在工作线程中使用std :: atomic_flag的问题 [英] Issue using std::atomic_flag with worker thread

问题描述

很抱歉-我已尽我所能将代码示例压缩为功能最少的类和main()方法.

sorry for the verbosity - I did my best to condense my code sample into a minimally functional class and main() method.

我正在尝试使用atomic_flag通知工作线程中的_rx()在调用stop()时退出.

I'm trying to use an atomic_flag to notify _rx() within my worker thread to quit when stop() is called.

我认为问题在于尝试创建我的工作线程，

I believe the issue is in trying to create my worker thread,

thread SanityTestThread(&SanityTest::_rx, *this);

与我的atomic_flag

代码示例(无法编译):

code sample (does not compile):

 #include <cstdio>
 #include <chrono>

 #include <unistd.h>
 #include <atomic>
 #include <iostream>
 #include <thread>

 using namespace std;

 class SanityTest
 {

   public:
     SanityTest(){}
     void start();
     void stop();

   private:
     void _rx();
     atomic_flag flag;

 }; // end class SanityTest

void SanityTest::_rx()
{
  while(flag.test_and_set())
  {
    this_thread::sleep_for(chrono::seconds(1));
    cout << "'sup foo" << endl;
  }
} // end _rx

void SanityTest::start()
{
  flag.test_and_set();
  thread SanityTestThread(&SanityTest::_rx, *this);
  SanityTestThread.detach();
} // end start

void SanityTest::stop()
{
  flag.clear();
} // end start

int main(){
  SanityTest s;// = SanityTest();
  s.start();
  this_thread::sleep_for(chrono::seconds(10));
  s.stop();
  return 0;
} // end main

为了记录，我可以通过删除对我的atomic_flag的所有引用并将我的_rx()循环替换为for循环来编译和运行程序，如下所示:

For the record, I can get my program to compile and run by removing all references to my atomic_flag and replacing my _rx() loop with a for loop like so:

void SanityTest::_rx()
{
  for(int i=0; i <=10; ++ i)
  {
    this_thread::sleep_for(chrono::seconds(1));
    cout << "'sup foo" << endl;
  }
} // end _rx

编译器错误:

In file included from ./SanityTest.cpp:1:0:
./SanityTest.hpp:14:7: note: ‘SanityTest::SanityTest(SanityTest&&)’ is implicitly deleted because the default definition would be ill-formed:
 class SanityTest
       ^
./SanityTest.hpp:14:7: error: use of deleted function ‘std::atomic_flag::atomic_flag(const std::atomic_flag&)’
In file included from /usr/include/c++/4.8/atomic:41:0,
                 from ./SanityTest.hpp:8,
                 from ./SanityTest.cpp:1:
/usr/include/c++/4.8/bits/atomic_base.h:275:5: error: declared here
     atomic_flag(const atomic_flag&) = delete;
     ^
In file included from /usr/include/c++/4.8/functional:55:0,
                 from /usr/include/c++/4.8/thread:39,
                 from ./SanityTest.hpp:10,
                 from ./SanityTest.cpp:1:

...

In file included from ./SanityTest.cpp:1:0:
./SanityTest.hpp:14:7: note: ‘SanityTest::SanityTest(SanityTest&&)’ is implicitly deleted because the default definition would be ill-formed:
 class SanityTest
       ^
./SanityTest.hpp:14:7: error: use of deleted function ‘std::atomic_flag::atomic_flag(const std::atomic_flag&)’
In file included from /usr/include/c++/4.8/atomic:41:0,
                 from ./SanityTest.hpp:8,
                 from ./SanityTest.cpp:1:
/usr/include/c++/4.8/bits/atomic_base.h:275:5: error: declared here
     atomic_flag(const atomic_flag&) = delete;
     ^
In file included from /usr/include/c++/4.8/functional:55:0,
                 from /usr/include/c++/4.8/thread:39,
                 from ./SanityTest.hpp:10,
                 from ./SanityTest.cpp:1:

p.s.这是用g++ -pthread -std=c++0x -o SanityTest ./SanityTest.cpp

推荐答案

只需替换

thread SanityTestThread(&SanityTest::_rx, *this);

与

thread SanityTestThread(&SanityTest::_rx, this);

您可能打算将指针传递给对象，而不是对象本身(这将导致复制该对象，并在该副本而不是原始对象上调用成员函数指针&SanityTest::_rx).

You probably intended to pass a pointer to the object and not the object itself (which would result in that object being copied and the member function pointer &SanityTest::_rx being invoked on that copy instead of the original object).

产生此错误消息的原因实质上是std::atomic_flag没有副本构造函数，因此编译器也不会为SanityTest类生成默认的构造函数，但是再次:您不想无论如何，请在此处复制您的SanityTest对象.

The reason for the error message is essentially that std::atomic_flag doesn't have a copy constructor and so the compiler doesn't generate a default one for your SanityTest class either, but again: you don't want to copy your SanityTest object here anyway.

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