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

     double balance_tmp = account->balance;
     sleep();
     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 < ){
         return 0.0;
     }

     double balance_tmp = account->balance;
     sleep();
     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 *);
 }

 /** 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 *);
 }

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

 /** 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(, );
     if(NULL == account){
         return ATM_ERROR_ACCOUNT_CREATE;
     }

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

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

     /** 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)) != ) {
         perror("pthread create error");
     }

     if((err = pthread_create(&girl, NULL, atm_handler_Withdraw, (void *)&usr2)) != ) {
         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[];   ///< 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 ;
 }

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：