Handle (computing)

In computer programming, a handle is an abstract reference to a resource that is used when application software references blocks of memory or objects that are managed by another system like a database or an operating system. A resource handle can be an opaque identifier, in which case it is often an integer number (often an array index in an array or "table" that is used to manage that type of resource), or it can be a pointer that allows access to further information. Common resource handles include s, network sockets, database connections, process identifiers (PIDs), and job IDs. PIDs and job IDs are explicitly visible integers; while file descriptors and sockets (which are often implemented as a form of file descriptor) are represented as integers, they are typically considered opaque. In traditional implementations, file descriptors are indices into a (per-process) , thence a (system-wide) . While a pointer contains the address of the item to which it refers, a handle is an abstraction of a reference which is managed externally; its opacity allows the referent to be relocated in memory by the system without invalidating the handle, which is impossible with pointers. The extra layer of indirection also increases the control that the managing system has over the operations performed on the referent. Typically the handle is an index or a pointer into a global array of tombstones. A handle leak is a type of software bug that occurs when a computer program asks for a handle to a resource but does not free the handle when it is no longer used; this is a form of resource leak, similar to a memory leak for a pointer to memory. In secure computing terms, because access to a resource via a handle is mediated by another system, a handle functions as a capability: it not only identifies an object, but also associates access rights. For example, while a filename is forgeable (it is just a guessable identifier), a handle is given to a user by an external system, and thus represents not just identity, but also granted access.