Creates a dispatch I/O channel and associates it with the specified file descriptor.


dispatch_io_t dispatch_io_create(dispatch_io_type_t type, dispatch_fd_t fd, dispatch_queue_t queue, void (^cleanup_handler)(int error));



The type of channel to create. For a list of possible options, see dispatch_io_type_t.


The file descriptor to associate with the channel.


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 error parameter contains a non zero value, control was relinquished because there was an error creating the channel; otherwise, this value should be 0.

Return Value

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.


You use this function to create a dispatch I/O channel for an already open file descriptor. After calling this function, the system takes control of the specified file descriptor until one of the following occurs:

  • You close the channel by calling the dispatch_io_close function.

  • An unrecoverable error occurs on the file descriptor.

  • All references to the channel are released.

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_NONBLOCK 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.

See Also

Creating a Dispatch I/O Object


Creates a new dispatch I/O channel from an existing channel.


Creates a dispatch I/O channel with the associated path name.


A dispatch I/O channel.


A file descriptor used for I/O operations.


The type of a dispatch I/O channel.