Question

I want to check in viewDidLoad that a thread is running or not,
how can I achieve such concept?

Answer 1

Yes, you can.

NSThread has methods for determining thread state

isExecuting
isCancelled
isFinished 

you can use these methods.

for example in viewDidLoad you can write

BOOL stillRunning = [[NSThread currentThread] isExecuting];

UPDATION :

[NSThread currentThread] will return current running thread. its static method of NSThread class.
for your own thread

BOOL isStillRunning = [yourThreadObject isExecuting];