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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.
The C programming language manages memory statically, automatically, or dynamically.Static-duration variables are allocated in main memory, usually along with the executable code of the program, and persist for the lifetime of the program; automatic-duration variables are allocated on the stack and come and go as functions are called and return.
C uses the malloc function; C++ and Java use the new operator; and many other languages (such as Python) allocate all objects from the free store. Determining when an object ought to be created ( object creation ) is generally trivial and unproblematic, though techniques such as object pools mean an object may be created before immediate use.
These functions are typically called from a higher-level memory management library function such as malloc. In the original Unix system, brk and sbrk were the only ways in which applications could acquire additional heap space; later versions allowed this to also be done using the mmap call.
Program C requests memory 35 K, order 0. An order 0 block is available, so it is allocated to C. Program D requests memory 67 K, order 1. No order 1 blocks are available, so an order 2 block is split, creating two order 1 blocks. Now an order 1 block is available, so it is allocated to D. Program B releases its memory, freeing one order 1 block.
To expose dangling pointer errors, one common programming technique is to set pointers to the null pointer or to an invalid address once the storage they point to has been released. When the null pointer is dereferenced (in most languages) the program will immediately terminate—there is no potential for data corruption or unpredictable behavior.
Many Unix-like systems as well as Microsoft Windows implement a function called alloca for dynamically allocating stack memory in a way similar to the heap-based malloc.A compiler typically translates it to inlined instructions manipulating the stack pointer, similar to how variable-length arrays are handled. [4]
Object caching leads to less frequent invocation of functions which initialize object state: when a slab-allocated object is released after use, the slab allocation system typically keeps it cached (rather than doing the work of destroying it) ready for re-use next time an object of that type is needed (thus avoiding the work of constructing ...