Deadlocks and threads

Question

Which one of the following  is false about user threads

1. User threads can switch fast since it does noy invoke kernel

2.user threads are light weight since they do not require system call

3.kernel is not aware of the behavior  of every user threads ie if it is blocking or run able

4.none of these

Comments

2) ???

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Sir why the answer is 2.I also think the answer is 2 because  it require a kernel system call but in this it is not mention any system call. And kernel user thread is a light weight thread. So I think option 2 is false. Sir is it right

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First of all, thanks for respect, but I am not Sir,

Secondly, consider you have built a software, when user run that software, then to make it more responsive, we use thread, know one of the thread will show "LOADING..." while some other threads working background and loading all required file to run the software.

In this the thread, which is showing "LOADING..." using the system call, and in that system call it is using IO device.

So, the statement,"user threads are light weight since they do not require system call" is false.

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The question seems ambiguous. I think Answer is 2

Answer 1

I think to create user level thread we don't need a system call but it doesn't mean that user thread can't make system call.

e.g one thread can request for an hard-disk by making a system call.

So the 2nd options seems right but still ambiguous.