<!--
{
  "availability" : [
    "iOS: -",
    "iPadOS: -",
    "macCatalyst: -",
    "macOS: -",
    "tvOS: -",
    "visionOS: -",
    "watchOS: -"
  ],
  "documentType" : "symbol",
  "framework" : "Dispatch",
  "identifier" : "/documentation/Dispatch/dispatch_io_handler_t",
  "metadataVersion" : "0.1.0",
  "role" : "Type Alias",
  "symbol" : {
    "kind" : "Type Alias",
    "modules" : [
      "Dispatch"
    ],
    "preciseIdentifier" : "c:@T@dispatch_io_handler_t"
  },
  "title" : "dispatch_io_handler_t"
}
-->

# dispatch_io_handler_t

A handler block used to process operations on a dispatch I/O channel.

```
typedef void (^)(_Bool, NSObject<OS_dispatch_data> *, int) dispatch_io_handler_t;
```

## Discussion

The parameters of a dispatch I/O handler are as follows:

- `done` - A flag indicating whether the operation is complete.
- `data` - The data object to be handled. This object is retained by the system for the duration of the handler’s execution and is released when the handler block returns.
- `error` - The error number (if any) reported for the operation. An error number of `0` typically indicates the operation was successful.

---

Copyright &copy; 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)