主题：【倡议】Java SE 5.0和.NET 2.0擂台赛 -- Highway

System.gc()对JVM来说是一个Hint，而不是强制性指令。所以到底什么JVM开始回收内存，是一个不确定的事情。一旦Background thread开始回收内存，前台的程序就会受到极大的影响。这是我们测试的一个难点。

Calling the gc method suggests that the Java Virtual Machine expend effort toward recycling unused objects in order to make the memory they currently occupy available for quick reuse. When control returns from the method call, the Java Virtual Machine has made a best effort to reclaim space from all discarded objects.

理论上讲，Thread-safe的操作是有代价的。如果情况允许，我们尽可能避开这个开销！