1 ThreadSanitizer 2 =============== 3 4 Introduction 5 ------------ 6 7 ThreadSanitizer is a tool that detects data races. It consists of a compiler 8 instrumentation module and a run-time library. Typical slowdown introduced by 9 ThreadSanitizer is about **5x-15x**. Typical memory overhead introduced by 10 ThreadSanitizer is about **5x-10x**. 11 12 How to build 13 ------------ 14 15 Follow the `Clang build instructions <../get_started.html>`_. CMake build is 16 supported. 17 18 Supported Platforms 19 ------------------- 20 21 ThreadSanitizer is supported on Linux x86_64 (tested on Ubuntu 10.04 and 12.04). 22 Support for MacOS 10.7 (64-bit only) is planned for 2013. Support for 32-bit 23 platforms is problematic and not yet planned. 24 25 Usage 26 ----- 27 28 Simply compile your program with ``-fsanitize=thread -fPIE`` and link it with 29 ``-fsanitize=thread -pie``. To get a reasonable performance add ``-O1`` or 30 higher. Use ``-g`` to get file names and line numbers in the warning messages. 31 32 Example: 33 34 .. code-block:: c++ 35 36 % cat projects/compiler-rt/lib/tsan/lit_tests/tiny_race.c 37 #include <pthread.h> 38 int Global; 39 void *Thread1(void *x) { 40 Global = 42; 41 return x; 42 } 43 int main() { 44 pthread_t t; 45 pthread_create(&t, NULL, Thread1, NULL); 46 Global = 43; 47 pthread_join(t, NULL); 48 return Global; 49 } 50 51 $ clang -fsanitize=thread -g -O1 tiny_race.c -fPIE -pie 52 53 If a bug is detected, the program will print an error message to stderr. 54 Currently, ThreadSanitizer symbolizes its output using an external 55 ``addr2line`` process (this will be fixed in future). 56 57 .. code-block:: bash 58 59 % ./a.out 60 WARNING: ThreadSanitizer: data race (pid=19219) 61 Write of size 4 at 0x7fcf47b21bc0 by thread T1: 62 #0 Thread1 tiny_race.c:4 (exe+0x00000000a360) 63 64 Previous write of size 4 at 0x7fcf47b21bc0 by main thread: 65 #0 main tiny_race.c:10 (exe+0x00000000a3b4) 66 67 Thread T1 (running) created at: 68 #0 pthread_create tsan_interceptors.cc:705 (exe+0x00000000c790) 69 #1 main tiny_race.c:9 (exe+0x00000000a3a4) 70 71 ``__has_feature(thread_sanitizer)`` 72 ------------------------------------ 73 74 In some cases one may need to execute different code depending on whether 75 ThreadSanitizer is enabled. 76 :ref:`\_\_has\_feature <langext-__has_feature-__has_extension>` can be used for 77 this purpose. 78 79 .. code-block:: c 80 81 #if defined(__has_feature) 82 # if __has_feature(thread_sanitizer) 83 // code that builds only under ThreadSanitizer 84 # endif 85 #endif 86 87 ``__attribute__((no_sanitize_thread))`` 88 ----------------------------------------------- 89 90 Some code should not be instrumented by ThreadSanitizer. 91 One may use the function attribute 92 :ref:`no_sanitize_thread <langext-thread_sanitizer>` 93 to disable instrumentation of plain (non-atomic) loads/stores in a particular function. 94 ThreadSanitizer may still instrument such functions to avoid false positives. 95 This attribute may not be 96 supported by other compilers, so we suggest to use it together with 97 ``__has_feature(thread_sanitizer)``. Note: currently, this attribute will be 98 lost if the function is inlined. 99 100 Limitations 101 ----------- 102 103 * ThreadSanitizer uses more real memory than a native run. At the default 104 settings the memory overhead is 5x plus 1Mb per each thread. Settings with 3x 105 (less accurate analysis) and 9x (more accurate analysis) overhead are also 106 available. 107 * ThreadSanitizer maps (but does not reserve) a lot of virtual address space. 108 This means that tools like ``ulimit`` may not work as usually expected. 109 * Libc/libstdc++ static linking is not supported. 110 * ThreadSanitizer requires ``-fPIE -pie`` compiler flags. 111 112 Current Status 113 -------------- 114 115 ThreadSanitizer is in beta stage. It is known to work on large C++ programs 116 using pthreads, but we do not promise anything (yet). C++11 threading is 117 supported with llvm libc++. The test suite is integrated into CMake build 118 and can be run with ``make check-tsan`` command. 119 120 We are actively working on enhancing the tool --- stay tuned. Any help, 121 especially in the form of minimized standalone tests is more than welcome. 122 123 More Information 124 ---------------- 125 `http://code.google.com/p/thread-sanitizer <http://code.google.com/p/thread-sanitizer/>`_. 126 127
