(emacs)Emergency Escape


Emergency Escape
----------------

   Because at times there have been bugs causing Emacs to loop without
checking `quit-flag', a special feature causes Emacs to be suspended
immediately if you type a second `C-g' while the flag is already set,
so you can always get out of GNU Emacs.  Normally Emacs recognizes and
clears `quit-flag' (and quits!) quickly enough to prevent this from
happening.  (On MS-DOS and compatible systems, type `C-<BREAK>' twice.)

   When you resume Emacs after a suspension caused by multiple `C-g', it
asks two questions before going back to what it had been doing:

     Auto-save? (y or n)
     Abort (and dump core)? (y or n)

Answer each one with `y' or `n' followed by <RET>.

   Saying `y' to `Auto-save?' causes immediate auto-saving of all
modified buffers in which auto-saving is enabled.

   Saying `y' to `Abort (and dump core)?' causes an illegal instruction
to be executed, dumping core.  This is to enable a wizard to figure out
why Emacs was failing to quit in the first place.  Execution does not
continue after a core dump.  If you answer `n', execution does
continue.  With luck, GNU Emacs will ultimately check `quit-flag' and
quit normally.  If not, and you type another `C-g', it is suspended
again.

   If Emacs is not really hung, just slow, you may invoke the double
`C-g' feature without really meaning to.  Then just resume and answer
`n' to both questions, and you will arrive at your former state.
Presumably the quit you requested will happen soon.

   The double `C-g' feature is turned off when Emacs is running under
the X Window System, since you can use the window manager to kill Emacs
or to create another window and run another program.

   On MS-DOS and compatible systems, the emergency escape feature is
sometimes unavailable, even if you press `C-<BREAK>' twice, when some
system call (MS-DOS or BIOS) hangs, or when Emacs is stuck in a very
tight endless loop (in C code, *not* in Lisp code).

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