Handle (computing)

In computer programming, a handle is an abstract reference to a resource. Handles are used when application software references blocks of memory or objects managed by another system, such as 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 are file descriptors, network sockets, database connections, process identifiers (PIDs), and job IDs. Process IDs 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, but are typically considered opaque. In traditional implementations, file descriptors are indices into a (per-process) file descriptor table, thence a (system-wide) file table.

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.

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