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9.7.3 Conditional Entry Calls

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A conditional_entry_call issues an entry call that is then cancelled if it is not selected immediately (or if a requeue-with-abort of the call is not selected immediately). A procedure call may appear rather than an entry call for cases where the procedure can be implemented by an entry. 

Syntax

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conditional_entry_call ::= 
  select
   entry_call_alternative
  else
   sequence_of_statements
  end select;

Dynamic Semantics

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The execution of a conditional_entry_call is defined to be equivalent to the execution of a timed_entry_call with a delay_alternative specifying an immediate expiration time and the same sequence_of_statements as given after the reserved word else. 
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NOTE   A conditional_entry_call can briefly increase the Count attribute of the entry, even if the conditional call is not selected.

Examples

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Example of a conditional entry call: 
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procedure Spin(R : in out Resource) is  -- see 9.4
begin
   loop
      select
         R.Seize;
         return;
      else
         null;  --  busy waiting
      end select;
   end loop;
end;
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