c++ - GoogleMock 在 Linux 上不是线程安全的吗？

Question

我开始在 Windows 上测试 GoogleMock(1.8.0 版)。我想展示一个它不是线程安全的例子。成功证明后，我想证明相同的测试在 Linux 上运行良好。然而，那失败了。这与我的预期不符。由于 GoogleMock 文档说它在具有 pthreads 的系统上是或者应该是线程安全的，因此它在 Linux 上应该是线程安全的。我确实必须将 -pthread 添加到链接器命令行以构建可执行文件。这意味着 GoogleMock 或 GoogleTest 确实使用了 pthreads。

这是我用来测试的代码:

#include <thread>
#include <vector>

#include "gmock/gmock.h"

class Dummy
{
public:
    virtual void SomeMethod(int) {}
};

class DummyMock : public Dummy
{
public:
    MOCK_METHOD1(SomeMethod, void(int));
};

using ::testing::Exactly;

constexpr static int nrCallsPerThread = 100 * 1000;
constexpr static int nrThreads = 10;

TEST(SomeTest, Test100)
{
    DummyMock dummy;

    std::vector<std::thread> threads;
    for (int i = 0; i < nrThreads; i++)
    {
        EXPECT_CALL(dummy, SomeMethod(i)).Times(Exactly(nrCallsPerThread));
        threads.emplace_back([&dummy, i]
        {
            for (int j = 0; j < nrCallsPerThread; j++)
            {
                dummy.SomeMethod(i);
            }
        });
    }

    for (auto& t: threads)
    {
        t.join();
    }
}

int main(int argc, char** argv)
{
    testing::InitGoogleMock(&argc, argv);
    return RUN_ALL_TESTS();
}

问题是，在 Linux 上，并不是每次执行都公开。但是使用 --gtest_repeat=100 运行可执行文件的命中率接近 100%。

在 Windows 上，使用 Visual Studio 2015，如果收到 Debug Assertion Failed! 消息，其中包含 Expression: vector iterator not decrementable。

在 Linux Ubuntu 17.04 上，当我从命令行运行调试构建时，我得到 [ FATAL ] ../googletest-release-1.8.0/googletest/include/gtest/internal/gtest-port。 h:1928::pthread_mutex_lock(&mutex_) 失败，错误 22。

在 Linux 上的调试器中运行时，程序(通常)在 gtest-port.h 的第 1100 行中断，也就是此调用堆栈中的第 2 行:

0 0x5555555a6633 testing::Cardinality::ConservativeUpperBound() const () (??:??)
1 0x5555555a1a13 testing::internal::ExpectationBase::CheckActionCountIfNotDone() const () (??:??)
2 0x555555563f98 testing::internal::TypedExpectation<void (int)>::ShouldHandleArguments(std::tuple<int> const&) const(this=0x5555557f58a0, args=std::tuple containing = {...}) (../googletest-release-1.8.0/googlemock/include/gmock/gmock-spec-builders.h:1100)
3 0x55555556397d testing::internal::FunctionMockerBase<void (int)>::FindMatchingExpectationLocked(std::tuple<int> const&) const(this=0x7fffffffde38, args=std::tuple containing = {...}) (../googletest-release-1.8.0/googlemock/include/gmock/gmock-spec-builders.h:1723)
4 0x555555563578 testing::internal::FunctionMockerBase<void (int)>::UntypedFindMatchingExpectation(void const*, void const**, bool*, std::ostream*, std::ostream*)(this=0x7fffffffde38, untyped_args=0x7fffde7fbe14, untyped_action=0x7fffde7fb7d0, is_excessive=0x7fffde7fb7c7, what=0x7fffde7fb900, why=0x7fffde7fba90) (../googletest-release-1.8.0/googlemock/include/gmock/gmock-spec-builders.h:1687)
5 0x5555555a265e testing::internal::UntypedFunctionMockerBase::UntypedInvokeWith(void const*) () (??:??)
6 0x55555555fcba testing::internal::FunctionMockerBase<void (int)>::InvokeWith(std::tuple<int> const&)(this=0x7fffffffde38, args=std::tuple containing = {...}) (../googletest-release-1.8.0/googlemock/include/gmock/gmock-spec-builders.h:1585)
7 0x55555555f16c testing::internal::FunctionMocker<void (int)>::Invoke(int)(this=0x7fffffffde38, a1=1) (../googletest-release-1.8.0/googlemock/include/gmock/gmock-generated-function-mockers.h:101)
8 0x55555555ecb6 DummyMock::SomeMethod(this=0x7fffffffde30, gmock_a1=1) (/home/jos/Programming/ThreadSafeGMock/main.cpp:16)
9 0x55555555d31e SomeTest_Test100_Test::<lambda()>::operator()(void) const(__closure=0x5555557f5478) (/home/jos/Programming/ThreadSafeGMock/main.cpp:36)
10 0x55555555de98 std::_Bind_simple<SomeTest_Test100_Test::TestBody()::<lambda()>()>::_M_invoke<>(std::_Index_tuple<>)(this=0x5555557f5478) (/usr/include/c++/6/functional:1391)
11 0x55555555de22 std::_Bind_simple<SomeTest_Test100_Test::TestBody()::<lambda()>()>::operator()(void)(this=0x5555557f5478) (/usr/include/c++/6/functional:1380)
12 0x55555555ddf2 std::thread::_State_impl<std::_Bind_simple<SomeTest_Test100_Test::TestBody()::<lambda()>()> >::_M_run(void)(this=0x5555557f5470) (/usr/include/c++/6/thread:197)
13 0x7ffff7b0a83f ??() (/usr/lib/x86_64-linux-gnu/libstdc++.so.6:??)
14 0x7ffff76216da start_thread(arg=0x7fffde7fc700) (pthread_create.c:456)
15 0x7ffff735b17f clone() (../sysdeps/unix/sysv/linux/x86_64/clone.S:105)

既然应该是线程安全的，我怀疑我做错了什么。但我没有看到什么。还是我遇到了 GoogleTest 或 GoogleMock 中的错误？

Answer 1

来自精品手册:

Important note: Google Mock requires expectations to be set before the mock functions are called, otherwise the behavior is undefined. In particular, you mustn't interleave EXPECT_CALL()s and calls to the mock functions.

您的原始代码在我的系统 (cygwin) 上间歇性地失败并出现错误 22，或者有时没有任何消息/错误代码。此修改完美无缺:

for (int i = 0; i < nrThreads; i++)
{
    EXPECT_CALL(dummy, SomeMethod(i)).Times(Exactly(nrCallsPerThread));
}

std::vector<std::thread> threads;
for (int i = 0; i < nrThreads; i++)
{
    threads.emplace_back([&dummy, i] ...