[xv6]:pipe

直接看代码

• pipe结构

  struct pipe {
    struct spinlock lock;
    char data[PIPESIZE];
    uint nread;     // number of bytes read
    uint nwrite;    // number of bytes written
    int readopen;   // read fd is still open
    int writeopen;  // write fd is still open
  };

  • pipe中的data使用环型计数
  • nread以及nwrite不使用环型计数
  • 缓冲区满: nwrite == nread + PIPESIZE
  • 缓冲区空: nwrite == n

• pipewrite()

  int
  pipewrite(struct pipe *pi, uint64 addr, int n)
  {
    int i;
    char ch;
    struct proc *pr = myproc();
  
    acquire(&pi->lock);
    for(i = 0; i < n; i++){
      // 缓冲区满, 唤醒那些reader进程, writer进程陷入sleep
      while(pi->nwrite == pi->nread + PIPESIZE){  //DOC: pipewrite-full
        if(pi->readopen == 0 || pr->killed){
          release(&pi->lock);
          return -1;
        }
        wakeup(&pi->nread);
        sleep(&pi->nwrite, &pi->lock);
      }
       // 每字节写入
      if(copyin(pr->pagetable, &ch, addr + i, 1) == -1)
        break;
      pi->data[pi->nwrite++ % PIPESIZE] = ch;
    }
    wakeup(&pi->nread);
    release(&pi->lock);
    return i;
  }

• piperead()

  int
  piperead(struct pipe *pi, uint64 addr, int n)
  {
    int i;
    struct proc *pr = myproc();
    char ch;
  
    acquire(&pi->lock);
    // 没有数据可读
    while(pi->nread == pi->nwrite && pi->writeopen){  //DOC: pipe-empty
      if(pr->killed){
        release(&pi->lock);
        return -1;
      }
      sleep(&pi->nread, &pi->lock); //DOC: piperead-sleep
    }
    // 每字节读取数据到addr
    for(i = 0; i < n; i++){  //DOC: piperead-copy
      if(pi->nread == pi->nwrite)
        break;
      ch = pi->data[pi->nread++ % PIPESIZE];
      if(copyout(pr->pagetable, addr + i, &ch, 1) == -1)
        break;
    }
    // 读取完毕之后唤醒writer进程
    wakeup(&pi->nwrite);  //DOC: piperead-wakeup
    release(&pi->lock);
    return i;
  }