pthread_kill issue

[Parikshat Dubey]

Hi All!
I  need your help.I want to know how to check whether thread is alive or 
not.I go through pthread_kill function

pthread_kill(thread_id,0);

i have read If sig(2nd argument) is 0, a  validity check is performed for 
the existence of the  target
thread (thread_id(1st Argument)).

Upon successful completion, the function returns a value  of
 0. Otherwise  the  function returns an error number. If the
 pthread_kill() function fails, no signal is sent.

I want to know few things:
i)pthread_kill will be successfully executed(in that case it will return 
0)but how do we check whether thread_id exists or not.
ii)i want to know how the successful execution of pthread_kill function 
determines whether thread_id exists or not.
iii) or if possible i want to know how it is related to successful execution 
of function pthread_kill.

in very simple   terms, i want to know if thread_id doesnot exist,i will get 
value other than 0 and if exists i will get the value 0.That this what i 
have mentioned just now means in above synopsis of pthread_kill function.

Dear all ! I need your help inresolving the fundas behind it.please help me 
and give me precise justification that will let concepts clear about 
pthread_function.

thanksandregards
parikshatdubey

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