system.cc

本次实验的目的在于掌握使用nachos中的线程序解决较为复杂的并发问题。实验内容分三部分：实现事件栅栏原语并进行正确性测试；实现闹钟原语并进行正确性测试；利用事件栅栏和闹钟原语来解决电梯问题（详细内容

// system.cc 
//  Nachos initialization and cleanup routines.
//
// Copyright (c) 1992-1993 The Regents of the University of California.
// All rights reserved.  See copyright.h for copyright notice and limitation 
// of liability and disclaimer of warranty provisions.

#include "copyright.h"
#include "system.h"
#include "Alarm.h"


// This defines *all* of the global data structures used by Nachos.
// These are all initialized and de-allocated by this file.

Thread *currentThread;          // the thread we are running now
Thread *threadToBeDestroyed;        // the thread that just finished
Scheduler *scheduler;           // the ready list
Interrupt *interrupt;           // interrupt status
Statistics *stats;          // performance metrics
Timer *timer;               // the hardware timer device,
                    // for invoking context switches

Alarm *alarmclock;
#ifdef FILESYS_NEEDED
FileSystem  *fileSystem;
#endif

#ifdef FILESYS
SynchDisk   *synchDisk;
#endif

#ifdef USER_PROGRAM // requires either FILESYS or FILESYS_STUB
Machine *machine;   // user program memory and registers
#endif

#ifdef NETWORK
PostOffice *postOffice;
#endif


// External definition, to allow us to take a pointer to this function
extern void Cleanup();


//----------------------------------------------------------------------
// TimerInterruptHandler
//  Interrupt handler for the timer device.  The timer device is
//  set up to interrupt the CPU periodically (once every TimerTicks).
//  This routine is called each time there is a timer interrupt,
//  with interrupts disabled.
//
//  Note that instead of calling Yield() directly (which would
//  suspend the interrupt handler, not the interrupted thread
//  which is what we wanted to context switch), we set a flag
//  so that once the interrupt handler is done, it will appear as 
//  if the interrupted thread called Yield at the point it is 
//  was interrupted.
//
//  "dummy" is because every interrupt handler takes one argument,
//      whether it needs it or not.
//----------------------------------------------------------------------
static void
TimerInterruptHandler(int dummy)
{
    alarmclock->WakeUp();
    if (interrupt->getStatus() != IdleMode)
    interrupt->YieldOnReturn();
}

//----------------------------------------------------------------------
// Initialize
//  Initialize Nachos global data structures.  Interpret command
//  line arguments in order to determine flags for the initialization.  
// 
//  "argc" is the number of command line arguments (including the name
//      of the command) -- ex: "nachos -d +" -> argc = 3 
//  "argv" is an array of strings, one for each command line argument
//      ex: "nachos -d +" -> argv = {"nachos", "-d", "+"}
//----------------------------------------------------------------------
void
Initialize(int argc, char **argv)
{
    int argCount;
    char* debugArgs = "";
    bool randomYield = FALSE;

#ifdef USER_PROGRAM
    bool debugUserProg = FALSE; // single step user program
#endif
#ifdef FILESYS_NEEDED
    bool format = FALSE;    // format disk
#endif
#ifdef NETWORK
    double rely = 1;        // network reliability
    int netname = 0;        // UNIX socket name
#endif
    
    for (argc--, argv++; argc > 0; argc -= argCount, argv += argCount) {
    argCount = 1;
    if (!strcmp(*argv, "-d")) {
        if (argc == 1)
        debugArgs = "+";    // turn on all debug flags
        else {
            debugArgs = *(argv + 1);
            argCount = 2;
        }
    } else if (!strcmp(*argv, "-rs")) {
        ASSERT(argc > 1);
        RandomInit(atoi(*(argv + 1)));  // initialize pseudo-random
                        // number generator
        randomYield = TRUE;
        argCount = 2;
    }
#ifdef USER_PROGRAM
    if (!strcmp(*argv, "-s"))
        debugUserProg = TRUE;
#endif
#ifdef FILESYS_NEEDED
    if (!strcmp(*argv, "-f"))
        format = TRUE;
#endif
#ifdef NETWORK
    if (!strcmp(*argv, "-l")) {
        ASSERT(argc > 1);
        rely = atof(*(argv + 1));
        argCount = 2;
    } else if (!strcmp(*argv, "-m")) {
        ASSERT(argc > 1);
        netname = atoi(*(argv + 1));
        argCount = 2;
    }
#endif
    }

    DebugInit(debugArgs);           // initialize DEBUG messages
    stats = new Statistics();           // collect statistics
    interrupt = new Interrupt;          // start up interrupt handling
    scheduler = new Scheduler();        // initialize the ready queue
    alarmclock = new Alarm("alarmclock");
    if (randomYield)                // start the timer (if needed)
    timer = new Timer(TimerInterruptHandler, 0, randomYield);

    threadToBeDestroyed = NULL;

    // We didn't explicitly allocate the current thread we are running in.
    // But if it ever tries to give up the CPU, we better have a Thread
    // object to save its state. 
    currentThread = new Thread("main");     
    currentThread->setStatus(RUNNING);

    interrupt->Enable();
    CallOnUserAbort(Cleanup);           // if user hits ctl-C
    
#ifdef USER_PROGRAM
    machine = new Machine(debugUserProg);   // this must come first
#endif

#ifdef FILESYS
    synchDisk = new SynchDisk("DISK");
#endif

#ifdef FILESYS_NEEDED
    fileSystem = new FileSystem(format);
#endif

#ifdef NETWORK
    postOffice = new PostOffice(netname, rely, 10);
#endif
}

//----------------------------------------------------------------------
// Cleanup
//  Nachos is halting.  De-allocate global data structures.
//----------------------------------------------------------------------
void
Cleanup()
{
    printf("\nCleaning up...\n");
#ifdef NETWORK
    delete postOffice;
#endif
    
#ifdef USER_PROGRAM
    delete machine;
#endif

#ifdef FILESYS_NEEDED
    delete fileSystem;
#endif

#ifdef FILESYS
    delete synchDisk;
#endif
    
    delete timer;
    delete scheduler;
    delete interrupt;
    
    Exit(0);
}