进程间同步——互斥锁与条件变量

#include<pthread.h>

互斥锁——用于主动获取共享资源时的互斥与等待

• 多个线程锁定同一临界区时，解锁后，优先级最高的线程被优先执行

• 静态初始化

static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;

• API

int pthread_mutexattr_init(pthread_mutexattr_t*);

int pthread_mutexattr_setpshared(pthread_mutexattr_t*， int);

PTHREAD_PROCESS_SHARED/PTHREAD_PROCESS_PRIVATE

在<uinstd.h>中定义了_POSIX_THREAD_PROCESS_SHARED时才能指定进程间共享属性

int pthread_mutexattr_getpshared(pthread_mutexattr_t*， int);

int pthread_mutexattr_destroy(pthread_mutexattr_t*);

int pthread_mutex_init(pthread_mutex_t* ， pthread_mutexattr_t*);

int pthread_mutex_lock(pthread_mutex_t*);

int pthread_mutex_trylock(pthread_mutex_t*);

int pthread_mutex_unlock(pthread_mutex_t*);

int pthread_mutex_destroy(pthread_mutex_t*);

条件变量——用于获取共享资源时受到被动的提醒

• 静态初始化

static pthread_cond_t cond = PTHREAD_COND_INITIALIZER;

• API

int pthread_condattr_init(pthread_mutexattr_t*);

int pthread_condattr_setpshared(pthread_condattr_t*, int);

int pthread_condattr_getpshared(pthread_condattr_t*, int);

int pthread_condattr_destroy(pthread_mutexattr_t*);

int pthread_cond_init(pthread_cond_t * );

int pthread_cond_wait(pthread_cond_t *，pthread_mutex_t* );

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

此处采用绝对时间，好处是，若因为捕获到信号而提前解阻塞，再次进入阻塞态时无须修改时间参数

int pthread_cond_signal(pthread_cond_t *);

int pthread_cond_broadcast(pthread_cond_t *);

int pthread_cond_destroy(pthread_cond_t *);

• 调用例程

pthread_mutex_lock(mutex4test); //保护对测试变量的读取

while(test) //测试变量

pthread_cond_wait(cond，mutex4test ); //解锁对测试变量的保护并阻塞等待 解阻塞后继续锁定测试变量

pthread_mutex_unlock(mutex4test); //解除对测试变量的保护