The pthread_kill() function requests from the kernel to deliver a specified signal be to a specified thread. Just like in the kill() function, error checking shall be performed but no signal shall actually be sent, if sig is zero. The function shall return a value of zero, upon successful completion. The function shall return an error number otherwise. No signal shall be sent if the pthread_kill() function fails. [EINVAL] The value of the sig argument is an invalid or unsupported signal number. The pthread_kill () function shall not return an error code of [EINTR].