Linux内核同步，进程，线程同步

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包括我自己在内，很多人对内核，进程，线程同步都不是很清楚，下面稍微总结一下：

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);