先抛出问题：
有一全局变量，一个任务读，一个任务写，有没有问题？
先抛出答案，不建议这么做。
临界资源：各任务/线程采取互斥的方式，实现共享的资源称作临界资源。属于临界资源的硬件串口打印、显示等,软件有消息缓冲队列、变量、数组、缓冲区等。多任务/线程间应采取互斥方式，从而实现对这种资源的共享。最近做的几个项目遇到的一些特殊场景：
多任务/多线程情况下在写模块时，只需要封装进保护机制即可。常见的保护机制有关中断、信号量、互斥锁等。
1.校时 定义全局变量
typedef struct{
/*应用软件时间*/
unsigned int year;
unsigned char month;
unsigned char day;
unsigned char hour;
/*时*/
unsigned char minute;
/*分*/
unsigned char second;
/*秒*/
unsigned int millisecond;
/*毫秒*/
unsigned int microsecond;
/*微秒*/
unsigned int nanosecond;
/*纳秒*/
unsigned int u40mic;
intdelta;
/*日历时与本地RTC的差值*/
intdelta_rtc;
/*同步RTC与本地RTC的差值*/
intdelta_year;
/*用于操作系统年份维护*/
inttimeElapse;
/*系统上电后运行了多少秒*/
char DateValid;
/*年月日有效标识,1为有效*/
char TimeValid;
/*时分秒有效标志,1为有效*/
char BusVaild;
/*总线时间有效, 1为有效, 用于飞参授时及文件夹创建*/
}STRUCT_CORE_TIME;
STRUCT_CORE_TIME gst_TimeState;
int TIME_Regulate_Time(int year, int month, int date, int hour, int minute, int second)
{
struct timespec NewSetTime;
struct tmDownTime;
SYSTEM_TIME_TYPE sys_Time = 0;
RETURN_CODE_TYPE retCode;
if((year < 2000)||(year > 2255))
return -1;
if((month < 1) || (month > 12))
return -2;
if((date < 1) || (date>31))
return -3;
if((hour > 23) || (minute > 59) || (second > 59))
return -4;
/*当超出年限时，获取delta*/
if(year > 2100){
if(((year % 4 == 0) && (year % 100 != 0)) || (year % 400 == 0)){
gst_TimeState.delta_year = year - 2096;
year = 2096;
}else{
gst_TimeState.delta_year = year - 2100;
year = 2100;
}
}else{
gst_TimeState.delta_year = 0;
}GET_TIME(&sys_Time, &retCode);
DownTime.tm_hour = hour;
DownTime.tm_min = minute;
DownTime.tm_sec = second;
DownTime.tm_mday = date;
DownTime.tm_mon = month - 1;
DownTime.tm_year = year - 1900;
DownTime.tm_isdst = 0;
/*设置为非夏令时*/
NewSetTime.tv_sec = mktime(&DownTime);
/*时间直接用delta维护，不涉及系统时间*/
gst_TimeState.delta = NewSetTime.tv_sec - sys_Time / Time_1S;
/*LOG4C日志系统时间更新*/
sd_settimeofday(gst_TimeState.delta);
gst_TimeState.TimeValid = 1;
gst_TimeState.DateValid = 1;
return 0;
}void TIME_Gather_Time()
{
struct timespec NewSetTime;
struct tmDownTime;
SYSTEM_TIME_TYPE sys_Time = 0;
RETURN_CODE_TYPE retCode;
GET_TIME(&sys_Time, &retCode);
NewSetTime.tv_sec = sys_Time / Time_1S + gst_TimeState.delta;
localtime_r(&NewSetTime.tv_sec, &DownTime);
gst_TimeState.year = DownTime.tm_year + 1900 + gst_TimeState.delta_year;
gst_TimeState.month = DownTime.tm_mon + 1;
gst_TimeState.day = DownTime.tm_mday;
gst_TimeState.hour = DownTime.tm_hour;
gst_TimeState.minute = DownTime.tm_min;
gst_TimeState.second = DownTime.tm_sec;
gst_TimeState.millisecond = sys_Time / 1000000 % 1000;
gst_TimeState.microsecond = sys_Time / 1000 % 1000;
gst_TimeState.nanosecond = sys_Time % 1000;
gst_TimeState.u40mic = ((gst_TimeState.hour * 3600 + gst_TimeState.minute * 60 + gst_TimeState.second)*1000
+ gst_TimeState.millisecond)*25;
}校时线程做如下的周期调用：
if(stBusTime.delta和gst_TimeState.delta相差2秒)
{/*校正应用时间*/
Ret = TIME_Regulate_Time(stBusTime.year + 2000, stBusTime.month, stBusTime.day, stBusTime.hour, stBusTime.minute, stBusTime.second);
/*只要VCM校时，就给DLR也校时。有的时候音视频文件创建太早，导致视频头内容有问题*/
TIME_Gather_Time();
/*立刻TIME_Gather_Time数据，更新gst_TimeState结构体所有内容*/
}另一个线程直接取全局变量gst_TimeState内的年月日时分秒。
这种情况实际上是不加保护的一个线程读，另一个线程写，但是不加保护也能使用的原因有两点：
1.外界有卫星绝对时间更新gst_TimeState本地时间
2.对时间的精度要求不高
获取卡状态 嵌入式系统下，任务1进行获取卡状态操作：
static void Msg_04_Process(void * const Handler, unsigned char * const Message, int const LenBytes)
{
DEVICE_INNER_TYPE *pDevice = (DEVICE_INNER_TYPE*)Handler;
/*04消息处理（周期接收）*/
memcpy(&DLR_2_CPM_04, Message, sizeof(DLR_2_CPM_04));
/*IDR端的定义是相反的*/
pDevice->CardState = !DLR_2_CPM_04.Card_State;
}任务2周期获取卡状态，并进行一些操作
int PSSS_DLR_Card_State(void * const Handler)
{
DEVICE_INNER_TYPE *pDevice = (DEVICE_INNER_TYPE*)Handler;
int cardState = 0;
cardState = pDevice->CardState;
return cardState;
}【全局变量和多线程】应用场景：
Msg_04_Process获取卡号的周期是2秒，而PSSS_DLR_Card_State大约20ms就要被调用一次。
方案：
1.给pDevice->CardState加信号量保护
2.PSSS_DLR_Card_State中多次判断pDevice->CardState的值，例如连续3次是同一个值才表示获取成功
