intelligent memory-allocation library or as provided by higher-level languages, such as Lisp. The term aliasing bug is nowadays associated with C programming, but it was already in use in a very similar sense in the ALGOL 60 and Fortran programming language communities in the 1960s.
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Discussion questions
- Summarise the article in your own words. Which single claim would you verify first, and why?
- Which claim in this article is most likely to be revised as the sources update? How would you check its current status?
- If two sources disagreed about one of these facts, what would you need in order to trust one over the other?
Bibliography
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Key claims and bibliography are generated from the same tracked claims and sources as the article page.