Thread pool - C language

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Thread pool introduction and video explanation

threadpool.h

#ifndef _THREADPOOL_H
#define _THREADPOOL_H
typedef struct ThreadPool ThreadPool;
// Create a thread pool and initialize 
ThreadPool* threadPoolCreate(int min, int max, int queueCapacity);

// Destroy thread pool 
int threadPoolDestroy(ThreadPool* pool);

// Add tasks to the thread pool 
void threadPoolAdd(ThreadPool* pool, void(*func)(void*), void* arg);

// Get the number of threads working in the thread pool 
int threadPoolBusyNum(ThreadPool* pool);

// Get the number of threads alive in the thread pool 
int threadPoolAliveNum(ThreadPool* pool);

void* worker(void* arg);
void* manager(void* arg);
void threadExit(ThreadPool* pool);
#endif

threadpool.c

#include"threadpool.h"
#include<pthread.h>
#include<stdlib.h>
#include<stdio.h>
#include<string.h>
#include<unistd.h>

const int NUMBER = 2;

// Task structure 
typedef struct Task
{
    
    void (*function)(void* arg);
    void* arg;
}Task;

// Thread pool structure 
struct ThreadPool
{
    
    // Task queue 
    Task* taskQ;
    int queueCapacity;  // Capacity 
    int queueSize;      // Number of current tasks 
    int queueFront;     // Team head  ->  Take the data 
    int queueRear;      // A party  ->  Put the data 

    pthread_t managerID;    // Manager thread ID
    pthread_t* threadIDs;   // Threads of work ID

    int minNum;             // Minimum number of threads 
    int maxNum;             // Maximum number of threads 
    int busyNum;            // Number of busy threads 
    int liveNum;            // Number of surviving threads 
    int exitNum;            // Number of threads to kill 

    pthread_mutex_t mutexPool;  // Lock the entire thread pool 
    pthread_mutex_t mutexBusy;  // lock busyNum Variable 
    pthread_cond_t notFull;     // Is the task queue full 
    pthread_cond_t notEmpty;    // Is the task queue empty 

    int shutdown;          // Do you want to destroy the thread pool , Destroy as 1, Not destroyed as 0
};

ThreadPool* threadPoolCreate(int min, int max, int queueCapacity)
{
    
    ThreadPool* pool = (ThreadPool*)malloc(sizeof(ThreadPool));
    do
    {
    
        if(pool == NULL)
        {
    
            printf("malloc threadpool fail...\n");
            break;
        }

        pool->threadIDs = (pthread_t*)malloc(sizeof(pthread_t)*max);
        if(pool->threadIDs == NULL)
        {
    
            printf("malloc threadIDs fail...\n");
            break;
        }
        memset(pool->threadIDs, 0, sizeof(pthread_t));

        pool->minNum = min;
        pool->maxNum = max;
        pool->busyNum = 0;
        pool->liveNum = min;        // Equal to the minimum number 
        pool->exitNum = 0;

        if( pthread_mutex_init(&pool->mutexPool, NULL) != 0 ||
            pthread_mutex_init(&pool->mutexBusy, NULL) != 0 ||
            pthread_cond_init(&pool->notEmpty, NULL) != 0 ||
            pthread_cond_init(&pool->notFull, NULL) != 0 )
        {
    
            printf("mutex or condition init fail...\n");
            break;
        }

        // Task queue 
        pool->taskQ = (Task*)malloc(sizeof(Task) * queueCapacity);
        pool->queueCapacity = queueCapacity;
        pool->queueSize = 0;
        pool->queueFront = 0;
        pool->queueRear = 0;

        pool->shutdown = 0;

        // Create thread 
        pthread_create(&pool->managerID, NULL, manager, pool);
        for(int i=0; i<min; i++)
        {
    
            pthread_create(&pool->threadIDs[i], NULL, worker, pool);
        }
        return pool;
    }while(0);

