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我正在尝试使用 pthread 在 C++ 中实现线程池。我想将与线程管理相关的逻辑封装在一个拥有这些线程所有权的对象中。这意味着每当该对象被销毁时，必须停止并清理线程。

我一直在测试我的代码，结果发现当我在调用 boost::function 时销毁 WorkerThreadManager 对象时出现分段错误。请参阅 GDB 的代码和回溯。我真的不明白为什么会发生这种情况，据我所知 boost::function 是可复制的，所以一旦我从队列中获取它的副本，我就可以 pop() 它甚至销毁整个队列（我在一些小测试），然后调用函数的副本。

WorkerThreadManager.h：

#include "WorkerThreadManagerInterface.h"
#include "utils/mutex.h"
#include <queue>
#include <semaphore.h>

#include <iostream>

class WorkerThreadManager : public WorkerThreadManagerInterface
{
    public:
        WorkerThreadManager(unsigned threadsNumber = 5);
        virtual ~WorkerThreadManager();

        virtual void    PushTask(thread_function_t A_threadFun, result_function_t A_resultFun);
        void    SignalResults();

    private:
        static void*    WorkerThread(void* A_data);

        void    PushResult(int A_result, result_function_t A_resultFun);

        typedef boost::function<void ()> signal_function_t;

        struct worker_thread_data_t
        {
            worker_thread_data_t(thread_function_t A_threadFun, result_function_t A_resultFun) :
                threadFun(A_threadFun), resultFun(A_resultFun) {}
            worker_thread_data_t() {}

            thread_function_t       threadFun;
            result_function_t       resultFun;
        };


        const unsigned                      m_threadsNumber;
        pthread_t*                          m_pthreads;

        utils::Mutex                        m_tasksMutex;
        sem_t                               m_tasksSem;
        std::queue<worker_thread_data_t>    m_tasks;

        utils::Mutex                        m_resultsMutex;
        std::queue<signal_function_t>       m_results;
};

WorkerThreadManager.cpp：

#include "WorkerThreadManager.h"
#include "gateway_log.h"
#include <pthread.h>

/**
 * @brief Creates semaphore and starts threads.
 */
WorkerThreadManager::WorkerThreadManager(unsigned threadsNumber) : m_threadsNumber(threadsNumber)
{
    if ( sem_init(&m_tasksSem, 0, 0) )
    {
        std::stringstream ss;
        ss << "Semaphore could not be initialized: " << errno << " - " << strerror(errno);
        LOG_FATAL(ss);
        throw std::runtime_error(ss.str());
    }

    m_pthreads = new pthread_t[m_threadsNumber];
    for (unsigned i = 0; i < m_threadsNumber; ++i)
    {
        int rc = pthread_create(&m_pthreads[i], NULL, WorkerThreadManager::WorkerThread, (void*) this );
        if(rc)
        {
            std::stringstream ss;
            ss << "Pthread could not be started: " << errno << " - " << strerror(errno);
            LOG_FATAL(ss.str());

            if ( sem_destroy(&m_tasksSem) )
                LOG_ERROR("Semaphore could not be destroyed: " << errno << " - " << strerror(errno));

            delete [] m_pthreads;

            throw std::runtime_error(ss.str());
        }
        else
        {
            LOG_DEBUG("Worker thread started " << m_pthreads[i]);

            if(pthread_detach(m_pthreads[i]))
                LOG_WARN("Failed to detach worker thread");
        }
    }
}

/**
 * @brief Cancels all threads, destroys semaphore
 */
WorkerThreadManager::~WorkerThreadManager()
{
    LOG_DEBUG("~WorkerThreadManager()");

    for(unsigned i = 0; i < m_threadsNumber; ++i)
    {
        if ( pthread_cancel(m_pthreads[i]) )
            LOG_ERROR("Worker thread cancellation failed");
    }

    if ( sem_destroy(&m_tasksSem) )
        LOG_ERROR("Semaphore could not be destroyed: " << errno << " - " << strerror(errno));

    delete [] m_pthreads;
}

/**
 * @brief Adds new task to queue, so worker threads can
 * @param A_threadFun function which will be executed by thread
 * @param A_resultFun function which will be enqueued for calling with return value of A_threadFun as parameter
 *          after worker thread executes A_threadFun.
 */
void WorkerThreadManager::PushTask(thread_function_t A_threadFun, result_function_t A_resultFun)
{
    utils::ScopedLock mutex(m_tasksMutex);

    worker_thread_data_t    data(A_threadFun, A_resultFun);
    m_tasks.push( data );
    sem_post(&m_tasksSem);
    LOG_DEBUG("Task for worker threads has been added to queue");
}

