Re: pgbnech: allow to cancel queries during benchmark

Hello Yugo-san,

>>> In thread #0, setup_cancel_handler is called before the loop, the
>>> CancelRequested flag is set when Ctrl+C is issued. In the loop, cancel
>>> requests are sent when the flag is set only in thread #0. SIGINT is
>>> blocked in other threads, but the threads will exit after their query
>>> are cancelled. If thread safety is disabled or OS is Windows, the signal
>>> is not blocked because pthread_sigmask cannot be used.
>>> (I didn't test the patch on WIndows yet, though.)
>>>
>>> I choose the design that the signal handler and the query cancel are
>>> performed only in thread #0 because I wanted to make the behavior as
>>> predicable as possible. However, another design that all thread can
>>> received SIGINT and that the first thread that catches the signal is
>>> responsible to sent cancel requests for all connections may also work.
>>>
>>> Also, the array of CState that contains all clients state is changed to
>>> a global variable so that all connections can be accessed within a thread.

> As a side note, actually I thought another design to create a special thread
> for handling query cancelling in which SIGINT would be catched by sigwait,
> I quit the idea because it would add complexity due to code for Windows and
> --disabled-thread-safe.

I agree that the simpler the better.

> I would appreciate it if you could kindly review and test the patch!

I'll try to have a look at it.

--
Fabien.