Identifies forms which should not be preempted during execution, in non-SMP LispWorks only
The forms to be evaluated atomically.
The result of executing
Identifies forms which should not be preempted during execution.
is not supported in SMP LispWorks, that is on Microsoft Windows, Mac OS X, Linux, FreeBSD and x86/x64 Solaris platforms.
LispWorks User Guide and Reference Manual - 21 Dec 2011