163528369Sfslongjin# 锁的类型及其规则 263528369Sfslongjin 363528369Sfslongjin## 简介 463528369Sfslongjin 563528369Sfslongjin  DragonOS内核实现了一些锁,大致可以分为两类: 663528369Sfslongjin 763528369Sfslongjin- 休眠锁 863528369Sfslongjin- 自旋锁 963528369Sfslongjin 1063528369Sfslongjin## 锁的类型 1163528369Sfslongjin 1263528369Sfslongjin### 休眠锁 1363528369Sfslongjin 1463528369Sfslongjin  休眠锁只能在可抢占的上下文之中被获取。 1563528369Sfslongjin 1663528369Sfslongjin  在DragonOS之中,实现了以下的休眠锁: 1763528369Sfslongjin 1863528369Sfslongjin- semaphore 19311a6181Sfslongjin- mutex_t 2063528369Sfslongjin 2163528369Sfslongjin### 自旋锁 2263528369Sfslongjin 2363528369Sfslongjin- spinlock_t 24*ec53d23eSlogin- {ref}`RawSpinLock <_spinlock_doc_rawspinlock>`(Rust版本的spinlock_t,但与spinlock_t不兼容) 25*ec53d23eSlogin- {ref}`SpinLock <_spinlock_doc_spinlock>` —— 在RawSpinLock的基础上,封装了一层守卫(Guard), 将锁及其要保护到的数据绑定在一个结构体内,并能在编译期避免未加锁就访问数据的问题。 2663528369Sfslongjin 2763528369Sfslongjin  进程在获取自旋锁后,将改变pcb中的锁变量持有计数,从而隐式地禁止了抢占。为了获得更多灵活的操作,spinlock还提供了以下的方法: 2863528369Sfslongjin 2963528369Sfslongjin| 后缀 | 说明 | 3063528369Sfslongjin| ------------------------ | -------------------------- | 3163528369Sfslongjin| _irq() | 在加锁时关闭中断/在放锁时开启中断 | 3263528369Sfslongjin| _irqsave()/_irqrestore() | 在加锁时保存中断状态,并关中断/在放锁时恢复中断状态 | 3363528369Sfslongjin 34112775fdSfslongjin  当您同时需要使用自旋锁以及引用计数时,一个好的方法是:使用`lockref`. 这是一种额外的加速技术,能额外提供“无锁修改引用计数”的功能。详情请见:{ref}`lockref <_lockref>` 3563528369Sfslongjin 36311a6181Sfslongjin## 详细介绍 37*ec53d23eSlogin 38*ec53d23eSlogin### 自旋锁的详细介绍 39*ec53d23eSlogin 40*ec53d23eSlogin  关于自旋锁的详细介绍,请见文档:{ref}`自旋锁 <_spinlock_doc>` 41*ec53d23eSlogin 4263528369Sfslongjin### semaphore信号量 4363528369Sfslongjin 4463528369Sfslongjin  semaphore信号量是基于计数实现的。 4563528369Sfslongjin 4663528369Sfslongjin  当可用资源不足时,尝试对semaphore执行down操作的进程将会被休眠,直到资源可用。 47311a6181Sfslongjin 48311a6181Sfslongjin### mutex互斥量 49311a6181Sfslongjin 50311a6181Sfslongjin  mutex是一种轻量级的同步原语,只有0和1两种状态。 51311a6181Sfslongjin 52311a6181Sfslongjin  当mutex被占用时,尝试对mutex进行加锁操作的进程将会被休眠,直到资源可用。 53311a6181Sfslongjin 54311a6181Sfslongjin#### 特性 55311a6181Sfslongjin 56311a6181Sfslongjin- 同一时间只有1个任务可以持有mutex 57311a6181Sfslongjin- 不允许递归地加锁、解锁 58311a6181Sfslongjin- 只允许通过mutex的api来操作mutex 59311a6181Sfslongjin- 在硬中断、软中断中不能使用mutex 60311a6181Sfslongjin 61311a6181Sfslongjin#### 数据结构 62311a6181Sfslongjin 63311a6181Sfslongjin  mutex定义在`common/mutex.h`中。其数据类型如下所示: 64311a6181Sfslongjin 65311a6181Sfslongjin```c 66311a6181Sfslongjintypedef struct 67311a6181Sfslongjin{ 68311a6181Sfslongjin 69311a6181Sfslongjin atomic_t count; // 锁计数。1->已解锁。 0->已上锁,且有可能存在等待者 70311a6181Sfslongjin spinlock_t wait_lock; // mutex操作锁,用于对mutex的list的操作进行加锁 71311a6181Sfslongjin struct List wait_list; // Mutex的等待队列 72311a6181Sfslongjin} mutex_t; 73311a6181Sfslongjin``` 74311a6181Sfslongjin 75311a6181Sfslongjin#### API 76311a6181Sfslongjin 77311a6181Sfslongjin##### mutex_init 78311a6181Sfslongjin 79311a6181Sfslongjin**`void mutex_init(mutex_t *lock)`** 80311a6181Sfslongjin 81311a6181Sfslongjin  初始化一个mutex对象。 82311a6181Sfslongjin 83311a6181Sfslongjin##### mutex_lock 84311a6181Sfslongjin 85311a6181Sfslongjin**`void mutex_lock(mutex_t *lock)`** 86311a6181Sfslongjin 87311a6181Sfslongjin  对一个mutex对象加锁。若mutex当前被其他进程持有,则当前进程进入休眠状态。 88311a6181Sfslongjin 89311a6181Sfslongjin##### mutex_unlock 90311a6181Sfslongjin 91311a6181Sfslongjin**`void mutex_unlock(mutex_t *lock)`** 92311a6181Sfslongjin 93311a6181Sfslongjin  对一个mutex对象解锁。若mutex的等待队列中有其他的进程,则唤醒下一个进程。 94311a6181Sfslongjin 95311a6181Sfslongjin##### mutex_trylock 96311a6181Sfslongjin 97311a6181Sfslongjin**`void mutex_trylock(mutex_t *lock)`** 98311a6181Sfslongjin 99311a6181Sfslongjin  尝试对一个mutex对象加锁。若mutex当前被其他进程持有,则返回0.否则,加锁成功,返回1. 100311a6181Sfslongjin 101311a6181Sfslongjin##### mutex_is_locked 102311a6181Sfslongjin 103311a6181Sfslongjin**`void mutex_is_locked(mutex_t *lock)`** 104311a6181Sfslongjin 105311a6181Sfslongjin  判断mutex是否已被加锁。若给定的mutex已处于上锁状态,则返回1,否则返回0。 106311a6181Sfslongjin 107