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GO Classes DPP | GATE CS | Operating System | Multithreading Models

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3 3 votes

Which of the following statements about threading models are correct?

  1. User-level threads can be implemented without modifying the operating-system kernel.
     
  2. In a pure user-level threading model, a blocking I/O operation by one thread may block all threads of the process.
     
  3. Kernel-level threads belonging to the same process cannot execute simultaneously on multiple processors.
     
  4. A hybrid threading model can map multiple user-level threads onto a smaller number of kernel scheduling entities.

1 Answer

1 1 vote

Statement (A) is correct.
User-level threads are managed by a user-space thread library.
They can therefore be implemented without adding thread-management support to the kernel.

Statement (B) is correct.
In a many-to-one user-level model, the kernel sees the entire process as one schedulable entity.
If one user thread performs blocking I/O, the kernel may block the entire process.

Statement (C) is incorrect.
Kernel-level threads are independently visible to the operating-system scheduler.
Different threads of the same process can therefore be scheduled simultaneously on different processors.

Statement (D) is correct.
A hybrid or many-to-many model multiplexes several user-level threads over a set of kernel-level threads.
It combines user-level management with kernel-supported parallelism.

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