It just occurred to me that our map from numeric file descriptors to
open channels doesn't need to be weak, and indeed making it weak could
actualy be *incorrect*.
In libc, if you open a file, you get a file descriptor as an integer.
That descriptor is guaranteed to be kept open for you until the process
terminates or you close the fd yourself. So our allowing the channel
associated with a numeric fd to possibly GC and finalize breaks that model.
Also, the case we're trying to prevent with a weak descriptor map--that
of an application spinning up lots of IO objects and never closing
them--would be a leak under libc as well; you'd quickly reach an open fd
limit before garbage collection kicks in.
It seems like what we really want here is for the ChannelDescriptor
associated with the fd to only unregister itself on GC or close, and
have the map be hard references. This allows e.g. sysopen to work
correctly all the time (rather than having a separate hard-referencing
map as we do now) and probably wouldn't lead to any more descriptor
leakage than we have today, since the expectation is that all channels
are being properly closed to begin with. And the finalization of
ChannelDescriptor would help ensure the map gets cleaned up if an
application really is leaking descriptors.
Does this make sense?
- Charlie
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