Library: Foundation
Package: Notifications
Header: Poco/NObserver.h
Description
This template class implements an adapter that sits between a NotificationCenter and an object receiving notifications from it. It is quite similar in concept to the RunnableAdapter, but provides some NotificationCenter specific additional methods. See the NotificationCenter class for information on how to use this template class.
This class template is quite similar to the Observer class template. The differences are:
- NObserver expects the callback function to accept a const AutoPtr& instead of a plain pointer as argument, thus simplifying memory management.
- In addition to dispatching notifications based on the Notification runtime type, NObserver can also notify subscribers based on the Notification name. To enable this functionality, a matcher function must be provided. Null matcher means no matching is performed and all notificiations of the type subscribed to are dispatched.
Thread Safety:
The handle() method uses atomic load for _pObject and does not hold any lock during callback invocation. This prevents lock-order-inversion deadlocks when handlers call back into NotificationCenter (e.g., to remove themselves during disconnect).
Callers must ensure:
- The observed object outlives all pending notifications. This is inherent to the observer pattern: if object C is destroyed while notifications are in flight (e.g., queued in AsyncObserver), undefined behavior occurs.
- Assignment operators should not be used concurrently with notification delivery. Observer instances are typically created once and registered; concurrent modification during active notification dispatch is not supported.
Inheritance
Direct Base Classes: AbstractObserver
All Base Classes: AbstractObserver
Member Summary
Member Functions: accepts, acceptsSync, clone, disable, equals, handle, handleSync, hasMatcher, match, notify, notifySync, operator =
Inherited Functions: accepts, acceptsSync, backlog, clone, disable, equals, notify, notifySync, operator =, start
Types Aliases
Handler
using Handler = void (C::*)(const NotificationPtr &);
Matcher
using Matcher = bool (C::*)(const std::string &)const;
MatcherFunc
using MatcherFunc = std::function < bool (const std::string &)>;
NotificationPtr
using NotificationPtr = AutoPtr < N >;
SyncHandler
using SyncHandler = NotificationResult (C::*)(const NotificationPtr &);
Type
using Type = NObserver < C, N >;
Constructors
NObserver
NObserver() = delete;
NObserver 
NObserver(
const NObserver & observer
);
NObserver
NObserver(
NObserver && observer
);
NObserver
NObserver(
C & object,
Handler method,
Matcher matcher = nullptr,
SyncHandler syncMethod = nullptr
);
NObserver
NObserver(
C & object,
Handler method,
MatcherFunc matcherFunc,
SyncHandler syncMethod = nullptr
);
Destructor
~NObserver 
~NObserver() override = default;
Member Functions
accepts
bool accepts(
Notification * pNf,
const char * pName
) const override;
See also: Poco::AbstractObserver::accepts()
accepts
bool accepts(
const Notification::Ptr & pNf
) const override;
See also: Poco::AbstractObserver::accepts()
acceptsSync
bool acceptsSync() const override;
See also: Poco::AbstractObserver::acceptsSync()
clone
AbstractObserver * clone() const override;
See also: Poco::AbstractObserver::clone()
disable
void disable() override;
See also: Poco::AbstractObserver::disable()
equals
bool equals(
const AbstractObserver & abstractObserver
) const override;
See also: Poco::AbstractObserver::equals()
notify
void notify(
Notification * pNf
) const override;
See also: Poco::AbstractObserver::notify()
notifySync
NotificationResult notifySync(
Notification * pNf
) const override;
See also: Poco::AbstractObserver::notifySync()
operator =
NObserver & operator = (
const NObserver & observer
);
operator =
NObserver & operator = (
NObserver && observer
);
handle 
void handle(
const NotificationPtr & ptr
) const;
handleSync
NotificationResult handleSync(
const NotificationPtr & ptr
) const;
hasMatcher
bool hasMatcher() const;
match
bool match(
const Notification::Ptr & ptr
) const;