Strange behaviour of select() call when ^Z typed, (4.2BSD)

[Brett Galloway]

The following program illustrates what may be a bug in the select() call
(and the underlying kernel code):

----------- Start of file -----------------
#include	<stdio.h>

main(argc,argv)
{
	char	buf[32];
	int	readfds;
	int	i;

	while(1) {

		printf("Type something: ");
		fflush(stdout);

		readfds=1;
		if(select(1,&readfds,0,0,0) > 0) {
			gets(buf);
			printf("'%s' typed.\n",buf);
			if(buf[0] == '~')
				break;
		}
	}
}

------------ End of file -------------

When this is executed, and ^Z is typed at the prompt (i.e. while the
program is sitting in the select()), the program does stop, but then
its status changes.  The csh detects a stopped state, but the program's
process in fact exits.  This bug is (seemingly) intermittent.  I have
other programs which sit on select()'s for input which may or may not
die when a SIGTSTP signal is sent to them.

Sending SIGTSTP instead of typing ^Z may also cause the process to die.
Sending SIGTSTP to a process on a pipe, however, never caused it to
die, so I assume that this problem involves some interaction with the
(new) tty driver.

Does anyone out there know what is happening?  If so, I would appreciate
hearing about it.