ev_run() pipe_write_wanted improvement idea

[Olivier Langlois]

Hi,

this is the first time that it happens to me that I have a possible way
to improve libev. I thought that it was impossible but I think that I
got a good idea!

In ev_run(), there is this code:

        /* from now on, we want a pipe-wake-up */
        pipe_write_wanted = 1;

        ECB_MEMORY_FENCE; /* make sure pipe_write_wanted is visible
before we check for potential skips */

        if (ecb_expect_true (!(flags & EVRUN_NOWAIT || idleall ||
!activecnt || pipe_write_skipped)))


I think that it could be changed to:

        /* from now on, we want a pipe-wake-up */
        pipe_write_wanted = !(flags & EVRUN_NOWAIT || idleall ||
!activecnt || pipe_write_skipped);

        ECB_MEMORY_FENCE; /* make sure pipe_write_wanted is visible
before we check for potential skips */

        // retest pipe_write_skipped
        if (ecb_expect_true (pipe_write_wanted && !pipe_write_skipped))

in that way, if the backend_poll is going to be invoked without
blocking, the loop will not request to receive async notifications
through the eventfd.

Greetings,