VDM-10 Language Manual

VDM-10 Language Manual
16.2 Procedural Thread Definitions
A procedural thread provides a mechanism to explicitly define the external behaviour of an active
object through the use of statements, which are executed when the object is started (see section
13.14).
Syntax: procedural thread definition = statement ;
Semantics: A procedural thread is scheduled for execution following the application of a start
statement to the object owning the thread. The statements in the thread are then executed
sequentially, and when execution of the statements is complete, the thread dies. Synchronization
between multiple threads is achieved using permission predicates on shared objects.
Examples: The example below demonstrates procedural threads by using them to compute the
factorial of a given integer concurrently.
✞
class Factorial
instance variables
result : nat := 5;
operations
public factorial : nat ==> nat
factorial(n) ==
if n = 0
then return 1
else (dcl m : Multiplier;
m := new Multiplier();
m.calculate(1,n);
start(m);
result:= m.giveResult();
return result
)
end Factorial
class Multiplier
instance variables
i : nat1;
j : nat1;
k : nat1;
result : nat1
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