Linux内核同步，进程，线程同步各种方法
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);Tries to lock the mutex, sleeps otherwise.Caution: can't be interrupted, resulting in processes you cannot kill!
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!!!
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.
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：Staticspinlock_t my_lock = SPIN_LOCK_UNLOCKED;Dynamicvoid 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);
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