Jonas Maebe wrote:
On 27/02/16 12:40, Mark Morgan Lloyd wrote:
Is there a way of sending an unambiguous system-level kill signal to a
thread? KillThread(ThreadID) doesn't appear to be brutal enough, and I'm
unsure of the correct way to access pthread_kill().
You cannot asynchronously kill threads on Unix platforms with the
cthreads unit, and even on platforms where you can, you should never do
it. All resources held by that thread will leak, and locks it held will
never be unlocked.
Ouch. But as I said, this is specifically at termination, I'd like to
shut down in good order so that I can output the number of times each
thread's spun and none of them will be reused.
KillThread() on Unix calls pthread_cancel(), which indicates to the
system libraries (or any other libraries that include support for this)
that that as soon as they know it is safe to kill the current thread,
they should abort it and call its registered cleanup functions.
Since you are in an emulator, the way to solve this is probably to have
your own threads regularly check the "terminated" property of the
tthread and if it's set (which you can do by calling thread.terminate
"on it" from another thread), to clean up everything and abort.
It's not so much /in/ an emulator as the code /is/ an emulator.
The threads check for various termination conditions every time they
spin, but in this test case one of them's gone into a syscall that can't
be completed.
Interestingly, this is /exactly/ why a dot was added after the final END
in a number of ALGOL dialects: the emulator is for a B5500 and the
hardware doesn't have a "no more cards in hopper" signal.
"The first thing that Dijkstra wanted to see was BEGIN END.
compiled and executed.
"We apologized for the “.” being required since that was not a part of
Algol. The “.” did not bother him at all. He thought it was a good idea."
And that's obviously why we've got it in Pascal as well.
--
Mark Morgan Lloyd
markMLl .AT. telemetry.co .DOT. uk
[Opinions above are the author's, not those of his employers or colleagues]
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