You don't mix epoll with io_submit; they are two completely different
methods for doing IO. The former is for use with bsd style non blocking
IO, and the latter is truly async io. epoll will signal you whenever a
file can be read ( the read ahead buffer is non empty ) or written (
there's memory available to buffer writes ). io_getevents() won't
notify you of anything until you actually request a read or write, in
which case, it lets you know when that has completed.
The two systems are completely non interchangeable. With the former you
wait first, then request some IO, which completes immediately. With the
latter, you request some IO ( possibly many ), then wait for some to
finish.
Li, Peng wrote:
I apologize if I should not post this on LKML, but there seems to be
some lack of documentation for using epoll/AIO with threads. Are
these interfaces thread-safe? Can I use them safely in the following
way:
Thread A: while(1) { io_getevents(); ... }
// wait forever until an event occurs, then handles the event and loop
Thread B: while(1) { epoll_wait(); ... }
// same as thread A
Thread C: ... io_submit(); ...
Thread D: ... epoll_ctl(); ....
Suppose thread B calls epoll_wait and blocks before thread D calls
epoll_ctl. Is it safe to do so? Will thread B be notified for the
event submitted by thread D? Thread A and C pose the same question
for AIO.
I wrote a simple program to test these interfaces and they seem to
work without problems, but I am not sure if it is really safe to do so
in general. If all of them works, it seems easy to use epoll and AIO
together as I can simply use another thread to harvest events from
thread A and B and make it look like a unified event notification
interface.
Peng
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