Add support for release() on serial ports

Fixes #1182

Author: Lkzeu

include/asio/basic_serial_port.hpp

@@ -491,6 +491,37 @@ class basic_serial_port
     return impl_.get_service().native_handle(impl_.get_implementation());
   }
 
+  /// Release ownership of the underlying native serial port.
+  /*
+   * This function causes all outstanding asynchronous read operations to
+   * finish immediately, and the handlers for cancelled operations will be
+   * passed the asio::error::operation_aborted error. Ownership of the
+   * native serial port is then transferred to the caller.
+   *
+   * @throws asio::system_error Thrown on failure.
+   */
+  native_handle_type release()
+  {
+    asio::error_code ec;
+    native_handle_type s = impl_.get_service().release(
+            impl_.get_implementation(), ec);
+    asio::detail::throw_error(ec, "release");
+    return s;
+  }
+
+  /// Release ownership of the underlying native serial port.
+  /*
+   * This function causes all outstanding asynchronous read operations to
+   * finish immediately, and the handlers for cancelled operations will be
+   * passed the asio::error::operation_aborted error. Ownership of the
+   * native serial port is then transferred to the caller.
+   *
+   * @param ec Set to indicate what error occurred, if any.
+   */
+  native_handle_type release(asio::error_code& ec)
+  {
+    return impl_.get_service().release(impl_.get_implementation(), ec);
+  }
   /// Cancel all asynchronous operations associated with the serial port.
   /**
    * This function causes all outstanding asynchronous read or write operations

include/asio/detail/posix_serial_port_service.hpp

@@ -122,6 +122,13 @@ class posix_serial_port_service :
     return descriptor_service_.native_handle(impl);
   }
 
+  // Release ownership of the native serial port representation.
+  native_handle_type release(implementation_type& impl,
+      asio::error_code& ec)
+  {
+    return descriptor_service_.release(impl, ec);
+  }
+
   // Cancel all operations associated with the serial port.
   asio::error_code cancel(implementation_type& impl,
       asio::error_code& ec)