1、程序简介
该程序是基于OpenHarmony的C++公共基础类库的读写锁：rwlock。
本案例主要完成如下工作：
创建3个读线程，每个读线程循环5次，每次循环获取读锁，将公共资源变量打印，睡眠1秒，然后释放读锁，最后再睡眠1秒。
创建3个写线程，每个写线程循环5次，每次循环获取写锁，将公共资源变量打印，睡眠1秒，然后释放读锁，最后再睡眠1秒。
本案例已基于凌蒙派-RK3568开发板验证过，如有需要相关代码，请参考：
https://gitee.com/Lockzhiner-Electronics/lockzhiner-rk3568-openharmony/tree/master/samples/a25_utils_rwlock
2、基础知识
C++公共基础类库为标准系统提供了一些常用的C++开发工具类，包括：
文件、路径、字符串相关操作的能力增强接口
读写锁、信号量、定时器、线程增强及线程池等接口
安全数据容器、数据序列化等接口
各子系统的错误码相关定义
2.1、添加C++公共基础类库依赖
修改需调用模块的BUILD.gn，在external_deps或deps中添加如下：
ohos_shared_library("xxxxx") {...external_deps = [...# 动态库依赖(可选)"c_utils:utils",# 静态库依赖(可选)"c_utils:utilsbase",# Rust动态库依赖(可选)"c_utils:utils_rust",]...}
一般而言，我们只需要填写"c_utils:utils"即可。
2.2、rwlock头文件
C++公共基础类库的rwlock头文件在：//commonlibrary/c_utils/base/include/rwlock.h
可在源代码中添加如下：
OpenHarmony读写锁分为如下三大类：
（1）RWLock类
OHOS::RWLock（2）UniqueWriteGuard类
OHOS::UniqueWriteGuard（3）UniqueReadGuard类
OHOS::UniqueReadGuard2.3、OHOS::Utils::RWLock接口说明
2.3.1、RWLock
构造函数。
RWLock() : RWLock(true);RWLock(bool writeFirst);
参数说明：
| 参数名称 | 类型 | 参数说明 |
|---|---|---|
| writeFirst | bool | 是否优先写模式 |
2.3.2、~RWLock
析构函数。
~RWLock();2.3.3、LockRead
获取读锁。
void LockRead();2.3.4、UnLockRead
释放读锁。
void UnLockRead();2.3.5、LockWrite
获取写锁。
void LockWrite();2.3.6、UnLockWrite
获取写锁。
void UnLockWrite();2.4、OHOS::Utils::UniqueWriteGuard接口说明
2.4.1、UniqueWriteGuard
构造函数。
UniqueWriteGuard(RWLockable &rwLockable)参数说明：
| 参数名称 | 类型 | 参数说明 |
|---|---|---|
| rwLockable | RWLockable | template <typename RWLockable> |
2.4.2、~UniqueWriteGuard
析构函数。
~UniqueWriteGuard();2.5、OHOS::Utils::UniqueReadGuard接口说明
2.5.1、UniqueReadGuard
构造函数。
UniqueReadGuard(RWLockable &rwLockable)参数说明：
| 参数名称 | 类型 | 参数说明 |
|---|---|---|
| rwLockable | RWLockable | template <typename RWLockable> |
2.5.2、~UniqueReadGuard
析构函数。
~UniqueReadGuard();3、程序解析
3.1、创建编译引导
在上一级目录BUILD.gn文件添加一行编译引导语句。
import("//build/ohos.gni")group("samples") {deps = ["a25_utils_rwlock:utils_rwlock",]}
"a25_utils_rwlock:utils_rwlock",该行语句表示引入 参与编译。
3.2、创建编译项目
创建a25_utils_rwlock目录，并添加如下文件：
a25_utils_rwlock├── utils_rwlock_sample.cpp # .cpp源代码├── BUILD.gn # GN文件
3.3、创建BUILD.gn
编辑BUILD.gn文件。
import("//build/ohos.gni")ohos_executable("utils_rwlock") {sources = [ "utils_rwlock_sample.cpp" ]include_dirs = ["//commonlibrary/c_utils/base/include","//commonlibrary/c_utils/base:utils","//third_party/googletest:gtest_main","//third_party/googletest/googletest/include"]external_deps = ["c_utils:utils"]part_name = "product_rk3568"install_enable = true}
注意：
（1）BUILD.gn中所有的TAB键必须转化为空格，否则会报错。如果自己不知道如何规范化，可以：
# 安装gn工具sudo apt-get install ninja-buildsudo apt install generate-ninja# 规范化BUILD.gngn format BUILD.gn
3.4、创建源代码
3.4.1、创建读写锁和公共资源变量
static OHOS::Utils::RWLock m_rwlock(true);static int m_count = 0;
3.4.2、创建线程池并设置
int main(int argc, char **argv){OHOS::ThreadPool threads("name_semaphore_threads");int threads_start = 6;......threads.SetMaxTaskNum(128);threads.Start(threads_start);......}
3.4.3、启动3个读线程和3个写线程
调用AddTask()添加子线程。
