实现线程调度程序循环和线程取消

Question

I'm very new in C language and linux and English is not my mother language. Sorry for those in advance.

I'm working on school project which is to implement a round robin scheduler on linux and I have some problems on implementing scheduler and thread_self.

Scheduler checks if ready queue is empty first, if yes set time slice and alarm(timeslice). Otherwise, look up a new thread from ready list, dispatch TCB of new thread, set timeslice, context switch to new thread and set alarm(timeslice). But I keep getting error at some point and I couldn't find where to fix.

Another thing is about thread_cancel. int thread_cancel(thread_t tid) function removes target tcb and I need to find the tcb using tid. I tried like

Thread* temp = getpid();
kill(pid, SIGKILL);

but I couldn't figure out how to remove tcb from queue. Please give me some better idea!

Thread.h

typedef struct _Thread{
    ThreadStatus status;
    pid_t pid;
    Thread* pPrev;
    Thread* pNext;
}Thread;
Thread* ReadyQHead;
Thread* ReadyQTail;

-Queue

typedef struct _queue{
    Thread* head;
    Thread* tail;
    unsigned int num;
} queue;

queue* runList;
queue* readyList;
queue* waitList; 

-Queue.c

void enqueue(queue * q, Thread* tcb)
{
    if(q->num == 0) {
        q->head = tcb;
        q->tail = tcb;
    } else {
        q->tail->pNext = tcb;
        q->tail = tcb;
    }
    q->num ++;
}

Thread * dequeue(queue * q)
{
    Thread * tmp;
    if(q->num == 0) return NULL;
    else if(q->num == 1) {
        tmp = q->head;
        q->head = NULL;
        q->tail = NULL;
    } else {
        tmp = q->head;
        q->head = q->head->pNext;
    }
    q->num --;
    return tmp;
}

-Scheduler

void alarmHandler(int signal)
{
    printf("Scheduler awake!!");
    /*Do schedule*/
}

int RunScheduler( void )
{
    //check if ready queue is empty
    if(is_empty(readyList) != 0)
    {
        printf("this is weird");
        signal(SIGALRM, alarmHandler);
    }
    else {
        /*Look up a new thread from ready list*/
        Thread* tmp = ReadyQHead;

        /*send sigcont*/
        kill(tmp->pid, SIGCONT);

        //dispatch TCB of new thread
        if(is_empty(runList) != 0 && runList->head->status == 0)
            enqueue(readyList, tmp);

        //pick thread at head of ready list as first thread to dispatch
        tmp->status = 0; // tmp == runningTcb
        printf("alive tcb : %d\n", tmp->pid);

        ReadyQHead = dequeue(readyList);
        //set timeslice
        signal(SIGALRM, alarmHandler);
        //context switch to new thread
        _ContextSwitch(tmp->pid, ReadyQHead->pid);

    }

    while(1){
        alarm(TIMESLICE);
    }

    return 0;
}


void _ContextSwitch(int curpid, int tpid)
{
    kill(curpid, SIGSTOP);
    kill(tpid, SIGCONT);
}

Answer 1

here is an simple example of round robin

while(1)
{
    process1();
    process2();
    process3();
    process4();
    ....
    processN();
}

anything more complex, such as context switching while a process is 'sleeping' or context switching while waiting for I/O or context switching because a process needs to be run on a timed basis or due to an interrupt event adds massive complexity.

So exactly what is your goal/objective?