假设我有一个类
class c {
// ...
void *print(void *){ cout << "Hello"; }
}
然后我有一个c
的向量vector<c> classes; pthread_t t1;
classes.push_back(c());
classes.push_back(c());
现在，我想在c.print();
以下是我的问题：pthread_create(&t1, NULL, &c[0].print, NULL);
错误输出：无法将'void *（tree_item :: ）（void ）'转换为'void * （）（void ）'用于参数'3'到'int pthread_create（pthread_t *，const） pthread_attr_t *，void *（）（void ），void *）'
答案 0 :(得分：138)
您不能按照编写它的方式执行此操作，因为C ++类成员函数传入了隐藏的this参数。pthread_create()不知道this的值是什么使用，所以如果你试图通过将方法转换为适当类型的函数指针来绕过编译器，你将得到一个segmetnation错误。您必须使用静态类方法（没有this参数）或普通的普通函数来引导类：
class C
{
public:
void *hello(void)
{
std::cout << "Hello, world!" << std::endl;
return 0;
}
static void *hello_helper(void *context)
{
return ((C *)context)->hello();
}
};
...
C c;
pthread_t t;
pthread_create(&t, NULL, &C::hello_helper, &c);
答案 1 :(得分：75)
我最喜欢的处理线程的方法是将其封装在C ++对象中。这是一个例子：
class MyThreadClass
{
public:
MyThreadClass() {/* empty */}
virtual ~MyThreadClass() {/* empty */}
/** Returns true if the thread was successfully started, false if there was an error starting the thread */
bool StartInternalThread()
{
return (pthread_create(&_thread, NULL, InternalThreadEntryFunc, this) == 0);
}
/** Will not return until the internal thread has exited. */
void WaitForInternalThreadToExit()
{
(void) pthread_join(_thread, NULL);
}
protected:
/** Implement this method in your subclass with the code you want your thread to run. */
virtual void InternalThreadEntry() = 0;
private:
static void * InternalThreadEntryFunc(void * This) {((MyThreadClass *)This)->InternalThreadEntry(); return NULL;}
pthread_t _thread;
};
要使用它，您只需创建一个MyThreadClass的子类，并实现InternalThreadEntry（）方法以包含线程的事件循环。当然，你需要在删除线程对象之前调用线程对象上的WaitForInternalThreadToExit（）（并且有一些机制来确保线程实际退出，否则WaitForInternalThreadToExit（）永远不会返回）
答案 2 :(得分：8)
您必须为pthread_create提供与其正在寻找的签名相匹配的功能。你传递的东西不起作用。
您可以实现您喜欢的任何静态函数，它可以引用c的实例并在线程中执行您想要的操作。 pthread_create不仅用于指向函数指针，还指向“上下文”指针。在这种情况下，您只需将指针传递给c的实例。
例如：
static void* execute_print(void* ctx) {
c* cptr = (c*)ctx;
cptr->print();
return NULL;
}
void func() {
...
pthread_create(&t1, NULL, execute_print, &c[0]);
...
}
答案 3 :(得分：2)
上面的答案很好，但在我的情况下，将函数转换为静态的第一种方法不起作用。我试图将现有代码转换为线程函数，但该代码已经有很多引用非静态类成员。封装到C ++对象的第二个解决方案有效，但是有3级包装器来运行一个线程。
我有一个使用现有C ++构造的替代解决方案 - “朋友”功能，它适用于我的情况。 我如何使用'朋友'的一个示例（将使用上面相同的示例显示如何使用朋友将其转换为紧凑形式的名称）
class MyThreadClass
{
public:
MyThreadClass() {/* empty */}
virtual ~MyThreadClass() {/* empty */}
bool Init()
{
return (pthread_create(&_thread, NULL, &ThreadEntryFunc, this) == 0);
}
/** Will not return until the internal thread has exited. */
void WaitForThreadToExit()
{
(void) pthread_join(_thread, NULL);
}
private:
//our friend function that runs the thread task
friend void* ThreadEntryFunc(void *);
pthread_t _thread;
};
//friend is defined outside of class and without any qualifiers
void* ThreadEntryFunc(void *obj_param) {
MyThreadClass *thr = ((MyThreadClass *)obj_param);
//access all the members using thr->
return NULL;
}
当然，我们可以使用boost :: thread并避免所有这些，但我试图修改C ++代码以不使用boost（代码只是为了这个目的而连接到boost）
答案 4 :(得分：1)
我的第一个答案是希望它对某人有用： 我现在这是一个老问题，但我遇到了与上述问题完全相同的错误，因为我正在编写TcpServer类，而我正在尝试使用pthreads。我发现了这个问题，我现在明白为什么会这样。我最终这样做了：
#include <thread>
运行线程的方法 - ＆gt; void* TcpServer::sockethandler(void* lp) {/*code here*/}
我用lambda调用它 - ＆gt; std::thread( [=] { sockethandler((void*)csock); } ).detach();
答案 5 :(得分：0)
很多次我找到了解决你要求的方法，在我看来太复杂了。 例如，您必须定义新的类类型，链接库等。 所以我决定写几行代码，允许最终用户 基本上能够“线程化”任何类的“void :: method（void）”。 当然，我实施的这个解决方案可以扩展，改进等，所以， 如果您需要更多特定的方法或功能，请添加它们，请非常友好地让我保持在循环中。
这里有3个文件显示了我的所作所为。
// A basic mutex class, I called this file Mutex.h
#ifndef MUTEXCONDITION_H_
#define MUTEXCONDITION_H_
#include <pthread.h>
#include <stdio.h>
class MutexCondition
{
private:
bool init() {
//printf("MutexCondition::init called\n");
pthread_mutex_init(&m_mut, NULL);
