The C language implements a thread pool that supports dynamic expansion and destruction

This article introduces the implementation of C language thread pool, support dynamic expansion and destruction, to share with you for your reference, the specific content is as follows

Realize the function

#include <stdio.h>
#include <pthread.h>
#include <stdlib.h>
#include <signal.h>
 

/* A thread's task queue is formed by , Functions and arguments , Tasks are managed by linked lists */
typedef struct thread_worker_s{
  void *(*process)(void *arg); // The processing function 
  void *arg;          // parameter 
  struct thread_worker_s *next;
}thread_worker_t;
 
#define bool int
#define true 1
#define false 0
 
/* State description of each thread in the thread pool */
#define THREAD_STATE_RUN        0
#define THREAD_STATE_TASK_WAITING   1
#define THREAD_STATE_TASK_PROCESSING  2
#define THREAD_STATE_TASK_FINISHED   3
#define THREAD_STATE_EXIT       4   
 
 
typedef struct thread_info_s{
  pthread_t id;
  int    state; 
  struct thread_info_s *next;
}thread_info_t;
 
static char* thread_state_map[] ={" create "," Wait for the task "," In the processing "," Processing is complete "," Have withdrawn from the "};
/* Only when the thread is compressed  0,1,2,4  Threads of state can be destroyed */
 
 
/* Thread pool manager */
#define THREAD_BUSY_PERCENT 0.5  /* thread : task  = 1:2  The smaller the value, the more tasks , Increase the thread */
#define THREAD_IDLE_PERCENT 2   /* thread : task  = 2:1  Value is greater than 1, More threads than tasks , Destroy some threads */
 
typedef struct thread_pool_s{
  pthread_mutex_t queue_lock ; // Queue mutex , Locks are required when queue modifications are involved 
  pthread_cond_t queue_ready; // Queue conditional lock , The queue satisfies a condition, triggering the thread waiting for that condition to continue execution , Let's say the queue is full , The queue is empty 
 
  thread_worker_t *head   ;    // Task queue header pointer 
  bool    is_destroy   ;    // Whether the thread pool has been destroyed 
  int num;              // Number of threads 
  int rnum;         ;    // Running thread 
  int knum;         ;    // Killed threads 
  int queue_size       ;    // The size of the work queue  
  thread_info_t *threads   ;    // Thread group id, through pthread_join(thread_ids[0],NULL)  To execute the thread 
  pthread_t   display   ;    // Print the thread 
  pthread_t   destroy   ;    // A thread that periodically destroys threads id
  pthread_t   extend    ;
  float percent       ;    // The ratio of threads to tasks  rnum/queue_size
  int  init_num      ;
  pthread_cond_t  extend_ready     ;    // If you want to add threads 
}thread_pool_t;
 
/*------------------------- Function declaration ----------------------*/
/**
 * 1. Initialize the mutually exclusive variable 
 * 2. Initialize the wait variable 
 * 3. Creates a specified number of threads 
 */
thread_pool_t* thread_pool_create(int num);
void *thread_excute_route(void *arg);
 
 
/* Debug function */
void debug(char *message,int flag){
  if(flag)
    printf("%s\n",message);
}
 
void *display_thread(void *arg);
/**
 *  The add task consists of the following operations 
 * 1. Adds the task to the end of the queue 
 * 2. Notifies the waiting process to process the task  pthread_cond_singal();
*/
int thread_pool_add_worker(thread_pool_t *pool,void*(*process)(void *arg),void *arg); // Net thread pool in the queue 1 The functions that need to be executed are called tasks 
 
/**
 *  Destroy thread pool , It includes the following sections 
 * 1. Notify all waiting processes  pthread_cond_broadcase
 * 2. Wait for all threads to finish executing 
 * 3. Destroy task list 
 * 4. Release lock, release condition 
 * 4. Destroys the thread pool object 
 */
 
 
 
void *thread_pool_is_need_recovery(void *arg);
void *thread_pool_is_need_extend(void *arg);
void thread_pool_destory(thread_pool_t *pool);
 
 
thread_pool_t *thread_pool_create(int num){
  if(num<1){
    return NULL;
  }
  thread_pool_t *p;
  p = (thread_pool_t*)malloc(sizeof(struct thread_pool_s));
  if(p==NULL)
    return NULL;
  p->init_num = num;
  /* Initializes mutually exclusive and conditional variables */
  pthread_mutex_init(&(p->queue_lock),NULL);
  pthread_cond_init(&(p->queue_ready),NULL);
 