    // Release resources 
    if(pool && pool->threadIDs) free(pool->threadIDs);
    if(pool && pool->taskQ) free(pool->taskQ);
    if(pool) free(pool);

    return NULL;
}

int threadPoolDestroy(ThreadPool* pool)
{
    
    if(pool == NULL)
    {
    
        return -1;
    }
    // Close thread pool 
    pool->shutdown = 1;
    // Blocking the recycle manager thread 
    pthread_join(pool->managerID, NULL);
    // Wake up blocked consumer threads 
    for(int i=0; i<pool->liveNum; i++)
    {
    
        pthread_cond_signal(&pool->notEmpty);
    }
    // Free heap memory 
    if(pool->taskQ)
    {
    
        free(pool->taskQ);
    }
    if(pool->threadIDs)
    {
    
        free(pool->threadIDs);
    }
    pthread_mutex_destroy(&pool->mutexPool);
    pthread_mutex_destroy(&pool->mutexBusy);
    pthread_cond_destroy(&pool->notEmpty);
    pthread_cond_destroy(&pool->notFull);

    free(pool);
    pool = NULL;

    return 0;
}

// producer 
void threadPoolAdd(ThreadPool* pool, void(*func)(void*), void* arg)
{
    
    pthread_mutex_lock(&pool->mutexPool);
    while(pool->queueSize == pool->queueCapacity && !pool->shutdown)
    {
    
        // Block producer thread 
        pthread_cond_wait(&pool->notFull, &pool->mutexPool);
    }
    if(pool->shutdown)
    {
    
        pthread_mutex_unlock(&pool->mutexPool);
        return;
    }

    // Add tasks 
    pool->taskQ[pool->queueRear].function = func;
    pool->taskQ[pool->queueRear].arg = arg;
    pool->queueRear = (pool->queueRear+1) % pool->queueCapacity;
    pool->queueSize++;

    pthread_cond_signal(&pool->notEmpty);
    pthread_mutex_unlock(&pool->mutexPool);
}

int threadPoolBusyNum(ThreadPool* pool)
{
    
    pthread_mutex_lock(&pool->mutexBusy);
    int busyNum = pool->busyNum;
    pthread_mutex_unlock(&pool->mutexBusy);
    return busyNum;
}

int threadPoolAliveNum(ThreadPool* pool)
{
    
    pthread_mutex_lock(&pool->mutexPool);
    int liveNum = pool->liveNum;
    pthread_mutex_unlock(&pool->mutexPool);
    return liveNum;
}

void* worker(void* arg)
{
    
    ThreadPool* pool = (ThreadPool*)arg;

    while(1)
    {
    
        pthread_mutex_lock(&pool->mutexPool);
        // Whether the current task is empty 
        // Why while Judge, not if Judge ？
        // because , If there are multiple threads blocking , A backward execution after unlocking , Others must judge whether the queue is empty in the loop ,
        // Otherwise, the queue is empty, and the execution will continue 
        while(pool->queueSize == 0 && !pool->shutdown)
        {
    
            // Blocked working threads 
            pthread_cond_wait(&pool->notEmpty, &pool->mutexPool);
            // Judge whether to destroy 
            if(pool->exitNum>0)
            {
    
                pool->exitNum--;
                if(pool->liveNum > pool->minNum)
                {
    
                    pool->liveNum--;
                    pthread_mutex_unlock(&pool->mutexPool);
                    threadExit(pool);
                }
            }
        }

