Re: alarm_signal_handler is called too frequently

[Jan D.]

I made my question very unclear, I'll try again.  Sorry if this is 
obvious for others, but I just don't understand.

Say we have three functions, aL, bL and cL, all written in Lisp (hence 
the L).  Now, obviously aL calling bL calling cL is safe (<-- denotes 
return, not cL calls bL).

1:

  aL    bL    cL
  | --> |     |
  |     | --> |
  |     | <-- |
  | <-- |     |

If we replace bL with code in C instead, is this safe?

2:

  aL    bC    cL
  | --> |     |
  |     | --> |
  |     | <-- |
  | <-- |     |

I think it must be, there are places in Emacs where C code calls Lisp 
functions.  Say now that bC calls cL within BLOCK/UNBLOCK_INPUT:

3:

  aL    bC    cL
  | --> |     |
  |   BLOCK   |
  |     | --> |
  |     | <-- |
  |   UNBLOCK |
  | <-- |     |

Why is this unsafe, if 2 was safe (if indeed it is)?  It is not as 
though the signal handler is calling Lisp code, that is obviously 
unsafe.  But when a dialog or popup menu is popped up, the signal 
handler is not involved in processing X events, it is all done inside 
bC.

I'm sorry if this is a stupid question, but I just don't get it.

        Jan D.