Problem Statement

Create a temporary file, securely and exclusively (opening it such that there are no possible race conditions). It's fine assuming local filesystem semantics (NFS or other networking filesystems can have signficantly more complicated semantics for satisfying the "no race conditions" criteria). The function should automatically resolve name collisions and should only fail in cases where permission is denied, the filesystem is read-only or full, or similar conditions exist (returning an error or raising an exception as appropriate to the language/environment).

Let's start with the solution:

set chan [file tempfile filenameVar]