以下哪一项是FALSE?
(A)用户级别的线程不是由内核调度的。
(B)当用户级线程被阻止时，其进程的所有其他线程也将被阻止。
(C)在用户级线程之间进行上下文切换要比在内核级线程之间进行上下文切换快。
(D)内核级线程无法共享代码段答案： (D)
解释：
| User level thread | Kernel level thread |
|---|---|
| User thread are implemented by user processes. | kernel threads are implemented by OS. |
| OS doesn’t recognized user level threads. | Kernel threads are recognized by OS. |
| Implementation of User threads is easy. | Implementation of Kernel thread is complicated. |
| Context switch time is less. | Context switch time is more. |
| Context switch requires no hardware support. | Hardware support is needed. |
| If one user level thread perform blocking operation then entire process will be blocked. | If one kernel thread perform blocking operation then another thread can continue execution. |
| Example : Java thread, POSIX threads. | Example : Window Solaris. |
来源：http：//quiz.geeksforgeeks.org/operating-system-user-level-thread-vs-kernel-level-thread/
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