text: #include "types.h"
  #include "defs.h"
  #include "param.h"
  #include "memlayout.h"
  #include "mmu.h"
  #include "x86.h"
  #include "proc.h"
  #include "spinlock.h"
  struct {
    struct spinlock lock;
    struct proc proc[NPROC];
  } ptable;
  static struct proc *initproc;
  int nextpid = 1;
  extern void forkret(void);
  extern void trapret(void);
  
  static void wakeup1(void *chan);
  
  void
  pinit(void)
  {
    initlock(&ptable.lock, "ptable");
  }
  
  // Must be called with interrupts disabled
  int
  cpuid() {
    return mycpu()-cpus;
  }
  
  // Must be called with interrupts disabled to avoid the caller being
  // rescheduled between reading lapicid and running through the loop.
  struct cpu*
  mycpu(void)
  {
    int apicid, i;
    
    if(readeflags()&FL_IF)
      panic("mycpu called with interrupts enabled\n");
    
    apicid = lapicid();
    // APIC IDs are not guaranteed to be contiguous. Maybe we should have
    // a reverse map, or reserve a register to store &cpus[i].
    for (i = 0; i < ncpu; ++i) {
      if (cpus[i].apicid == apicid)
        return &cpus[i];
    }
    panic("unknown apicid\n");
  }
  
  // Disable interrupts so that we are not rescheduled
  // while reading proc from the cpu structure
  struct proc*
  myproc(void) {
    struct cpu *c;
    struct proc *p;
    pushcli();
    c = mycpu();
    p = c->proc;
    popcli();
    return p;
  }
  
  // Look in the process table for an UNUSED proc.
  // If found, change state to EMBRYO and initialize
  // state required to run in the kernel.
  // Otherwise return 0.
  static struct proc*
  allocproc(void)
  {
    struct proc *p;
    char *sp;
  
    acquire(&ptable.lock);
  
    for(p = ptable.proc; p < &ptable.proc[NPROC]; p++)
      if(p->state == UNUSED)
        goto found;
  
    release(&ptable.lock);
    return 0;
  
  found:
    p->state = EMBRYO;
    p->pid = nextpid++;
    p->tid = 1;
    release(&ptable.lock);
  
    // Allocate kernel stack.
    if((p->kstack = kalloc()) == 0){
      p->state = UNUSED;
      return 0;
    }
    sp = p->kstack + KSTACKSIZE;
  
    // Leave room for trap frame.
    sp -= sizeof *p->tf;
    p->tf = (struct trapframe*)sp;
  
    // Set up new context to start executing at forkret,
    // which returns to trapret.
    sp -= 4;
    *(uint*)sp = (uint)trapret;
  
    sp -= sizeof *p->context;
    p->context = (struct context*)sp;
    memset(p->context, 0, sizeof *p->context);
    p->context->eip = (uint)forkret;
    p->priority=10;
    p->tickets=10;
    return p;
  }
  
  // Set up first user process.
  void
  userinit(void)
  {
    struct proc *p;
    extern char _binary_initcode_start[], _binary_initcode_size[];
  
    p = allocproc();
    
    initproc = p;
    if((p->pgdir = setupkvm()) == 0)
      panic("userinit: out of memory?");
    inituvm(p->pgdir, _binary_initcode_start, (int)_binary_initcode_size);
    p->sz = PGSIZE;
    memset(p->tf, 0, sizeof(*p->tf));
    p->tf->cs = (SEG_UCODE << 3) | DPL_USER;
    p->tf->ds = (SEG_UDATA << 3) | DPL_USER;
    p->tf->es = p->tf->ds;
    p->tf->ss = p->tf->ds;
    p->tf->eflags = FL_IF;
    p->tf->esp = PGSIZE;
    p->tf->eip = 0;  // beginning of initcode.S
  
    safestrcpy(p->name, "initcode", sizeof(p->name));
    p->cwd = namei("/");
  
