signals/threads

Hi

I have some basic questions on signals in Linux

a) In which context the signal handler is executed - (the thread that
registered for the handler, or something else)
b) What happens if the same signal comes again while the signal handler
execution is still not complete ? Will the new signal be lost ?
c)Can a deadlock possible in this case - Say thread acquires a
semaphore and is in the middle of the CS. Then signal handler comes in
execution and tries to grab the same semaphore.
d) In general is it advisable to use mutexes/sempahores inside signal
handlers ?

Thanks

.

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