Multicast on Android doesn't want to work when the screen is off

Question

I'm trying to develop a Multicast application for Android. It works however, when the screen is turned off, it doesn't. I know it's not my device as Winamp works fine when the screen is off. I'm running this as a service.

AndroidManifest.xml defenition for the service:

<service android:exported="true" android:name="AndroidRocketService"></service>

Java code for the service: http://tinypaste.com/c569a/fullscreen.php?hash=e7495a255a33a99ea8cc48bf24ea2b01&toolbar=true&linenum=true

(The application will be open source when it works, so I'm not bothered about posting the whole thing non-working)

Thanks in advance,

Joe

Aleadam · Answer 1 · 2011-05-09T18:06:34.973

3

The obvious ones:

Make sure you set the permissions in the manifest:

<uses-permission android:name="android.permission.WAKE_LOCK" /> <uses-permission android:name="android.permission.CHANGE_WIFI_MULTICAST_STATE" />

and that the phone did not go to sleep before the wake.acquire() line is executed (use boolean bool = wake.isHeld(); to check it).

edited May 09 '11 at 18:06

answered May 07 '11 at 20:52

Aleadam

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Okay, So I moved the setDeamon and the app just FC's and reading your quote shows why. This can only be done *before* the thread starts! – Joe Simpson May 08 '11 at 11:50
Oh, my. I need to take a break. – Aleadam May 08 '11 at 13:54
Yeah, It's still not working. Thanks for you help, I might just cheat and use Bluetooth :) – Joe Simpson May 09 '11 at 17:46
@Joe I'm re-reading the title: you say the screen is off but you have a SCREEN_DIM_WAKE_LOCK held? – Aleadam May 09 '11 at 18:04
@Joe take a look at this question also: http://stackoverflow.com/questions/3998214/android-multicast-socket-stops-listening . Perhaps you need a wifi lock also? – Aleadam May 09 '11 at 21:39
I am having a Wake Lock + Wifi Lock and it's not working. Could this be a bug with the software as I can press the power button on my device and it sleeps? – Joe Simpson May 10 '11 at 20:58
@Joe did you try another device? – Aleadam May 10 '11 at 21:42
Unfortunately I don't have access to another device – Joe Simpson May 11 '11 at 20:17
@Joe Zip up the project and post the link here. I'll give it a try – Aleadam May 14 '11 at 16:34
It's quite complex as it's python on both sides. Also, I seem to have broken it completely now somehow :/ – Joe Simpson May 14 '11 at 19:12

score 3 · Answer 2 · edited May 23 '17 at 12:12

Aleadam's answer is correct. You also need to make sure that you acquire the multicast locks as mentioned in the comments and at:

Android Multicast socket stops listening << Look at Erich's answer (not the accepted one)

The much larger problem is that, prior to Gingerbread, Android did not follow the proper standards with its multicast algorithms, as noted in several (angry) exchanges with Google developers here. There's also another bug on their forums where pre Gingbread phones didn't due the multicast join properly -- but I can't find that one right now.

The bottom line is that pre Gingbread phones set the TTL of the multicast packets to 1. So, if anything along the way decrements the TTL (usually some intermediate router) your packet will "die on the vine."

Google posted a fix for the TTL bug in the post I linked, but to implement the fix you have to build your own custom kernel and deploy it to the phone.

It's also worth noting, that several very popular phones don't do multicasting properly. One that comes to mind is the HTC Incredible, which can send but cannot receive. If you use a 3rd party firmware (ie. Cyanogen), then multicasting works fine.

Off the top of my head - here's a few that I know work / don't work

HTC Incredibe (Can't receive)
Nexus One (OK)
Nexus S (OK)
Motorola Droid / Droid Pro (OK)

I am using Cyanogen and that's Gingerbread, however it still doesn't work — Joe Simpson, May 14 '11 at 19:12

Multicast on Android doesn't want to work when the screen is off

2 Answers2