- set-umask! umaskprocedure
Sets the file protection mask to the exact integer umask and returns an unspecified value.
Warning: Although POSIX specifies that changing the umask affects all threads in the current process, some Scheme implementations maintain a separate simulated umask for each thread. As a result, the effects of this procedure in a multi-threaded program are only partly predictable. This SRFI recommends (but does not require) that in multi-threaded programs the mask be set in the primordial thread before any other threads are created and never changed again.