pthread_cond_init(&m_con, NULL);
return true;
}
bool destroy() {
pthread_mutex_destroy(&m_mut);
pthread_cond_destroy(&m_con);
return true;
}
public:
pthread_mutex_t m_mut;
pthread_cond_t m_con;
MutexCondition() {
init();
}
virtual ~MutexCondition() {
destroy();
}
bool lock() {
pthread_mutex_lock(&m_mut);
return true;
}
bool unlock() {
pthread_mutex_unlock(&m_mut);
return true;
}
bool wait() {
lock();
pthread_cond_wait(&m_con, &m_mut);
unlock();
return true;
}
bool signal() {
pthread_cond_signal(&m_con);
return true;
}
};
#endif
// End of Mutex.h
//包含所有工作的类，用于线程化方法（test.h）：
#ifndef __THREAD_HANDLER___
#define __THREAD_HANDLER___
#include <pthread.h>
#include <vector>
#include <iostream>
#include "Mutex.h"
using namespace std;
template <class T>
class CThreadInfo
{
public:
typedef void (T::*MHT_PTR) (void);
vector<MHT_PTR> _threaded_methods;
vector<bool> _status_flags;
T *_data;
MutexCondition _mutex;
int _idx;
bool _status;
CThreadInfo(T* p1):_data(p1), _idx(0) {}
void setThreadedMethods(vector<MHT_PTR> & pThreadedMethods)
{
_threaded_methods = pThreadedMethods;
_status_flags.resize(_threaded_methods.size(), false);
}
};
template <class T>
class CSThread {
protected:
typedef void (T::*MHT_PTR) (void);
vector<MHT_PTR> _threaded_methods;
vector<string> _thread_labels;
MHT_PTR _stop_f_pt;
vector<T*> _elements;
vector<T*> _performDelete;
vector<CThreadInfo<T>*> _threadlds;
vector<pthread_t*> _threads;
int _totalRunningThreads;
static void * gencker_(void * pArg)
{
CThreadInfo<T>* vArg = (CThreadInfo<T> *) pArg;
vArg->_mutex.lock();
int vIndex = vArg->_idx++;
vArg->_mutex.unlock();
vArg->_status_flags[vIndex]=true;
MHT_PTR mhtCalledOne = vArg->_threaded_methods[vIndex];
(vArg->_data->*mhtCalledOne)();
vArg->_status_flags[vIndex]=false;
return NULL;
}
public:
CSThread ():_stop_f_pt(NULL), _totalRunningThreads(0) {}
~CSThread()
{
for (int i=_threads.size() -1; i >= 0; --i)
pthread_detach(*_threads[i]);
for (int i=_threadlds.size() -1; i >= 0; --i)
delete _threadlds[i];
for (int i=_elements.size() -1; i >= 0; --i)
if (find (_performDelete.begin(), _performDelete.end(), _elements[i]) != _performDelete.end())
delete _elements[i];
}
int runningThreadsCount(void) {return _totalRunningThreads;}
int elementsCount() {return _elements.size();}
void addThread (MHT_PTR p, string pLabel="") { _threaded_methods.push_back(p); _thread_labels.push_back(pLabel);}
void clearThreadedMethods() { _threaded_methods.clear(); }
void getThreadedMethodsCount() { return _threaded_methods.size(); }
void addStopMethod(MHT_PTR p) { _stop_f_pt = p; }
string getStatusStr(unsigned int _elementIndex, unsigned int pMethodIndex)
{
char ch[99];
if (getStatus(_elementIndex, pMethodIndex) == true)
sprintf (ch, "[%s] - TRUE\n", _thread_labels[pMethodIndex].c_str());
else
sprintf (ch, "[%s] - FALSE\n", _thread_labels[pMethodIndex].c_str());
return ch;
}
bool getStatus(unsigned int _elementIndex, unsigned int pMethodIndex)
{
if (_elementIndex > _elements.size()) return false;
return _threadlds[_elementIndex]->_status_flags[pMethodIndex];
}
bool run(unsigned int pIdx)
{
T * myElem = _elements[pIdx];
_threadlds.push_back(new CThreadInfo<T>(myElem));
_threadlds[_threadlds.size()-1]->setThreadedMethods(_threaded_methods);
int vStart = _threads.size();
for (int hhh=0; hhh<_threaded_methods.size(); ++hhh)
_threads.push_back(new pthread_t);
for (int currentCount =0; currentCount < _threaded_methods.size(); ++vStart, ++currentCount)
{
if (pthread_create(_threads[vStart], NULL, gencker_, (void*) _threadlds[_threadlds.size()-1]) != 0)
{
// cout <<"\t\tThread " << currentCount << " creation FAILED for element: " << pIdx << endl;
return false;
}
else
{
++_totalRunningThreads;
// cout <<"\t\tThread " << currentCount << " creation SUCCEDED for element: " << pIdx << endl;
