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Commit 01aafde

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更新视频代码
1 parent 7877d0e commit 01aafde

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6 files changed

+176
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lines changed

6 files changed

+176
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lines changed
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#include <iostream>
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#include <atomic>
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#include <mutex>
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#include <thread>
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class spinlock_mutex {
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std::atomic_flag flag{};
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public:
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spinlock_mutex()noexcept = default;
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void lock()noexcept {
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while (flag.test_and_set(std::memory_order_acquire));
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}
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void unlock()noexcept {
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flag.clear(std::memory_order_release);
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}
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};
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spinlock_mutex m;
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void f() {
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std::lock_guard<spinlock_mutex> lc{ m };
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std::cout << "😅😅" << "❤️❤️\n";
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}
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int main(){
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std::thread t{ f };
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std::thread t1{ f };
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std::thread t2{ f };
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std::thread t3{ f };
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std::thread t4{ f };
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std::thread t5{ f };
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t.join();
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t1.join();
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t2.join();
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t3.join();
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t4.join();
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t5.join();
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}
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#include <atomic>
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#include <iostream>
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#include <thread>
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std::atomic<bool> flag{ false };
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bool expected = false;
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void try_set_flag() {
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// 尝试将 flag 设置为 true,如果当前值为 false
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if (flag.compare_exchange_strong(expected, true)) {
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std::cout << "flag 为 false,flag 设为 true。\n";
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}
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else {
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std::cout << "flag 为 true, expected 设为 true。\n";
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}
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}
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int main() {
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std::thread t1{ try_set_flag };
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std::thread t2{ try_set_flag };
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t1.join();
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t2.join();
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std::cout << "flag: " << std::boolalpha << flag << '\n';
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std::cout << "expected: " << std::boolalpha << expected << '\n';
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}
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#include <iostream>
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struct X{
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int v{};
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void f()const {
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std::cout << v << '\n';
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}
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};
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int main(){
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int arr[10]{ 1,2 };
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std::atomic<int*> p{ arr };
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p.fetch_add(1);
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std::cout << *(p.load()) << '\n';
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p.fetch_sub(1);
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std::cout << *(p.load()) << '\n';
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p += 1;
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std::cout << *(p.load()) << '\n';
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p -= 1;
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std::cout << *(p.load()) << '\n';
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X xs[3]{ {10},{20},{30} };
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std::atomic<X*> p2{ xs };
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p2.load()->f();
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p2 += 2;
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p2.load()->f();
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}
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#include <iostream>
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#include <memory>
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#include <thread>
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#include <chrono>
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#include <syncstream>
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using namespace std::chrono_literals;
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class Data {
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public:
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Data(int value = 0) : value_(value) {}
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int get_value() const { return value_; }
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void set_value(int new_value) { value_ = new_value; }
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private:
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int value_;
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};
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std::atomic<std::shared_ptr<Data>> data = std::make_shared<Data>();
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void writer() {
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for (int i = 0; i < 10; ++i) {
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std::shared_ptr<Data> new_data = std::make_shared<Data>(i);
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data.store(new_data);
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std::this_thread::sleep_for(100ms);
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}
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}
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void reader() {
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for (int i = 0; i < 10; ++i) {
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if (auto sp = data.load()) {
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std::cout << "读取线程值: " << sp->get_value() << std::endl;
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}
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else {
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std::cout << "没有读取到数据" << std::endl;
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}
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std::this_thread::sleep_for(100ms);
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}
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}
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std::atomic<std::shared_ptr<int>> ptr = std::make_shared<int>();
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void wait_for_wake_up() {
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std::osyncstream{ std::cout }
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<< "线程 "
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<< std::this_thread::get_id()
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<< " 阻塞,等待更新唤醒\n";
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// 等待 ptr 变为其它值
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ptr.wait(ptr.load());
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std::osyncstream{ std::cout }
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<< "线程 "
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<< std::this_thread::get_id()
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<< " 已被唤醒\n";
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}
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void wake_up() {
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std::this_thread::sleep_for(5s);
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// 更新值并唤醒
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ptr.store(std::make_shared<int>(10));
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ptr.notify_one();
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}
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int main() {
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//std::thread writer_thread{ writer };
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//std::thread reader_thread{ reader };
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//writer_thread.join();
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//reader_thread.join();
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//std::atomic<std::shared_ptr<int>> ptr = std::make_shared<int>(10);
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//std::atomic_ref<int> ref{ *ptr.load() };
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//ref = 100; // 原子地赋 100 给被引用的对象
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//std::cout << *ptr.load() << '\n';
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std::thread t1{ wait_for_wake_up };
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wake_up();
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t1.join();
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}

‎code/ModernCpp-ConcurrentProgramming-Tutorial/CMakeLists.txt

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@@ -12,7 +12,7 @@ elseif(CMAKE_CXX_COMPILER_ID STREQUAL "GNU" OR CMAKE_CXX_COMPILER_ID STREQUAL "C
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add_compile_options("-finput-charset=UTF-8" "-fexec-charset=UTF-8" "-fopenmp")
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endif()
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add_executable(${PROJECT_NAME} "41实现一个线程池.cpp")
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add_executable(${PROJECT_NAME} "45原子特化shared_ptr.cpp")
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set(SFML_DIR "D:/lib/SFML-2.6.1-windows-vc17-64-bit/SFML-2.6.1/lib/cmake/SFML")
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find_package(SFML 2.6.1 COMPONENTS system window graphics audio network REQUIRED)

‎md/05内存模型与原子操作.md

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稍微聊一下原理,我们的 `spinlock_mutex` 对象中存储的 `flag` 对象在默认构造时是清除 (`false`) 状态。在 `lock()` 函数中调用 `test_and_set` 函数,它是原子的,只有一个线程能成功调用并将 `flag` 的状态原子地更改为设置 (`true`),并返回它先前的值 (`false`)。此时,该线程成功获取了锁,退出循环。
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当 `flag` 对象的状态为设置 (`true`) 时,其线程调用 `test_and_set` 函数会返回 `true`,导致它们继续在循环中自旋,无法退出。直到先前持有锁的线程调用 `unlock()` 函数,将 `flag` 对象的状态原子地更改为清除 (`false`) 状态。此时,等待的线程中会有一个线程成功调用 `test_and_set` 返回 `false`,然后退出循环,成功获取锁。
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当 `flag` 对象的状态为设置 (`true`) 时,其它线程调用 `test_and_set` 函数会返回 `true`,导致它们继续在循环中自旋,无法退出。直到先前持有锁的线程调用 `unlock()` 函数,将 `flag` 对象的状态原子地更改为清除 (`false`) 状态。此时,等待的线程中会有一个线程成功调用 `test_and_set` 返回 `false`,然后退出循环,成功获取锁。
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> 值得注意的是,我们只是稍微的讲一下使用 `std::atomic_flag` 实现自旋锁。不过并不推荐各位在实践中使用它,具体可参见 [**Linus Torvalds**](https://en.wikipedia.org/wiki/Linus_Torvalds) 的[文章](https://www.realworldtech.com/forum/?threadid=189711&curpostid=189723)。其中有一段话说得很直接:
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>

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