[pulseaudio-discuss] [PATCH v7] pipe-source: implement autosuspend option
Raman Shishniou
rommer at ibuffed.com
Tue Feb 20 16:08:18 UTC 2018
On 02/20/2018 06:44 PM, Georg Chini wrote:
> On 20.02.2018 16:28, Raman Shishniou wrote:
>>
>> On 02/20/2018 06:22 PM, Georg Chini wrote:
>>> On 20.02.2018 16:13, Georg Chini wrote:
>>>> On 20.02.2018 15:47, Raman Shishniou wrote:
>>>>> 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:
>>>> Why would you get POLLHUP spam here with the code I proposed above?
>>>> Because the source is suspended by user but not suspended by you,
>>>> the code would open the pipe for writing (and close it again as soon
>>>> as the user suspend cause is removed). And on the first iteration, you
>>>> can discard the data immediately when the source is not opened.
>>> The way you are doing it now, the source will in fact keep running, even if it is
>>> suspended by the user. One mistake above - you cannot immediately discard
>>> the data because at that time you do not know if the source is user suspended
>>> so you would have to discard any remaining data at some other point like that:
>>>
>>> if (SOURCE_IS_OPENED(source) || is_suspended) {
>>> if (!is_suspended && u->corkfd >= 0) {
>>> close pipe for writing
>>> discard remaining data
>>> }
>>>
>>> do all your other processing
>>>
>>> } else if (u->corkfd < 0)
>>> open pipe for writing
>>>
>> The whole loop can be much easier if I can just discard user data :)
>> But why I need to discard any data? I can just wait for source to be
>> resumed temporary removing pipe from polling. The source will not keep
>> running. It will just wait until it will be resumed.
>>
>> This is exactly what the original pipe-source is doing.
>>
> Not executing all that unnecessary code would be better. I never said that
> the old code did the right thing.
> Regarding discarding the data: If data was read while the source was suspended
> by the user, it needs to be discarded on resume, because the the source is not
> expected to have some old data.
>
I can just set pollfd->fd = -1 when no polling is needed instead of freeing
the whole rtpoll_item. But I'm not sure if it's supported by any platform
except of linux.
I think the old code is doing the right thing. If the source is suspended
by user, it was done for a reason. And we don't know if the writer tries to
prefill the pipe and than resume the source to avoid underruns or user just
stopped the annoying sound. Anyway I think we shouldn't take into account
the suspend cause. Even if it automatically suspended.
--
Raman
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