Bugs when cancelling a waiting fiber about janet HOT 5 CLOSED

@czkz Check now for examples 1 and 3. Example 2 I think should still have some strange behavior, but that is because the construction is strange. I have not yet decided on why the correct behavior here should be - my current thought is that "edefer end" and "main end" should not print, but everything else should.

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The issue here seems to be with the os_shell function, and the fact that is implemented to run on a another thread, and then schedule the original fiber when it completes.

The second instance is a bit more complex, as the initial deadline cancellation triggers the second piece of code to run, which should also immediately expire the deadline.

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Hard to tell from just the valgrind output, but I think the invalid read is from calling strlen on a symbol created by (gensym). Most function internal to Janet don't require a trailing 0 byte for strings, but all created strings should have such a byte just in case.

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The issue here seems to be with the os_shell function

Note: replacing os/shell with os/spawn resulted in the same behavior (but both are now fixed).

Check now for examples 1 and 3.

Example 1 is fixed for both os/shell and os/spawn.
Example 3 now produces less errors :)

the invalid read is from calling strlen on a symbol created by (gensym)

Indeed!
This example triggers the valgrind error (even on the new version):

(ev/cancel
  (ev/spawn (ev/sleep 1e9))
  (gensym))

It also spits random garbage in the error, e.g.

error: _00000r0Mw\
                  A
  in _spawn [tst2.janet] on line 2, column 13

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I have not yet decided on why the correct behavior here should be - my current thought is that "edefer end" and "main end" should not print, but everything else should.

It could work as if edefer body was offloaded to a new fiber.
Not necessarily one-to-one, but something similar to this:

(ev/spawn
  (ev/deadline 0.1)
  (edefer
    (ev/spawn # the only line different from example 2
      (print "edefer start")
      (os/shell "sleep 10 && echo sh_edefer")
      (print "edefer end"))
    (print "main start")
    (os/shell "sleep 5 && echo sh_main")
    (print "main end")))

output:

main start
error: deadline expired
edefer start
sh_main
sh_edefer
edefer end

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