misc channels

[timotheecour]

/cc @xflywind

links

• [std/channels]fix recv leaks(Part One) nim-lang/Nim#17394

[timotheecour]

• add func recv*[T](c: Channel[T]): T {.inline.} = overload to system/channels_builtin

so that it's easy to migrate back and forth bw std/channels and system/channels_builtin

let dest = chan.recv()

[timotheecour]

• add channels.clear (or channels.flush) to flush (and destroy) all messages in flight not yet received

functionally equivalent to:

block:
  var dst: T
  while true:
    if not tryRecv(chan, dst): break

or (maybe less efficient?)

while true:
  var dst: T
  if not tryRecv(chan, dst): break

(need to ensure it's as efficient as possible and doesn't leak, ie destructors for isolate data should be called on each received item)

[timotheecour]

• we need an overload for recv with a timeout (tryRecv is not a substitute for that)

[timotheecour]

• use a std/deques based implementation (with a capacityMax) instead of the wasteful BoundedQueue design, as explained in New channels implementation for ORC nim-lang/Nim#17305 (comment)