内存绝不会被应用程序显式释放，而是被垃圾收集器定期回收。
Memory is never explicitly freed by the application but is instead reclaimed periodically by the garbage collector.
当较高级（第 1 级或第 2 级）垃圾回收发生时此计数器被显式递增。
This counter is explicitly incremented when a higher generation (generation 1 or 2) garbage collection occurs.
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