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# asio::io_service Class Reference

Inherits noncopyable.

Inheritance diagram for asio::io_service:

List of all members.

## Detailed Description

Provides core I/O functionality.

The io_service class provides the core I/O functionality for users of the asynchronous I/O objects, including:

- asio::ip::tcp::socket
- asio::ip::tcp::acceptor
- asio::ip::udp::socket
- asio::deadline_timer.

The io_service class also includes facilities intended for developers of custom asynchronous services.

Thread Safety
  Distinct objects: Safe.
  Shared objects: Safe, with the exception that calling reset() while there are unfinished run() calls results in undefined behaviour.

Concepts:
  Dispatcher.

Effect of exceptions thrown from handlers

If an exception is thrown from a handler, the exception is allowed to propagate through the throwing thread's invocation of asio::io_service::run(), asio::io_service::run_one(), asio::io_service::poll() or asio::io_service::poll_one(). No other threads that are calling any of these functions are affected. It is then the responsibility of the application to catch the exception.

After the exception has been caught, the asio::io_service::run(), asio::io_service::run_one(), asio::io_service::poll() or asio::io_service::poll_one() call may be restarted without the need for an intervening call to asio::io_service::reset(). This allows the thread to rejoin the io_service's thread pool without impacting any other threads in the pool.

For example:

     asio::io_service io_service;
     ...
     for (;;)
     {
       try
       {
         io_service.run();
         break; // run() exited normally
       }
       catch (my_exception& e)
       {
         // Deal with exception as appropriate.
       }
     }

## Public Member Functions

| io_service ()
| Constructor.
| io_service (std::size_t concurrency_hint)
| Constructor.
| ~io_service ()
| Destructor.
std::size_t | run ()
| Run the io_service's event processing loop.
std::size_t | run (asio::error_code &ec)
| Run the io_service's event processing loop.
std::size_t | run_one ()
| Run the io_service's event processing loop to execute at most one handler.
std::size_t | run_one (asio::error_code &ec)
| Run the io_service's event processing loop to execute at most one handler.
std::size_t | poll ()
| Run the io_service's event processing loop to execute ready handlers.
std::size_t | poll (asio::error_code &ec)
| Run the io_service's event processing loop to execute ready handlers.
std::size_t | poll_one ()
| Run the io_service's event processing loop to execute one ready handler.
std::size_t | poll_one (asio::error_code &ec)
| Run the io_service's event processing loop to execute one ready handler.
void | stop ()
| Stop the io_service's event processing loop.
void | reset ()
| Reset the io_service in preparation for a subsequent run() invocation.
template<typename CompletionHandler>
void | dispatch (CompletionHandler handler)
| Request the io_service to invoke the given handler.
template<typename CompletionHandler>
void | post (CompletionHandler handler)
| Request the io_service to invoke the given handler and return immediately.
template<typename Handler>
unspecified | wrap (Handler handler)
| Create a new handler that automatically dispatches the wrapped handler on the io_service.

## Friends

template<typename Service>
Service & | use_service (io_service &ios)
| Obtain the service object corresponding to the given type.
template<typename Service>
void | add_service (io_service &ios, Service *svc)
| Add a service object to the io_service.
template<typename Service>
bool | has_service (io_service &ios)
| Determine if an io_service contains a specified service type.

## Classes

class | id
| Class used to uniquely identify a service. More...
class | service
| Base class for all io_service services. More...
class | strand
| Provides serialised handler execution. More...
class | work
| Class to inform the io_service when it has work to do. More...

## Constructor & Destructor Documentation

asio::io_service::io_service | ( |  | ) |

Constructor.

asio::io_service::io_service | ( | std::size_t | concurrency_hint | ) | `[explicit]`

Constructor.

Construct with a hint about the required level of concurrency.

Parameters:

  | concurrency_hint | A suggestion to the implementation on how many threads it should allow to run simultaneously.

asio::io_service::~io_service | ( |  | ) |

Destructor.

## Member Function Documentation

std::size_t asio::io_service::run | ( |  | ) |

Run the io_service's event processing loop.

The run() function blocks until all work has finished and there are no more handlers to be dispatched, or until the io_service has been stopped.

Multiple threads may call the run() function to set up a pool of threads from which the io_service may execute handlers. All threads that are waiting in the pool are equivalent and the io_service may choose any one of them to invoke a handler.

The run() function may be safely called again once it has completed only after a call to reset().

Returns:
  The number of handlers that were executed.

Exceptions:

  | asio::system_error | Thrown on failure.

std::size_t asio::io_service::run | ( | asio::error_code & | ec | ) |

Run the io_service's event processing loop.

The run() function blocks until all work has finished and there are no more handlers to be dispatched, or until the io_service has been stopped.

Multiple threads may call the run() function to set up a pool of threads from which the io_service may execute handlers. All threads that are waiting in the pool are equivalent and the io_service may choose any one of them to invoke a handler.

The run() function may be safely called again once it has completed only after a call to reset().

Parameters:

  | ec | Set to indicate what error occurred, if any.

Returns:
  The number of handlers that were executed.

std::size_t asio::io_service::run_one | ( |  | ) |

Run the io_service's event processing loop to execute at most one handler.

The run_one() function blocks until one handler has been dispatched, or until the io_service has been stopped.

Returns:
  The number of handlers that were executed.

Exceptions:

  | asio::system_error | Thrown on failure.

std::size_t asio::io_service::run_one | ( | asio::error_code & | ec | ) |

Run the io_service's event processing loop to execute at most one handler.

