Linux内核同步，进程，线程同步

内核同步：
主要是防止多核处理器同时访问修改某段代码，或者在对设备驱动程序进行临界区保护。主要有一下几种方式：
1. Mutex（互斥）
头文件：
#include <linux/mutex.h>
初始化方法：
DEFINE_MUTEX(name);
或者
void mutex_init(struct mutex *lock);
使用方法：
void mutex_lock (struct mutex *lock);
尝试得到互斥量，否则进入睡眠，不能被中断，否则会导致进程无法杀死

int mutex_lock_interruptible (struct mutex *lock);

Same, but can be interrupted. If interrupted, returns a non zero value and doesn't
hold the lock.

Test the return value!!!
可以被中断

int mutex_trylock (struct mutex *lock);

Never waits. Returns a non zero value if the mutex is not available.int mutex_is_locked

(struct mutex *lock);Just tells whether the mutex is locked or not.
无等待

void mutex_unlock (struct mutex *lock);

Releases the lock. Make sure you do it as quickly as possible!

2. Reader/writer semphopres 读写信号量
Allow shared access by unlimited readers, or by only 1 writer. Writers get priority.
允许有限数量的读访问，但是只能有一个写访问。

void init_rwsem (struct rw_semaphore *sem);

void down_read (struct rw_semaphore *sem);

int down_read_trylock (struct rw_semaphore *sem);

int up_read (struct rw_semaphore *sem);

void down_write (struct rw_semaphore *sem);

int down_write_trylock (struct rw_semaphore *sem);

int up_write (struct rw_semaphore *sem);

Well suited for rare writes, holding the semaphore briefly. Otherwise,
readers get starved,waiting too long for the semaphore to be released.

3. Spinlocks 自旋锁
初始化：
Static

spinlock_t my_lock = SPIN_LOCK_UNLOCKED;

Dynamic

void spin_lock_init (spinlock_t *lock);
使用：
void spin_[un]lock (spinlock_t *lock);

Doesn't disable interrupts. Used for locking in process context
(critical sections in which you do not want to sleep).

void spin_lock_irqsave / spin_unlock_irqrestore (spinlock_t *lock, unsigned long flags);

Disables / restores IRQs on the local CPU.

Typically used when the lock can be accessed in both process and interrupt context,

to prevent preemption by interrupts

进程同步/通信
1. Semaphore 信号量
简单过程：
semaphore sv = 1;

loop forever {

P(sv);

critical code section;

V(sv);

noncritical code section;

}
头文件以及函数：
#include <sys/sem.h>

int semctl(int sem_id, int sem_num, int command, ...);

int semget(key_t key, int num_sems, int sem_flags);

int semop(int sem_id, struct sembuf *sem_ops, size_t num_sem_ops);

2.Share Memory 共享内存
头文件以及函数
#include <sys/shm.h>

void *shmat(int shm_id, const void *shm_addr, int shmflg);

int shmctl(int shm_id, int cmd, struct shmid_ds *buf);

int shmdt(const void *shm_addr);

int shmget(key_t key, size_t size, int shmflg);

3.Message Queues 消息队列
头文件以及函数
#include <sys/msg.h>

int msgctl(int msqid, int cmd, struct msqid_ds *buf);

int msgget(key_t key, int msgflg);

int msgrcv(int msqid, void *msg_ptr, size_t msg_sz, long int msgtype, int msgflg);

int msgsnd(int msqid, const void *msg_ptr, size_t msg_sz, int msgflg);

线程同步
1. semophore 信号量
简单用法：
#include <semaphore.h>
sem_t bin_sem;
res = sem_init(&bin_sem, 0, 0);
sem_wait(&bin_sem);
sem_post(&bin_sem);
sem_destroy(&bin_sem);

2. Mutex 互斥
头文件以及函数
#include <pthread.h>

int pthread_mutex_init(pthread_mutex_t *mutex, const pthread_mutexattr_t *mutexattr);

int pthread_mutex_lock(pthread_mutex_t *mutex));

int pthread_mutex_unlock(pthread_mutex_t *mutex);

int pthread_mutex_destroy(pthread_mutex_t *mutex);

3. 读写锁
头文件以及函数

#include <pthread.h>

int pthread_rwlock_init(pthread_rwlock_t *restrict
rwlock,
const pthread_rwlockattr_t *restrict
attr);
int pthread_rwlock_destroy(pthread_rwlock_t *rwlock);
int pthread_rwlock_rdlock(pthread_rwlock_t *rwlock);

int pthread_rwlock_wrlock(pthread_rwlock_t *rwlock);
int pthread_rwlock_unlock(pthread_rwlock_t *rwlock);
int pthread_rwlock_tryrdlock(pthread_rwlock_t *rwlock);
int pthread_rwlock_trywrlock(pthread_rwlock_t *rwlock);

4.
条件变量
#include
<pthread.h>

pthread_cond_t cond = PTHREAD_COND_INITIALIZER;

int pthread_cond_init(pthread_cond_t *cond, pthread_condattr_t *cond_attr);

int pthread_cond_signal(pthread_cond_t *cond);

int pthread_cond_broadcast(pthread_cond_t *cond);

int pthread_cond_wait(pthread_cond_t *cond, pthread_mutex_t *mutex);

int pthread_cond_timedwait(pthread_cond_t *cond,
pthread_mutex_t *mutex,
const struct timespec *abstime);

int pthread_cond_destroy(pthread_cond_t *cond);