RE: What's the difference between a "coroutine" and a "thread" in Lua?

["Jerome Vuarand" <jerome.vuarand@...>]

Gregg Reynolds wrote:
> If it were clear, questions like "what's the difference between
> threads and coroutines" would never arise.  The text may work for
> you, but it's utterly misleading for me.  First, I can only know that
> Lua uses an idiosyntractic meaning for "thread" if I happen to have
> read and understood the other relevant sections of the manual.  Even
> worse, the second sentence of 2.11 states:  "A coroutine in Lua
> represents an independent thread of execution. "  Some may consider
> that clear, but it's clear as mud to me, because "independent thread"
> strongly implies to me that we're talking about multithreading
> (whether implemented in         
> kernel or user space).   (Even worse worse, look at the definition of
> the type thread, which could not possibly be more obscure.)  In my
> view Lua coroutines are by definition _not_ independent, since they
> must cooperate.  It would be more accurate if not more clear to a)
> remove all reference to threads, and b) call them distinct,
> sequestered,  or the like, but not "independent".  Why not just use a
> standard definition of coroutine?  E.g.  a coroutine is a subroutine
> that supports suspend/resume operations and multiple entry points. 
> It has nothing to do with threads, unless you're willing to say that
> every routine (function) is a thread.  You could stipulate that every
> jump represents a jump to a different "thread" but that seems kind of
> pointless.          

I think you are confusing multithreading and preemptive multithreading.
Cooperative multithreading is a kind of multithreading. Any chunk of
code (function, subroutine, procedure, whatever...) that can be
interrupted, be it preemptively by the kernel or cooperatively by the
chunk itself, and later resumed is an independant thread (you doesn't
need anything but the thread itself to resume it).