Christian Tismer wrote:
rushing@nightmare.com wrote:
[...]
I haven't tested it thoroughly, but I have successfully saved and invoked (and reinvoked) a continuation. Caveat: I have to turn off Py_DECREF in order to keep it from crashing.
It is possible, but a little hard. To take a working snapshot of the current thread's stack, one needs not only the stack snapshot which continue.c provides, but also a restorable copy of all frame objects involved so far. A copy of the current frame chain must be built, with proper reference counting of all involved elements. And this is the crux: The current stack pointer of the VM is not present in the frame objects, but hangs around somewhere on the machine stack. Two solutions: 1) modify PyFrameObject by adding a field which holds the stack pointer, when a function is called. I don't like to change the VM in any way for this. 2) use the lasti field which holds the last VM instruction offset. Then scan the opcodes of the code object and calculate the current stack level. This is possible since Guido's code generator creates code with the stack level lexically bound to the code offset. Now we can incref all the referenced objects in the frame. This must be done for the whole chain, which is copied and relinked during that. This chain is then held as a property of the continuation object. To throw the continuation, the current frame chain must be cleared, and the saved one is inserted, together with the machine stack operation which Sam has already. A little hefty, isn't it? ciao - chris -- Christian Tismer :^) <mailto:tismer@appliedbiometrics.com> Applied Biometrics GmbH : Have a break! Take a ride on Python's Kaiserin-Augusta-Allee 101 : *Starship* http://starship.python.net 10553 Berlin : PGP key -> http://wwwkeys.pgp.net PGP Fingerprint E182 71C7 1A9D 66E9 9D15 D3CC D4D7 93E2 1FAE F6DF we're tired of banana software - shipped green, ripens at home