This sounds cool, I started implementing the other half of this a couple
days ago.  My broad idea of a source cleanup (that sipa largely wrote)
is to have a central notification interface which wallet(s)/net/block
store/etc all communicate with, and then an interface, like the one
proposed here, which GUI/RPC/etc use to communicate with wallet/net.
This should allow for very clean separation of pieces and large-scale
rewrites of one or another part (or drop-in replacements) without
touching anything but the parts that are being redone.  This should also
allow for cool programs (like pushpoold/a block notification server/etc)
to use Bitcoin as a library fairly efficiently.

Matt

On Thu, 2011-07-14 at 05:19 +0000, John Smith wrote:
> Hello all,
> 
> I'd like to add notifications to the client and wallet, to decouple UI
> and core communication, and especially so that UIs no longer have to
> poll for changes. 
> 
> I propose to use the boost::signal mechanism for that. It is basically
> a glorified callback system, but allows decoupled delivery of
> 'signals' from an object. Multiple other objects can listen in on an
> event without the emitting object having to care. 
> 
> Wallet:
> 
> class CWallet { ...
>     boost::signal<void(int64)> balanceChanged;
> }
> 
> 
> void CWallet::newTx (...) {
> 
>     ...
>     balanceChanged(new_balance);
>     ...
> }
> 
> 
> 
> UI:
> 
> GUI::GUI(CWallet *wallet) {
>    ...
>    wallet->balanceChanged.connect(boost::bind(&GUI::balanceChanged,
> this, _1));
> }
> GUI::balanceChanged(int64 new_balance) {
>    someWidget->setValue(new_balance);
> }
> 
> 
> Specific notifications that would be useful:
> 
> Wallet:
>       * balanceChanged(int64): spendable balance changed
>       * transactionAdded(int256): new transaction added to wallet
>       * transactionUpdated(int256): transaction info changed
>       * transactionRemoved(int256): transaction removed from wallet
>         (can this happen? for completeness)
>       * addressAdded(int160): address was added to address book
>       * addressUpdated(int160): address label/other metadata was
>         modified
>       * addressRemoved(int160): address was removed from address book
>       * notification(std::string message, int severity): warning/error
>         occured in wallet processing, notify user
>       * int askFee(std::string message, ...): ask user for fee
> Network client:
>       * numConnectionsChanged(int): new connections / connections
>         broken
>       * numBlocksChanged(int): new blocks came in or other changes to
>         block chain
>       * notification(std::string message, int severity): warning/error
>         occured in network processing, notify user
> 
> JS