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One of the disadvantages of user level threads compared to Kernel level thread is

  1. If a user level thread of a process executes a system call, all threads in that process are blocked.
  2. Scheduling is application dependent.
  3. Thread switching doesn’t require kernel mode privileges.
  4. The library procedures invoked for thread management in user level threads are local procedures.
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4 Answers

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option A is a disadvantage....because in user level thread ...kernel has no idea that does process implement 1 thread or 100 threads...so when any one thread makes i/o request or system call , then form kernel point of view ....the whole process is making i/o or system call....hence rather than blocking only one thread ....we will block the complete process hence its a disadvantage...
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2 votes

User Level Threads

Advantages

  • Thread switching does not require Kernel mode privileges.
  • User level thread can run on any operating system.
  • Scheduling can be application specific in the user level thread.
  • User level threads are fast to create and manage.

Disadvantages

  • In a typical operating system, most system calls are blocking.
  • Multithreaded application cannot take advantage of multiprocessing.

Thus, ans is A, rest are advantages of User Level Threads.

ref: https://www.tutorialspoint.com/operating_system/os_multi_threading.htm

      http://www.cs.iit.edu/~cs561/cs450/ChilkuriDineshThreads/dinesh%27s%20files/User%20and%20Kernel%20Level%20Threads.html

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option A is the answer because os treats user level threads of a process, as if it is a single process.
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Ans : A
If a user level thread of a process executes a system call, all threads in that process are blocked.
Answer:

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