[SailfishDevel] Preventing deep sleep for a few seconds?

[Thomas Perl]

On 01 Feb 2014, at 21:32, Ove Kåven <ovek at arcticnet.no> wrote:
> If a synchronization starts with the screen off, there's a chance that the phone enters "deep suspend" during the synchronization. If so, the other side might time out and the sync will fail.
> 
> So I want prevent the CPU from suspending before the synchronization is complete, which might take a few seconds (and there might not be network activity all the time while it's running). I've read that to get periodic wakeups, you could use libiphb or maybe timed, but what's the recommended way to temporarily prevent suspending completely for a few seconds?

You can talk to MCE via the system D-Bus, this is quite low-level, but works already:

https://github.com/nemomobile/mce-dev/blob/master/include/mce/dbus-names.h#L329

To quote the documentation:

 * The idea is: if some process needs to do non-interactive
 * background processing, it can prevent the system from
 * entering late suspend by
 *
 * 1) get timer period via #MCE_CPU_KEEPALIVE_PERIOD_REQ call
 *
 * 2) call #MCE_CPU_KEEPALIVE_START_REQ
 *
 * 3) repeat #MCE_CPU_KEEPALIVE_START_REQ calls in interval
 *    that is shorter than the maximum obtained at (1)
 *
 * 4) call #MCE_CPU_KEEPALIVE_STOP_REQ when finished
 *
 * MCE keeps track of active clients and blocks late suspend
 * until all clients have called #MCE_CPU_KEEPALIVE_STOP_REQ,
 * lost D-Bus connection (exit, crash, ...) or all timeouts
 * have been missed.

There might be a higher-level API for this in the future (Qt-flavored C++ and QML), for a preview, see:
https://github.com/nemomobile/nemo-keepalive

HTH :)
Thomas