Linux内核同步，进程，线程同步
作者 佚名技术
来源 Linux系统
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发布时间 2012-05-03
| 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. 拥有帝国一切，皆有可能。欢迎访问phome.net3. 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 |
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