On 02/20/2018 04:55 PM, Georg Chini wrote:
> 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.
>
If I open pipe for writing before all data was read, i.e. when I see
POLLHUP - read() will never return 0. Also send suspend message when
I see POLLHUP is too early. I should open pipe for writing and send
suspend message when read() return 0.
>
>> 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
>
>
I need to stop polling to wait for source to be resumed if some bytes was
read and cannot be posted.
I can get POLLHUP spam if source is suspended, some data is waiting for source
to be resumed and writer closed pipe.
Example: source suspended by user and by autosuspend, pipe is waiting
for event (POLLIN), someone opened a pipe and send us data:
First iteration:
1. poll:
events = POLLIN
pa_rtpoll_run()
revents == POLLIN
2. read:
read() return 100 bytes
send message to resume source
3. post:
source suspended, keep data in memchunk.
Second iteration, 100 bytes waiting for source to be resumed:
1. poll:
events = 0
pa_rtpoll_run() (processed resume message, but source stays suspended)
revents == 0
2. read:
some data still pending, do nothing
3. post:
source still suspended, keep pending data
***writer closed pipe***
Third iteration, POLLHUP spam, 100 bytes still waiting for source to be resumed:
1. poll:
events = 0
pa_rtpoll_run()
revents == POLLHUP
2. read:
some data still pending, do nothing
3. post:
source still suspended, keep pending data
--
Raman
