网站被k换域名 老域名能不能跳转,WordPress怎么文章分类,外贸原单童装哪个网站做,大连建设网水电费查询官网这个例程为使用多线程配合互斥量进行点乘计算#xff0c;相关的数据通过全局变量的形式存在#xff0c;因此可以被各个线程访问#xff1b;每个线程会在相关数据的不同区域上进行处理#xff0c;主线程等待子线程完成操作后#xff0c;将最后的结果打印出来。 代码如下
#… 这个例程为使用多线程配合互斥量进行点乘计算相关的数据通过全局变量的形式存在因此可以被各个线程访问每个线程会在相关数据的不同区域上进行处理主线程等待子线程完成操作后将最后的结果打印出来。 代码如下
#include pthread.h
#include stdio.h
#include stdlib.h/* The following structure contains the necessary information* to allow the function dotprod to access its input data and* place its output into the structure.*/typedef struct
{double *a;double *b;double sum;int veclen;
} DOTDATA;/* Define globally accessible variables and a mutex */#define NUMTHRDS 4
#define VECLEN 100DOTDATA dotstr;
pthread_t callThd[NUMTHRDS];
pthread_mutex_t mutexsum;/* The function dotprod is activated when the thread is created.* All input to this routine is obtained from a structure* of type DOTDATA and all output from this function is written into* this structure. The benefit of this approach is apparent for the* multi-threaded program: when a thread is created we pass a single* argument to the activated function - typically this argument* is a thread number. All the other information required by the* function is accessed from the globally accessible structure.*/void *dotprod(void *arg)
{/* Define and use local variables for convenience */int i, start, end, len;long offset;double mysum, *x, *y;offset (long)arg;len dotstr.veclen;start offset * len;end start len;x dotstr.a;y dotstr.b;/*Perform the dot product and assign resultto the appropriate variable in the structure.*/mysum 0;for (i start; i end ; i) {mysum (x[i] * y[i]);}/*Lock a mutex prior to updating the value in the sharedstructure, and unlock it upon updating.*/pthread_mutex_lock(mutexsum);dotstr.sum mysum;pthread_mutex_unlock(mutexsum);pthread_exit((void*) 0);
}/* The main program creates threads which do all the work and then* print out result upon completion. Before creating the threads,* the input data is created. Since all threads update a shared structure,* we need a mutex for mutual exclusion. The main thread needs to wait for* all threads to complete, it waits for each one of the threads. We specify* a thread attribute value that allow the main thread to join with the* threads it creates. Note also that we free up handles when they are* no longer needed.*/int main (int argc, char *argv[])
{long i;double *a, *b;void *status;pthread_attr_t attr;/* Assign storage and initialize values */a (double*) malloc (NUMTHRDS * VECLEN * sizeof(double));b (double*) malloc (NUMTHRDS * VECLEN * sizeof(double));for (i 0; i VECLEN * NUMTHRDS; i) {a[i] 1.0;b[i] a[i];}dotstr.veclen VECLEN;dotstr.a a;dotstr.b b;dotstr.sum 0;pthread_mutex_init(mutexsum, NULL);/* Create threads to perform the dot product */pthread_attr_init(attr);pthread_attr_setdetachstate(attr, PTHREAD_CREATE_JOINABLE);for(i 0; i NUMTHRDS; i) {/* Each thread works on a different set of data. The offset is specified* by i. The size of the data for each thread is indicated by VECLEN.*/pthread_create(callThd[i], attr, dotprod, (void *)i);}pthread_attr_destroy(attr);/* Wait on the other threads */for(i 0; i NUMTHRDS; i) {pthread_join(callThd[i], status);}/* After joining, print out the results and cleanup */printf(Sum %f\n, dotstr.sum);free(a);free(b);pthread_mutex_destroy(mutexsum);pthread_exit(NULL);
}
