On 12:06 am, [EMAIL PROTECTED] wrote:
[EMAIL PROTECTED] wrote:
Can you suggest any use-cases for thread termination which will *not*
result in a completely broken and unpredictable heap after the thread
has died?
Suppose you have a GUI and you want to launch a
long-running computation without blocking the
user interface. You don't know how long it will
take, so you want the user to be able to cancel
it if he gets bored.
That's a perfectly reasonable use-case which doesn't require this
feature at all ;).
Interaction with the rest of the program is
extremely limited -- some data is passed in,
it churns away, and some data is returned. It
doesn't matter what happens to its internal
state if it gets interrupted, as it's all going
to be thrown away.
If that's true, then the state-sharing features of threads aren't
required, which is the right way to design concurrent software anyway.
In that situation, it doesn't seem unreasonable
to me to want to be able to just kill the thread.
I don't see how it could do any more harm than
using KeyboardInterrupt to kill a program,
because that's all it is -- a subprogram running
inside your main program.
The key distinction between threads and processes is the sharing of
internal program state.
How would you handle this situation?
Spawn a process, deliver the result via an event.
If you're allergic to event-driven programming, then you can spawn a
process *in* a thread, and block in the thread on reading from the
process's output, then kill the *process* and have that terminate the
output, which terminates the read(). This is a lot like having a queue
that you can put a "stop" object into, except the "file" interface
provided by OSes is kind of crude. Still no need to kill the thread.
At the end of the day though, you're writing a GUI in this use-case and
so you typically *must* be cognizant of event-driven issues anyway.
Many GUIs (even in the thread-happy world of Windows) aren't thread-safe
except for a few specific data-exchange methods, which behave more or
less like a queue.
One of the 35 different existing ways in which one can spawn a process
from Python, I hope, will be sufficient for this case :).
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