    // this assignment to p->state lets other cores
    // run this process. the acquire forces the above
    // writes to be visible, and the lock is also needed
    // because the assignment might not be atomic.
    acquire(&ptable.lock);
  
    p->state = RUNNABLE;
  
    release(&ptable.lock);
  }
  
  // Grow current process's memory by n bytes.
  // Return 0 on success, -1 on failure.
  int
  growproc(int n)
  {
    uint sz;
    struct proc *curproc = myproc();
  
    sz = curproc->sz;
    if(n > 0){
      if((sz = allocuvm(curproc->pgdir, sz, sz + n)) == 0)
        return -1;
    } else if(n < 0){
      if((sz = deallocuvm(curproc->pgdir, sz, sz + n)) == 0)
        return -1;
    }
    curproc->sz = sz;
    switchuvm(curproc);
    return 0;
  }
  
  // Create a new process copying p as the parent.
  // Sets up stack to return as if from system call.
  // Caller must set state of returned proc to RUNNABLE.
  int
  fork(void)
  {
    int i, pid;
    struct proc *np;
    struct proc *curproc = myproc();
  
    // Allocate process.
    if((np = allocproc()) == 0){
      return -1;
    }
  
    // Copy process state from proc.
    if((np->pgdir = copyuvm(curproc->pgdir, curproc->sz)) == 0){
      kfree(np->kstack);
      np->kstack = 0;
      np->state = UNUSED;
      return -1;
    }
    np->sz = curproc->sz;
    np->parent = curproc;
    *np->tf = *curproc->tf;
  
    // Clear %eax so that fork returns 0 in the child.
    np->tf->eax = 0;
  
    for(i = 0; i < NOFILE; i++)
      if(curproc->ofile[i])
        np->ofile[i] = filedup(curproc->ofile[i]);
    np->cwd = idup(curproc->cwd);
  
    safestrcpy(np->name, curproc->name, sizeof(curproc->name));
  
    pid = np->pid;
  
    acquire(&ptable.lock);
  
    np->state = RUNNABLE;
  
    release(&ptable.lock);
  
    return pid;
  }
  
  // Exit the current process.  Does not return.
  // An exited process remains in the zombie state
  // until its parent calls wait() to find out it exited.
  void
  exit(void)
  {
    struct proc *curproc = myproc();
    struct proc *p;
    int fd;
  
    if(curproc == initproc)
      panic("init exiting");
  
    // Close all open files.
    for(fd = 0; fd < NOFILE; fd++){
      if(curproc->ofile[fd]){
        fileclose(curproc->ofile[fd]);
        curproc->ofile[fd] = 0;
      }
    }
  
    begin_op();
    iput(curproc->cwd);
    end_op();
    curproc->cwd = 0;
  
    acquire(&ptable.lock);
  
    // Parent might be sleeping in wait().
    wakeup1(curproc->parent);
  
    // Pass abandoned children to init.
    for(p = ptable.proc; p < &ptable.proc[NPROC]; p++){
      if(p->parent == curproc){
        p->parent = initproc;
        if(p->state == ZOMBIE)
          wakeup1(initproc);
      }
    }
  
    // Jump into the scheduler, never to return.
    curproc->state = ZOMBIE;
    sched();
    panic("zombie exit");
  }
  
  // Wait for a child process to exit and return its pid.
  // Return -1 if this process has no children.
  int
  wait(void)
  {
    struct proc *p;
    int havekids, pid;
    struct proc *curproc = myproc();
    
    acquire(&ptable.lock);
    for(;;){
      // Scan through table looking for exited children.
      havekids = 0;
      for(p = ptable.proc; p < &ptable.proc[NPROC]; p++){
        if(p->parent != curproc)
          continue;
        havekids = 1;
        if(p->state == ZOMBIE){
          // Found one.
          pid = p->pid;
          kfree(p->kstack);
          p->kstack = 0;
          freevm(p->pgdir);
          p->pid = 0;
          p->parent = 0;
          p->name[0] = 0;
          p->killed = 0;
          p->state = UNUSED;
          release(&ptable.lock);
          return pid;
        }
      }
  
