Passing context data via a custom dispatch source (basic)

custom_dispatch_source.m

// Prints 'x = 2.0' to the Console log

#import "custom_dispatch_source.h"

typedef struct ContextData
{
    double x;
} ContextData;

@interface custom_dispatch_source ()
{
    dispatch_queue_t dispatch_queue;
    dispatch_source_t dispatch_source;
}

@end

@implementation custom_dispatch_source

- (void)dispatch_custom_source {
  
    dispatch_queue = dispatch_queue_create("dispatch_queue", DISPATCH_QUEUE_CONCURRENT);
    dispatch_source = dispatch_source_create(DISPATCH_SOURCE_TYPE_DATA_ADD, 0, 0, dispatch_queue);
    dispatch_source_set_event_handler(dispatch_source, ^{
        struct ContextData * data = dispatch_get_context(dispatch_source);
        printf("x = %f", data->x);
    });
    
    dispatch_resume(dispatch_source);
    
    struct ContextData *context_data = malloc(sizeof(struct ContextData));
    context_data->x = 2.0;
    dispatch_set_context(dispatch_source, context_data);
    dispatch_source_merge_data(dispatch_source, 1);
}


@end