Using Guards

Guards can enforce different queuing disciplines:

message Request { ename requester; int count;};

• First Fit

  receive (Request r) when (r.count <= units)
  

• FIFO (first in, first out): use function qhead(msg) or qposition (msg,n)

  receive (Request r) when ((qhead(r)).count <= units)
  

• Priority: use function qlength(msg) or qempty(msg)

  receive (Request r) when (qempty(Release) && r.count <= units)
  

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