      // No point waiting if we don't have any children.
      if(!havekids || curproc->killed){
        release(&ptable.lock);
        return -1;
      }
  
      // Wait for children to exit.  (See wakeup1 call in proc_exit.)
      sleep(curproc, &ptable.lock);  //DOC: wait-sleep
    }
  }
  
  // Per-CPU process scheduler.
  // Each CPU calls scheduler() after setting itself up.
  // Scheduler never returns.  It loops, doing:
  //  - choose a process to run
  //  - swtch to start running that process
  //  - eventually that process transfers control
  //      via swtch back to the scheduler.
  int random_variable=0;
  int rand()
  {
  	random_variable+=37*random_variable+2;
  	return random_variable%1007;
  }
  #define NULL 0
  void
  scheduler(void)
  {
    struct proc *p;
    struct cpu *c = mycpu();
    struct proc *p1;
    c->proc = 0;
    
    for(;;){
      // Enable interrupts on this processor.
      sti();
      //struct proc *highP = NULL;
      // Loop over process table looking for process to run.
      acquire(&ptable.lock);
      for(p = ptable.proc; p < &ptable.proc[NPROC]; p++){
      		if(p->state != RUNNABLE)
          continue;
  	/* ----------CODE-FOR-HIGHEST-PRIORITY-FIRST-SCHEDULING--------
  	highP=p;
        // Switch to chosen process.  It is the process's job
        // to release ptable.lock and then reacquire it
        // before jumping back to us.
  	// choose the one with highest priority
  	for(p1 = ptable.proc; p1 < &ptable.proc[NPROC]; p1++)
  	{
  		if(p1->state != RUNNABLE)
  			continue;
  		if ( highP->priority > p1->priority )
  		// larger value, lower priority
  		highP = p1;
  	}
  	p=highP;
        c->proc = p;
        switchuvm(p);
        p->state = RUNNING;
  
        swtch(&(c->scheduler), p->context);
        switchkvm();
  
        // Process is done running for now.
        // It should have changed its p->state before coming back.
        c->proc = 0;
  	--------------CODE-DONE---------------------------------------	
  	*/
        // Switch to chosen process.  It is the process's job
        // to release ptable.lock and then reacquire it
        // before jumping back to us.
  	// choose the one with highest priority
  	int total=0;
  	for(p1 = ptable.proc; p1 < &ptable.proc[NPROC]; p1++)
  	{
  		if(p1->state != RUNNABLE)
  			continue;
  		total+=p1->tickets;
  	}	
  	int num=rand()%total+1;
  	int cur=0;
  	for(p1 = ptable.proc; p1 < &ptable.proc[NPROC]; p1++)
  	{
  		if(p1->state != RUNNABLE)
  			continue;
  		if(num<cur)
  		{
  			p=p1;
  			break;
  		}
  		cur+=p1->tickets;
  	}
  	//p=highP;
        c->proc = p;
        switchuvm(p);
        p->state = RUNNING;
  
        swtch(&(c->scheduler), p->context);
        switchkvm();
  	
        // Process is done running for now.
        // It should have changed its p->state before coming back.
        c->proc = 0;
      }
      release(&ptable.lock);
  
    }
  }
  
  // Enter scheduler.  Must hold only ptable.lock
  // and have changed proc->state. Saves and restores
  // intena because intena is a property of this
  // kernel thread, not this CPU. It should
  // be proc->intena and proc->ncli, but that would
  // break in the few places where a lock is held but
  // there's no process.
  void
  sched(void)
  {
    int intena;
    struct proc *p = myproc();
  
    if(!holding(&ptable.lock))
      panic("sched ptable.lock");
    if(mycpu()->ncli != 1)
      panic("sched locks");
    if(p->state == RUNNING)
      panic("sched running");
    if(readeflags()&FL_IF)
      panic("sched interruptible");
    intena = mycpu()->intena;
    swtch(&p->context, mycpu()->scheduler);
    mycpu()->intena = intena;
  }
  
