多线程的互斥—互斥锁（互斥量）

//account.h

#ifndef     _ACCOUNT_H
#define     _ACCOUNT_H
#include <pthread.h>

typedef struct{
    int code;
    double balance;    
    //定义一把互斥锁，用来对多线程操作的银行账户（共享资源）进行加锁（保护）的
    
    /* 建议一把互斥锁和一个共享资源（银行账户）绑定，尽量不要设置成全局变量，否则可能出现
    一把互斥锁去锁几百个账户（即一个线程获得锁，其他线程将阻塞），导致并发性的降低 
    */
    pthread_mutex_t mutex;
}Account;

//创建账户
extern Account *create_account(int code, double balance);

//销毁账户
extern void destroy_account(Account *a);

//取款
extern double get_momney(Account *a, double momney);

//存款
extern double save_momney(Account *a, double momney);

//获得余额
extern double get_balance(Account *a);


#endif

//account.c

#include "account.h"
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>

//创建账户
Account *create_account(int code, double balance)
{
    Account *a = (Account *)malloc(sizeof(Account));
    if(a == NULL){
        printf("create_account failed\n");
        return (Account *)0;
    }
    
    a->code = code;
    a->balance = balance;
    if(pthread_mutex_init(&a->mutex, NULL) != 0){
        printf("pthread_mutex_init failed\n");
    }
    
    return a;
}

//销毁账户
extern void destroy_account(Account *a)
{
    if(a == NULL){
        printf("destroy_account failed\n");
    }
    
    if(pthread_mutex_destroy(&a->mutex) != 0){
        printf("pthread_mutex_destroy failed\n");
    }
    free(a);
}

//取款
extern double get_momney(Account *a, double momney)
{
    if(a == NULL){
        printf("get_momney failed\n");
    }
    
    pthread_mutex_lock(&a->mutex);
    if(momney < 0 || a->balance < momney)
    {
        printf("momney not enough\n");
        pthread_mutex_unlock(&a->mutex);
        return 0.0;
    }
    
    double balance = a->balance;
    sleep(1);
    balance = balance - momney;
    a->balance = balance;
    pthread_mutex_unlock(&a->mutex);
    
    return momney;
}


//存款
extern double save_momney(Account *a, double momney)
{
    if(a == NULL){
        printf("save_momney failed\n");
    }
    
    pthread_mutex_lock(&a->mutex);
    if(momney < 0){
        pthread_mutex_unlock(&a->mutex);
        return 0.0;
    }
    
    double balance = a->balance;
    sleep(1);
    balance = balance + momney;
    a->balance = balance;
    pthread_mutex_unlock(&a->mutex);
    
    return momney;
}


//获得余额
extern double get_balance(Account *a)
{
    if(a == NULL){
        printf("get_balance failed\n");
    }
    
    pthread_mutex_lock(&a->mutex);
    double balance = a->balance;
    pthread_mutex_unlock(&a->mutex);
    
    return balance;
}

//account_test.c

#include <stdio.h>
#include <pthread.h>
#include "account.h"
#include <string.h>
#include <stdlib.h>



/* void *memcpy(void *dest, const void *src, size_t n); */


 /* int pthread_create(pthread_t *thread, const pthread_attr_t *attr,
                          void *(*start_routine) (void *), void *arg); */
typedef struct{
    Account *account;
    char name[20];
    double momney;    
}operArg;

void *getmomney_fn(void *arg)
{
    operArg *o = (operArg *)arg;
    double momney = get_momney(o->account, o->momney);

    
    printf("%s from %d getmomney %f\n",o->name, o->account->code, momney);
    
    return (void *)0;
}

int main()
{    
    pthread_t boy,girl;
    
    Account *a = create_account(1001,10000);
    
    operArg o1,o2;
    o1.account = a;
    o1.momney = 10000;
    memcpy(o1.name, "boy", sizeof("boy"));
    
    o2.account = a;
    o2.momney = 10000;
    memcpy(o2.name, "girl", sizeof("girl"));
    
    if(pthread_create(&boy, NULL, getmomney_fn, (void *)&o1) < 0){
        printf("pthread_create failed\n");
        exit(1);
    }
    
    if(pthread_create(&girl, NULL, getmomney_fn, (void *)&o2) < 0){
        printf("pthread_create failed\n");
        exit(1);
    }
    
    pthread_join(boy, NULL);
    pthread_join(girl, NULL);
    
    printf("get balance = %f\n",get_balance(a));
    
    destroy_account(a);
    
    return 0;
}