14.4 使用ThreadSaniiser向CDash報告數據爭用 · cmake-cookbook

# 14.4 使用ThreadSaniiser向CDash報告數據爭用 **NOTE**:*此示例代碼可以在 https://github.com/dev-cafe/cmake-cookbook/tree/v1.0/chapter-14/recipe-03 中找到，其中包含一個C++示例。該示例在CMake 3.5版(或更高版本)中是有效的，并且已經在GNU/Linux、macOS和Windows上進行過測試。* 在這個示例中，我們將重用前一個示例中的方法，但是使用ThreadSanitizer或TSan，結合CTest和CDash，來檢查數據競爭，并將它們報告給CDash。ThreadSanitizer的文檔可以在網上找到，https://github.com/google/sanitizers/wiki/ThreadSanitizerCppManual ## 準備工作這個示例中，我們將使用以下示例代碼(`example.cpp`): ```c++ #include <chrono> #include <iostream> #include <thread> static const int num_threads = 16; void increase(int i, int &s) { std::this_thread::sleep_for(std::chrono::seconds(1)); std::cout << "thread " << i << " increases " << s++ << std::endl; } int main() { std::thread t[num_threads]; int s = 0; // start threads for (auto i = 0; i < num_threads; i++) { t[i] = std::thread(increase, i, std::ref(s)); } // join threads with main thread for (auto i = 0; i < num_threads; i++) { t[i].join(); } std::cout << "final s: " << s << std::endl; return 0; } ``` 這個示例代碼中，我們啟動16個線程，每個線程都調用`increase`函數。`increase`函數休眠1s，然后打印并遞增一個整數`s`。我們預計此示例代碼將顯示數據競爭，因為所有線程讀取和修改相同的地址，而不需要任何顯式同步或協調。換句話說，我們期望在代碼末尾打印的最終`s`，每次的結果都不同。代碼有bug，我們將嘗試在ThreadSanitizer的幫助下識別數據競爭。如果不運行ThreadSanitizer，我們可能不會看到代碼有任何問題: ```shell $ ./example thread thread 0 increases 01 increases 1 thread 9 increases 2 thread 4 increases 3 thread 10 increases 4 thread 2 increases 5 thread 3 increases 6 thread 13 increases 7 thread thread 7 increases 8 thread 14 increases 9 thread 8 increases 10 thread 12 increases 11 thread 15 increases 12 thread 11 increases 13 5 increases 14 thread 6 increases 15 final s: 16 ``` ## 具體實施 1. 文件`CMakeLists.txt`首先定義一個受支持的最低版本、項目名稱、受支持的語言。在本例中，定義了C++11標準項目: ```cmake cmake_minimum_required(VERSION 3.5 FATAL_ERROR) project(recipe-04 LANGUAGES CXX) set(CMAKE_CXX_STANDARD 11) set(CMAKE_CXX_EXTENSIONS OFF) set(CMAKE_CXX_STANDARD_REQUIRED ON) ``` 2. 接下來，找到線程庫，定義可執行文件，并將其鏈接到線程庫: ```cmake find_package(Threads REQUIRED) add_executable(example example.cpp) target_link_libraries(example PUBLIC Threads::Threads ) ``` 3. 然后，提供編譯選項和代碼，并鏈接到ThreadSanitizer: ```cmake option(ENABLE_TSAN "Enable ThreadSanitizer" OFF) if(ENABLE_TSAN) if(CMAKE_CXX_COMPILER_ID MATCHES GNU) message(STATUS "ThreadSanitizer enabled") target_compile_options(example PUBLIC -g -O1 -fsanitize=thread -fno-omit-frame-pointer -fPIC ) target_link_libraries(example PUBLIC tsan ) else() message(WARNING "ThreadSanitizer not supported for this compiler") endif() endif() ``` 4. 