introspection.h

Includes:

"headerdoc.h"
<dispatch/dispatch.h>

Introduction

Interposable introspection hooks for libdispatch.

Discussion

These hooks are only available in the introspection version of the library, loaded by running a process with the environment variable DYLD_LIBRARY_PATH=/usr/lib/system/introspection

Functions

dispatch_introspection_hook_queue_callout_begin: Interposable hook function called when a client function is about to be called out to on a dispatch queue.
dispatch_introspection_hook_queue_callout_end: Interposable hook function called after a client function has returned from a callout on a dispatch queue.
dispatch_introspection_hook_queue_create: Interposable hook function called when a dispatch queue was created.
dispatch_introspection_hook_queue_destroy: Interposable hook function called when a dispatch queue is about to be destroyed.
dispatch_introspection_hook_queue_item_complete: Interposable hook function called when an item previously dequeued from a dispatch queue has completed processing.
dispatch_introspection_hook_queue_item_dequeue: Interposable hook function called when an item was dequeued from a dispatch queue.
dispatch_introspection_hook_queue_item_enqueue: Interposable hook function called when an item is about to be enqueued onto a dispatch queue.

dispatch_introspection_hook_queue_callout_begin

Interposable hook function called when a client function is about to be called out to on a dispatch queue.

(
    macos(
        10.9),
    ios(
        7.0))  void dispatch_introspection_hook_queue_callout_begin(
    dispatch_queue_t queue, 
    void *_Nullable context,
    dispatch_function_t function);

Parameters

queue: The dispatch queue the callout is performed on.
context: The context parameter passed to the function. For a callout to a block, this is a pointer to the block object.
function: The client function about to be called out to. For a callout to a block, this is the block object's invoke function.

dispatch_introspection_hook_queue_callout_end

Interposable hook function called after a client function has returned from a callout on a dispatch queue.

(
    macos(
        10.9),
    ios(
        7.0))  void dispatch_introspection_hook_queue_callout_end(
    dispatch_queue_t queue, 
    void *_Nullable context,
    dispatch_function_t function);

Parameters

queue: The dispatch queue the callout was performed on.
context: The context parameter passed to the function. For a callout to a block, this is a pointer to the block object.
function: The client function that was called out to. For a callout to a block, this is the block object's invoke function.

dispatch_introspection_hook_queue_create

Interposable hook function called when a dispatch queue was created.

(
    macos(
        10.9),
    ios(
        7.0))  void dispatch_introspection_hook_queue_create(
    dispatch_queue_t queue);

Parameters

queue: The newly created dispatch queue.

dispatch_introspection_hook_queue_destroy

Interposable hook function called when a dispatch queue is about to be destroyed.

(
    macos(
        10.9),
    ios(
        7.0))  void dispatch_introspection_hook_queue_destroy(
    dispatch_queue_t queue);

Parameters

queue: The dispatch queue about to be destroyed.

dispatch_introspection_hook_queue_item_complete

Interposable hook function called when an item previously dequeued from a dispatch queue has completed processing.

(
    macos(
        10.10),
    ios(
        7.1))  void dispatch_introspection_hook_queue_item_complete(
    dispatch_object_t item);

Parameters

item: Opaque dentifier for completed item. Must NOT be dereferenced.

Discussion

The object pointer value passed to this function must be treated as a value only. It is intended solely for matching up with an earlier call to a dequeue hook function and must NOT be dereferenced.

dispatch_introspection_hook_queue_item_dequeue

Interposable hook function called when an item was dequeued from a dispatch queue.

(
    macos(
        10.9),
    ios(
        7.0))  void dispatch_introspection_hook_queue_item_dequeue(
    dispatch_queue_t queue, 
    dispatch_object_t item);

Parameters

queue: The dispatch queue dequeued from.
item: The dequeued object.

dispatch_introspection_hook_queue_item_enqueue

Interposable hook function called when an item is about to be enqueued onto a dispatch queue.

(
    macos(
        10.9),
    ios(
        7.0))  void dispatch_introspection_hook_queue_item_enqueue(
    dispatch_queue_t queue, 
    dispatch_object_t item);

Parameters

queue: The dispatch queue enqueued onto.
item: The object about to be enqueued.

Last Updated: October 10, 2025