On 20.02.2018 14:30, Raman Shishniou wrote:
> On 02/20/2018 03:11 PM, Georg Chini wrote:
>> On 19.02.2018 16:01, Raman Shyshniou wrote:
>>> Currently the pipe-source will remain running even if no
>>> writer is connected and therefore no data is produced.
>>> This patch adds the autosuspend=<bool> option to prevent this.
>>> Source will stay suspended if no writer is connected.
>>> This option is enabled by default.
>>> ---
>>> src/modules/module-pipe-source.c | 279 ++++++++++++++++++++++++++++++---------
>>> 1 file changed, 215 insertions(+), 64 deletions(-)
>>>
>>> +
>>> for (;;) {
>>> int ret;
>>> - struct pollfd *pollfd;
>>> - pollfd = pa_rtpoll_item_get_pollfd(u->rtpoll_item, NULL);
>>> + if (chunk.length) {
>>> + /* We have a pending data, let's stop polling pipe.
>>> + * Setting up pollfd->events = 0 is not enough to stop
>>> + * POLLHUP spam if all writers are closed pipe.
>>> + * We need to stop polling pipe completely */
>>> + if (rtpoll_item) {
>>> + pa_rtpoll_item_free(rtpoll_item);
>>> + rtpoll_item = NULL;
>>> + }
>>> + } else {
>>> + /* We have no pending data, let's start polling pipe */
>>> + if (rtpoll_item == NULL) {
>>> + rtpoll_item = pa_rtpoll_item_new(u->rtpoll, PA_RTPOLL_NEVER, 1);
>>> + pollfd = pa_rtpoll_item_get_pollfd(rtpoll_item, NULL);
>>> + pollfd->events = POLLIN;
>>> + pollfd->fd = u->fd;
>>> + }
>>> + }
>> Why do you need to do that? As in your previous patches you
>> open the pipe for writing if all writers are disconnected, which
>> should stop POLLHUP's.
> This patch tries to be platform-independent.
> Unfortunately not all platforms set POLLHUP when a writer closed pipe.
Well, all platforms either set POLLIN or POLLHUP. If you have POLLHUP,
you know the pipe was closed. If you have POLLIN and l = 0 on your
read, you also know the pipe was closed.
Then you open your corkfd and stop the POLLHUP/POLLIN.
So why do you have to stop polling completely? When the next
POLLIN comes, you know that data has been written and POLLHUP
can no longer happen.
> Moreover, when POLLHUP was set there may be data in pipe that must be read
> before suspend. Linux sets POLLIN in that case. Freebsd and macos sets
> POLLIN|POLLHUP even if no any data in pipe, but no writers left. Some platforms
> do not set POLLHUP at all. So do read() and check it return 0 must be the only
> condition to suspend source and open pipe for writing.
Yes, I agree, see above, but I still don't understand why you stop polling.
>
> Also it cover cases when source suspended by user - we read data from pipe,
> send resume, but source stays suspended. We must stop polling pipe, but
> pollfd->events = 0 is not enough. If the writer make a open-write-close
> while source stays suspended we will get endless POLLHUPs
I think this could be covered differently. You can set a flag "is_suspended"
when you have suspended the source because the writer disconnected.
Then you can do something like
if (SOURCE_IS_OPENED(source) || is_suspended) {
   if (!is_suspended && u->corkfd >= 0)
      close pipe for writing
...
} else if (u->corkfd < 0)
   open pipe for writing
