iAPX 286 Operating System Writers Guide 1983

DATA SHARING, ALIASING, AND SYNCHRONIZATIONPL/M-286 COMPILER 960-504 date PAGE 1system-I 0 PL/M-286 Vx.y COMPILATION OF MODULE SEMAPHOBJECT MODULE PLACED IN :Fl:SEMAPH.OBJCOMPILER INVOKED BY: PLM286.86 :Fl:SEMAPH.PLM DEBUG$ PAGEWIDTH(71) TITLE('960-504') INCLUDE (:Fl:NUCSUB.PLM)$ NOLIST1SEMAPH:DO;23456789121221221/*****************************************************'**//* Externals */DISPATCHER: PROCEDURE EXTERNAL;END DISPATCHER;ENQUEUE WAIT: PROCEDURE(QUEUE ID) EXTERNAL;DECLARE QUEUE ID SELECTOR;END ENQUEUE_WAIT;DEQUEUE WAIT: PROCEDURE(QUEUE ID,EXCEP P) EXTERNAL;DECLARE QUEUE ID SELECTOR, EXCEP P POINTER;END DEQUEUE_WAIT; -/*******************************************************//* Semaphore Data Structures */DECLARE SEMAPHORMAT LITERALLY'FILLER (2) WORD,COUNTER WORD';111DECLARE OKLITERALLY '0';121314151617181920212223122222233332/*******************************************************//* Test a semaphore; wait if not set */WAIT SEMAPHORE: PROCEDURE (SEMAPH ID, EXCEP P)PUBLIC-REENTRANT;DECLARE SEMAPH ID SELECTOR,SEMAPH-BASED SEMAPH ID STRUCTURE(SEMAPHORMAT);DECLARE EXCEP PEXCEP-BASED EXCEP PPOINTER,WORD;DISABLE;SEMAPH.COUNTER=SEMAPH.COUNTER-l;IF ZERO /* Test the zero flag. */THEN /* Semaphore was set. */ DO;ENABLE;EXCEP=OK;RETURN;END;/* Semaphore is not set; this task must wait. */CALL ENQUEUE_WAIT (SEMAPH 10);Figure 5·5. Semaphore Example5-8 121960-001