iOS里的sleep函数会阻塞什么

Question

偶然发现Objective-C里的 sleep 函数，是一个宏定义，如下

unsigned int
	 sleep(unsigned int) __DARWIN_ALIAS_C(sleep);

那么这个sleep会阻塞哪些东西呢？是不是所有的Operation都会被阻塞？还是只有主线程被阻塞？
通过 detachNewThreadSelector: toTarget: withObject: 方法出来的线程会不会受影响？
另外，如果我连续运行两次：

sleep(1);
sleep(1);

这样，第二个sleep是从第一个sleep的1s结束后才开始计算么？

Answer 1

Block the current thread. Once this sentence is seen, the current thread hangs for a given time and then executes the next sentence.

Answer 2

This sleep() function should only sleep the thread currently executing this method

sleep(1);
sleep(1);

Looking at these two lines of code alone, they are just synchronization methods. The second line must be executed only after the first line is executed