三十九、Linux 线程——线程的同步和互斥

39.1 概念

• 线程同步
  • 是一个宏观概念，在微观上包含线程的相互排斥和线程先后执行的约束问题
  • 解决同步方式
    • 条件变量
    • 线程信号量
• 线程互斥
  • 线程执行的相互排斥
  • 解决互斥的方式
    • 互斥锁
    • 读写锁
    • 线程信号量

39.2 案例

　　

atm_account.c

#include "atm_account.h"

/** 创建账户 */
atm_Account *atm_account_Create(int code, double balance)
{
    atm_Account *account = (atm_Account *)malloc(sizeof(atm_Account));
    if(NULL == account) {
        return NULL;
    }

    account->code = code;
    account->balance = balance;

    return account;
}

/** 销毁账户 */
void atm_account_Destroy(atm_Account *account)
{
    if(NULL == account){
        return ;
    }

    free(account);
}

/** 取款: 成功，则返回取款金额 */
double atm_account_Withdraw(atm_Account *account, double amt)
{
    if(NULL == account) {
        return 0.0;
    }

    if(amt < 0 || amt > account->balance) {
        return 0.0;
    }

    double balance_tmp = account->balance;
    sleep(1);
    balance_tmp -= amt;
    account->balance = balance_tmp;

    return amt;
}

/** 存款: 返回存款的金额 */
double atm_account_Desposit(atm_Account *account, double amt)
{
    if(NULL == account){
        return 0.0;
    }
    if(amt < 0){
        return 0.0;
    }

    double balance_tmp = account->balance;
    sleep(1);
    balance_tmp += amt;
    account->balance = balance_tmp;

    return amt;
}

/** 查看账户余额 */
double atm_account_BalanceGet(atm_Account *account)
{
    if(NULL == account){
        return 0.0;
    }

    double balance_tmp = account->balance;
    return balance_tmp;
}

atm_account.h

#ifndef __ATM_ACCOUNT_H__
#define __ATM_ACCOUNT_H__

#include <math.h>
#include <malloc.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>

/** 账户信息 */
typedef struct {
    int         code;       ///< 银行账户的编码
    double      balance;    ///< 账户余额
}atm_Account;

/** 创建账户 */
extern atm_Account *atm_account_Create(int code, double balance);
/** 销毁账户 */
extern void atm_account_Destroy(atm_Account *account);
/** 取款 */
extern double atm_account_Withdraw(atm_Account *account, double amt);
/** 存款 */
extern double atm_account_Desposit(atm_Account *account, double amt);
/** 查看账户余额 */
extern double atm_account_BalanceGet(atm_Account *account);

#endif

atm_handler.c

#include "atm_handler.h"

/** 定义取款操作的线程运行函数 */
void *atm_handler_Withdraw(void *arg)
{
    atm_handler_t *handler_tmp = (atm_handler_t *)arg;
    double amt = atm_account_Withdraw(handler_tmp->account, handler_tmp->amt);

    printf("%10s(0x%lu) withdraw %f from account %d\n", handler_tmp->name, pthread_self(), amt, handler_tmp->account->code);

   return (void *)0;
}

/** 定义存款操作的线程运行函数 */
void *atm_handler_Desposit(void *arg)
{
    atm_handler_t *handler_tmp = (atm_handler_t *)arg;
    double amt = atm_account_Desposit(handler_tmp->account, handler_tmp->amt);

    printf("%10s(0x%lu) deposit %f from account %d\n", handler_tmp->name, pthread_self(), amt, handler_tmp->account->code);

   return (void *)0;
}

/** 定义检查银行账户的线程运行函数 */
void *atm_handler_AccountCheck(void *arg)
{
    return (void *)0;
}

