%\pagebreak
\section{Restrictions on Nesting of Regions}
\label{sec:nesting_restrict}

\index{region nesting rules}
The examples in this section illustrate the region nesting rules. 

The following example is non-conforming because the inner and outer loop regions 
are closely nested:

\cexample{nesting_restrict}{1}

\fexample{nesting_restrict}{1}

The following orphaned version of the preceding example is also non-conforming:

\cexample{nesting_restrict}{2}

\fexample{nesting_restrict}{2}

The following example is non-conforming because the loop and \kcode{single} regions 
are closely nested:

\cexample{nesting_restrict}{3}
\pagebreak

\fexample{nesting_restrict}{3}

The following example is non-conforming because a \kcode{barrier} region cannot 
be closely nested inside a loop region:

\cexample{nesting_restrict}{4}

\fexample{nesting_restrict}{4}

The following example is non-conforming because the \kcode{barrier} region cannot 
be closely nested inside the \kcode{critical} region. If this were permitted, 
it would result in deadlock due to the fact that only one thread at a time can 
enter the \kcode{critical} region:

\cexample{nesting_restrict}{5}

\fexample{nesting_restrict}{5}

The following example is non-conforming because the \kcode{barrier} region cannot 
be closely nested inside the \kcode{single} region. If this were permitted, it 
would result in deadlock due to the fact that only one thread executes the \kcode{single} 
region:

\cexample{nesting_restrict}{6}

\fexample{nesting_restrict}{6}