/**
 * @brief   Executes result functions (if there are any) to give feedback 
 *  to classes which requested task execution in worker thread.
 */
void WorkerThreadManager::SignalResults()
{
    while(true)
    {
        signal_function_t signal;
        {
            utils::ScopedLock mutex(m_resultsMutex);
            if(m_results.size())
            {
                signal = m_results.front();
                m_results.pop();
            }
            else
                return;
        }

        signal();
    }
}

/**
 * @brief Enqueues result of function executed in worker thread.
 * @param A_result return value of function executed in worker thread
 * @param A_resultFun function which will be enqueued for calling with A_result as a parameter.
 */
void WorkerThreadManager::PushResult(int A_result, result_function_t A_resultFun)
{
    utils::ScopedLock mutex(m_resultsMutex);

    signal_function_t signal = boost::bind(A_resultFun, A_result);
    m_results.push( signal );
}


/**
 * @brief   worker thread body
 * @param A_data pointer to WorkerThreadManager instance
 */
void* WorkerThreadManager::WorkerThread(void* A_data)
{
    WorkerThreadManager* manager = reinterpret_cast<WorkerThreadManager*>(A_data);
    LOG_DEBUG("Starting worker thread loop");
    while (1)
    {
        if ( -1 == sem_wait(&manager->m_tasksSem) && errno == EINTR )
        {
            LOG_DEBUG("sem_wait interrupted with signal");
            continue;
        }
        LOG_DEBUG("WorkerThread:::::: about to call lock mutex");

        worker_thread_data_t data;
        {
            utils::ScopedLock mutex(manager->m_tasksMutex);
            data = manager->m_tasks.front();
            manager->m_results.pop();
        }

        LOG_DEBUG("WorkerThread:::::: about to call resultFun");
        int result  = data.threadFun();
        LOG_DEBUG("WorkerThread:::::: after call resultFun");
        pthread_testcancel();

        manager->PushResult(result, data.resultFun);
    }

    return NULL;
}

主.cpp：

#include "gateway_log.h"
#include "WorkerThreadManager.h"
#include <memory>

class A {
public:
    int Fun() { LOG_DEBUG("Fun before sleep"); sleep(8); LOG_DEBUG("Fun after sleep");return 0; }
    void Result(int a) { LOG_DEBUG("Result: " << a); }
};


int main()
{
    sd::auto_ptr<WorkerThreadManager> workerThreadManager = new WorkerThreadManager;
    A a;
    workerThreadManager->PushTask(boost::bind(&A::Fun, &a), boost::bind(&A::Result, &a, _1));
    sleep(3);
    LOG_DEBUG("deleting workerThreadManager");
    workerThreadManager.reset();                    // <<<--- CRASH
    LOG_DEBUG("deleted workerThreadManager");
    sleep(10);
    LOG_DEBUG("after sleep");    

