Nested blocks discussion

NestedBlocks.m

void RetrieveFriends(GameCenter& gameCenter, GKLocalPlayer* localPlayer)
{
	[localPlayer loadFriendsWithCompletionHandler:^(NSArray* friends, NSError* error) 
	{
		// 1. this block is copied and retained by loadFriendsWithCompletionHandler
		// 2. When called, loadPlayersForIdentifiers:withCompletionHandler will copy and retain the block below,
		//    which doesn't exist until the outer block is called
		[GKPlayer loadPlayersForIdentifiers:friends withCompletionHandler:^(NSArray* players, NSError* error2) 
		{
			// Finally, dispatch_async will copy and retain the block which is passed to it below
			dispatch_async(dispatch_get_main_queue(), ^(void)
			{ 
				TestLala(gameCenter); //, friends, players, error2); 
			});
		}];
	}];
}

NestedBlocks.s

	.globl	_RetrieveFriends
	.align	2
	.code	16
	.thumb_func	_RetrieveFriends
_RetrieveFriends:
Leh_func_begin1:
	push	{r4, r5, r7, lr}
	add	r7, sp, #8
	sub	sp, #56
	add	r2, sp, #20
	movs	r3, #0
	str	r0, [r2, #32]
	str	r1, [r2, #28]
	str	r2, [sp, #16]
	add	r2, sp, #24
	ldr.n	r4, LCPI1_0
LPC1_0:
	add	r4, pc
	ldr	r4, [r4]
	ldr	r5, [sp, #16]
	str	r4, [r5, #4]
	movs	r4, #1
	lsls	r4, r4, #30
	str	r4, [r5, #8]
	str	r3, [r5, #12]
	ldr.n	r3, LCPI1_1
LPC1_1:
	add	r3, pc
	str	r3, [r5, #16]
	ldr.n	r3, LCPI1_2
LPC1_2:
	add	r3, pc
	str	r3, [r5, #20]
	ldr	r3, [r5, #32]
	str	r3, [r5, #24]
	ldr	r3, [r5, #28]
	str	r3, [r5]
	ldr.n	r4, LCPI1_3
LPC1_3:
	add	r4, pc
	str	r1, [sp, #12]
	ldr	r1, [r4]
	str	r0, [sp, #8]
	mov	r0, r3
	blx	_objc_msgSend
	ldr	r0, [sp, #12]
	ldr	r1, [sp, #8]
	str	r1, [sp, #4]
	str	r0, [sp]
	subs	r4, r7, #7
	subs	r4, #1
	mov	sp, r4
	pop	{r4, r5, r7, pc}
	.align	2
LCPI1_0:
	.long	L__NSConcreteStackBlock$non_lazy_ptr-(LPC1_0+4)
	.align	2
LCPI1_1:
	.long	___RetrieveFriends_block_invoke_1-(LPC1_1+4)
	.align	2
LCPI1_2:
	.long	___block_descriptor_tmp_3.54-(LPC1_2+4)
	.align	2
LCPI1_3:
	.long	L_OBJC_SELECTOR_REFERENCES_1-(LPC1_3+4)
Leh_func_end1:

	.align	2
	.code	16
	.thumb_func	___RetrieveFriends_block_invoke_1
___RetrieveFriends_block_invoke_1:
Leh_func_begin2:
	push	{r4, r5, r6, r7, lr}
	add	r7, sp, #12
	sub	sp, #72
	add	r3, sp, #28
	movs	r4, #0
	str	r0, [r3, #40]
	str	r1, [r3, #36]
	str	r2, [r3, #32]
	ldr	r5, [r3, #40]
	ldr	r5, [r5, #20]
	str	r5, [r3]
	str	r3, [sp, #24]
	add	r3, sp, #36
	ldr.n	r5, LCPI2_0
LPC2_0:
	add	r5, pc
	ldr	r5, [r5]
	ldr	r6, [sp, #24]
	str	r5, [r6, #8]
	movs	r5, #1
	lsls	r5, r5, #30
	str	r5, [r6, #12]
	str	r4, [r6, #16]
	ldr.n	r4, LCPI2_1
LPC2_1:
	add	r4, pc
	str	r4, [r6, #20]
	ldr.n	r4, LCPI2_2
LPC2_2:
	add	r4, pc
	str	r4, [r6, #24]
	ldr	r4, [r6]
	str	r4, [r6, #28]
	ldr.n	r4, LCPI2_3
LPC2_3:
	add	r4, pc
	ldr	r4, [r4]
	str	r4, [r6, #4]
	ldr.n	r5, LCPI2_4
LPC2_4:
	add	r5, pc
	str	r1, [sp, #20]
	ldr	r1, [r5]
	str	r2, [sp, #16]
	ldr	r2, [r6, #36]
	str	r0, [sp, #12]
	mov	r0, r4
	blx	_objc_msgSend
	ldr	r0, [sp, #16]
	ldr	r1, [sp, #20]
	ldr	r2, [sp, #12]
	str	r2, [sp, #8]
	str	r0, [sp, #4]
	str	r1, [sp]
	subs	r4, r7, #7
	subs	r4, #5
	mov	sp, r4
	pop	{r4, r5, r6, r7, pc}
	.align	2
LCPI2_0:
	.long	L__NSConcreteStackBlock$non_lazy_ptr-(LPC2_0+4)
	.align	2
LCPI2_1:
	.long	___RetrieveFriends_block_invoke_2-(LPC2_1+4)
	.align	2
LCPI2_2:
	.long	___block_descriptor_tmp_2.52-(LPC2_2+4)
	.align	2
LCPI2_3:
	.long	L_OBJC_CLASSLIST_REFERENCES_$_0-(LPC2_3+4)
	.align	2
LCPI2_4:
	.long	L_OBJC_SELECTOR_REFERENCES_0-(LPC2_4+4)
Leh_func_end2:

