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dispatch_data_create(3) Library Functions Manual dispatch_data_create(3) NAME dispatch_data_create, dispatch_data_create_concat, dispatch_data_create_subrange, dispatch_data_create_map, dispatch_data_apply, dispatch_data_copy_region, dispatch_data_get_size -- create and manipulate dispatch data objects SYNOPSIS #include <dispatch/dispatch.h> dispatch_data_t dispatch_data_create(const void* buffer, size_t size, dispatch_queue_t queue, dispatch_block_t destructor); dispatch_data_t dispatch_data_create_concat(dispatch_data_t data1, dispatch_data_t data2); dispatch_data_t dispatch_data_create_subrange(dispatch_data_t data, size_t offset, size_t length); dispatch_data_t dispatch_data_create_map(dispatch_data_t data, const void **buffer_ptr, size_t *size_ptr); bool dispatch_data_apply(dispatch_data_t data, bool (^applier)(dispatch_data_t, size_t, const void *, size_t)); dispatch_data_t dispatch_data_copy_region(dispatch_data_t data, size_t location, size_t *offset_ptr); size_t dispatch_data_get_size(dispatch_data_t data); dispatch_data_t dispatch_data_empty; DESCRIPTION Dispatch data objects are opaque containers of bytes that represent one or more regions of memory. They are created either from memory buffers managed by the application or the system or from other dispatch data objects. Dis- patch data objects are immutable and the memory regions they represent are required to remain unchanged for the lifetime of all data objects that ref- erence them. Dispatch data objects avoid copying the represented memory as much as possible. Multiple data objects can represent the same memory re- gions or subsections thereof. CREATION The dispatch_data_create() function creates a new dispatch data object of given size from a buffer. The provided destructor block will be submitted to the specified queue when the object reaches the end of its lifecycle, indicating that the system no longer references the buffer. This allows the application to deallocate the associated storage. The queue argument is ignored if one of the following predefined destructors is passed: DISPATCH_DATA_DESTRUCTOR_FREE indicates that the provided buffer can be deallocated with free(3) di- rectly. DISPATCH_DATA_DESTRUCTOR_DEFAULT indicates that the provided buffer is not managed by the application and should be copied into memory managed and automatically deallo- cated by the system. The dispatch_data_create_concat() function creates a new data object repre- senting the concatenation of the memory regions represented by the provided data objects. The dispatch_data_create_subrange() function creates a new data object rep- resenting the sub-region of the provided data object specified by the offset and length parameters. The dispatch_data_create_map() function creates a new data object by map- ping the memory represented by the provided data object as a single con- tiguous memory region (moving or copying memory as necessary). If the buffer_ptr and size_ptr references are not NULL, they are filled with the location and extent of the contiguous region, allowing direct read access to the mapped memory. These values are valid only as long as the newly cre- ated object has not been released. ACCESS The dispatch_data_apply() function provides read access to represented mem- ory without requiring it to be mapped as a single contiguous region. It traverses the memory regions represented by the data argument in logical order, invokes the specified applier block for each region and returns a boolean indicating whether traversal completed successfully. The applier block is passed the following arguments for each memory region and returns a boolean indicating whether traversal should continue: dispatch_data_t rgn data object representing the region size_t offset logical position of the region in data const void *loc memory location of the region size_t size extent of the region The rgn data object is released by the system when the applier block re- turns. The associated memory location loc is valid only as long as rgn has not been deallocated; if loc is needed outside of the applier block, the rgn object must be retained in the block. The dispatch_data_copy_region() function finds the contiguous memory region containing the logical position specified by the location argument among the regions represented by the provided data object and returns a newly created copy of the data object representing that region. The variable specified by the offset_ptr argument is filled with the logical position where the returned object starts in the data object. The dispatch_data_get_size() function returns the logical size of the mem- ory region or regions represented by the provided data object. EMPTY DATA OBJECT The dispatch_data_empty object is the global singleton object representing a zero-length memory region. It is a valid input to any dispatch_data functions that take data object parameters. MEMORY MODEL Dispatch data objects are retained and released via calls to dispatch_re- tain() and dispatch_release(). Data objects passed as arguments to a dis- patch data create or copy function can be released when the function re- turns. The newly created object holds implicit references to their con- stituent memory regions as necessary. The functions dispatch_data_create_map() and dispatch_data_apply() return an interior pointer to represented memory that is only valid as long as an associated object has not been released. When Objective-C Automated Refer- ence Counting is enabled, care needs to be taken if that object is held in a variable with automatic storage. It may need to be annotated with the objc_precise_lifetime attribute, or stored in a __strong instance variable instead, to ensure that the object is not released prematurely before mem- ory accesses via the interor pointer have been completed. SEE ALSO dispatch(3), dispatch_object(3), dispatch_io_read(3) Darwin December 1, 2010 dispatch_data_create(3)
NAME | SYNOPSIS | DESCRIPTION | CREATION | ACCESS | EMPTY DATA OBJECT | MEMORY MODEL | SEE ALSO
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