  // Give up the CPU for one scheduling round.
  void
  yield(void)
  {
    acquire(&ptable.lock);  //DOC: yieldlock
    myproc()->state = RUNNABLE;
    sched();
    release(&ptable.lock);
  }
  
  // A fork child's very first scheduling by scheduler()
  // will swtch here.  "Return" to user space.
  void
  forkret(void)
  {
    static int first = 1;
    // Still holding ptable.lock from scheduler.
    release(&ptable.lock);
  
    if (first) {
      // Some initialization functions must be run in the context
      // of a regular process (e.g., they call sleep), and thus cannot
      // be run from main().
      first = 0;
      iinit(ROOTDEV);
      initlog(ROOTDEV);
    }
  
    // Return to "caller", actually trapret (see allocproc).
  }
  
  // Atomically release lock and sleep on chan.
  // Reacquires lock when awakened.
  void
  sleep(void *chan, struct spinlock *lk)
  {
    struct proc *p = myproc();
    
    if(p == 0)
      panic("sleep");
  
    if(lk == 0)
      panic("sleep without lk");
  
    // Must acquire ptable.lock in order to
    // change p->state and then call sched.
    // Once we hold ptable.lock, we can be
    // guaranteed that we won't miss any wakeup
    // (wakeup runs with ptable.lock locked),
    // so it's okay to release lk.
    if(lk != &ptable.lock){  //DOC: sleeplock0
      acquire(&ptable.lock);  //DOC: sleeplock1
      release(lk);
    }
    // Go to sleep.
    p->chan = chan;
    p->state = SLEEPING;
  
    sched();
  
    // Tidy up.
    p->chan = 0;
  
    // Reacquire original lock.
    if(lk != &ptable.lock){  //DOC: sleeplock2
      release(&ptable.lock);
      acquire(lk);
    }
  }
  
  // Wake up all processes sleeping on chan.
  // The ptable lock must be held.
  static void
  wakeup1(void *chan)
  {
    struct proc *p;
  
    for(p = ptable.proc; p < &ptable.proc[NPROC]; p++)
      if(p->state == SLEEPING && p->chan == chan)
        p->state = RUNNABLE;
  }
  
  // Wake up all processes sleeping on chan.
  void
  wakeup(void *chan)
  {
    acquire(&ptable.lock);
    wakeup1(chan);
    release(&ptable.lock);
  }
  
  // Kill the process with the given pid.
  // Process won't exit until it returns
  // to user space (see trap in trap.c).
  int
  kill(int pid)
  {
    struct proc *p;
  
    acquire(&ptable.lock);
    for(p = ptable.proc; p < &ptable.proc[NPROC]; p++){
      if(p->pid == pid){
        p->killed = 1;
        // Wake process from sleep if necessary.
        if(p->state == SLEEPING)
          p->state = RUNNABLE;
        release(&ptable.lock);
        return 0;
      }
    }
    release(&ptable.lock);
    return -1;
  }
  
  // Print a process listing to console.  For debugging.
  // Runs when user types ^P on console.
  // No lock to avoid wedging a stuck machine further.
  void
  procdump(void)
  {
    static char *states[] = {
    [UNUSED]    "unused",
    [EMBRYO]    "embryo",
    [SLEEPING]  "sleep ",
    [RUNNABLE]  "runble",
    [RUNNING]   "run   ",
    [ZOMBIE]    "zombie"
    };
    int i;
    struct proc *p;
    char *state;
    uint pc[10];
  