        // Judge whether the thread pool is closed 
        // The thread pool destruction will also wake up all blocked threads , At this time, the task queue will end regardless of whether it is empty 
        // So we have to add this if Judge 
        if(pool->shutdown)
        {
    
            pthread_mutex_unlock(&pool->mutexPool);
            threadExit(pool);
        }

        // Take a task out of the task queue 
        Task task;
        task.function = pool->taskQ[pool->queueFront].function;
        task.arg = pool->taskQ[pool->queueFront].arg;
        // Mobile head node 
        pool->queueFront = (pool->queueFront+1) % pool->queueCapacity;
        pool->queueSize--;
        // Unlock 
        pthread_cond_signal(&pool->notFull);
        pthread_mutex_unlock(&pool->mutexPool);

        printf("thread start working...\n");
        pthread_mutex_lock(&pool->mutexBusy);
        pool->busyNum++;
        pthread_mutex_unlock(&pool->mutexBusy);

        task.function(task.arg);
        //(*task.function)(task.arg);
        free(task.arg);
        task.arg = NULL;

        printf("thread end working...\n");
        pthread_mutex_lock(&pool->mutexBusy);
        pool->busyNum--;
        pthread_mutex_unlock(&pool->mutexBusy);
    }

    return NULL;
}

void* manager(void* arg)
{
    
    ThreadPool* pool = (ThreadPool*)arg;

    //shutdown Only the manager thread can modify , So there's no need to lock 
    while(!pool->shutdown)
    {
    
        // every other 3s Test once 
        sleep(3);

        // Take out the number of tasks in the thread pool and the number of current threads 
        pthread_mutex_lock(&pool->mutexPool);
        int queueSize = pool->queueSize;
        int liveNum = pool->liveNum;
        pthread_mutex_unlock(&pool->mutexPool);

        // Get the number of busy threads 
        pthread_mutex_lock(&pool->mutexBusy);
        int busyNum = pool->busyNum;
        pthread_mutex_unlock(&pool->mutexBusy);

        // Add thread 
        // The number of tasks > Number of threads alive  &&  Number of threads alive < Maximum number of threads 
        if(queueSize>liveNum && liveNum<pool->maxNum)
        {
    
            pthread_mutex_lock(&pool->mutexPool);
            int counter = 0;
            for(int i=0; i<pool->maxNum && counter<NUMBER && pool->liveNum<pool->maxNum; i++)
            {
    
                if(pool->threadIDs[i] == 0)
                {
    
                    pthread_create(&pool->threadIDs[i], NULL, worker, pool);
                    counter++;
                    pool->liveNum++;
                }
            }
            pthread_mutex_unlock(&pool->mutexPool);
        }

        // Destruction of the thread 
        // Busy thread *2< Number of threads alive  &&  Surviving threads > Minimum number of threads 
        if(busyNum*2<liveNum && liveNum>pool->minNum)
        {
    
            pthread_mutex_lock(&pool->mutexPool);
            pool->exitNum = NUMBER;
            pthread_mutex_unlock(&pool->mutexPool);
            // Let the working thread commit suicide 
            for(int i=0; i<NUMBER; i++)
            {
    
                pthread_cond_signal(&pool->notEmpty);
            }
        }
    }
}

void threadExit(ThreadPool* pool)
{
    
    pthread_t tid = pthread_self();
    for(int i=0; i<pool->maxNum; i++)
    {
    
        if(pool->threadIDs[i] == tid)
        {
    
            pool->threadIDs[i] = 0;
            printf("%s called, %ld exiting...\n", __FUNCTION__, tid);
            break;
        }
    }
    pthread_exit(NULL);
}

Test code

#include<stdio.h>
#include<stdlib.h>
#include<unistd.h>
#include<pthread.h>
#include"threadpool.h"

void taskFunc(void* arg)
{
    
    int num = *(int*)arg;
    printf("thread %ld is working, number = %d\n", pthread_self(), num);
    sleep(1);
}

int main()
{
    
    // Create a thread pool 
    ThreadPool* pool = threadPoolCreate(3, 10, 100);
    for(int i=0; i<100; i++)
    {
    
        int* num = (int*)malloc(sizeof(int));
        *num = i + 100;
        threadPoolAdd(pool, taskFunc, num);
    }
    sleep(30);
    threadPoolDestroy(pool);
    return 0;
}