LockedResource.m

#include <stdio.h>
#include <pthread.h>
#include <Foundation/Foundation.h>

typedef void (^LockedResourceWorker)(void *resource);
typedef void (^LockedResourceAcquirer)(LockedResourceWorker worker);

LockedResourceAcquirer LockedResource(void *resource)
{
	NSLock *lock = [[NSLock new] autorelease];
	return Block_copy(^(LockedResourceWorker worker) {
		[lock lock];
		worker(resource);
		[lock unlock];
	});
}

struct something_s {
	LockedResourceAcquirer locked_buffer;
};

void doingSomething(struct something_s something, int i);


int main (int argc, const char * argv[]) {
	NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
	struct something_s something;
	int *resource = malloc(sizeof(int));
	
	something.locked_buffer = LockedResource(resource);
	
	dispatch_apply(10, dispatch_get_global_queue(0, 0), ^(size_t i){doingSomething(something, i);});
	
	something.locked_buffer(^ (void *buffer) {
		printf("Buffer should be 45: %d", *((int*)buffer));
	});
	
	Block_release(something.locked_buffer);
	
	[pool drain];
    return 0;
}

void doingSomething(struct something_s something, int i)
{
	something.locked_buffer(^ (void *buffer) {
		*((int*)buffer) += i;
	});
}