Page 184 - DCAP507_SYSTEM_SOFTWARE

System Software

Notes asio_handler_deallocate(pointer, size, &this_handler->handler_);
}
template<class F, class ReadHandler>

void handler_invoke(const F& f,
bound_read_handler<ReadHandler>* this_handler)
{
using namespace boost::asio;

handler_invoke(f, &this_handler->handler_);
}
If the thread that begins an asynchronous operation finishes before the related handler is invoked,
the behaviour is implementation-defined. Particularly, onWindows versions prior to Vista,
unfinished operations are cancelled when the initiating thread exits.
The handler argument to an initiating function defines a handler identity. Specifically, the original
handler argument and any copies of the handler argument will be measured equivalent. If the
implementation requires to allocate storage for an asynchronous operation, the execution will
perform asio_handler_allocate(size, &h), where size is the required size in bytes, and h is the
handler. The execution will carry out asio_handler_deallocate(p, size, &h), where p is a pointer to
the storage, to deallocate the storage before the invocation of the handler via asio_handler_invoke.
Numerous storage blocks may be assigned for a single asynchronous operation.

Task Illustrate the arguments to initiating functions.

Self Assessment

Fill in the blanks:
6. The ............................. class offers the BeginRead and EndRead methods to asynchronously
read bytes from a file.
7. For every call to BeginOperationName, the application should also call .............................
to obtain the results of the operation.
8. The BeginOperationName method starts asynchronous operation OperationName and
returns an object that executes the ............................. interface.

9. If the BeginOperationNamemethod throws exceptions, the ............................. method is not
invoked.
10. An asynchronous operation is initiated by a function that is named with the prefix async_.
These functions will be pointed to as ..............................
11. A ............................. handler is a handler object that includes a copy of a user-supplied
handler, where the user-supplied handler accepts one or more arguments.

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