On Mon, Sep 21, 2015 at 6:39 PM, Stefan Beller <sbeller@xxxxxxxxxx> wrote:
> From the man page:
> [...]
> So if we get an EAGAIN or EWOULDBLOCK error the fd must be nonblocking.
s/So/&,/
s/error/&,/
> As the intend of xread is to read as much as possible either until the
s/intend/intent/
> fd is EOF or an actual error occurs, we can ease the feeder of the fd
> by not spinning the whole time, but rather wait for it politely by not
> busy waiting.
>
> Signed-off-by: Stefan Beller <sbeller@xxxxxxxxxx>
> ---
> --- a/wrapper.c
> +++ b/wrapper.c
> @@ -201,8 +201,23 @@ ssize_t xread(int fd, void *buf, size_t len)
> len = MAX_IO_SIZE;
> while (1) {
> nr = read(fd, buf, len);
> - if ((nr < 0) && (errno == EAGAIN || errno == EINTR))
> - continue;
> + if (nr < 0) {
> + if (errno == EINTR)
> + continue;
> + if (errno == EAGAIN || errno == EWOULDBLOCK) {
> + struct pollfd pfd;
> + int i;
> + pfd.events = POLLIN;
> + pfd.fd = fd;
> + i = poll(&pfd, 1, 100);
Why is this poll() using a timeout? Isn't that still a busy wait of
sorts (even if less aggressive)?
> + if (i < 0) {
> + if (errno == EINTR || errno == ENOMEM)
> + continue;
> + else
> + die_errno("poll");
> + }
> + }
> + }
> return nr;
> }
> }
> --
> 2.5.0.275.ge015d2a
--
To unsubscribe from this list: send the line "unsubscribe git" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html