This is more intuitive and avoids the possibilty of strange code
to resume or cancel a fiber after it was scheduled but before it was
entered for the first time.
The main issue was cancellation of fiber using `cancel` rather than
`ev/cancel` could cause issues with the event loop internal ref count.
Since this is almost certainly bad usage (and is not something I want to
encourage or support), we will warn against trying to resume or error
fibers that have already been suspended or scheduled on the event loop.
The distinction between "task" fibers and normal fibers is now kept by a
flag that is set when a fiber is resumed - if it is the outermost fiber
on the stack, it is considered a root fiber. All fibers scheduled with
ev/go or by the event loop are root fibers, and thus cannot be cancelled
or resumed with `cancel` or `resume` - instead, use `ev/cancel` or
`ev/go`.
janet_loop1_interrupt makes the event loop compatible
with safe interruptions for custom scheduling. Does this by exposing
custom events on the event loop. A custom event schedules a function pointer
to run in a way that can interrupt
epoll_wait/poll/GetQueuedCompletionStatus.
This would allow an embedder to suspend the current Janet fiber
via an external event like a signal, other thread, or really anything.
This is a useful primitive for custom schedulers that would call
janet_interpreter_interupt periodically (say, in an interval with SIG_ALRM),
do some work, and then use janet_continue on the janet_root_fiber, or
for embedding into other soft-realtime applications like a game. To say,
only allow about 5ms per frame of interpreter time.
This fixes a regression from changes to janet_try. In some cases, we
would not update the status of a fiber when signaling, which left the
fiber's status as whatever it had previously. This could lead to strange
control flow issues.
Rather than trying to be clever with pinning/unpinning, always
mark the root fiber and that should serve as thei singular common root in almost
all cases.
Do not restore pc when returning from top most fiber frame.
Also add JANET_DEBUG config define for various debugging related
configurations. In fiber.c, when debug is enabled we reallocate the
entire stack everytime we push a frame to help uncover use after free
errors.
Before, these bindings we just ignored. However, it useful for
controlling janet_printf and janet_eprintf, for example. These can
be called from C code without being inside a call to janet_continue.
This makes these operatios use constant stack space rather
than linear stackspace given the size of the inputs. This is important
to prevent certain parser input from causing a stack overflow - in
general, we try to avoid unbounded recursion.
