pthread_sigmask(2) on macOS
The text edcc7dc052b9, as Mac OS X 10.4.11.x86, Mac OS X 10.4.11.ppc, Mac OS X 10.4.10.x86, Mac OS X 10.4.10.ppc, Mac OS X 10.4.9.x86, Mac OS X 10.4.9.ppc, Mac OS X 10.4.8.x86, Mac OS X 10.4.8.ppc, Mac OS X 10.4.7.x86, Mac OS X 10.4.7.ppc, Mac OS X 10.4.6.x86, Mac OS X 10.4.6.ppc, Mac OS X 10.4.5.x86, Mac OS X 10.4.5.ppc, Mac OS X 10.4.4.x86, Mac OS X 10.4.4.ppc, Mac OS X 10.4.3, Mac OS X 10.4.2, Mac OS X 10.4.1, Mac OS X 10.4 shipped it.
examine and/or change a thread's signal mask