ios - NSMutableArray Thread Concurrency with GCD -

i have nsmutablearray in "sharedstore"-pattern singleton.

publicly, it's accessible through methods cast nsarray. within class, it's

@property (nonatomic, copy) nsmutablearray *myitems; 

this array never gets manipulated outsdie singleton viewcontrollers send singleton messages manipulate controller. of these messages empty array, re-populate it, etc.

having ended in situation array empty in 1 method call , not yet empty in next, i've started implementing concurrency behaviour.

here's i'm doing far:

in .m file of singleton, have

@property (nonatomic, strong) dispatch_queue_t arrayaccessqueue; 

in singleton's initializer gets created serial queue. , then, every method has mutating array within dispatch_sync call, example:

dispatch_sync(self.arrayaccessqueue, ^{     [_myitems removeallobjects]; }); 

this has made things better , has made app behave more smoothly. however, have no way of quantifying beyond having fixed 1 odd behaviour described above. kind of feel i'm in dark problems may lurking beneath surface.

this pattern makes sense me, should using else, @synchronize or nslock or nsoperationqueue? come bite me?

using dispatch_sync fine long wrap array reads , writes , ensure serial queue.

but improve things allowing concurrent reads. this, use dispatch_sync around array reads , use dispatch_barrier_sync around array writes. , setup queue concurrent.

do ensures single write can happen @ time, reads block until write done, , write wait until current reads done.