CincomSmalltalkWiki: Description of HUP Handler

VisualWorks 7 has one not terribly well known new feature - Signal handliing. While this is mostly useful on Unix and Linux, there are some Windows events that this framework can handle as well. The place to start looking is


ObjectMemory class>>registerObject: anObject withEngineFor: purposeString

That method allows you to register objects as handlers. Typically, one uses a semaphore which signals Smalltalk when the signal of interest arrives. Other messages of interest:

registrationNames
	"Answer an Array of the registration purposes supported by this VM."

objectRegisteredWithEngineFor: purposeString
	"Answer the object registered with the engine for the purpose specified by
	 purposeString, or nil if none.  The set of purpose names is answered by
	 registrationNames.

	 The primitive fails informatively.  If the purpose argument does not
	 encode an ASCII string the failure code is #'bad argument'.  If the
	 purpose argument names an unknown purpose the failure code is
	 #'no match'."

The comments in the first method listed above are quite instructive, and I've copied them here:


Register the first argument, an arbitrary object, to be used for a purpose
	 specified by the second argument, a ByteString or ByteArray in ASCII
	 encoding.  The list of purposes and appropriate objects is:
		ScavengeSemaphore;	a semaphore to signal after each scavenge
	 and on Unix platforms most of the following:
		SIGCHLD;	a semaphore signalled when the VM process receives the SIGCHLD signal
		SIGCONT;	a semaphore signalled when the VM process receives the SIGCONT signal
		SIGHUP;	a semaphore signalled when the VM process receives the SIGHUP signal
		SIGINT;	a semaphore signalled when the VM process receives the SIGINT signal
		SIGIO;		a semaphore signalled when the VM process receives the SIGIO signal (a.k.a. SIGPOLL)
		SIGPIPE;	a semaphore signalled when the VM process receives the SIGPIPE signal
		SIGQUIT;	a semaphore signalled when the VM process receives the SIGQUIT signal
		SIGTERM;	a semaphore signalled when the VM process receives the SIGTERM signal
		SIGURG;	a semaphore signalled when the VM process receives the SIGURG signal
		SIGUSR1;	a semaphore signalled when the VM process receives the SIGUSR1 signal
		SIGUSR2;	a semaphore signalled when the VM process receives the SIGUSR2 signal
	 The definitive list of the purposes is answered by ObjectMemory class>>#registrationNames,
	 and is more dependable than this comment.

	 The primitive fails informatively.  If the purpose argument does not
	 encode an ASCII string the failure code is #'bad argument'.  If the
	 purpose argument names an unknown purpose the failure code is
	 #'no match'. If the object is not a valid type for the purpose the
	 failure code is #'inappropriate operation'.

The code example I've uploaded - HUPHandler installs a handler onto a Unix/Linux system that catches SIGHUP. This signal is commonly used to re-initialize a server application; I'm using it on this server to catch SIGHUP and:

Remove all Wave and Web Toolkit servers and services
Re-load all Parcels loaded at startup
Re-set and restart all Wave and Web Toolkit services.

This is really useful thing, since it enables me to minimize the downtime for a server.