[REBOL] System Port Trap Example

From: carl::s::rebol::com at: 12-Oct-2002 17:24

Here is a short script that uses the REBOL system-port to intercept
shutdown
 types of interrupts from various operating systems.

Why?  For example, you would want to do this if you had a REBOL server
process on Linux that has internal state. You may want the chance to
write out information to files before quitting. This is the code you need
to make it happen.

The code below will detect both CTRL-C and REBOL ESCAPE key.

enable-system-trap: does [
     ; Trap OS interrupts
     if not system/ports/system [
         if none? attempt [system/ports/system: open [scheme: 'system]][
             print "NOTE: Missing System Port" exit
         ]
     ]
     if find get-modes system/ports/system 'system-modes 'signal [
         set-modes system/ports/system [
             signal: intersect get-modes system/ports/system 'signal-names [
                 sigquit sigterm sigint sighup
             ]
         ]
     ]
     system/console/break: 'signal
     append system/ports/wait-list system/ports/system
]

check-system-trap: func [port /local msg] [
     ; Process OS interrupts
     if not port? port [return none]
     if any [port/scheme <> 'system  port <> system/ports/system][return port]
     if not system/ports/system [return none]
     while [msg: pick system/ports/system 1] [
         if find [signal escape] msg/1 [
             print ["System Trap:" msg]
             ; (save files here)
             quit
         ]
     ]
     none
]

print "Starting..."

enable-system-trap

forever [
     wake-port: wait 20 ; timeout period
     check-system-trap wake-port
]

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