[Jython-dev] Resource release in PySystemState.cleanup()

[Jeff A. <ja...@fa...>]

I've adapted the Closer object Philip provided in _io.fileio to apply to 
I/O objects in general. As before, it engages the general mechanism 
register/unregisterCloser() in PySystemState. The container that holds 
the closers, although it is a set, guarantees iteration in the order 
objects were added.

My thought in extending use of Closer is that simply closing the file 
(at the handle level) on exit is not all you want: you'd like any data 
in a BufferedWriter to be flushed as well. And first. There's a couple 
of things wrong with what I'm doing at the moment, that I think would be 
solved by: 1. invoking the closers in reverse order of their addition; 
and 2. either working from a copy or disabling removal once we start 
iterating the list.

The reverse order is what guarantees (in most circumstances) flushing 
the buffers before force-closing the file into which they should go. And 
the copy would fix the concurrent modification error that occurs when 
the downstream file tries to remove itself during flush-and-close 
propagation.

Does anyone see a problem with messing with the order in this way?

There can be multiple PySystemState objects. Should I think of these as 
distinct interpreters, or is there some chance a Python object from one 
of them would be in use in another at the time clean up occurs? Do 
PySystemState objects always hang around until JVM exit or might they 
clean up sooner?

Jeff