Re: Time constraint in Lua pattern functions

["Soni L." <fakedme@...>]

On 30/03/16 08:11 AM, Viacheslav Usov wrote:
> On Mon, Mar 14, 2016 at 9:54 PM, Sean Conner <sean@conman.org 
> <mailto:sean@conman.org>> wrote:
>
> > If the code was purely Lua, then time_restricted_pcall() would be 
> easily written.  However, if any calls to C are made, then it gets 
> complicated and requires system specific code to handle.
>
> That is hardly different from a native application being blocked on a 
> kernel call, and we all know that being able to break user-mode 
> execution is still very useful for debugging. By the same token, it 
> would be very useful to be able to break just the Lua VM when it is 
> not running any native code.
>
> We have debug hooks, which almost do the right thing with the "break 
> on N instructions" feature, but they need to be set in advance, and 
> choosing the N is not straightforward because it implies a performance 
> vs responsiveness trade-off. It would be nice to have something like 
> lua_break() that can be called on a Lua environment (which may be 
> running some Lua code in another native thread), which would 
> essentially call a user-supplied function before the next VM 
> instruction gets executed, or at some other convenient VM execution 
> milestone not very distant in future, in the original native thread.
>
> Speaking of blocking native code, I do not think a fully generic 
> portable solution is possible. Library writers, however, know (in 
> principle) when their native code can possibly take a while (or block 
> on a kernel call), and could then make that interruptible and/or 
> cancellable. Then all it takes is a way to communicate to Lua that a 
> given native function is interruptible/cancellable, and some 
> convention to request interruption/cancellation.
>
> Cheers,
> V.
Allowing native code to trigger debug hooks and stuff would be nice.

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