sleeplock 与死锁

Spin Lock 回顾

1. acquire
2. release
3. 并发编程
   • mutex
   • atomic

Sleep Lock 睡眠锁

1. 磁盘 IDE 读写
   • 慢
   • 依赖 interrupt
2. disk 竞争
   • spinlock ???
     • while loop
3. sleeplock 睡眠锁
   • spinlock 内涵
   • locked 记录是否上锁

../../study/os/xv6-public/sleeplock.h

rg -n initsleeplock $PWD | sort

/data/gitana/study/os/xv6-public/bio.c:51:    initsleeplock(&b->lock, "buffer");
/data/gitana/study/os/xv6-public/defs.h:139:void            initsleeplock(struct sleeplock*, char*);
/data/gitana/study/os/xv6-public/fs.c:178:    initsleeplock(&icache.inode[i].lock, "inode");
/data/gitana/study/os/xv6-public/sleeplock.c:14:initsleeplock(struct sleeplock *lk, char *name)

Sleep Lock 死锁场景

1. 死锁 deadlock
2. 经典案例
   • 生产者/消费者
   • 哲学家

S: Sleep Lock
X: Spin Lock
a: acquire
r: release

分析流程:
TIME
--------------------------- Long Time --------------------------->
T1:(S)|  (S/a) |     (S/r)     ...      (S/a)            |
   (X)|        |               ...         (X/a)         |
      |        |               ...            x          |
      |        |               ...            x          |
      |        |               ...            x          |
      |        |               ...            x          |
T2:(S)|        |               ...            (S/a)      |
   (X)|        |(X/a)          ...            x          |
      |        |               ...            x          |
      |        |               ...            x          |
      |        |               ...            x          |
      |        |               ...            x          |

                                              T1: hold S, wait X
                                              T2: hold X, wait S

Sleep Lock 实现

1. 获取锁 acquiresleep
2. 释放锁 releasesleep
3. acquiresleep/releasesleep
   • 包裹 spinlock: acquire/release