POSIX 提供了互斥函数来创建临界区，用于实施单线程对对象（一块内存）的独占访问。
POSIX provides the mutex function to create critical sections that enforce exclusive access to an object (a piece of memory) by a single thread.
当第一个线程退出 synchronized 块时，等待着的线程进入并创建另一个 Singleton 对象。
When the first thread exits the synchronized block, the waiting thread enters and creates another Singleton object.
开发者会创建一个指定大小的Scoped内存域，当实例化一个对象的时候，会从这个域内分配一块空间给它。
A developer will create a scoped memory area of a specific size and when objects are instantiated the space for them will be allocated from this area.
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