TITLE: Writing a "new_handler"


PROBLEM: jeffery@flood.com (Jeffery Cavallaro)

2.  Are there rules to what _new_handler is supposed to do if it returns.
    With the BC++ 3.1 compiler it appears that the new operator is re-executed,
    thus causing the exception again unless the handler has freed something.
    It seems that the only reasonable thing to do is exit.  Any insights here?


RESPONSE: steve@taumet.com (Steve Clamage), 9 Dec 92
	  Vice Chair, ANSI C++ Committee, X3J16

The new_handler function is supplied by you, not by the system.  If
you arrange for it to be called, you have to be sure it does something
that operator new() will find useful.

The standard operator new() is supposed to work like this pseudo-code:

	do {
	    result = get_memory();
	    if( new_handler && result==0 )
		new_handler();
	} while( new_handler && result==0 );
	return result;

If you supply a new_handler routine, it should do something to make
memory available.  If it can't, it should un-install itself to
terminate the above loop.  Routines which install the new_handler
should therefore not be surprised to find that it has un-installed itself.

In addition, you can provide a replacement operator new() which
co-operates with the new_handler you also provide.

Messing with the memory-management routines is not for the faint of
heart.  In the C++ Committee we have been working on a specification
for the new and delete routines, and on what user replacements for
them must do.