done learning thread in C++ 11

DavidingPlus · DavidingPlus · commit f661cdf0a0b9 · 2024-10-28T13:20:52.000+08:00
diff --git a/snippet/CppThreadLearning/AsyncTest/main.cpp b/snippet/CppThreadLearning/AsyncTest/main.cpp
@@ -11,7 +11,7 @@ int main()
     // std::launch::deferred	0x2（2）	                    在调用 future::get、future::wait 时同步启动
     // std::launch::async | std::launch::defereed	0x3（3）	同步或异步，根据操作系统而定
 
-    std::async(
+    auto f = std::async(
         std::launch::async,
 
         [](const std::string &message)
diff --git a/snippet/CppThreadLearning/CMakeLists.txt b/snippet/CppThreadLearning/CMakeLists.txt
@@ -1,5 +1,7 @@
+add_subdirectory (AsyncTest)
 add_subdirectory (AtomicTest)
+add_subdirectory (FutureTest)
 add_subdirectory (MutexTest)
+add_subdirectory (PromiseTest)
+add_subdirectory (ThisThreadTest)
 add_subdirectory (ThreadTest)
-add_subdirectory (AsyncTest)
-add_subdirectory (FutureTest)
diff --git a/snippet/CppThreadLearning/FutureTest/main2.cpp b/snippet/CppThreadLearning/FutureTest/main2.cpp
@@ -5,7 +5,7 @@
 
 void countNumber()
 {
-    for (int i = 0; i < 1000000000; ++i)
+    for (int i = 0; i < 1e9; ++i)
         ;
 }
 
diff --git a/snippet/CppThreadLearning/PromiseTest/main.cpp b/snippet/CppThreadLearning/PromiseTest/main.cpp
@@ -1,8 +1,34 @@
 #include <iostream>
+#include <thread>
+#include <future>
+
+#include "sum.h"
+
+
+template <class... Args>
+void doIt(std::promise<int> &p, Args &&...args)
+{
+    // 成员函数 set_value()
+    // 设置 promise 的值并将 future_status 设为 ready。
+    // void 特化：只将共享状态设为 ready。
+    p.set_value(sum(args...));
+}
 
 
 int main()
 {
+    // std::promise 本质上是 std::future 的一个包装。std::future的值不能被改变，但可以通过 std::promise 来创建一个拥有特定值的 std::future。
+    // std::promise 的原理就是不改变已有 std::future 的值，而是创建新的 std::future 对象。
+
+    std::promise<int> p;
+
+    std::thread t(doIt<int, int, int>, std::ref(p), 1, 10, 100);
+
+    t.join();
+
+    // 成员函数 get_future()
+    // 构造一个 std::future 对象，其值与 std::promise 相同，status 也与 promise 相同。
+    std::cout << p.get_future().get() << std::endl;
 
 
     return 0;
diff --git a/snippet/CppThreadLearning/PromiseTest/sum.h b/snippet/CppThreadLearning/PromiseTest/sum.h
@@ -0,0 +1,32 @@
+#ifndef _SUM_H_
+#define _SUM_H_
+
+// copy from ./snippet/CppThreadLearning/FutureTest/sum.h
+
+
+template <typename T, typename... Args>
+struct LSum
+{
+
+    auto operator()(const T &val, Args &&...args)
+        -> decltype(val + LSum<Args...>()(std::forward<Args>(args)...)) { return val + LSum<Args...>()(std::forward<Args>(args)...); }
+};
+
+template <typename T>
+struct LSum<T>
+{
+
+    auto operator()(const T &val)
+        -> decltype(val) { return val; }
+};
+
+
+template <typename... Args>
+auto sum(Args &&...args)
+    -> decltype(LSum<Args...>()(std::forward<Args>(args)...))
+{
+    return LSum<Args...>()(std::forward<Args>(args)...);
+}
+
+
+#endif
diff --git a/snippet/CppThreadLearning/ThisThreadTest/CMakeLists.txt b/snippet/CppThreadLearning/ThisThreadTest/CMakeLists.txt
@@ -0,0 +1 @@
+add_executable (ThisThreadTest main.cpp)
diff --git a/snippet/CppThreadLearning/ThisThreadTest/main.cpp b/snippet/CppThreadLearning/ThisThreadTest/main.cpp
@@ -0,0 +1,47 @@
+#include <iostream>
+#include <thread>
+#include <atomic>
+
+
+std::atomic<bool> ready(false);
+
+
+void count()
+{
+    // std::this_thread::yield()：暂时放弃线程的执行，将主动权交给其他线程（放心，主动权还会回来）。
+    // 这里刻意这么设计，在主函数中就是为了让主线程先睡眠一段时间，改变 ready 条件以后，再执行子线程，刚好也测试了这个函数的用法。
+    while (!ready) std::this_thread::yield();
+
+    for (int i = 0; i <= 2000000000; i++)
+        ;
+
+    // std::this_thread::get_id()：获得当前线程 ID。
+    std::cout << "Thread " << std::this_thread::get_id() << " finished!" << std::endl;
+
+
+    return;
+}
+
+
+int main()
+{
+    constexpr int threadNum = 10;
+
+    std::thread th[threadNum];
+
+    for (int i = 0; i < threadNum; ++i) th[i] = std::thread(count);
+
+    std::cout << "Main Thread is Sleeping!" << std::endl;
+
+    // std::this_thread::sleep_for()：睡眠一段时间。
+    std::this_thread::sleep_for(std::chrono::milliseconds(5000));
+
+    ready = true;
+
+    std::cout << "Child Threads Start!" << std::endl;
+
+    for (int i = 0; i < threadNum; ++i) th[i].join();
+
+
+    return 0;
+}

Original file line number	Diff line number	Diff line change
`@@ -5,7 +5,7 @@`
`5`	`5`
`6`	`6`	`void countNumber()`
`7`	`7`	`{`
`8`		`- for (int i = 0; i < 1000000000; ++i)`
	`8`	`+ for (int i = 0; i < 1e9; ++i)`
`9`	`9`	`;`
`10`	`10`	`}`
`11`	`11`
Original file line number	Diff line number	Diff line change
`@@ -0,0 +1 @@`
	`1`	`+add_executable (ThisThreadTest main.cpp)`