shmarr2.pll

来自「一个嵌入式系统的C代码」· PLL 代码 · 共 55 行

PROGRAM myshm (INPUT, OUTPUT);

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

VAR
  count, mysemA, mysemB, myshm, value, result, temp : INTEGER;

BEGIN
  mysemA := SYSTEM(SEM_OPEN, 'sem1');

  IF mysemA > 0  THEN
  BEGIN
    { wait for other process to signal it's }
    { placed a value in the shared memory }
    mysemB := SYSTEM(SEM_OPEN, 'sem2');
    Writeln( 'I am now waiting for a signal from other process ' );
    temp := SYSTEM( SEM_WAIT, mysemB );
    myshm := SYSTEM(SHR_OPEN, 'myshm' );

    IF myshm > 0 THEN
    BEGIN
      FOR count := 1 TO 10 DO
      BEGIN
        { Get Value from shared memory }
        value := SYSTEM(SHR_READ, myshm, count-1 );
     
        Write( 'I read ', value# );
        WriteLn( ' from shared memory, squaring it..' );
        result := value * value;

        temp := SYSTEM(SHR_WRITE, myshm, count-1, result )
      END;    
      
      { tell other process I've squared the value }
      temp := SYSTEM(SEM_SIGNAL, mysemA );

      temp := SYSTEM(SEM_CLOSE, mysemA);
      temp := SYSTEM(SEM_CLOSE, mysemB);
      temp := SYSTEM(SHR_CLOSE, myshm)
    END
    ELSE
    BEGIN
      Writeln( 'ERROR: You must execute shmarr1 before this program.' )
    END
  END
END.

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