虹口网站建设公司,不用付费的正能量软件,品牌推广的具体方法,湛江定制建站企业网站一、条件变量 【互斥量】解决了线程间同步的问题#xff0c;避免了多线程对同一块临界资源访问产生的冲突#xff0c;但同一时刻对临界资源的访问#xff0c;不论是生产者还是消费者#xff0c;都需要竞争互斥锁#xff0c;由此也带来了竞争的问题。即生产者和消费者、消费…一、条件变量 【互斥量】解决了线程间同步的问题避免了多线程对同一块临界资源访问产生的冲突但同一时刻对临界资源的访问不论是生产者还是消费者都需要竞争互斥锁由此也带来了竞争的问题。即生产者和消费者、消费者和消费者之间时刻都在竞争这把锁而临界资源是有限的当临界资源为空的时候消费者之间的竞争便没有意义反而降低了运行效率。 有没有什么办法可以等生产者线程生产出资源消费者线程再去竞争锁消费呢这就是条件变量的作用。 正如互斥量保护了【临界资源】条件变量也保护【条件】资源当条件不符合时即【条件】资源空缺消费者线程休眠等待当【条件】资源产生消费者线程被唤醒然后去消费资源。这样便解决了线程间等待的问题提高了运行效率。
pthread_cond_t cond //定义条件变量
pthread_cond_init(cond) //动态初始化pthread_cond_t cond PTHREAD_COND_INITIALIZER //静态创建并初始化/*消费者线程休眠等待生产者线程通知*/
int pthread_cond_wait(pthread_cond_t *restrict cond,pthread_mutex_t *restrict mutex)/*生产者线程生产完资源后发送通知*/
int pthread_cond_signal(pthread_cond_t *cond) //唤醒一个休眠的线程
int pthread_cond_broadcast(pthread_cond_t *cond) //广播唤醒所有休眠的线程 条件变量的使用要绑定互斥锁 因为条件变量的使用过程中对于生产者线程需要产生资源当然要上锁对于消费者线程需要消费资源甚至还要判断资源是否为空也要上锁 【wait】函数的具体动作 进入等待的线程列表中休眠并释放锁 被唤醒后返回同时上锁 wait函数的每个动作都是【原子操作】动作连续并且不会被别的程序干扰意味着CPU调度一定能保证动作粒一气呵成 消费线程不判断资源是否为空直接等待的话容易丢失signal信号假设生产线程提前生产出资源也signal了 唤醒也可以用broadcast这种情况消费线程一定要判断资源是否为空否则链表形式的资源容易出现【段错误】因为多个线程去争抢资源时总有抢不到的 二、线程池
若干线程的集合可用结构体来构造
必要性当会出现大量执行时间短的任务时甚至这个时间比线程创建销毁的时间还短这时候再创建多个线程就不划算了可以未雨绸缪构建线程池提前创建多个线程来节省开销 线程池的实现过程
1.创建任务队列、线程池的结构体、定义一个线程池
#define pool_num (10)typedef struct Task{struct Task *next;void *(*func)(void *);void *arg;}Task;typedef struct{pthread_mutex_t mutex;pthread_cond_t cond;Task *task_head;int busywork;pthread_t tid[pool_num];}ThreadPool;ThreadPool *pool;
2.初始化线程池、线程的工作
void pool_init()
{pool (ThreadPool *)malloc(sizeof(ThreadPool));pthread_mutex_init(pool-mutex,NULL);pthread_cond_init(pool-cond,NULL);pool-task_head NULL;pool-busywork 0;for(i0;ipool_num;i){pthread_create(pool-tid[i],NULL,workthread,NULL);}
}void *workthread(void *arg)
{while(1){ // usleep(10000); //avoid other process couldnt rob the lock and several process repeatedly rob the lockpthread_mutex_lock(pool-mutex);while(pool-task_head NULL){pthread_cond_wait(pool-cond,pool-mutex);}Task *ptask pool-task_head;//任务取走线程池的头个线程pool-task_head ptask-next;//重置线程池的头个线程为下一个pool-busywork--;//pthread_mutex_unlock(pool-mutex);printf(%ld start task %d\n,pthread_self(),(int)ptask-arg);ptask-func(ptask-arg);}
}
3.添加任务
void *realwork(void *arg)
{usleep(100000);printf(finish task %d\n,(int)arg);}void add_task(int arg)
