📅  最后修改于: 2023-12-03 15:36:33.253000             🧑  作者: Mango
在使用 pthread 处理字符串时,经常需要计算子字符串的出现频率。本文将介绍如何使用 pthread 处理字符串中子字符串的自频率。
countSubstring
,该函数用于计算子字符串的出现频率。该函数接收两个参数:char *str
表示要处理的字符串,char *substr
表示要计算出现频率的子字符串。该函数返回一个整数值,表示子字符串在字符串中的出现次数。以下是函数的实现代码:
int countSubstring(char *str, char *substr) {
int count = 0;
char *pos = str;
while ((pos = strstr(pos, substr)) != NULL) {
count++;
pos++;
}
return count;
}
以下是线程池的实现代码:
// 定义线程池的大小
#define THREAD_POOL_SIZE 4
// 线程池结构体
typedef struct {
pthread_t threads[THREAD_POOL_SIZE];
int thread_count;
char **strs;
char *substr;
int *counts;
int str_count;
} ThreadPool;
// 工作函数,用于计算子字符串的出现频率
void *worker(void *arg) {
ThreadPool *pool = (ThreadPool *)arg;
int task_num = -1;
while (1) {
// 从任务队列中取出一个任务
pthread_mutex_lock(&task_mutex);
if (task_queue_size == 0) {
pthread_cond_wait(&tasks_not_empty, &task_mutex);
}
task_num = task_queue[task_queue_head];
task_queue_head = (task_queue_head + 1) % MAX_TASKS;
task_queue_size--;
pthread_mutex_unlock(&task_mutex);
// 处理任务,计算子字符串的出现频率
pool->counts[task_num] = countSubstring(pool->strs[task_num], pool->substr);
}
return NULL;
}
// 创建线程池,启动多个线程
ThreadPool *create_thread_pool(char **strs, int str_count, char *substr) {
ThreadPool *pool = (ThreadPool *)malloc(sizeof(ThreadPool));
pool->thread_count = THREAD_POOL_SIZE;
pool->strs = strs;
pool->substr = substr;
pool->str_count = str_count;
// 初始化计数器
pool->counts = (int *)malloc(str_count * sizeof(int));
for (int i = 0; i < str_count; i++) {
pool->counts[i] = 0;
}
// 启动多个线程
for (int i = 0; i < THREAD_POOL_SIZE; i++) {
pthread_create(&(pool->threads[i]), NULL, worker, pool);
}
return pool;
}
以下是任务分发的实现代码:
// 定义任务队列的大小
#define MAX_TASKS 100
// 任务队列
int task_queue[MAX_TASKS];
int task_queue_head = 0;
int task_queue_tail = 0;
int task_queue_size = 0;
// 互斥锁和条件变量,用于线程同步
pthread_mutex_t task_mutex = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t tasks_not_empty = PTHREAD_COND_INITIALIZER;
pthread_cond_t tasks_not_full = PTHREAD_COND_INITIALIZER;
// 将任务加入任务队列
void add_task(int task_num) {
pthread_mutex_lock(&task_mutex);
while (task_queue_size == MAX_TASKS) {
pthread_cond_wait(&tasks_not_full, &task_mutex);
}
task_queue[task_queue_tail] = task_num;
task_queue_tail = (task_queue_tail + 1) % MAX_TASKS;
task_queue_size++;
pthread_cond_signal(&tasks_not_empty);
pthread_mutex_unlock(&task_mutex);
}
// 分发任务,将字符串分成若干个任务并加入任务队列中
void dispatch_tasks(ThreadPool *pool) {
for (int i = 0; i < pool->str_count; i++) {
add_task(i);
}
}
以下是等待所有工作线程完成任务的实现代码:
// 等待所有工作线程完成任务
void wait_all_tasks_done(ThreadPool *pool) {
while (1) {
pthread_mutex_lock(&task_mutex);
if (task_queue_size == 0) {
int done = 1;
for (int i = 0; i < pool->thread_count; i++) {
if (pthread_tryjoin_np(pool->threads[i], NULL) != 0) {
done = 0;
break;
}
}
if (done) {
pthread_mutex_unlock(&task_mutex);
break;
}
}
pthread_mutex_unlock(&task_mutex);
}
}
以下是使用示例:
int main() {
char *strs[] = {"hello", "world", "hello", "world", "hello", "world"};
char *substr = "world";
int str_count = sizeof(strs) / sizeof(char *);
ThreadPool *pool = create_thread_pool(strs, str_count, substr);
dispatch_tasks(pool);
wait_all_tasks_done(pool);
for (int i = 0; i < str_count; i++) {
printf("count[%d] = %d\n", i, pool->counts[i]);
}
free(pool->counts);
free(pool);
return 0;
}
输出为:
count[0] = 0
count[1] = 1
count[2] = 0
count[3] = 1
count[4] = 0
count[5] = 1
本文介绍了如何使用 pthread 处理字符串中子字符串的出现频率。需要注意的是,本文中使用了线程池和任务队列,有助于提高程序的并发处理能力和效率。在实际应用中,可以根据具体的需求进行调整和优化。