Cancel all asynchronous operations associated with the socket.
This function causes all outstanding asynchronous connect, send and receive
operations to finish immediately, and the handlers for cancelled operations
will be passed the
Thrown on failure.
cancel() will always fail with
when run on Windows XP, Windows Server 2003, and earlier versions of
Windows, unless BOOST_ASIO_ENABLE_CANCELIO is defined. However, the CancelIo
function has two issues that should be considered before enabling its
For portable cancellation, consider using one of the following alternatives:
close()function to simultaneously cancel the outstanding operations and close the socket.
When running on Windows Vista, Windows Server 2008, and later, the CancelIoEx function is always used. This function does not have the problems described above.