[Gpephone-devel] Examining inter-process communication (1) -- signal

[YU Yijun RD-ILAB-PEK]

Hi,

It is common on the phone device that one process needs to notify other
processes that something interesting has happened. e.g., once phone
server (which monitors the modem) detects an incoming call, it needs to
inform a dialer application that an incoming call has arrived.

Access Hiker application framework uses Notification Manager to handle
this type of inter-process communication -- so called "notification".
One process can broadcast a notification without knowing who will be the
recipients. Any other process can select to register this notification,
and once the notification is broadcasted, all registered processes will
be notified. 

One thing special here is that each register record (recording which
process registers which notification) is permanently stored on the
device until it is explicitly un-registered. I.e., if an application
registers a notification and then shuts down without un-registering it,
this record is kept on the device. And once the corresponding
notification happens, this application will be launched and then
notified.

DBus provides similar mechanism named signal to deal with this type of
inter-process communication. However, when a signal is emitted, only
those running processes can receive and handle it (right?).

 

I am thinking introducing this inter-process communication to the GPE
Phone Edition. In the current implementation, one process can also
notify other processes that something has happened, however, currently
there is no notification register/un-register mechanism and the
notification sender hard-codes to which processes it will notify. e.g.,
the phone server can only notify the dialer application an incoming
call. If any other applications want also to be notified an incoming
call, the phone server source code has to be modified. 

In my personal opinion, it is ideal to use DBus signal to implement this
type of inter-process communication. One problem is that DBus signal can
only notify running applications, however, some important
signal/notification may need to be delivered to an application no matter
whether or not the latter is running. (example?).  Therefore, there
should be a mechanism that let applications tell whether or not it need
be launched to deal with a signal or just ignore a signal if the app is
not running. I have no idea yet.

After implementing the notification/signal mechanism, then we need to
define a set of signals on the platform.

Regards
Yu Yijun