[PD] netreceive vs mrpeach/udpreceive in batch mode

[Christof Ressi]

Hi,

> Messages can
> be sent to a subprocess from a parent--but I had to start using
> udpsend to send messages back.
You can send messages from the subprocess to the parent process with 
[stdout], check the help file of [pd~].

> I'm looking at long-duration signals analysis on command from a
> real-time process, and I'd like that analysis to run with minimal
> disruption to the real-time process.
Note that the subprocess is slaved to the parent process, so if the 
subprocess blocks, the parent also blocks. You can absorb occasional CPU 
spikes by setting "-fifo" to a high value, but you can never make it 
100% non-blocking.

Now that you've described your setup, I think you should rather run a 
seperate instance of Pd (probably with the "-nrt" flag) and communicate 
with [netsend]/[netreceive] as you're already doing. Currently, there's 
no Vanilla way to start external processes (yet), but you can either 
find an external (there are some, but I keep forgetting the name) or 
start both instances together with a simple shell script.

Finally, you can simplify the communication by using TCP, because with 
[netreceive] - without "-u" - you just have to listen for an incoming 
message and then you can send a reply with the [send( method - no need 
to open another socket!

Christof

On 28.01.2020 06:22, Charles Z Henry wrote:
> Thanks for your replies, Christof
>
> On Mon, Jan 27, 2020 at 4:40 AM Christof Ressi <christof.ressi at gmx.at> wrote:
>> Hi,
>>
>>> I'm guessing that mrpeach/udpreceive and netreceive have different
>>> polling behavior that can explain this, but I don't see it yet.  Is
>>> there anyone reading, who's dealt with this issue before?
>> They actually use the same polling mechanism. I tried to receive OSC messages with [mrpeach/udpreceive] while running it batch mode and it doesn't work, just like I expected. Are saying this works for you? I would be quite surprised...
>>
>> As the ticket on sourceforge mentions, there's no explicit call to sys_pollgui() in batch mode *) - which by the way is a misnomer because it polls *all* sockets -, so I don't see how [mrpeach/udpreceive] could work under such circumstances.
> I think I was unclear--as I'm editing the test patch to compare
> udpsend/netsend, the key difference I'm finding is how the process
> gets started from pd~
> and it looks like I was wrong about this being true batch mode.
> When pd~ starts up a new subprocess with "-batch", it suppresses the
> GUI as expected, but it also starts the new process with "-schedlib"
> which substitutes for the subprocess scheduler behavior.
>
>>> I have been writing a patch to send messages to/from a subprocess in
>>> batch mode.  First, I wrote the patch with mrpeach's
>>> udpsend/udpreceive and got it working.  It's just a simple handshake:
>> I think the real problem is that you're using batch mode for the wrong job. In batch mode, Pd will run as fast as possible to get a certain task done. If you wait for incoming network traffic while in batch mode, you're just busy waiting and wasting lots of CPU cycles. Just use Pd in realtime mode instead!
>>
>> Or is there a specific reason why you think you need to receive messages while running in batch mode?
> I'm looking at long-duration signals analysis on command from a
> real-time process, and I'd like that analysis to run with minimal
> disruption to the real-time process.
> At first, I was just buffering signals in, but decided to try using
> shmem to copy tables back/forth.  That requires some coordination
> between the processes to know when to read from shmem.  Messages can
> be sent to a subprocess from a parent--but I had to start using
> udpsend to send messages back.
>
> That's why it occurred to me to start trying batch mode and see if I
> could use udpsend or netsend as out-of-band communication to control
> it.  It wouldn't have to start/stop an entire process or access the
> disk at all.  It could all stay in memory waiting to run the long
> analysis until the parent asks it to.
>
>>> Here the cpu load goes to 100%
>> This is totally expected, as you want to run your task as fast as possible.
>>
>> Christof
>>
>> *) to be correct, there is a hidden call to sys_pollgui() if there are more than 5000 clock timeouts in a given scheduler tick (see sched_tick())
> Thank you, I'll read through more of the sched_tick() and
> sys_pollgui() code next.
>
>
>>> Gesendet: Montag, 27. Januar 2020 um 02:20 Uhr
>>> Von: "Charles Z Henry" <czhenry at gmail.com>
>>> An: Pd-List <pd-list at lists.iem.at>
>>> Betreff: [PD] netreceive vs mrpeach/udpreceive in batch mode
>>>
>>> Hi list,
>>>
>>> I have been writing a patch to send messages to/from a subprocess in
>>> batch mode.  First, I wrote the patch with mrpeach's
>>> udpsend/udpreceive and got it working.  It's just a simple handshake:
>>>
>>> the toplevel process starts listening on port 16000 for a message [1
>>> 1(.  When it receives that message, it sends back a message [1
>>> subprocess#( to localhost port 15999.
>>>
>>> The subprocess starts up, listens on port 15999 and sends a message [1
>>> 1( to localhost port 16000.  When it gets a message [1 n( on port
>>> 15999, it outputs n as the subprocess #, and opens a new port 16000+n
>>> (and closes 15999).
>>>
>>> This was fine, except udpsend/receive pairs exchange binary numbers
>>> (0-255).  It will work, but it doesn't make the patches as easily
>>> readable.  It will still be possible to pass integers larger than 255
>>> with a little patching, but some flexibility would be nice.
>>>
>>> I thought "netsend -u"/"netreceive -u" would make a good replacement
>>> with text instead.
>>>
>>> It runs fine during the first part of testing with the GUI.  I test
>>> "-nogui".  Also fine.  Then, "-batch" added.  Here the cpu load goes
>>> to 100% (which didn't happen with mrpeach udpsend/receive).  I'm able
>>> to strace and see the first message [1 1( sent.  Then, the process
>>> keeps on going but doesn't receive any further UDP messages.
>>>
>>> I'm able to find a sourceforge ticket from 2012:
>>> https://sourceforge.net/p/pure-data/bugs/943/
>>> and basically, I'm looking for the same usage case which is batch mode
>>> processing under supervision from another Pd process.
>>>
>>> I'm guessing that mrpeach/udpreceive and netreceive have different
>>> polling behavior that can explain this, but I don't see it yet.  Is
>>> there anyone reading, who's dealt with this issue before?
>>>
>>> Chuck
>>>
>>>
>>>
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