最后，編譯測試用例: ```cmake enable_testing() # allow to report to a cdash dashboard include(CTest) add_test( NAME example COMMAND $<TARGET_FILE:example> ) ``` 5. ` CTestConfig.cmake`沒有變化: ```cmake set(CTEST_DROP_METHOD "http") set(CTEST_DROP_SITE "my.cdash.org") set(CTEST_DROP_LOCATION "/submit.php?project=cmake-cookbook") set(CTEST_DROP_SITE_CDASH TRUE) ``` 6. `dashboard.cmake `需要為TSan進行簡單修改: ```cmake set(CTEST_PROJECT_NAME "example") cmake_host_system_information(RESULT _site QUERY HOSTNAME) set(CTEST_SITE ${_site}) set(CTEST_BUILD_NAME "${CMAKE_SYSTEM_NAME}-${CMAKE_HOST_SYSTEM_PROCESSOR}") set(CTEST_SOURCE_DIRECTORY "${CTEST_SCRIPT_DIRECTORY}") set(CTEST_BINARY_DIRECTORY "${CTEST_SCRIPT_DIRECTORY}/build") include(ProcessorCount) ProcessorCount(N) if(NOT N EQUAL 0) set(CTEST_BUILD_FLAGS -j${N}) set(ctest_test_args ${ctest_test_args} PARALLEL_LEVEL ${N}) endif() ctest_start(Experimental) ctest_configure( OPTIONS -DENABLE_TSAN:BOOL=ON ) ctest_build() ctest_test() set(CTEST_MEMORYCHECK_TYPE "ThreadSanitizer") ctest_memcheck() ctest_submit() ``` 7. 讓我們以這個例子為例。通過`CTEST_CMAKE_GENERATOR`選項來設置生成器: ```shell $ ctest -S dashboard.cmake -D CTEST_CMAKE_GENERATOR="Unix Makefiles" Each . represents 1024 bytes of output . Size of output: 0K Each symbol represents 1024 bytes of output. '!' represents an error and '*' a warning. . Size of output: 0K ``` 8. 在面板上，我們將看到以下內容: ![](https://img.kancloud.cn/3d/90/3d9017a5c0ac007db492b3f85af9d559_2754x759.png) 9. 我們可以看到更詳細的動態分析: ![](https://img.kancloud.cn/5d/71/5d71fbc88dbed3a2ca0b8ce806fa249a_1401x487.png) ## 工作原理該示例`CMakeLists.txt`的核心部分: ```cmake option(ENABLE_TSAN "Enable ThreadSanitizer" OFF) if(ENABLE_TSAN) if(CMAKE_CXX_COMPILER_ID MATCHES GNU) message(STATUS "ThreadSanitizer enabled") target_compile_options(example PUBLIC -g -O1 -fsanitize=thread -fno-omit-frame-pointer -fPIC ) target_link_libraries(example PUBLIC tsan ) else() message(WARNING "ThreadSanitizer not supported for this compiler") endif() endif() ``` `dashboard.cmake`也需要更新: ```cmake # ... ctest_start(Experimental) ctest_configure( OPTIONS -DENABLE_TSAN:BOOL=ON ) ctest_build() ctest_test() set(CTEST_MEMORYCHECK_TYPE "ThreadSanitizer") ctest_memcheck() ctest_submit() ``` 和上一個示例一樣，我們也可以在本地查看ThreadSanitizer的輸出: ```shell $ mkdir -p build $ cd build $ cmake -DENABLE_TSAN=ON .. $ cmake --build . $ cmake --build . --target test Start 1: example 1/1 Test #1: example ..........................***Failed 1.07 sec 0% tests passed, 1 tests failed out of 1 $ ./build/example thread 0 increases 0 ================== WARNING: ThreadSanitizer: data race (pid=24563) ... lots of output ... SUMMARY: ThreadSanitizer: data race /home/user/cmake-recipes/chapter-14/recipe-04/cxx-example/example ``` ## 更多信息對使用OpenMP的應用TSan是很常見的，但是請注意，在某些情況下，OpenMP會在TSan下生成誤檢的結果。對于Clang編譯器，一個解決方案是用`-DLIBOMP_TSAN_SUPPORT=TRUE`重新編譯編譯器本身及其`libomp`。通常，以合理的方式使用TSan可能需要重新編譯整個工具堆棧，以避免誤報。在使用pybind11的C++項目的情況，我們可能需要重新編譯Python，并啟用TSan來獲得有意義的東西。或者，Python綁定可以通過使用TSan抑制而被排除在外，如 https://github.com/google/sanitizers/wiki/threadsanitizersuppression 。例如：如果一個動態庫同時被一個經過TSan的二進制文件和一個Python插件調用，那么這種情況可能是不可能使用TSan。下面的博客文章討論了如何添加對動態分析工具的支持：https://blog.kitware.com/ctest-cdash-add-support-for-new-dynamic-analysis-tools/