input: avoid using wakeup pipe if it's not needed

If input is not waiting for select(), writing to the wakeup pipe is
wasteful, and, if there are many wakeups, might even block the wakeup
threads if the pipe gets full.

However, if it's waiting for select(), the wakup pipe must be used to
unblock the waiting thread. Actually there's a small race condition: we
might determine that the main thread is in select(), and write to the
wakeup pipe (whether we do this while unlocked or locked doesn't really
matter). Then, the main thread might leave select() before reading from
the wakup pipe. This should be harmless, because at worst more wakeups
than needed happen, but never fewer.

0 files changed, 0 insertions, 0 deletions