REL takes a message out of the IL of an R type node

Syntax:

    REL(<internal list of node R>, <logical expression>) <associated instruction>;

This instruction is used to extract a message from the IL of a R type node.

When executed, a search starts at the IL of the node, looking for the first message for which <logical expression> is true. If there is not such a message nothing is done. If it is found, it is extracted from the IL and the <associated instruction> is executed. If a time of exit is scheduled for a normal release of the resource, the corresponding event of the FEL is removed to eliminate the scheduling.

If there is extraction of message, the boolean variable EXTREL is put to TRUE, otherwise, it remains FALSE. The values in the fields of the extracted messages are passed to the corresponding O_<variables>.

The <associated instruction> must have a SENDTO instruction to dispose of the extracted instruction. Before the SENDTO is executed, instructions can be used to change the values of the fields. To do this, the names of the O_<fields> must be used.

This instruction can be used in nodes of any type.

Example:

   NETWORK
    Entry (I) :: IT := EXPO(3); Urgency := Round(TRIA(0, 5,7));
                 WRITELN('Enter # ', Number: 3,' Urgency ', Urgency: 2);
                 PAUSE;

    Ward  (R) :: USE := 1;

    Call  (A) Physician ::
                 REL(IL_Ward, O_Urgency + 0.2 * (TIME - O_Et) > 5)
                   SENDTO(Physician);
                 IF NOT EXTREL AND (U_Ward > 0) AND (LL(EL_Physician) < 4)
                  THEN EXTR(IL_Ward,FIRST) SENDTO(Physician);
                 IT := 10;

    Physician (R) :: STAY := TRIA(4, 6, 9);

    Exit (E) :: WRITELN('Exit  # ', Number: 3, ' Urgency ', Urgency: 2);
                PAUSE;


   INIT TSIM := 200; Urgency := 3; ACT(Entry, 0);  ACT(Call, 0);


   DECL MESSAGES Entry(Urgency: INTEGER);

Messages (patients) are admitted into the Ward if there is room enough. Each 10 minutes Call is activated. This extracts the first message for which the value of the field Urgency plus a multiple of the waiting time is greater than 5. The extracted message is sent to the node Physician. If no message fulfills this condition the first one in the queue is extracted and sent.

See example 10 (GLIDER examples book).