# Dispatch Source An object that coordinates the processing of specific low-level system events, such as file-system events, timers, and UNIX signals. ## Topics ### Creating a Dispatch Source [`extern dispatch_source_tdispatch_source_create(dispatch_source_type_t type, uintptr_t handle, uintptr_t mask, dispatch_queue_t queue);`](/documentation/Dispatch/dispatch_source_create) Creates a new dispatch source to monitor low-level system events. [`typealias dispatch_source_t`](/documentation/Dispatch/dispatch_source_t) An object that coordinates the processing of specific low-level system events, such as file-system events, timers, and UNIX signals. [`typedef const struct dispatch_source_type_s * dispatch_source_type_t;`](/documentation/Dispatch/dispatch_source_type_t) An identifier for the type of system object being monitored by a dispatch source. ### Managing Event Handlers [`extern void dispatch_source_set_registration_handler_f(dispatch_source_t source, dispatch_function_t handler);`](/documentation/Dispatch/dispatch_source_set_registration_handler_f) Sets the registration handler function for the given dispatch source. [`extern void dispatch_source_set_registration_handler(dispatch_source_t source, dispatch_block_t handler);`](/documentation/Dispatch/dispatch_source_set_registration_handler) Sets the registration handler block for the given dispatch source. [`extern void dispatch_source_set_event_handler_f(dispatch_source_t source, dispatch_function_t handler);`](/documentation/Dispatch/dispatch_source_set_event_handler_f) Sets the event handler function for the given dispatch source. [`extern void dispatch_source_set_event_handler(dispatch_source_t source, dispatch_block_t handler);`](/documentation/Dispatch/dispatch_source_set_event_handler) Sets the event handler block for the given dispatch source. [`extern void dispatch_source_set_cancel_handler_f(dispatch_source_t source, dispatch_function_t handler);`](/documentation/Dispatch/dispatch_source_set_cancel_handler_f) Sets the cancellation handler function for the given dispatch source. [`extern void dispatch_source_set_cancel_handler(dispatch_source_t source, dispatch_block_t handler);`](/documentation/Dispatch/dispatch_source_set_cancel_handler) Sets the cancellation handler block for the given dispatch source. ### Getting Dispatch Source Attributes [`extern uintptr_t dispatch_source_get_data(dispatch_source_t source);`](/documentation/Dispatch/dispatch_source_get_data) Returns pending data for the dispatch source. [`extern uintptr_t dispatch_source_get_mask(dispatch_source_t source);`](/documentation/Dispatch/dispatch_source_get_mask) Returns the mask of events monitored by the dispatch source. [`extern uintptr_t dispatch_source_get_handle(dispatch_source_t source);`](/documentation/Dispatch/dispatch_source_get_handle) Returns the underlying system handle associated with the specified dispatch source. [`extern void dispatch_source_merge_data(dispatch_source_t source, uintptr_t value);`](/documentation/Dispatch/dispatch_source_merge_data) Merges data into a dispatch source and submits its event handler block to its target queue. [`typedef unsigned long dispatch_source_proc_flags_t;`](/documentation/Dispatch/dispatch_source_proc_flags_t) Events related to a process. [`typedef unsigned long dispatch_source_vnode_flags_t;`](/documentation/Dispatch/dispatch_source_vnode_flags_t) Events involving a change to a file system object. [`typealias dispatch_source_mach_recv_flags_t`](/documentation/Dispatch/dispatch_source_mach_recv_flags_t) Mach receive-right flags. [`typedef unsigned long dispatch_source_mach_send_flags_t;`](/documentation/Dispatch/dispatch_source_mach_send_flags_t) Mach send-right flags. [`typedef unsigned long dispatch_source_memorypressure_flags_t;`](/documentation/Dispatch/dispatch_source_memorypressure_flags_t) Memory pressure events. ### Managing Timer Parameters [`extern void dispatch_source_set_timer(dispatch_source_t source, dispatch_time_t start, uint64_t interval, uint64_t leeway);`](/documentation/Dispatch/dispatch_source_set_timer) Sets a start time, interval, and leeway value for a timer source. [`typedef unsigned long dispatch_source_timer_flags_t;`](/documentation/Dispatch/dispatch_source_timer_flags_t) Flags to use when configuring a timer dispatch source. ### Canceling a Dispatch Source [`extern void dispatch_source_cancel(dispatch_source_t source);`](/documentation/Dispatch/dispatch_source_cancel) Asynchronously cancels the dispatch source, preventing any further invocation of its event handler block. [`extern intptr_t dispatch_source_testcancel(dispatch_source_t source);`](/documentation/Dispatch/dispatch_source_testcancel) Tests whether the given dispatch source has been canceled. --- Copyright © 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)