/** 账户操作主函数 */
atm_error_t atm_handler_main(void)
{
    int err;
    pthread_t boy, girl;
    atm_Account *account = atm_account_Create(1000001, 10000);
    if(NULL == account){
        return ATM_ERROR_ACCOUNT_CREATE;
    }

    atm_handler_t usr1, usr2;
    strcpy(usr1.name, "boy");
    usr1.account = account;
    usr1.amt = 10000;

    strcpy(usr2.name, "girl");
    usr2.account = account;
    usr2.amt = 10000;

    /** 启动两个线程（boy 和 girl 线程）同时去操作同一个银行账户 */
    if((err = pthread_create(&boy, NULL, atm_handler_Withdraw, (void *)&usr1)) != 0) {
        perror("pthread create error");
    }

    if((err = pthread_create(&girl, NULL, atm_handler_Withdraw, (void *)&usr2)) != 0) {
        perror("pthread create error");
    }
    
    /** 主线程阻塞 */
    pthread_join(boy, NULL);
    pthread_join(girl, NULL);

    printf("account balance: %f\n", atm_account_BalanceGet(account));
    atm_account_Destroy(account);

    return ATM_ERROR_NONE;
}

atm_handler.h

#ifndef __ATM_HANDLER_H__
#define __ATM_HANDLER_H__

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

typedef enum {
    ATM_ERROR_NONE,
    ATM_ERROR_ACCOUNT_CREATE
}atm_error_t;

/** 账户操作结构体 */
typedef struct {
    char            name[20];   ///< 操作人的姓名
    atm_Account     *account;   ///< 操作的账户
    double          amt;        ///< 操作的金额
}atm_handler_t;

extern atm_error_t atm_handler_main(void);

#endif

atm_test.c

#include "atm_handler.h"

int main(void)
{
    atm_handler_main();
    return 0;
}

Makefile

#PROJECT_ROOT = $(dir $(abspath $(lastword $(MAKEFILE_LIST))))
PROJECT_ROOT = $(shell pwd)
SRC_DIR = $(PROJECT_ROOT)/src
INCLUDE_DIR = $(PROJECT_ROOT)/include
OBJ_DIR = $(PROJECT_ROOT)/obj
BIN_DIR = $(PROJECT_ROOT)/bin


# 找出 src 目录下的所有 .c 文件
C_SRCS = $(wildcard $(SRC_DIR)/*.c)
# 将所有的 src 下的 .c 文件替换为 .o 文件
C_OBJS = $(patsubst %c, %o, $(C_SRCS))
TARGET = test
SHARE_LIB = libatm.a

C_SRC_MAIN = atm_test.c

CC = gcc
CCFLAGS += fPIC
LDFLAGS += -shared -fPIC
ASFLAGS +=
ARFLAGS = -crs
LIBS_FLAGS = -L$(BIN_DIR)

RM = rm -rf
 
CFLAGS += -Wall -g -I$(INCLUDE_DIR)
INCDIR += -I$(INCLUDE_DIR)



.PHONY: all clean test

all: $(TARGET)
    cp $(SHARE_LIB) $(BIN_DIR)
    cp $(SRC_DIR)/*.o $(OBJ_DIR)/
    $(RM) $(SHARE_LIB) $(SRC_DIR)/*.o

$(TARGET): $(SHARE_LIB)
    $(CC) $(C_SRC_MAIN) -o $(TARGET) $(CFLAGS) $(INCDIR) $(LIBS_FLAGS) -latm -lpthread

$(SHARE_LIB): $(C_OBJS)
    $(AR) $(ARFLAGS) $(SHARE_LIB) $(C_OBJS)
    cp $(SHARE_LIB) $(BIN_DIR)

$(C_OBJS) : %.o:%.c
    $(CC) -c $(CFLAGS) $(INCDIR) -o $@ $< -lpthread

clean:
    $(RM) mshell 
    $(RM) $(SHARE_LIB) 
    $(RM) $(OBJ_DIR)/$(OBJS)/*.o 
    $(RM) $(SRC_DIR)/*.o

编译运行结果：