  /* Set the number of threads */
  p->num  = num; 
  p->rnum = num;
  p->knum = 0;
 
  p->head = NULL;
  p->queue_size =0; 
  p->is_destroy = false;
 
   
  int i=0;
  thread_info_t *tmp=NULL;
  for(i=0;i<num;i++){
    /* Create a thread */
    tmp= (struct thread_info_s*)malloc(sizeof(struct thread_info_s));
    if(tmp==NULL){
      free(p);
      return NULL;
    }else{
      tmp->next = p->threads;
      p->threads = tmp;
    }
    pthread_create(&(tmp->id),NULL,thread_excute_route,p);
    tmp->state = THREAD_STATE_RUN;
  }
 
  /* According to */
  pthread_create(&(p->display),NULL,display_thread,p);
  /* Detects whether dynamic threads are required */
  //pthread_create(&(p->extend),NULL,thread_pool_is_need_extend,p);
  /* Dynamic destruction */
  pthread_create(&(p->destroy),NULL,thread_pool_is_need_recovery,p);
  return p;
}
 
int thread_pool_add_worker(thread_pool_t *pool,void*(*process)(void*arg),void*arg){
  thread_pool_t *p= pool;
  thread_worker_t *worker=NULL,*member=NULL;
  worker = (thread_worker_t*)malloc(sizeof(struct thread_worker_s));
  int incr=0;
  if(worker==NULL){
    return -1;
  }
  worker->process = process;
  worker->arg   = arg;
  worker->next  = NULL;
  thread_pool_is_need_extend(pool);
  pthread_mutex_lock(&(p->queue_lock));
  member = p->head;
  if(member!=NULL){
    while(member->next!=NULL)
      member = member->next;
    member->next = worker;
  }else{
    p->head = worker;
  }
  p->queue_size ++;
  pthread_mutex_unlock(&(p->queue_lock));
  pthread_cond_signal(&(p->queue_ready));
  return 1;
}
 
 
void thread_pool_wait(thread_pool_t *pool){
  thread_info_t *thread;
  int i=0;
  for(i=0;i<pool->num;i++){
    thread = (thread_info_t*)(pool->threads+i);
    thread->state = THREAD_STATE_EXIT;
    pthread_join(thread->id,NULL);
  }
}
void thread_pool_destory(thread_pool_t *pool){
  thread_pool_t  *p   = pool;
  thread_worker_t *member = NULL;
 
  if(p->is_destroy)
    return ;
  p->is_destroy = true;
  pthread_cond_broadcast(&(p->queue_ready));
  thread_pool_wait(pool);
  free(p->threads);
  p->threads = NULL;
  /* Destroy task list */
  while(p->head){
    member = p->head;
    p->head = member->next;
    free(member);
  }
  /* Destroy thread list */
  thread_info_t *tmp=NULL;
  while(p->threads){
    tmp = p->threads;
    p->threads = tmp->next;
    free(tmp);
  }
 
  pthread_mutex_destroy(&(p->queue_lock));
  pthread_cond_destroy(&(p->queue_ready));
  return ;
}
/* Through the thread id, Find the corresponding thread */
thread_info_t *get_thread_by_id(thread_pool_t *pool,pthread_t id){
  thread_info_t *thread=NULL;
  thread_info_t *p=pool->threads;
  while(p!=NULL){
    if(p->id==id)
      return p;
    p = p->next;
  }
  return NULL;
}
 
 
/* Each thread entry function */
void *thread_excute_route(void *arg){
  thread_worker_t *worker = NULL;
  thread_info_t  *thread = NULL; 
  thread_pool_t*  p = (thread_pool_t*)arg;
  //printf("thread %lld create success\n",pthread_self());
  while(1){
    pthread_mutex_lock(&(p->queue_lock));
 
    /* Gets the current thread's id*/
    pthread_t pthread_id = pthread_self();
    /* Set the current state */
    thread = get_thread_by_id(p,pthread_id);
 
