shm1.pll

来自「一个嵌入式系统的C代码」· PLL 代码 · 共 46 行

PROGRAM Shm1 (INPUT, OUTPUT);

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

VAR
  sem, shm, value, result, temp : INTEGER;

BEGIN
  { create semaphore and make sure it is set to 0 }
  sem := SYSTEM(SEM_CREATE, 'mysem', 0);
  shm := SYSTEM(SHR_CREATE, 'myshm', 1);

  IF (sem > 0) AND (shm > 0) THEN
  BEGIN
    Write('Enter a number ==> ' );
    Read( value# );
    
    Writeln( 'Value was read' );

    temp := SYSTEM(SHR_WRITE, shm, 0, value);

    { Signal other process that it now has a value to work with }
    temp := SYSTEM( SEM_SIGNAL, sem );    
    
    { Wait for other process to read value }
    { from shared memory and square it }
    Write('Waiting.. ');
    temp := SYSTEM(SEM_WAIT, sem);
    WriteLn;  WriteLn;

    result := SYSTEM(SHR_READ, shm, 0);
    WriteLn( value#, ' squared is ', result# );
    
    temp := SYSTEM(SEM_CLOSE, sem);
    temp := SYSTEM(SHR_CLOSE, shm)
  END;
END.

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