Which one of the following cannot be scheduled by the kernel ?

The correct answer is User level thread.

Key Points

• A user level thread is managed by a user-level library and not directly by the kernel.
  • The kernel is not aware of the user-level threads, it schedules the process as a whole.
  • Since user-level threads are managed in the user space, the kernel does not have visibility or control over them.
  • Context switching between user-level threads is faster because it does not involve kernel mode.
  • User-level threads provide better performance for applications that do not require frequent blocking system calls.
  • Examples of user-level thread libraries include POSIX Threads (Pthreads) and Java Threads.

Additional Information

• User-level threads can be scheduled independently of the kernel, which can lead to better performance in certain scenarios.
• However, one of the drawbacks is that if a user-level thread performs a blocking operation, the entire process is blocked.
• Kernel-level threads, on the other hand, are managed and scheduled directly by the kernel, which allows for better handling of blocking operations.
• Hybrid threading models combine the advantages of both user-level and kernel-level threads.
• Examples of hybrid threading models include the Solaris operating system, which uses lightweight processes (LWPs) that are visible to the kernel.