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>>>>> "Roberto" == Roberto Ierusalimschy <> writes:

 >> The problem for me is that if the Lua code does anything that raises
 >> a PostgreSQL error, I have to limit what further calls happen to
 >> other backend functions until some subtransaction level that
 >> encloses the error is properly aborted and released. At present, I
 >> can do that easily because Lua code has no way to catch errors
 >> except for pcall(), and I replace the normal pcall() function with
 >> one that creates a subtransaction, lua_pcall's the specified
 >> function, and releases the subtransaction on either return or error
 >> (and before calling the supplied error handler in the case of
 >> xpcall). This guarantees that the Lua code can not do anything
 >> unsafe in between the generation of the error and its being cleaned
 >> up.

 Roberto> What about Sony's suggestion, of running the sandboxed code
 Roberto> inside a coroutine and using yields to stop the code? (BTW,
 Roberto> that seems a good practice for any sandbox, independently of
 Roberto> this to-be-closed issue.)

I'm not sure that helps. It certainly presents a problem of how to
unwind the C stack safely, especially in the case where Lua code has
called a C function that calls a Lua callback.