"Takashima, Makoto" <[EMAIL PROTECTED]> writes:
> Hi,
>
> I found a problem with non-blocking write to pipe.
>
> Current code (2.0.43) is as following.
>
> ------------------------------------------------------------
> httpd-2.0.43/srclib/apr/file_io/unix/readwrite.c:apr_file_write()
FYI... this discussion belongs on [EMAIL PROTECTED] the
srclib/apr tree in the httpd-2.0 directory are a copy of the APR
project code...
> It seems assuming write request never fail when
> apr_wait_for_io_or_timeout() succeeded, but it is not true
> for pipe.
...
> - A write request for {PIPE_BUF} or fewer bytes will have
> the following effect: If there is sufficient space
> available in the pipe, write() will transfer all the
> data and return the number of bytes requested. Otherwise,
> write() will transfer no data and return -1 with errno
> set to [EAGAIN].
...
boy, this sucks :) no syscall to block until timeout occurs or we can
write the whole message...
note that most existing users of APR pipes don't care about atomic
writes... I wonder if it is appropriate to have a pipe setting that
says that atomic is important... if really important, I guess we'd
have to sleep before retry... otherwise maybe we should try to write
a smaller amount to the pipe... it would be a shame to waste our
timeslice, which could cause the reader to have to block too once the
other side is empty...
> I found this problem on HP-UX11.0 whose PIPE_BUF is 8192 with
> CGI that receive more than 8kbytes POST request.
>
> This problem can be fixed with the following code, however I
> do not know if there is better solution other than looping.
>
> ------------------------------------------------------------
> do {
> rv = write(thefile->filedes, buf, *nbytes);
> } while (rv == (apr_size_t)-1 && errno == EINTR);
> #ifdef USE_WAIT_FOR_IO
> if (rv == (apr_size_t)-1 &&
> (errno == EAGAIN || errno == EWOULDBLOCK) &&
> thefile->timeout != 0) {
> apr_status_t arv = apr_wait_for_io_or_timeout(thefile, NULL, 0);
> if (arv != APR_SUCCESS) {
> *nbytes = 0;
> return arv;
> }
> else {
> do {
> rv = write(thefile->filedes, buf, *nbytes);
>
> /* write request of {PIPE_BUF} bytes or less may fail */
> /* because it is atomic when writing to pipe or FIFO */
> while (rv == (apr_size_t)-1 &&
> *nbytes < PIPE_BUF && errno == EAGAIN)
> {
> apr_sleep(10000); /* sleep ~10ms */
> rv = write(thefile->filedes, buf, *nbytes);
> }
> } while (rv == (apr_size_t)-1 && errno == EINTR);
> }
> }
> #endif
> ------------------------------------------------------------
>
>
> --
> [EMAIL PROTECTED]
>
--
Jeff Trawick | [EMAIL PROTECTED]
Born in Roswell... married an alien...
