[新增 SafeCallback 模块]：实现生命周期安全的回调函数

- 在项目中新增 `SafeCallback` 模块，包含 `safecallback.hpp` 和 `safecallback_unittest.cc` 文件。
- `SafeCallback` 类通过 `std::weak_ptr` 管理对象生命周期，确保回调函数在对象销毁后不会被调用。
- 提供 `makeSafeCallback` 工厂函数，用于简化回调函数的创建。
- 编写单元测试 `safecallback_unittest.cc`，验证回调函数在对象存活和销毁后的行为。
- 更新 `CMakeLists.txt` 和 `README.md` 文件，将 `SafeCallback` 模块集成到项目中。

CMakeLists.txt

@@ -68,6 +68,7 @@ add_subdirectory(MonitorDir)
 add_subdirectory(MonitorDir_EFSW)
 add_subdirectory(Mutex)
 add_subdirectory(OpenSSL)
+add_subdirectory(SafeCallback)
 add_subdirectory(Thread)
 
 if(CMAKE_HOST_LINUX)

README.md

@@ -46,10 +46,11 @@
     7. [sm4](/OpenSSL/openssl_sm4.cc)——sm4加解密的例子；
     8. [x509](/OpenSSL/openssl_x509.cc)——x509证书的例子；
     9. [bash](/OpenSSL/openssl_bash.sh)——openssl命令行的例子；
-26. [Server](/Server)——linux server的一些例子；
+26. [SafeCallback](/SafeCallback/safecallback.hpp)——生命周期安全的回调函数的实现，参考[muduo WeakCallback](https://github.com/chenshuo/muduo/blob/cpp17/muduo/base/WeakCallback.h)；
+27. [Server](/Server)——linux server的一些例子；
     1. [server_epoll](/Server/server_epoll.cc)——epoll的例子；
     2. [server_poll](/Server/server_poll.cc)——poll的例子；
     3. [server_select](/Server/server_select.cc)——select的例子；
-27. [Thread](/Thread/)——基于std::thread实现的线程类，包括线程池；
+28. [Thread](/Thread/)——基于std::thread实现的线程类，包括线程池；
     1. [Thread](/Thread/thread.hpp)——线程类；
     2. [ThreadPool](/Thread/threadpool.hpp)——线程池；

SafeCallback/CMakeLists.txt

@@ -0,0 +1,5 @@
+add_executable(safecallback_unittest safecallback_unittest.cc safecallback.hpp)
+target_link_libraries(
+  safecallback_unittest PRIVATE GTest::gtest GTest::gtest_main GTest::gmock
+                                GTest::gmock_main)
+add_test(NAME safecallback_unittest COMMAND safecallback_unittest)

SafeCallback/safecallback.hpp

@@ -0,0 +1,45 @@
+#pragma once
+
+#include <functional>
+#include <iostream>
+#include <memory>
+#include <utility>
+
+template<typename CLASS, typename... ARGS>
+class SafeCallback
+{
+public:
+    SafeCallback(const std::weak_ptr<CLASS> &object,
+                 const std::function<void(CLASS *, ARGS...)> &function)
+        : m_object(object)
+        , m_function(function)
+    {}
+
+    template<typename... CallARGS>
+    void operator()(CallARGS &&...args) const
+    {
+        if (auto ptr = m_object.lock()) {
+            m_function(ptr.get(), std::forward<CallARGS>(args)...);
+        } else {
+            std::cout << "Callback object has been destroyed." << std::endl;
+        }
+    }
+
+private:
+    std::weak_ptr<CLASS> m_object;
+    std::function<void(CLASS *, ARGS...)> m_function;
+};
+
+template<typename CLASS, typename... ARGS>
+SafeCallback<CLASS, ARGS...> makeSafeCallback(const std::shared_ptr<CLASS> &object,
+                                              void (CLASS::*function)(ARGS...))
+{
+    return SafeCallback<CLASS, ARGS...>(object, function);
+}
+
+template<typename CLASS, typename... ARGS>
+SafeCallback<CLASS, ARGS...> makeSafeCallback(const std::shared_ptr<CLASS> &object,
+                                              void (CLASS::*function)(ARGS...) const)
+{
+    return SafeCallback<CLASS, ARGS...>(object, function);
+}

SafeCallback/safecallback_unittest.cc

@@ -0,0 +1,63 @@
+#include "safecallback.hpp"
+
+#include <gtest/gtest.h>
+#include <iostream>
+#include <memory>
+#include <thread>
+
+class MyClass
+{
+public:
+    void notify(int value)
+    {
+        std::cout << "Received value: " << value << std::endl;
+        received_value = value;
+    }
+
+    int received_value = -1;
+};
+
+int free_function_value = -1;
+
+void freeFunction(int value)
+{
+    std::cout << "Free function received value: " << value << std::endl;
+    free_function_value = value;
+}
+
+class SafeCallbackTest : public ::testing::Test
+{
+protected:
+    void SetUp() override { free_function_value = -1; }
+};
+
+TEST_F(SafeCallbackTest, MemberFunctionCallback)
+{
+    auto obj = std::make_shared<MyClass>();
+    SafeCallback callback = makeSafeCallback(obj, &MyClass::notify);
+
+    int test_value = 42;
+    callback(test_value);
+
+    EXPECT_EQ(obj->received_value, test_value);
+}
+
+TEST_F(SafeCallbackTest, MemberFunctionCallbackAfterObjectDestroyed)
+{
+    auto obj = std::make_shared<MyClass>();
+    SafeCallback callback = makeSafeCallback(obj, &MyClass::notify);
+
+    int initial_value = obj->received_value;
+    obj.reset();
+    int test_value = 42;
+    callback(test_value);
+
+    EXPECT_EQ(initial_value, -1);
+    EXPECT_EQ(free_function_value, -1);
+}
+
+int main(int argc, char **argv)
+{
+    ::testing::InitGoogleTest(&argc, argv);
+    return RUN_ALL_TESTS();
+}