	.align	2
	.code	16
	.thumb_func	___RetrieveFriends_block_invoke_2
___RetrieveFriends_block_invoke_2:
Leh_func_begin3:
	push	{r4, r5, r7, lr}
	add	r7, sp, #8
	sub	sp, #64
	add	r3, sp, #24
	movs	r4, #0
	str	r0, [r3, #36]
	str	r1, [r3, #32]
	str	r2, [r3, #28]
	ldr	r5, [r3, #36]
	ldr	r5, [r5, #20]
	str	r5, [r3]
	str	r1, [sp, #20]
	add	r1, sp, #28
	ldr.n	r5, LCPI3_0
LPC3_0:
	add	r5, pc
	ldr	r5, [r5]
	str	r5, [r3, #4]
	movs	r5, #1
	lsls	r5, r5, #30
	str	r5, [r3, #8]
	str	r4, [r3, #12]
	ldr.n	r4, LCPI3_1
LPC3_1:
	add	r4, pc
	str	r4, [r3, #16]
	ldr.n	r4, LCPI3_2
LPC3_2:
	add	r4, pc
	str	r4, [r3, #20]
	ldr	r4, [r3]
	str	r4, [r3, #24]
	ldr.n	r3, LCPI3_3
LPC3_3:
	add	r3, pc
	str	r0, [sp, #16]
	ldr	r0, [r3]
	str	r2, [sp, #12]
	blx	_dispatch_async
	ldr	r0, [sp, #12]
	ldr	r1, [sp, #20]
	ldr	r2, [sp, #16]
	str	r2, [sp, #8]
	str	r0, [sp, #4]
	str	r1, [sp]
	subs	r4, r7, #7
	subs	r4, #1
	mov	sp, r4
	pop	{r4, r5, r7, pc}
	.align	2
LCPI3_0:
	.long	L__NSConcreteStackBlock$non_lazy_ptr-(LPC3_0+4)
	.align	2
LCPI3_1:
	.long	___RetrieveFriends_block_invoke_3-(LPC3_1+4)
	.align	2
LCPI3_2:
	.long	___block_descriptor_tmp_1.50-(LPC3_2+4)
	.align	2
LCPI3_3:
	.long	L__dispatch_main_q$non_lazy_ptr-(LPC3_3+4)
Leh_func_end3:

	.align	1
	.code	16
	.thumb_func	___RetrieveFriends_block_invoke_3
___RetrieveFriends_block_invoke_3:
Leh_func_begin4:
	push	{r7, lr}
	mov	r7, sp
	sub	sp, #16
	add	r1, sp, #8
	str	r0, [r1, #4]
	ldr	r2, [r0, #20]
	str	r2, [r1]
	str	r0, [sp, #4]
	mov	r0, r2
	bl	_TestLala
	ldr	r0, [sp, #4]
	str	r0, [sp]
	mov	sp, r7
	pop	{r7, pc}
Leh_func_end4:

Looking at the assembly, you can see there are 3 separate symbols which represent each of the blocks (which are just functions), ___RetrieveFriends_block_invoke_1, ___RetrieveFriends_block_invoke_2 and ___RetrieveFriends_block_invoke_3.

The only object that is would potentially need to be retained is the localPlayer parameter, however it is used immediately and no longer needed for any of the nested calls. We're also assuming that the gameCenter reference is likely a singleton or lives for a long time.