    /* The thread pool is destroyed , And there are no tasks */
    if(p->is_destroy==true && p->queue_size ==0){
      pthread_mutex_unlock(&(p->queue_lock));
      thread->state = THREAD_STATE_EXIT;
      p->knum ++;
      p->rnum --;
      pthread_exit(NULL);
    }
    if(thread){
      thread->state = THREAD_STATE_TASK_WAITING; /* The thread is waiting for the task */
    }
    /* The thread pool is not destroyed , No mission comes 1 Straight wait */
    while(p->queue_size==0 && !p->is_destroy){
      pthread_cond_wait(&(p->queue_ready),&(p->queue_lock));
    }
    p->queue_size--;
    worker = p->head;
    p->head = worker->next;
    pthread_mutex_unlock(&(p->queue_lock));
     
 
    if(thread)
      thread->state = THREAD_STATE_TASK_PROCESSING; /* The thread is executing the task */
    (*(worker->process))(worker->arg);
    if(thread)
      thread->state = THREAD_STATE_TASK_FINISHED;  /* Mission accomplished */
    free(worker);
    worker = NULL;
  }
}
 
 
 
/* Expand the thread */
void *thread_pool_is_need_extend(void *arg){
  thread_pool_t *p = (thread_pool_t *)arg;
  thread_pool_t *pool = p;
  /* Determines whether additional threads are needed , The ultimate goal   thread : task =1:2*/
  if(p->queue_size>100){
    int incr =0;
    if(((float)p->rnum/p->queue_size) < THREAD_BUSY_PERCENT ){
      incr = (p->queue_size*THREAD_BUSY_PERCENT) - p->rnum; /* The computation needs to increase the number of threads */
      int i=0;
      thread_info_t *tmp=NULL;
      thread_pool_t *p = pool;
      pthread_mutex_lock(&pool->queue_lock);
      if(p->queue_size<100){
        pthread_mutex_unlock(&pool->queue_lock);
        return ;
      }
      for(i=0;i<incr;i++){
        /* Create a thread */
        tmp= (struct thread_info_s*)malloc(sizeof(struct thread_info_s));
        if(tmp==NULL){
          continue;
        }else{
          tmp->next = p->threads;
          p->threads = tmp;
        }
        p->num ++;
        p->rnum ++;
        pthread_create(&(tmp->id),NULL,thread_excute_route,p);
        tmp->state = THREAD_STATE_RUN;
      }
      pthread_mutex_unlock(&pool->queue_lock);
    }
  }
  //pthread_cond_signal(&pool->extend_ready);
}
pthread_cond_t sum_ready;
/* Restores the initial number of threads */
void *thread_pool_is_need_recovery(void *arg){
  thread_pool_t *pool = (thread_pool_t *)arg;
  int i=0;
  thread_info_t *tmp = NULL,*prev=NULL,*p1=NULL;
  /* If there is no task , The current thread is greater than the number of initialized threads */
  while(1){
    i=0;
    if(pool->queue_size==0 && pool->rnum > pool->init_num ){
      sleep(5);
      /*5s If I'm still in this state for a second , Destroy some threads */
      if(pool->queue_size==0 && pool->rnum > pool->init_num ){
        pthread_mutex_lock(&pool->queue_lock);
        tmp = pool->threads;
        while((pool->rnum != pool->init_num) && tmp){
          /* Find the idle thread */
          if(tmp->state != THREAD_STATE_TASK_PROCESSING){
            i++;
            if(prev)
              prev->next  = tmp->next;
            else
              pool->threads = tmp->next;
            pool->rnum --; /* Running thread minus 1*/
            pool->knum ++; /* Destroy the thread plus 1*/
            kill(tmp->id,SIGKILL); /* Destruction of the thread */
            p1 = tmp;
            tmp = tmp->next;
            free(p1);
            continue;
          }
          prev = tmp;
          tmp = tmp->next;
        }
        pthread_mutex_unlock(&pool->queue_lock);
        printf("5s There is no new task to destroy some threads , destroyed  %d  A thread \n",i);
      }
    }
    sleep(5);
  }
}
 
 
 
/* print 1 Some of the information */
void *display_thread(void *arg){
  thread_pool_t *p =(thread_pool_t *)arg;
  thread_info_t *thread = NULL;
  int i=0;
  while(1){
    printf("threads %d,running %d,killed %d\n",p->num,p->rnum,p->knum);  /* The total number of threads , Is running , Has been destroyed */
    thread = p->threads;
    while(thread){
      printf("id=%ld,state=%s\n",thread->id,thread_state_map[thread->state]);
      thread = thread->next;
    }
    sleep(5);
  }
}

I hope that this article is helpful for you to learn C language programming.