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In article 22h@galaxy.ucr.edu, thp@cs.ucr.edu (Tom Payne) writes:
>
>Implicit in a qestion of what the Standard says are the related
>questions of what it should say and why --- why shouldn't signal
>handlers be allowed to throw exceptions?  (The question seems both
>interesting and appropriate.)

Exceptions are synchronous, and unwind the stack from the point of the 
throw to the point of the handler. When an asynchronous signal arrives,
what is the state of the stack? Answer: unknown. In particular, the
stack might not even be in a consistent state -- arguments half pushed
during function entry or half popped during exit.

In C, a signal handler isn't allowed to do much of anything, precisely
because the program state can't be known and may be inconsistent. The
same is true in C++.

Allowing exceptions to be thrown from a signal handler would place a
noticeable penalty on all programs to provide locks on every function
entry and exit, even programs that didn't throw exceptions or use
signals.
---
Steve Clamage, stephen.clamage@eng.sun.com
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