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 SHARED DATA COMMUNICATION PATTERN
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Two periodic threads exhanging information through 
shared data components.

The behavior differs depending on the value of the 
Concurrency_Control_Protocol property of the shared resource.
- PCP : (also called Priority_Ceiling_Protocol) the thread who gets 
a shared resource cannot be pre-empted before it releases the resource.
- NONE_SPECIFIED: threads can be pre-empted while locking a shared 
resource, which may lead to a dead-lock situation.

The functional behavior of each thread is specified by a 
standard Behavior_Specification subclause. 
It defines the critical sections and the value that is assigned 
to each shared resource.