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Wait statements
The wait statement provides a more flexible way to specify how a process
should be suspended and resumed. A process without a sensitivity list
may contain 0 or more wait statements. There are three main components in
the wait statement, shown in the following rule:
When the wait statement is encountered, the process is unconditionally
suspended. The three parts of the wait statement specify when the process
may be resumed. The sensitivity list is a list of signals that will cause
the process to resume if an event occurs on them. If the condition part
appears, then when an event occurs on a signal in the sensitivity list or
referenced in the condition expression, the
condition expression is evaluated and the process is resumed only if the
resulting value is true. The time expression specifies a time out value.
When the wait statement is first encountered, the expression is evaluated
and the result is the maximum time that the process may be suspended
regardless of a sensitivity-list or condition clause. If none of the
three parts is used, then the process will never resume.