12.9.3.1 Running a child process on a Windows terminal

A child process gets a terminal on Windows by attaching to a pseudo console. The Epilog window (see swipl-win.exe) has no console of its own: it talks to its Prolog thread over two pipes, and a child handed those has nothing that echoes what it reads, no window size and no way to be interrupted. The functions below put such a child on the console of the terminal behind a stream. This is what shell/1 does, and what process_create/3 does for the streams the caller left alone. They exist on Windows only.

HANDLE Swinpseudoconsole(IOSTREAM *s)

Claim the pseudo console of the terminal behind s, or NULL if it has none to give. This is a claim rather than a query: the console reads and writes the same pipe ends as the stream, so the terminal runs one only while a client holds it, and the holder must touch neither the stream nor its companions meanwhile. Declared HANDLE because HPCON postdates SWI-Stream.h; they are the same.

void Swinrelease_pseudoconsole(IOSTREAM *s)

Hand the console back once the child is gone. The terminal closes it when the last client has released it.

void * Swinpseudoconsole_attributes(HANDLE hpcon)

Process attribute list that puts a child on hpcon, or NULL if it cannot be built. Pass it as the lpAttributeList of a STARTUPINFOEXW and create the process with EXTENDED_STARTUPINFO_PRESENT. Not with CREATE_NO_WINDOW: that asks for a console of the child's own, which is the opposite of what the attribute says and wins.

void Swinfree_pseudoconsole_attributes(void *attributes)

Free the list once the child is created. The console itself is held until Swinrelease_pseudoconsole().