    return 0;
}

广发银行：

(gdb) bt
#0  0xb7ad33a0 in ?? () from /lib/i386-linux-gnu/libc.so.6
#1  0x0807d3a7 in boost::function0<void>::clear (this=0x858db48) at /home/marcin/intel_build/boost_1_42_0/boost/function/function_template.hpp:856
#2  0x0807d17b in boost::function0<void>::~function0 (this=0x858db48, __in_chrg=<optimized out>) at /home/marcin/intel_build/boost_1_42_0/boost/function/function_template.hpp:752
#3  0x0807cec5 in boost::function<void()>::~function(void) (this=0x858db48, __in_chrg=<optimized out>) at /home/marcin/intel_build/boost_1_42_0/boost/function/function_template.hpp:1043
#4  0x0807ced8 in std::_Destroy<boost::function<void ()> >(boost::function<void ()>*) (__pointer=0x858db48) at /usr/include/c++/4.6/bits/stl_construct.h:94
#5  0x0807c868 in std::_Destroy_aux<false>::__destroy<boost::function<void ()>*>(boost::function<void ()>*, boost::function<void ()>*) (__first=0x858db48, __last=0x858d928) at /usr/include/c++/4.6/bits/stl_construct.h:104
#6  0x0807bd05 in std::_Destroy<boost::function<void ()>*>(boost::function<void ()>*, boost::function<void ()>*) (__first=0x858d938, __last=0x858d928) at /usr/include/c++/4.6/bits/stl_construct.h:127
#7  0x0807af23 in std::_Destroy<boost::function<void ()>*, boost::function<void ()> >(boost::function<void ()>*, boost::function<void ()>*, std::allocator<boost::function<void ()> >&) (__first=0x858d938, __last=0x858d928)
    at /usr/include/c++/4.6/bits/stl_construct.h:153
#8  0x0807a037 in std::deque<boost::function<void ()>, std::allocator<boost::function<void ()> > >::_M_destroy_data_aux(std::_Deque_iterator<boost::function<void ()>, boost::function<void ()>&, boost::function<void ()>*>, std::_Deque_iterator<boost::function<void ()>, boost::function<void ()>&, boost::function<void ()>*>) (this=0x858beec, __first=..., __last=...) at /usr/include/c++/4.6/bits/deque.tcc:795
#9  0x08076153 in std::deque<boost::function<void ()>, std::allocator<boost::function<void ()> > >::_M_destroy_data(std::_Deque_iterator<boost::function<void ()>, boost::function<void ()>&, boost::function<void ()>*>, std::_Deque_iterator<boost::function<void ()>, boost::function<void ()>&, boost::function<void ()>*>, std::allocator<boost::function<void ()> > const&) (this=0x858beec, __first=..., __last=...) at /usr/include/c++/4.6/bits/stl_deque.h:1816
#10 0x08073411 in std::deque<boost::function<void()>, std::allocator<boost::function<void()> > >::~deque(void) (this=0x858beec, __in_chrg=<optimized out>) at /usr/include/c++/4.6/bits/stl_deque.h:898
#11 0x0806a355 in std::queue<boost::function<void()>, std::deque<boost::function<void()>, std::allocator<boost::function<void()> > > >::~queue(void) (this=0x858beec, __in_chrg=<optimized out>)
    at /usr/include/c++/4.6/bits/stl_queue.h:92
#12 0x0815a054 in WorkerThreadManager::~WorkerThreadManager (this=0x858be98, __in_chrg=<optimized out>) at WorkerThreadManager.cpp:42
#13 0x0815a1e3 in WorkerThreadManager::~WorkerThreadManager (this=0x858be98, __in_chrg=<optimized out>) at WorkerThreadManager.cpp:56
#14 0x080c6c51 in std::auto_ptr<WorkerThreadManager>::reset (this=0x85463e4, __p=0x0) at /usr/include/c++/4.6/backward/auto_ptr.h:244
#15 0x080604a9 in main ()

我真的很感激任何帮助。

4

2 回答 2

1

不能保证pthread_cancel在返回之前等待目标的取消完成。成功后，它只是请求取消，但不等待它完成。您需要使用pthread_join等待线程完成。

我怀疑当析构函数在一个线程中进行时，其中一个线程被唤醒（由于sem_destroy），并错误地尝试读取/弹出队列。我不确定为什么它会导致主线程崩溃，但我会先消除这个潜在的问题。

最后，我强烈建议您将其中一些信号量和线程机制移到它们自己的类中，以使代码更加安全。

于 2012-09-17T21:19:27.950 回答
1

我发现了一个错误，这对我来说是微不足道的-耻辱:(

在函数中void* WorkerThreadManager::WorkerThread(void* A_data)，我弹出了m_results队列，而不是m_tasks我想要的：

worker_thread_data_t data;
{
    utils::ScopedLock mutex(manager->m_tasksMutex);
    data = manager->m_tasks.front();
    manager->m_results.pop();
}

无论如何，我真的不明白为什么它这么晚才导致崩溃 - 在队列的析构函数中。

于 2012-09-18T21:02:37.743 回答