# Poco::Net

# class SocketReactor

Library: Net
Package: Reactor
Header: Poco/Net/SocketReactor.h

## Description

This class, which is part of the Reactor pattern, implements the "Initiation Dispatcher".

The Reactor pattern has been described in the book "Pattern Languages of Program Design" by Jim Coplien and Douglas C. Schmidt (Addison Wesley, 1995).

The Reactor design pattern handles service requests that are delivered concurrently to an application by one or more clients. Each service in an application may consist of several methods and is represented by a separate event handler. The event handler is responsible for servicing service-specific requests. The SocketReactor dispatches the event handlers.

Event handlers (any class can be an event handler - there is no base class for event handlers) can be registered with the addEventHandler() method and deregistered with the removeEventHandler() method.

An event handler is always registered for a certain socket, which is given in the call to addEventHandler(). Any method of the event handler class can be registered to handle the event - the only requirement is that the method takes a pointer to an instance of SocketNotification (or a subclass of it) as argument.

Once started, the SocketReactor waits for events on the registered sockets, using Socket::select(). If an event is detected, the corresponding event handler is invoked. There are five event types (and corresponding notification classes) defined: ReadableNotification, WritableNotification, ErrorNotification, TimeoutNotification, IdleNotification and ShutdownNotification.

The ReadableNotification will be dispatched if a socket becomes readable. The WritableNotification will be dispatched if a socket becomes writable. The ErrorNotification will be dispatched if there is an error condition on a socket.

If the timeout expires and no event has occured, a TimeoutNotification will be dispatched to all event handlers registered for it. This is done in the onTimeout() method which can be overridden by subclasses to perform custom timeout processing.

If there are no sockets for the SocketReactor to pass to Socket::select(), an IdleNotification will be dispatched to all event handlers registered for it. This is done in the onIdle() method which can be overridden by subclasses to perform custom idle processing. Since onIdle() will be called repeatedly in a loop, it is recommended to do a short sleep or yield in the event handler.

Finally, when the SocketReactor is about to shut down (as a result of stop() being called), it dispatches a ShutdownNotification to all event handlers. This is done in the onShutdown() method which can be overridded by subclasses to perform custom shutdown processing.

The SocketReactor is implemented so that it can run in its own thread. It is also possible to run multiple SocketReactors in parallel, as long as they work on different sockets.

It is safe to call addEventHandler() and removeEventHandler() from another thread while the SocketReactor is running. Also, it is safe to call addEventHandler() and removeEventHandler() from event handlers.

## Inheritance

Direct Base Classes: Poco::Runnable

All Base Classes: Poco::Runnable

## Member Summary

Member Functions: addEventHandler, dispatch, getTimeout, onIdle, onShutdown, onTimeout, removeEventHandler, run, setTimeout, stop

Inherited Functions: run

## Constructors

### SocketReactor

SocketReactor();

Creates the SocketReactor.

### SocketReactor

explicit SocketReactor(
const Poco::Timespan & timeout
);

Creates the SocketReactor, using the given timeout.

## Destructor

### ~SocketReactor

virtual ~SocketReactor();

Destroys the SocketReactor.

## Member Functions

### addEventHandler

void addEventHandler(
const Socket & socket,
const Poco::AbstractObserver & observer
);

Registers an event handler with the SocketReactor.

Usage:

    Poco::Observer<MyEventHandler, SocketNotification> obs(*this, &MyEventHandler::handleMyEvent);
    reactor.addEventHandler(obs);

### getTimeout

const Poco::Timespan & getTimeout() const;

Returns the timeout.

### removeEventHandler

void removeEventHandler(
const Socket & socket,
const Poco::AbstractObserver & observer
);

Unregisters an event handler with the SocketReactor.

Usage:

    Poco::Observer<MyEventHandler, SocketNotification> obs(*this, &MyEventHandler::handleMyEvent);
    reactor.removeEventHandler(obs);

### run

void run();

Runs the SocketReactor. The reactor will run until stop() is called (in a separate thread).

See also: Poco::Runnable::run()

### setTimeout

void setTimeout(
const Poco::Timespan & timeout
);

Sets the timeout.

If no other event occurs for the given timeout interval, a timeout event is sent to all event listeners.

The default timeout is 250 milliseconds;

The timeout is passed to the Socket::select() method.

### stop

void stop();

Stops the SocketReactor.

The reactor will be stopped when the next event (including a timeout event) occurs.

### dispatch

void dispatch(
const Socket & socket,
SocketNotification * pNotification
);

Dispatches the given notification to all observers registered for the given socket.

### dispatch

void dispatch(
SocketNotification * pNotification
);

Dispatches the given notification to all observers.

### onIdle

virtual void onIdle();

Called if no sockets are available to call select() on.

Can be overridden by subclasses. The default implementation dispatches the IdleNotification and thus should be called by overriding implementations.

### onShutdown

virtual void onShutdown();

Called when the SocketReactor is about to terminate.

Can be overridden by subclasses. The default implementation dispatches the ShutdownNotification and thus should be called by overriding implementations.

### onTimeout

virtual void onTimeout();

Called if the timeout expires and no other events are available.

Can be overridden by subclasses. The default implementation dispatches the TimeoutNotification and thus should be called by overriding implementations.