Descriptorequivalent

Descriptor-equivalent describes a relation between two descriptors (such as file descriptors, handles, or similar resource identifiers) indicating that they reference the same underlying resource in a given system and are interchangeable for certain operations. The concept emphasizes the observable effect of using the descriptors rather than the identifiers themselves.

In practice, descriptor equivalence appears in operating systems that support descriptor duplication and sharing. In POSIX systems, two file descriptors are considered equivalent if they refer to the same open file description; they share the same file offset and status flags, and closing one descriptor does not close the resource until the last descriptor referring to it is closed. Conversely, descriptors referring to different resources are not equivalent, even if they point to the same file on disk.

The criteria for equivalence are context dependent. Commonly, two descriptors are equivalent if they reference the same resource and offer indistinguishable behavior for a given sequence of operations, such as read or write, within the current process state. Some contexts also require identical access modes and permissions. Equivalence may be partial or full: partial equivalence might ignore minor state differences, while full equivalence requires identical effect on the resource and its lifecycle.

Applications include resource management, optimization of descriptor usage, and correctness analysis in systems programming. Because descriptor semantics can vary across platforms, descriptor-equivalence is usually defined relative to a specific API, system call behavior, or resource type.

See also: file descriptor, handle, descriptor duplication, resource management, equivalence relation.