signals and system calls

[Michael Stenner]

On Wed, Apr 09, 2003 at 02:40:11PM -0400, Peter Hansen wrote:
> Michael Stenner wrote:
> > 
> > Just to be clear, I'm not trying to "use" signals here.  They exist,
> > they WILL be sent (when a system shuts down, for example), and I'm
> > just trying to tolerate them in a way that doesn't lose data.
> > 
> > So, the bottom line is:  what do people recommend?
> 
> Don't.
> 
> That is, don't try to be incredibly tolerant even in the face of
> system shutdown and signals that kill your program.
> 
> Instead, be tolerant of partially written data structures, half-completed
> operations, and so forth.
> 
> There is *no* way you can protect against a power outage, and no
> way you can protect against something like "kill -9" anyway, so
> you are trying to achieve an unattainable level of perfection if
> you insist that under other circumstances you *must not* ever
> lose data.
> 
> At least with this view, you'll find it much easier to deal with
> the particular nastiness of signals...  just my view.

Actually, this is really excellent advice.  I have only one minor
quibble: as stated, your argument comes off as a bit extreme.  It
seems akin to those argements that often lead security conversations
down that road to "why bother locking the case when a band of ogres
wielding crowbars and soldering irons can ....".

Just because you can't protect against a power outage or kill -9
(which are freak events in a stable and well-managed system) doesn't
mean you shouldn't _try_ to protect against _normal_ events such as
SIGTERM.  I take your advice more as "don't put all your eggs in one
basket", which is probably how you meant it anyway :)

I will take the latter part of your advice ("be tolerant of partially
written data structures...") but would still prefer to deal with the
signals if I can.

				Thanks,
				 Michael

-- 
  Michael Stenner                       Office Phone: 919-660-2513
  Duke University, Dept. of Physics       mstenner at phy.duke.edu
  Box 90305, Durham N.C. 27708-0305