Creates a new dispatch I/O channel from an existing channel.
- iOS 5.0+
- macOS 10.7+
- Mac Catalyst 13.0+
- tvOS 9.0+
- watchOS 2.0+
The type of channel to create. For a list of possible options, see
_io _type _t
An existing channel whose file descriptor or path name you want to use.
The dispatch queue to associate with the channel. This queue is used to execute the channel’s clean up handler. The channel retains this queue.
The block to enqueue when the system relinquishes control of the channel’s file descriptor. This channel takes a single parameter that indicates the reason why control was relinquished. If the
errorparameter contains a non zero value, control was relinquished because there was an error creating the channel; otherwise, this value should be
The dispatch I/O channel or
NULL if an error occurred. The returned object is retained before it is returned; it is your responsibility to close the channel and then release this object when you are done using it.
This function creates a new dispatch I/O channel that inherits the file descriptor or path name of the specified channel but whose channel type and policies you can set to be different.
If the existing channel is associated with a file descriptor, the system maintains control over the file descriptor until the new channel is also closed, an error occurs on the file descriptor, or all references to channels tied to that file descriptor are released. When the file descriptor is released, the
cleanup block is enqueued on the specified
queue and the system relinquishes control over the file descriptor.
While it controls the file descriptor, the system may modify that file descriptor on behalf of the application. For example, the system typically adds the
O flag to ensure that any operations on the file descriptor are non-blocking. During that time, it is an error for your application to modify the file descriptor directly. However, you may create additional channels using the same file descriptor.