Design question - static list in class

[Angus]

Hi all

I have a design which models a telephone system. Roughly the design has
these two items:

device class which models an extension on the telephone system. The device
constructor takes a extension number. So program starts by creating a
device object for each extension on the telephone system.

Each device object contains a static list of calls. Calls are modelled by a
class object. The class object takes an extension number in its destructor.

There are various find functions to find a call on a device. Usually on a
device there will be 0, 1 or 2 calls.

The list of calls in the device object is static because sometimes a device
object is created on the stack simply to find a call on the device and maybe
report on its status. If the call list were NOT static then I would get a
zero size call list each time I created the device object on the stack. Not
what I want.

I also have a device list - there is only ever one instance of the class
which accesses the device list. So the number of items in the device list
(a std::list) is set after the program starts.

Eg I get hold of the correct device object like this (device is the
extension object);

device* pDev=FindDevice ByDN(dn);

FindDeviceByDN retrieves a copy of the relevant device object in the device
list.

Then I might do something like this:
call* pCall=pDev->GetCallbyCallI D(callid);


I am concerned that the static call list might be bad design. But not sure?
What do people think? Does this design seem ok? Anyone see a better
design?

Angus

[Paavo Helde]

Re: Design question - static list in class

"Angus" <nospam@gmail.c omkirjutas:

I have a design which models a telephone system. Roughly the design
has these two items:
>
device class which models an extension on the telephone system. The
device constructor takes a extension number. So program starts by
creating a device object for each extension on the telephone system.
>
Each device object contains a static list of calls.

If the "static list" means static data in the C++ sense, then no, each
device object does not contain a list of calls; all device objects are
rather sharing a single list.

Calls are

modelled by a class object.

Sorry, cannot grok this...

The class object takes an extension
number in its destructor.

neither this...

I believe you should better post some sketch in C++ to get some useful
answers.

In general, static data is bad for reentrant code and for multithreading.
It should be used only if all running threads must see and/or alter the
same data state (with proper synchronization , of course). And if your
software is not using multithreading yet, the chances are good IMO that
it might to start to do that in a couple of years, just to make some use
of the multitude of cpu cores the new processors are sporting.

All the best
Paavo