在本声明的上下文中，ADictionarycansupportmultiplereadersconcurrently,aslongasthecollectionisnotmodified.Evenso,enumeratingthroughacollectionisintrinsicallynotathread-safeprocedure.Intherarecasewhereanenumerationcontendswithwriteaccesses,thecollectionmustbelockedduringtheentireenumeration.Toallowthecollect