kill signal sometimes can't be received

I wrote a multi-thread application. in thread A, i called kill as below to send a SIGTERM signal.

kill(getpid(), SIGTERM)

in thread B, I have following code to wait for the SIGTERM signal.

sigset_t waitsignalset;
sigemptyset(&waitsignalset);
// Add whatever signal(s) to be processed by this routine
sigaddset(&waitsignalset, SIGINT);
sigaddset(&waitsignalset, SIGQUIT);
sigaddset(&waitsignalset, SIGTERM);

// Examine and Change Blocked Signals
sigprocmask(SIG_BLOCK, &waitsignalset, NULL);
result = sigwait(&waitsignalset, &sig);

I also called sigaction to register my signal handling method. however, the problem I am having is that sometimes, the sigwait can't get the SIGTERM signal, I need to let thread A to send the SIGTERM signal again to let sigwait get the signal.

Anyone might have any clue on why this happened? thanks in advance.