On Jul 9, 2009, at 9:20 AM, Lie Ryan wrote:
Michael Mossey wrote:
I want to understand better what the "secret" is to responding to a
ctrl-C in any shape or form.
Are you asking: "when would the python interpreter process
KeyboardInterrupt?"
...
In single threaded python program, the currently running thread is
always the main thread (which can handle KeyboardInterrupt). I believe
SIGINT is checked at every ticks. But SIGINT cannot interrupt atomic
operations (i.e. it cannot interrupt long operations that takes a
single
tick).
Some otherwise atomic single-bytecode operations (like large integer
arithmetic) do manual checks for whether signals were raised (though
that won't help at all if the operation isn't on the main thread).
I believe a tick in python is equivalent to a single bytecode, but
please correct me if I'm wrong.
Not all opcodes qualify as a tick. In general, those opcodes that
cause control to remain in the eval loop (and not make calls to other
Python or C functions) don't qualify as ticks (but there are
exceptions, e.g. so that while True: pass is interruptible). In
Python/ceval.c: PyEval_EvalFrameEx(), those opcodes that don't end in
goto fast_next_opcode are ticks.
Please correct me if _I'm_ wrong! :)
-Miles
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