title: nsmutablearray meet NSGenericException 'Collection was mutated while being enumerated'
body: <p>I met the exception called 'Collection was mutated while being enumerated' yesterday and saw some solutions.I've got another idea.If I set an argument called 'lock' and each time I enumerate I lock it then unlock it after enumeration.Every time I'll operate it,like enumerating or add object, I lock it first then unlock it after the operation.
  Could someone tell me if it will work?</p>