尝试在 C++11 线程中使用已删除的函数

Question

我正在尝试创建一个具有这样的构造函数的 ThreadPool 类

    ThreadPool(size_t numberOfThreads)
    : workerThreads(numberOfThreads) {
      workerThreads.reserve(numberOfThreads);
      for(int i =0; i < numberOfThreads; i++) {
        workerThreads.emplace_back(std::thread(&ThreadPool::doJob, this));
      }
    }

这无法为我编译并引发以下错误

error: attempt to use a deleted function
    __invoke(_VSTD::move(_VSTD::get<1>(__t)), _VSTD::move(_VSTD::get<_Indices>(__t))...);
    ^
/Library/Developer/CommandLineTools/usr/include/c++/v1/thread:352:5: note: in instantiation of function template specialization
      'std::__1::__thread_execute<std::__1::unique_ptr<std::__1::__thread_struct, std::__1::default_delete<std::__1::__thread_struct> >, void
      (ThreadPool::*)(std::__1::function<void (char *, std::__1::list<std::__1::basic_string<char>,
      std::__1::allocator<std::__1::basic_string<char> > > *)>), ThreadPool *, 2>' requested here
    __thread_execute(*__p, _Index());

根据类似问题的其他答案，我也尝试过这样做

        workerThreads.emplace_back(std::thread(&ThreadPool::doJob, std::ref(*this)));

这也重现了同样的问题。我在 macos 上使用 clang c++14 编译我的代码

这是一个完整的程序，它再现了

class ThreadPool {
  public:
    ThreadPool(size_t numberOfThreads)
    : workerThreads(numberOfThreads) {
      for(int i =0; i < numberOfThreads; i++) {
        workerThreads[i] = std::make_shared<std::thread>(std::thread(&ThreadPool::doJob, this));
      }
    }

    ThreadPool(const ThreadPool& tp) {
      workerThreads = tp.workerThreads;
      jobQueue = tp.jobQueue;
    }

    std::function<void(char*, std::list<std::string>*)> getNextJob() {
      if(!jobQueue.empty()) {
        std::function<void(char*, std::list<std::string>*)> job = jobQueue.front();
        jobQueue.pop_front();
        return job;
      } 

      throw std::runtime_error("No jobs to process, thread finished");
    }

    void addWork(std::function<void(char*, std::list<std::string>*)> job) {
      lockListMutex.lock();
      jobQueue.push_back(job);
      lockListMutex.unlock();
    }

  private:
    // performs actual work
    void doJob(std::function<void(char*, std::list<std::string>*)> job) {
      try {
        lockListMutex.lock();
        getNextJob();
        lockListMutex.unlock();
      } catch (std::runtime_error &e) {

      }
    }

    // a vector containing worker threads
    std::vector<std::shared_ptr<std::thread>> workerThreads;

    // a queue for jobs
    std::list<std::function<void(char*, std::list<std::string>*)>> jobQueue;

    // a mutex for synchronized insertion and deletion from list
    std::mutex lockListMutex;
};

int main(int argc, char *argv[]) {
    int numThreads = 1;
    ThreadPool* pool = new ThreadPool(numThreads);
}

Answer 1

由于您的doJob 成员函数有一个job 类型为std::function<void(char*, std::list<std::string>*)> 的参数，因此您需要在调用此函数时提供相应的参数。因此，以这种方式在新线程中调用该函数是无效的：

std::thread(&ThreadPool::doJob, this)  // no argument for job passed

您要么需要提供一个参数，要么因为作业可能会从jobQueue 中出列，所以从doJob 中删除job 参数：

void doJob()
{
   ... // dequeue job from jobQueue and execute it