The cause, in two words, is that the debugger is not aware of process suspension and the debugger depends on it. So having a debugger that tries to open a debugger creates an endless loop that should be stopped with process suspension in the normal case.

On 25 nov 2015, at 9:32 p.m., Esteban A. Maringolo <emaringolo@gmail.com> wrote:

2015-11-25 6:32 GMT-03:00 Guillermo Polito <guillermopolito@gmail.com>:
I��ve seen this problem tons of times since Pharo4. But the worst is that I
never found a way to reproduce it.

To me there is some side effect somewhere. Because it does not happen in a
fresh image, but once you have it, you have it all the time.

I thought it had to do with how GLORP handles the exceptions and/or
block unwinding. But it doesn't seem so.

There is a bug report for this:
https://pharo.fogbugz.com/f/cases/16877/another-endless-debugger-loop

Esteban A. Maringolo