    for(p = ptable.proc; p < &ptable.proc[NPROC]; p++){
      if(p->state == UNUSED)
        continue;
      if(p->state >= 0 && p->state < NELEM(states) && states[p->state])
        state = states[p->state];
      else
        state = "???";
      cprintf("%d %s %s", p->pid, state, p->name);
      if(p->state == SLEEPING){
        getcallerpcs((uint*)p->context->ebp+2, pc);
        for(i=0; i<10 && pc[i] != 0; i++)
          cprintf(" %p", pc[i]);
      }
      cprintf("\n");
    }
  }
  int
  cps(struct procList *pl)
  {
  	struct proc *p;// this is sructure which holds infrmation about a process
  	sti(); // used to eable interupts on this processor
  	acquire(&ptable.lock); // get all details from process table 
  	cprintf("name\tpid\tstate\tpriority\ttickets\n");
  	p=ptable.proc;
  	for(int i=0,j=0;i<NPROC;i++)
  	{
  		if(p[i].state == SLEEPING)
  		{
  			cprintf("%s\t%d\tSLEEPING\t%d\t%d\n",p[i].name,p[i].pid,p[i].priority,p[i].tickets);
  			//(*sco)++;
  			pl->p[j].state=p[i].state;
  			pl->p[j].pid=p[i].pid;
  			//pl->p[j].name=p[i].name;
  			
  			pl->p[j].priority=p[i].priority;
  			pl->p[j].tickets=p[i].tickets;
  			j++;
  		}
  		else if(p[i].state == RUNNING)
  		{
  			cprintf("%s\t%d\tRUNNING \t%d\t%d\n",p[i].name,p[i].pid,p[i].priority,p[i].tickets);
  			//(*rco)++;
  			pl->p[j].state=p[i].state;
  			pl->p[j].pid=p[i].pid;
  			//pl->p[j].name=p[i].name;
  			pl->p[j].priority=p[i].priority;
  			pl->p[j].tickets=p[i].tickets;
  			j++;
  			
  		}
  		else if(p[i].state == RUNNABLE)
  		{
  			cprintf("%s\t%d\tRUNNABLE\t%d\t%d\n",p[i].name,p[i].pid,p[i].priority,p[i].tickets);
  			pl->p[j].state=p[i].state;
  			pl->p[j].pid=p[i].pid;
  			//pl->p[j].name=p[i].name;
  			pl->p[j].priority=p[i].priority;
  			pl->p[j].tickets=p[i].tickets;
  			j++;
  		}
  		
  	}	
  	release(&ptable.lock);
  	return 22;
  }
  //change priority
  int chpr( int pid, int priority )
  {
  	struct proc *p;
  	acquire(&ptable.lock);
  	for(p = ptable.proc; p < &ptable.proc[NPROC]; p++){
  		if(p->pid == pid ) {
  			p->priority = priority;
  			break;
  		}
  	}
  	release(&ptable.lock);
  	return pid;
  }
  // lottery scheduling problem
  int
  setTickets(int pid,int tickets)
  {
  	struct proc *p;// this is sructure which holds infrmation about a process
  	sti(); // used to eable interupts on this processor
  	acquire(&ptable.lock); // get all details from process table 
  	p=ptable.proc;
  	for(int i=0;i<NPROC;i++)
  	{
  		if(p[i].pid==pid)
  		{
  			p[i].tickets=tickets;
  			break;
  		}
  	}	
  	release(&ptable.lock);
  	return 24;
  }
  // thread creation function
  int
  thread_create(void (*function)(void*),void* arg,void* stack)
  {
  	int next_tid=1;
  	int number_of_threads=0;
  	struct proc *curproc=myproc();// current process proc structure or pcb
  	struct proc *np;// for new thread pcb
  	struct proc *p;// for iterating over ptable
  	acquire(&ptable.lock);
  	p=ptable.proc;
  	for(int i=0;i<NPROC;i++)
  	{
  		if(p[i].pid==curproc->pid)
  		{
  			if(p[i].tid>next_tid)
  			{
  				next_tid=p[i].tid;
  			}
  			if(p[i].state!=UNUSED)
  			{
  				number_of_threads++;
  			}
  		}
  	}
  	next_tid++;
  	release(&ptable.lock);
  	if(number_of_threads>=8)
  		return -1;
  	if((uint)stack%PGSIZE!=0)
  		return -1;
  	if((np=allocproc())==0)
  		return -1;
  	
