Re: canonical thread stop

On 7/24/2014 2:09 AM, mike75214@usa.com wrote:


     System.exit(status); // tee-hee

     That's only partly in jest. If you stop (or suspend) a thread "from
the outside" without its cooperation, you have absolutely no idea what
its state was. For example, it might have just stored the X position of
something and have been about to store the Y position when the rug was
ripped from beneath its feet; any other thread that subsequently uses
the combined (X,Y) will get a completely bogus location -- the X from a
moment ago and the Y from last week.

     The only safe way to stop or suspend a thread is with the thread's
cooperation. It needs to get to a "safe" state, it needs to "put its
affairs in order" before going to sleep or to the grave. And since
what constitutes "safe" and "in order" is application-dependent, there's
no one-size-fits-all pre-canned solution.

     Here's an analogy: You're driving down the highway when you hear a
siren and see flashing blue lights in your rear-view mirror. So you
pull over to the side of the road, slow down, stop, and await your
fate. That's the right way to stop a thread: Signal it to stop and
wait for it to do so safely.

     If instead the cop had zapped you with a phaser set on "stun,"
you'd find yourself hurtling down the road at high speed, paralyzed
and unable to operate the controls, a menace to yourself and to
others. That's the wrong way to stop a thread: Just halt it willy-
nilly and pray there won't be too much "collateral damage."

--
esosman@comcast-dot-net.invalid