Question

我试图在C ++中实现一个非常基本的Thread Local Singleton类 - 它是一个其他类继承的模板类。问题是它几乎总是有效，但不时（例如，15次运行），它将失败并出现以下错误：

*检测到glibc * ./myExe：free（）：下一个大小无效（快）：0x00002b61a40008c0 ***

请原谅下面相当人为的例子，但这有助于证明这个问题。

#include <thread>
#include <atomic>
#include <iostream>
#include <memory>
#include <vector>

using namespace std;

template<class T>
class ThreadLocalSingleton
{
public:
    /// Return a reference to an instance of the object
    static T& instance();

    typedef unique_ptr<T> UPtr;

protected:
    ThreadLocalSingleton() {}
    ThreadLocalSingleton(ThreadLocalSingleton const&);
    void operator=(ThreadLocalSingleton const&);
};

template<class T>
T& ThreadLocalSingleton<T>::instance()
{
    thread_local T m_instance;
    return m_instance;
}

// Create two atomic variables to keep track of the number of times the
// TLS class is created and accessed.
atomic<size_t> creationCount(0);
atomic<size_t> accessCount(0);

// Very simple class which derives from TLS
class MyClass : public ThreadLocalSingleton<MyClass>
{
    friend class ThreadLocalSingleton<MyClass>;
public:
    MyClass()
    {
        ++creationCount;
    }

    string getType() const
    {
        ++accessCount;
        return "MyClass";
    }
};

int main(int,char**)
{
    vector<thread> threads;
    vector<string> results;

    threads.emplace_back([&]() { results.emplace_back(MyClass::instance().getType()); MyClass::instance().getType(); });
    threads.emplace_back([&]() { results.emplace_back(MyClass::instance().getType()); MyClass::instance().getType(); });
    threads.emplace_back([&]() { results.emplace_back(MyClass::instance().getType()); MyClass::instance().getType(); });
    threads.emplace_back([&]() { results.emplace_back(MyClass::instance().getType()); MyClass::instance().getType(); });

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

    // Expecting 4 creations and 8 accesses.
    cout << "CreationCount: " << creationCount << " AccessCount: " << accessCount << endl;
}

我可以使用build命令在coliru上复制它： g ++ -std = c ++ 11 -O2 -Wall -pedantic -pthread main.cpp＆amp;＆amp; ./a.out

非常感谢！

Answer 1

感谢molbdnilo和Damon，他们很快指出了明显的 - vector :: \ templace_back不是线程安全的，所以不能保证这段代码是否真的有效。我用以下内容替换了main（）函数，这似乎更可靠。

int main(int,char**)
{
    vector<thread> threads;
    vector<string> results;

    auto addToResult = [&results](const string& val)
    {
        static mutex m_mutex;
        unique_lock<mutex> lock(m_mutex);
        results.emplace_back(val);
    };

    threads.emplace_back([&addToResult]() { addToResult(MyClass::instance().getType()); MyClass::instance().getType(); });
    threads.emplace_back([&addToResult]() { addToResult(MyClass::instance().getType()); MyClass::instance().getType(); });
    threads.emplace_back([&addToResult]() { addToResult(MyClass::instance().getType()); MyClass::instance().getType(); });
    threads.emplace_back([&addToResult]() { addToResult(MyClass::instance().getType()); MyClass::instance().getType(); });

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

    // Expecting 4 creations and 8 accesses.
    cout << "CreationCount: " << creationCount << " AccessCount: " << accessCount << endl;
}

谢谢！

C ++ Thread Local Singleton间歇性故障

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