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I've built a functioning C2DM app and generally it works very well, and the push messages arrive fast. However I find that fairly regularly when I first start the app or bring it back to focus, messages do not arrive.

They are definitely sent successfully (I get a 200 response) and the message format is certainly right (sending the same message later works fine). The failure can last for a small number of minutes, and then suddenly it starts working again, and works consistently thereafter.

However even after it starts working, the older messages have apparently disappeared and never arrive. The messages are definitely not arriving - I have extensive logging that highlights any C2DM messages that arrive.

I'm fully aware that C2DM will never guarantee delivery, so I expect some messages will fail, but in my experience, on some occasions, it just doesn't work. I obviously want to understand if that is something I am doing wrong in my app, or the C2DM service itself.

What could cause C2DM to fail to deliver messages? If messages cannot be delivered, why is the C2DM server not trying again from its queue? Related - should I get a new Registration ID only when the app starts the first time, or refresh it each time the app starts? I currently do the latter (in the Application, not an Activity).

Ollie C
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  • I have exactly the same problem with my app. I am frequently asked by my users why this happens... So I am really interested in the answer. Perhaps someone of the Google C2DM team can answer this question. Maybe you should ask at the official mailinglist - and if you get an answer post it here ;) – Mark Aug 30 '11 at 20:33

2 Answers2

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I realised I made a schoolboy error. I was re-registering with C2DM every time the app started. That process sometimes takes quite a few seconds, and during that time the app will not receive push messages sent to the old registration ID. This explains why push messages were particularly likely to fail to be received immediately after starting the app.

The solution was to ensure the registration ID is only requested if the app does not already have one. Push messages are now working much more reliably.

Ollie C
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  • I hadn't noticed this problem myself (yet), but reading through your answer realized I had made the same schoolboy error. So this was helpful :-) – Pēteris Caune Oct 31 '11 at 15:15
  • I did the same error. But now my question is... i executed registration at startup for seeing if reg_ID was changed. If i don't make this check, how can i know when reg_id is different? Sometime i have to make a check, what do you think about? – kinghomer Feb 27 '12 at 16:13
  • @kinghomer - start a new question to get help with your issue – Ollie C Feb 28 '12 at 10:03
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This is most likely the correct behaviour. Messages are not guarantied to be delivered at all. Let alone instantly.

What it most likely is is that the connection between your phone and the Google servers is being dropped and it takes a little while to come back up.

matto1990
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    I'm not convinced this is the problem. It happens regularly at start-up of the app, even when the network connection is good, and other push messages (e.g. app updates) work fine which suggests the open connection is there, but messages not being sent. C2DM is documented as queueing messages, and retrying, so where are they going? I suspect an issue with C2DM registration is black-holing them – Ollie C Aug 31 '11 at 13:09