The run_one() function blocks until one handler has been dispatched, or until the io_service has been stopped.

Parameters:

  | ec | Set to indicate what error occurred, if any.

Returns:
  The number of handlers that were executed.

std::size_t asio::io_service::poll | ( |  | ) |

Run the io_service's event processing loop to execute ready handlers.

The poll() function runs handlers that are ready to run, without blocking, until the io_service has been stopped or there are no more ready handlers.

Returns:
  The number of handlers that were executed.

Exceptions:

  | asio::system_error | Thrown on failure.

std::size_t asio::io_service::poll | ( | asio::error_code & | ec | ) |

Run the io_service's event processing loop to execute ready handlers.

The poll() function runs handlers that are ready to run, without blocking, until the io_service has been stopped or there are no more ready handlers.

Parameters:

  | ec | Set to indicate what error occurred, if any.

Returns:
  The number of handlers that were executed.

std::size_t asio::io_service::poll_one | ( |  | ) |

Run the io_service's event processing loop to execute one ready handler.

The poll_one() function runs at most one handler that is ready to run, without blocking.

Returns:
  The number of handlers that were executed.

Exceptions:

  | asio::system_error | Thrown on failure.

std::size_t asio::io_service::poll_one | ( | asio::error_code & | ec | ) |

Run the io_service's event processing loop to execute one ready handler.

The poll_one() function runs at most one handler that is ready to run, without blocking.

Parameters:

  | ec | Set to indicate what error occurred, if any.

Returns:
  The number of handlers that were executed.

void asio::io_service::stop | ( |  | ) |

Stop the io_service's event processing loop.

This function does not block, but instead simply signals the io_service to stop. All invocations of its run() or run_one() member functions should return as soon as possible. Subsequent calls to run(), run_one(), poll() or poll_one() will return immediately until reset() is called.

void asio::io_service::reset | ( |  | ) |

Reset the io_service in preparation for a subsequent run() invocation.

This function must be called prior to any second or later set of invocations of the run(), run_one(), poll() or poll_one() functions when a previous invocation of these functions returned due to the io_service being stopped or running out of work. This function allows the io_service to reset any internal state, such as a "stopped" flag.

This function must not be called while there are any unfinished calls to the run(), run_one(), poll() or poll_one() functions.

template<typename Handler>

void asio::io_service::dispatch | ( | CompletionHandler | handler | ) |

Request the io_service to invoke the given handler.

This function is used to ask the io_service to execute the given handler.

The io_service guarantees that the handler will only be called in a thread in which the run(), run_one(), poll() or poll_one() member functions is currently being invoked. The handler may be executed inside this function if the guarantee can be met.

Parameters:

  | handler | The handler to be called. The io_service will make a copy of the handler object as required. The function signature of the handler must be:
       void handler();

template<typename Handler>

void asio::io_service::post | ( | CompletionHandler | handler | ) |

Request the io_service to invoke the given handler and return immediately.

This function is used to ask the io_service to execute the given handler, but without allowing the io_service to call the handler from inside this function.

The io_service guarantees that the handler will only be called in a thread in which the run(), run_one(), poll() or poll_one() member functions is currently being invoked.

Parameters:

  | handler | The handler to be called. The io_service will make a copy of the handler object as required. The function signature of the handler must be:
       void handler();

template<typename Handler>

unspecified asio::io_service::wrap | ( | Handler | handler | ) |

Create a new handler that automatically dispatches the wrapped handler on the io_service.

This function is used to create a new handler function object that, when invoked, will automatically pass the wrapped handler to the io_service's dispatch function.

Parameters:

  | handler | The handler to be wrapped. The io_service will make a copy of the handler object as required. The function signature of the handler must be:
       void handler(A1 a1, ... An an);

Returns:
  A function object that, when invoked, passes the wrapped handler to the io_service's dispatch function. Given a function object with the signature:

       R f(A1 a1, ... An an);

  If this function object is passed to the wrap function like so:

       io_service.wrap(f);

  then the return value is a function object with the signature

       void g(A1 a1, ... An an);

  that, when invoked, executes code equivalent to:

       io_service.dispatch(boost::bind(f, a1, ... an));

## Friends And Related Function Documentation

template<typename Service>

Service& use_service | ( | io_service & | ios | ) | `[friend]`

Obtain the service object corresponding to the given type.

This function is used to locate a service object that corresponds to the given service type. If there is no existing implementation of the service, then the io_service will create a new instance of the service.

Parameters:

  | ios | The io_service object that owns the service.

Returns:
  The service interface implementing the specified service type. Ownership of the service interface is not transferred to the caller.

template<typename Service>

void add_service | ( | io_service & | ios,
|  | Service * | svc |
| ) |  |  | `[friend]`

Add a service object to the io_service.

This function is used to add a service to the io_service.

Parameters:

  | ios | The io_service object that owns the service.
  | svc | The service object. On success, ownership of the service object is transferred to the io_service. When the io_service object is destroyed, it will destroy the service object by performing:
       delete static_cast<io_service::service*>(svc)

Exceptions:

  | asio::service_already_exists | Thrown if a service of the given type is already present in the io_service.
  | asio::invalid_service_owner | Thrown if the service's owning io_service is not the io_service object specified by the ios parameter.

template<typename Service>

bool has_service | ( | io_service & | ios | ) | `[friend]`

Determine if an io_service contains a specified service type.

This function is used to determine whether the io_service contains a service object corresponding to the given service type.

Parameters:

  | ios | The io_service object that owns the service.

Returns:
  A boolean indicating whether the io_service contains the service.

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