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A free list (or freelist) is a data structure used in a scheme for dynamic memory allocation. It operates by connecting unallocated regions of memory together in a linked list, using the first word of each unallocated region as a pointer to the next. It is most suitable for allocating from a memory pool, where all objects have the same size.
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.
The default constructor for T, if any, is called to construct a T instance in the allocated memory buffer. If not enough memory is available in the free store for an object of type T, the new request indicates failure by throwing an exception of type std::bad_alloc. This removes the need to explicitly check the result of an allocation.
To achieve this, some form of dynamic memory allocation is usually required. Allocators handle all the requests for allocation and deallocation of memory for a given container. The C++ Standard Library provides general-purpose allocators that are used by default, however, custom allocators may also be supplied by the programmer.
Memory pools, also called fixed-size blocks allocation, is the use of pools for memory management that allows dynamic memory allocation. Dynamic memory allocation can, and has been achieved through the use of techniques such as malloc and C++'s operator new; although established and reliable implementations, these suffer from fragmentation ...
(See the article on C dynamic memory allocation for an example of dynamically allocated arrays.) Unlike automatic allocation, which can fail at run time with uncontrolled consequences, the dynamic allocation functions return an indication (in the form of a null pointer value) when the required storage cannot be allocated.
Data is stored non-contiguously in memory which allows the list data structure to avoid the reallocation of memory that can be necessary with vectors when new elements are inserted into the list. The list data structure allocates and deallocates memory as needed; therefore, it does not allocate memory that it is not currently using.
Illustration of cache coloring. Left is virtual memory spaces, center is the physical memory space, and right is the CPU cache.. A physically indexed CPU cache is designed such that addresses in adjacent physical memory blocks take different positions ("cache lines") in the cache, but this is not the case when it comes to virtual memory; when virtually adjacent but not physically adjacent ...