// 启动读线程for (int i = 0; i < 3; i++) {str_name = "thread_read_" + to_string(i);auto task = std::bind(funcRead, str_name);threads.AddTask(task);}// 启动写线程for (int i = 0; i < 3; i++) {str_name = "thread_write_" + to_string(i);auto task = std::bind(funcWrite, str_name);threads.AddTask(task);}
3.4.4、编写读线程
读线程完成如下步骤：
调用LockRead()获取读锁；
如果获取到读锁，打印公共资源变量，并睡眠1秒；
调用UnLockRead()释放读锁；
睡眠1秒；
上述操作循环5次；
static void funcRead(const string& name){cout << get_curtime() << ", " << name << ": start\n";for (int i = 0; i < 5; i++) {cout << get_curtime() << ", " << name << ": LockRead wait..." << endl;m_rwlock.LockRead();cout << get_curtime() << ", " << name << ": LockRead success and read count = " << m_count << " and sleep 1 sec" << endl;sleep(1);m_rwlock.UnLockRead();cout << get_curtime() << ", " << name << ": UnLockRead" << endl;sleep(1);}}
3.4.5、编写写线程
写线程完成如下步骤：
调用LockWrite()获取写锁；
如果获取到读锁，公共资源变量累加1，并睡眠1秒；
调用UnLockWrite()释放写锁；
睡眠1秒；
上述操作循环5次；
static void funcWrite(const string& name){cout << get_curtime() << ", " << name << ": start\n";for (int i = 0; i < 5; i++) {cout << get_curtime() << ", " << name << ": LockWrite wait..." << endl;m_rwlock.LockWrite();cout << get_curtime() << ", " << name << ": LockWrite success and write count++ and sleep 1 sec" << endl;m_count++;sleep(1);m_rwlock.UnLockWrite();cout << get_curtime() << ", " << name << ": UnLockWrite" << endl;sleep(1);}}
4、编译步骤
进入OpenHarmony编译环境，运行命令：
hb build -f5、运行结果
# utils_rwlock2017-8-5 20:7:8, thread_read_0: start2017-8-5 20:7:8, thread_read_0: LockRead wait...2017-8-5 20:7:8, thread_read_0: LockRead success and read count = 0 and sleep 1 sec2017-8-5 20:7:8, thread_read_1: start2017-8-5 20:7:8, thread_read_1: LockRead wait...2017-8-5 20:7:8, thread_read_1: LockRead success and read count = 0 and sleep 1 sec2017-8-5 20:7:8, thread_read_2: start2017-8-5 20:7:8, thread_read_2: LockRead wait...2017-8-5 20:7:8, thread_read_2: LockRead success and read count = 0 and sleep 1 sec2017-8-5 20:7:8, thread_write_0: start2017-8-5 20:7:8, thread_write_0: LockWrite wait...2017-8-5 20:7:8, thread_write_1: start2017-8-5 20:7:8, thread_write_1: LockWrite wait...2017-8-5 20:7:9, thread_read_0: UnLockRead2017-8-5 20:7:9, thread_read_1: UnLockRead2017-8-5 20:7:9, thread_read_2: UnLockRead2017-8-5 20:7:9, thread_write_1: LockWrite success and write count++ and sleep 1 sec2017-8-5 20:7:10, thread_read_0: LockRead wait...2017-8-5 20:7:10, thread_write_1: UnLockWrite2017-8-5 20:7:10, thread_write_0: LockWrite success and write count++ and sleep 1 sec2017-8-5 20:7:10, thread_read_1: LockRead wait...2017-8-5 20:7:10, thread_read_2: LockRead wait...2017-8-5 20:7:112017-8-5 20:7:11, thread_write_0, thread_read_0: LockRead success and read count = : UnLockWrite2 and sleep 1 sec2017-8-5 20:7:11, thread_read_1: LockRead success and read count = 2 and sleep 1 sec2017-8-5 20:7:11, thread_write_1: LockWrite wait...2017-8-5 20:7:12, thread_write_0: LockWrite wait...2017-8-5 20:7:12, thread_read_1: UnLockRead2017-8-5 20:7:12, thread_read_0: UnLockRead2017-8-5 20:7:12, thread_write_0: LockWrite success and write