shm2.pll

一个嵌入式系统的C代码

PROGRAM myshm (INPUT, OUTPUT);

{-----------------------------------------------------------}
{ PURPOSE: Simple Shared memory example                     }
{          Binary sem1aphore used to syncrhonize access      }
{                                                           }
{ AUTHOR:  David Jones                                      }
{ DATE:    18-APR-94                                        }
{-----------------------------------------------------------}

VAR
  mysem, myshm, value, result, temp : INTEGER;

BEGIN
  mysem := SYSTEM(SEM_OPEN, 'mysem');

  IF mysem > 0  THEN
  BEGIN
    { wait for other process to signal it's }
    { placed a value in the shared memory }
    Writeln( 'I am now waiting for a signal from other process ' );
    temp := SYSTEM( SEM_WAIT, mysem );

    myshm := SYSTEM(SHR_OPEN, 'myshm' );

    IF myshm > 0 THEN
    BEGIN
      { Get Value from shared memory }
      value := SYSTEM(SHR_READ, myshm, 0 );
     
      Write( 'I read ', value# );
      WriteLn( ' from shared memory, squaring it..' );
      result := value * value;

      temp := SYSTEM(SHR_WRITE, myshm, 0, result );
    
      { tell other process I've squared the value }
      temp := SYSTEM(SEM_SIGNAL, mysem );

      temp := SYSTEM(SEM_CLOSE, mysem);
      temp := SYSTEM(SHR_CLOSE, myshm)
    END
  END
END.

{------------------------------ EOF -----------------------------}