basic async operations

JNWAsyncGroupOperation.m

#import <Foundation/Foundation.h>
 
typedef void (^JNWGroupAsyncOperationCompletion)();
 
@interface JNWGroupAsyncOperation : NSObject
 
// The completion block that will be fired when all operations have completed.
@property (nonatomic, copy) void(^groupCompletion)();
 
// Adds an asynchronous operation and starts it on the main thread. The completion block _must_ 
// be called when the async operation has completed, otherwise the entire operation will never complete.
- (void)addAsynchronousOperation:(void (^)(JNWGroupAsyncOperationCompletion completion))operation;
 
// Waits for the operations to complete, then runs the `groupCompletion` block. If the operations
// have already completed by the time this is called, the completion will be called immediately.
- (void)start;
 
@end

JNWGroupAsyncOperation.m

#import "JNWGroupAsyncOperation.h"
 
@interface JNWGroupAsyncOperation()
@property (nonatomic, strong) dispatch_group_t dispatchGroup;
@end
 
@implementation JNWGroupAsyncOperation
 
- (instancetype)init {
    self = [super init];
    self.dispatchGroup = dispatch_group_create();
    return self;
}
 
- (void)addAsynchronousOperation:(void (^)(JNWGroupAsyncOperationCompletion))operation {
    dispatch_group_t dispatchGroup = self.dispatchGroup;
 
    void (^completion)() = ^{
        dispatch_group_leave(dispatchGroup);
    };
 
    dispatch_group_enter(dispatchGroup);
    dispatch_async(dispatch_get_main_queue(), ^{
        operation(completion);
    });
}
 
- (void)start {
    if (self.groupCompletion != NULL) {
        dispatch_group_notify(self.dispatchGroup, dispatch_get_main_queue(), self.groupCompletion);
    }
}
 
@end