[Python-bugs-list] PRIVATE: Threads and readline (PR#120)

[jack@oratrix.nl]

> As another bizarre data point: when I run a threaded python interpreter
> on a program which does not use threads, and pipe the output to less,
> less gets very confused and fails to update about half the screen,
> leaving it blank.  This happens after hitting SPACE a couple of times. 
> All the data is there, and if I jump less to the end of input and then
> go back through the the data, I can see it all normally. Same program
> and unthreaded python and less works just fine.  If you have ANY idea
> why adding thread support could affect a program further down a pipe I'd
> love to know.

As I like puzzles I spent some time thinking on this, and it must be
either (a) kernel bug, (b) a very strange stdio bug or (c) an incorrect 
observation. If your system supports memory-mapped I/O and stdio uses
it and it can somehow signal that a whole buffer is available while it 
isn't but only the tail end is available (because it uses an
overlapping memcopy which goes back-to-front, for instance) the reader 
in the pipe might wakeup too early and see null bytes. But if this was 
a bet I think I'd put my money on (c) (but absolutely no offense meant!).
--
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