{pthread_mutex_lock(pool-mutex);while(pool-busywork pool_num){pthread_mutex_unlock(pool-mutex);usleep(10000);pthread_mutex_lock(pool-mutex);}pthread_mutex_unlock(pool-mutex);//以上为判断任务数量是否超过线程池数量超过则不再允许添加任务Task *newtask;newtask (Task *)malloc(sizeof(Task));newtask-func realwork;newtask-arg (void *)arg;pthread_mutex_lock(pool-mutex);Task *p pool-task_head;if(p NULL){pool-task_head newtask;}else{while(p-next ! NULL){p p-next;}p-next newtask;pthread_cond_signal(pool-cond);pool-busywork;}pthread_mutex_unlock(pool-mutex);
}
4.销毁线程池、任务队列、互斥锁、条件变量
void pool_destroy()
{Task *p;while(pool-task_head ! NULL){p pool-task_head;pool-task_head p-next;free(p);}pthread_mutex_destroy(pool-mutex);pthread_cond_destroy(pool-cond);free(pool);
}
示例
#include pthread.h
#include stdio.h
#include unistd.h
#include sys/types.h
#include unistd.h
#include stdlib.h#define pool_num (10)
int i 0;typedef struct Task{struct Task *next;void *(*func)(void *);void *arg;}Task;typedef struct{pthread_mutex_t mutex;pthread_cond_t cond;Task *task_head;int busywork;pthread_t tid[pool_num];}ThreadPool;ThreadPool *pool;void *workthread(void *arg)
{while(1){ // usleep(10000); //avoid other process couldnt rob the lock and several process repeatedly rob the lockpthread_mutex_lock(pool-mutex);while(pool-task_head NULL){pthread_cond_wait(pool-cond,pool-mutex);}Task *ptask pool-task_head;//任务取走线程池的头个线程pool-task_head ptask-next;//重置线程池的头个线程为下一个pool-busywork--;//pthread_mutex_unlock(pool-mutex);printf(%ld start task %d\n,pthread_self(),(int)ptask-arg);ptask-func(ptask-arg);}
}void *realwork(void *arg)
{usleep(100000);printf(finish task %d\n,(int)arg);}void add_task(int arg)
{pthread_mutex_lock(pool-mutex);while(pool-busywork pool_num){pthread_mutex_unlock(pool-mutex);usleep(10000);pthread_mutex_lock(pool-mutex);}pthread_mutex_unlock(pool-mutex);Task *newtask;newtask (Task *)malloc(sizeof(Task));newtask-func realwork;newtask-arg (void *)arg;pthread_mutex_lock(pool-mutex);Task *p pool-task_head;if(p NULL){pool-task_head newtask;}else{while(p-next ! NULL){p p-next;}p-next newtask;pthread_cond_signal(pool-cond);pool-busywork;}pthread_mutex_unlock(pool-mutex);
} void pool_init()
{pool (ThreadPool *)malloc(sizeof(ThreadPool));pthread_mutex_init(pool-mutex,NULL);pthread_cond_init(pool-cond,NULL);pool-task_head NULL;pool-busywork 0;for(i0;ipool_num;i){pthread_create(pool-tid[i],NULL,workthread,NULL);}}void pool_destroy()
{Task *p;while(pool-task_head ! NULL){p pool-task_head;pool-task_head p-next;free(p);}pthread_mutex_destroy(pool-mutex);pthread_cond_destroy(pool-cond);free(pool);
}int main()
{printf(mypid is %d\n,getpid());pool_init();sleep(5);for(i1;i40;i){add_task(i);}sleep(5);pool_destroy();while(1){printf(now im alone\n);sleep(2);} }
