[D-runtime] A mechanism to kill threads

[Jonathan M Davis]

On Wednesday, May 16, 2012 17:19:02 David Simcha wrote:
> For the sake of argument, what are the most non-obvious reasons why killing
> threads is bad? The ones I can think of are because the thread may be in
> the middle of doing something important and bad things will happen if it's
> interrupted and because the thread might hold resources that will never get
> freed if it's killed before it gets to free them.
> 
> I was thinking at one point that I wanted a kill() primitive when I was
> designing std.parallelism, but I don't remember why I wanted it and
> obviously I've managed to do without it. Is it ok to kill threads if
> they're not doing useful work at the time and they're not holding onto any
> resources that will never get freed if you kill them?

It's the same reason that you don't want to continue executing after an 
assertion fails. Your program is by definition in an undefined state. In this 
case, it would be a single thread which was then in an undefined state. If it 
were sufficiently isolated (e.g. doesn't use shared _at all_), it _might_ mean 
that the rest of the program is okay, but there's no question that anything 
relating to that thread is then in an undefined state, and odds are that that 
means that the rest of the program is also in an undefined state, though the 
impact is likely to be much less if the thread was well isolated. If you were 
using shared much though, there's not really any question that your whole 
program is then in an undefined state, and who knows what could happen if you 
tried to continue. And even without using shared much, the threading stuff is 
still built on top of C primitives which _are_ shared (well, __gshared), so by 
definition, there's at least _some_ portion of the rest of your program which 
is in an undefined state.

- Jonathan M Davis