  	np->tid=next_tid;
  	np->pgdir=curproc->pgdir;
  	np->sz=curproc->sz;
  	np->parent=curproc;
  	*(np->tf)=(*curproc->tf);
  	np->tf->esp=(uint)stack+4096-8;
  	np->tf->eax=0;
  	np->tf->eip=(uint)function;
  	np->tf->ebp=(uint)stack+4096-8;
  	int *sp=stack+4096-8;
  	*(sp+1)=(uint)arg;
  	(*sp)=0xffffffff;
  	for(int i = 0; i < NOFILE; i++)
  	    if(curproc->ofile[i])
  	      np->ofile[i] = filedup(curproc->ofile[i]);
  	np->cwd = idup(curproc->cwd);
  	safestrcpy(np->name,curproc->name,sizeof(curproc->name));
  	np->pid=curproc->pid;
  	acquire(&ptable.lock);
  	np->state=RUNNABLE;
  	release(&ptable.lock);  
  	return next_tid;
  }
  void thread_exit(void *retval)
  {
  	struct proc* curproc=myproc();//my current process to exit
  	struct proc* p;// p variable to iterate over process table wherever necessary 
  	if(curproc==initproc)
  	{
  		panic("init exiting");
  	}
  	if(curproc->tid==1)// main thread
  	{
  		exit();
  		return; 
  	}
  	for(int i=0;i<NOFILE;i++)
  	{
  		if(curproc->ofile[i])
  		{
  			fileclose(curproc->ofile[i]);
  			curproc->ofile[i]=0;
  		}
  	}
  	
  	begin_op();
  	iput(curproc->cwd);
  	end_op();
  	curproc->cwd=0;
  	
  	acquire(&ptable.lock);
  	p=ptable.proc;
  	wakeup1(curproc->parent);
  	for(int i=0;i<NPROC;i++)
  	{
  		if(p[i].pid==curproc->pid)
  		{
  			p[i].parent=initproc;
  			if(p[i].state==ZOMBIE)
  			{
  				wakeup1(p[i].parent);
  			}
  		}
  	}
  	for(int i=0;i<NPROC;i++)
  	{
  		if(p[i].pid==curproc->pid&&p[i].tid!=curproc->tid)
  		{
  			wakeup1(&p[i]);
  		}
  	}
  	release(&ptable.lock);
  	curproc->state=ZOMBIE;
  	sched();
  	panic("zombie Exit");
  }
  int thread_join(int tid,void** retval)
  {
  	struct proc* p;
  	struct proc* curproc=myproc();
  	acquire(&ptable.lock);
  	p=ptable.proc;
  	int flag=0;
  	for(;;)
  	{
  		for(int i=0;i<NPROC;i++)
  		{
  			if(p[i].pid!=curproc->pid)
  				continue;
  			if(p[i].tid==tid)
  			{
  				flag=1;
  				if(p[i].state==ZOMBIE)
  				{
  					kfree(p[i].kstack);
  					p[i].state=UNUSED;
  					p[i].tid=0;
  					p[i].pid=0;
  					p[i].parent=0;
  					p[i].killed=0;
  					*retval=(void*)p[i].retval;
  					p[i].retval=0;
  					release(&ptable.lock);
  					return 0;
  				}
  				if(p[i].state==UNUSED)
  				{
  					release(&ptable.lock);
  					return 0;
  				}
  			}
  		}
  		release(&ptable.lock);	
  		if(curproc->killed||flag==0)
  		{
  			release(&ptable.lock);
  			return -1;
  		}
  		sleep(curproc,&ptable.lock);
  	}
  	return 0;
  }
  int gettid(void)
  {
  	return myproc()->tid;
  }
  
  