count++ and sleep 1 sec2017-8-5 20:7:13, thread_read_1: LockRead wait...2017-8-5 20:7:13, thread_read_0: LockRead wait...2017-8-5 20:7:13, thread_write_0: UnLockWrite2017-8-5 20:7:13, thread_write_1: LockWrite success and write count++ and sleep 1 sec2017-8-5 20:7:14, thread_write_0: LockWrite wait...2017-8-5 20:7:14, thread_write_1: UnLockWrite2017-8-5 20:7:14, thread_write_0: LockWrite success and write count++ and sleep 1 sec2017-8-5 20:7:15, thread_read_0: LockRead success and read count = 2017-8-5 20:7:15, thread_write_0: UnLockWrite2017-8-5 20:7:15, thread_write_1: LockWrite wait...2017-8-5 20:7:15, thread_read_1: LockRead success and read count = 5 and sleep 1 sec5 and sleep 1 sec2017-8-5 20:7:16, thread_write_0: LockWrite wait...2017-8-5 20:7:16, thread_read_1: UnLockRead2017-8-5 20:7:16, thread_read_0: UnLockRead2017-8-5 20:7:16, thread_write_1: LockWrite success and write count++ and sleep 1 sec2017-8-5 20:7:17, thread_read_1: LockRead wait...2017-8-5 20:7:17, thread_read_0: LockRead wait...2017-8-5 20:7:17, thread_write_1: UnLockWrite2017-8-5 20:7:17, thread_write_0: LockWrite success and write count++ and sleep 1 sec2017-8-5 20:7:18, thread_write_1: LockWrite wait...2017-8-5 20:7:18, thread_write_1: LockWrite success and write count++ and sleep 1 sec2017-8-5 20:7:18,thread_write_0: UnLockWrite2017-8-5 20:7:192017-8-5 20:7:19, thread_write_0, thread_write_1: UnLockWrite: LockWrite wait...2017-8-5 20:7:19,thread_read_1: LockRead success and read count = 8 and sleep 1 sec2017-8-5 20:7:19, thread_read_0: LockRead success and read count = 8 and sleep 1 sec2017-8-5 20:7:19, thread_read_2: LockRead success and read count = 8 and sleep 1 sec2017-8-5 20:7:20, thread_write_1: LockWrite wait...2017-8-5 20:7:20, thread_read_1: UnLockRead2017-8-5 20:7:20, thread_read_0: UnLockRead2017-8-5 20:7:20, thread_read_2: UnLockRead2017-8-5 20:7:20, thread_write_1: LockWrite success and write count++ and sleep 1 sec2017-8-5 20:7:21, thread_read_1: LockRead wait...2017-8-5 20:7:21, thread_read_0: LockRead wait...2017-8-5 20:7:21, thread_read_2: LockRead wait...2017-8-5 20:7:21, thread_write_1: UnLockWrite2017-8-5 20:7:21, thread_write_0: LockWrite success and write count++ and sleep 1 sec2017-8-5 20:7:22, thread_write_0: UnLockWrite2017-8-5 20:7:22, thread_read_0: LockRead success and read count = 10 and sleep 1 sec2017-8-5 20:7:22, thread_read_1: LockRead success and read count = 10 and sleep 1 sec2017-8-5 20:7:22, thread_read_2: LockRead success and read count = 10 and sleep 1 sec2017-8-5 20:7:23, thread_read_0: UnLockRead2017-8-5 20:7:23, thread_read_1: UnLockRead2017-8-5 20:7:23, thread_read_2: UnLockRead2017-8-5 20:7:24, thread_read_2: LockRead wait...2017-8-5 20:7:24, thread_read_2: LockRead success and read count = 10 and sleep 1 sec2017-8-5 20:7:25, thread_read_2: UnLockRead2017-8-5 20:7:26, thread_read_2: LockRead wait...2017-8-5 20:7:26, thread_read_2: LockRead success and read count = 10 and sleep 1 sec2017-8-5 20:7:27, thread_read_2: UnLockRead#