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# asio::io_service::strand Class Reference

List of all members.

## Detailed Description

Provides serialised handler execution.

The io_service::strand class provides the ability to post and dispatch handlers with the guarantee that none of those handlers will execute concurrently.

Thread Safety
  Distinct objects: Safe.
  Shared objects: Safe.

Concepts:
  Dispatcher.

## Public Member Functions

| strand (asio::io_service &io_service)
| Constructor.
| ~strand ()
| Destructor.
asio::io_service & | io_service ()
| Get the io_service associated with the strand.
template<typename Handler>
void | dispatch (Handler handler)
| Request the strand to invoke the given handler.
template<typename Handler>
void | post (Handler handler)
| Request the strand 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 strand.

## Constructor & Destructor Documentation

asio::io_service::strand::strand | ( | asio::io_service & | io_service | ) | `[explicit]`

Constructor.

Constructs the strand.

Parameters:

  | io_service | The io_service object that the strand will use to dispatch handlers that are ready to be run.

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

Destructor.

Destroys a strand.

Handlers posted through the strand that have not yet been invoked will still be dispatched in a way that meets the guarantee of non-concurrency.

## Member Function Documentation

asio::io_service& asio::io_service::strand::io_service | ( |  | ) |

Get the io_service associated with the strand.

This function may be used to obtain the io_service object that the strand uses to dispatch handlers for asynchronous operations.

Returns:
  A reference to the io_service object that the strand will use to dispatch handlers. Ownership is not transferred to the caller.

template<typename Handler>

void asio::io_service::strand::dispatch | ( | Handler | handler | ) |

Request the strand to invoke the given handler.

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

The strand object guarantees that handlers posted or dispatched through the strand will not be executed concurrently. The handler may be executed inside this function if the guarantee can be met. If this function is called from within a handler that was posted or dispatched through the same strand, then the new handler will be executed immediately.

The strand's guarantee is in addition to the guarantee provided by the underlying io_service. The io_service guarantees that the handler will only be called in a thread in which the io_service's run member function is currently being invoked.

Parameters:

  | handler | The handler to be called. The strand 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::strand::post | ( | Handler | handler | ) |

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

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

The strand object guarantees that handlers posted or dispatched through the strand will not be executed concurrently. The strand's guarantee is in addition to the guarantee provided by the underlying io_service. The io_service guarantees that the handler will only be called in a thread in which the io_service's run member function is currently being invoked.

Parameters:

  | handler | The handler to be called. The strand 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::strand::wrap | ( | Handler | handler | ) |

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

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

Parameters:

  | handler | The handler to be wrapped. The strand 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 strand'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:

       strand.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:

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

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