Consider the following statements about user-level threads and kernel-level threads. Which one of the following statements is FALSE?

Context switch time is longer for kernel-level threads than for user-level threads.
User-level threads do not need any hardware support.
Related kernel-level threads can be scheduled on different processors in a multiprocessor system.
Blocking one kernel thread blocks all related threads.

Correct answer: Blocking one kernel thread blocks all related threads.

Solution

Kernel-level threads are known to the operating system, so one blocked thread does not necessarily block all other threads of the same process. In contrast, user-level threads are managed by a user-space library and may all be affected if the underlying kernel entity blocks.

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