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From: Heiher <r@hev.cc>
To: Davidlohr Bueso <dave@stgolabs.net>
Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: Why the edge-triggered mode doesn't work for epoll file descriptor?
Date: Mon, 19 Aug 2019 08:58:04 +0800	[thread overview]
Message-ID: <CAHirt9jvRPjg=PPJEso-gKhXBto3=MPu_+50D+L=6O35M0BzBw@mail.gmail.com> (raw)
In-Reply-To: <CAHirt9jesMHB_sXx7PyXTxrzLR=3xw9bHERueNMVkWOUkg6XXQ@mail.gmail.com>

On Sun, Aug 18, 2019 at 12:36 AM Heiher <r@hev.cc> wrote:
>
> Hello,
>
> I've added a pipe file descriptor (fd1) to an epoll (fd3) with
> EPOLLOUT in edge-triggered mode, and then added the fd3 to another
> epoll (fd4) with EPOLLIN in edge-triggered too.
>
> Next, waiting for fd4 without timeout. When fd1 to be writable, i
> think epoll_wait(fd4, ...)  only return once, because all file
> descriptors are added in edge-triggered mode.
>
> But, the actual result is returns many and many times until do once
> eopll_wait(fd3, ...).
>
> #include <stdio.h>
> #include <unistd.h>
> #include <sys/epoll.h>
>
> int
> main (int argc, char *argv[])
> {
>     int efd[2];
>     struct epoll_event e;
>
>     efd[0] = epoll_create (1);
>     if (efd[0] < 0)
>         return -1;
>
>     efd[1] = epoll_create (1);
>     if (efd[1] < 0)
>         return -2;
>
>     e.events = EPOLLIN | EPOLLET;
>     e.data.u64 = 1;
>     if (epoll_ctl (efd[0], EPOLL_CTL_ADD, efd[1], &e) < 0)
>         return -3;
>
>     e.events = EPOLLOUT | EPOLLET;
>     e.data.u64 = 2;
>     if (epoll_ctl (efd[1], EPOLL_CTL_ADD, 1, &e) < 0)
>         return -4;
>
>     for (;;) {
>         struct epoll_event events[16];
>         int nfds;
>
>         nfds = epoll_wait (efd[0], events, 16, -1);
>         printf ("nfds: %d\n", nfds);
>     }
>
>     close (efd[1]);
>     close (efd[0]);
>
>     return 0;
> }
>
> --
> Best regards!
> Hev
> https://hev.cc

Is this behavior correct? any help?

-- 
Best regards!
Hev
https://hev.cc

  reply	other threads:[~2019-08-19  0:58 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-17 16:36 Heiher
2019-08-19  0:58 ` Heiher [this message]
2019-08-26  6:22 ` Eric Wong
2019-08-28 15:33   ` Heiher

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