}
}
return true;
}
bool run()
{
for (int vI = 0; vI < _elements.size(); ++vI)
if (run(vI) == false) return false;
// cout <<"Number of currently running threads: " << _totalRunningThreads << endl;
return true;
}
T * addElement(void)
{
int vId=-1;
return addElement(vId);
}
T * addElement(int & pIdx)
{
T * myElem = new T();
_elements.push_back(myElem);
pIdx = _elements.size()-1;
_performDelete.push_back(myElem);
return _elements[pIdx];
}
T * addElement(T *pElem)
{
int vId=-1;
return addElement(pElem, vId);
}
T * addElement(T *pElem, int & pIdx)
{
_elements.push_back(pElem);
pIdx = _elements.size()-1;
return pElem;
}
T * getElement(int pId) { return _elements[pId]; }
void stopThread(int i)
{
if (_stop_f_pt != NULL)
{
( _elements[i]->*_stop_f_pt)() ;
}
pthread_detach(*_threads[i]);
--_totalRunningThreads;
}
void stopAll()
{
if (_stop_f_pt != NULL)
for (int i=0; i<_elements.size(); ++i)
{
( _elements[i]->*_stop_f_pt)() ;
}
_totalRunningThreads=0;
}
};
#endif
// end of test.h
//我在linux上编译的一个用法示例文件“test.cc” 包含所有工作以线程化方法的类： g ++ -o mytest.exe test.cc -I。 -lpthread -lstdc ++
#include <test.h>
#include <vector>
#include <iostream>
#include <Mutex.h>
using namespace std;
// Just a class for which I need to "thread-ize" a some methods
// Given that with OOP the objecs include both "functions" (methods)
// and data (attributes), then there is no need to use function arguments,
// just a "void xxx (void)" method.
//
class TPuck
{
public:
bool _go;
TPuck(int pVal):_go(true)
{
Value = pVal;
}
TPuck():_go(true)
{
}
int Value;
int vc;
void setValue(int p){Value = p; }
void super()
{
while (_go)
{
cout <<"super " << vc << endl;
sleep(2);
}
cout <<"end of super " << vc << endl;
}
void vusss()
{
while (_go)
{
cout <<"vusss " << vc << endl;
sleep(2);
}
cout <<"end of vusss " << vc << endl;
}
void fazz()
{
static int vcount =0;
vc = vcount++;
cout <<"Puck create instance: " << vc << endl;
while (_go)
{
cout <<"fazz " << vc << endl;
sleep(2);
}
cout <<"Completed TPuck..fazz instance "<< vc << endl;
}
void stop()
{
_go=false;
cout << endl << "Stopping TPuck...." << vc << endl;
}
};
int main(int argc, char* argv[])
{
// just a number of instances of the class I need to make threads
int vN = 3;
// This object will be your threads maker.
// Just declare an instance for each class
// you need to create method threads
//
CSThread<TPuck> PuckThreadMaker;
//
// Hera I'm telling which methods should be threaded
PuckThreadMaker.addThread(&TPuck::fazz, "fazz1");
PuckThreadMaker.addThread(&TPuck::fazz, "fazz2");
PuckThreadMaker.addThread(&TPuck::fazz, "fazz3");
PuckThreadMaker.addThread(&TPuck::vusss, "vusss");
PuckThreadMaker.addThread(&TPuck::super, "super");
PuckThreadMaker.addStopMethod(&TPuck::stop);
for (int ii=0; ii<vN; ++ii)
{
// Creating instances of the class that I need to run threads.
// If you already have your instances, then just pass them as a
// parameter such "mythreadmaker.addElement(&myinstance);"
TPuck * vOne = PuckThreadMaker.addElement();
}
if (PuckThreadMaker.run() == true)
{
cout <<"All running!" << endl;
}
else
{
cout <<"Error: not all threads running!" << endl;
}
sleep(1);
cout <<"Totale threads creati: " << PuckThreadMaker.runningThreadsCount() << endl;
for (unsigned int ii=0; ii<vN; ++ii)
{
unsigned int kk=0;
cout <<"status for element " << ii << " is " << PuckThreadMaker.getStatusStr(ii, kk++) << endl;
cout <<"status for element " << ii << " is " << PuckThreadMaker.getStatusStr(ii, kk++) << endl;
cout <<"status for element " << ii << " is " << PuckThreadMaker.getStatusStr(ii, kk++) << endl;
cout <<"status for element " << ii << " is " << PuckThreadMaker.getStatusStr(ii, kk++) << endl;
cout <<"status for element " << ii << " is " << PuckThreadMaker.getStatusStr(ii, kk++) << endl;
}
sleep(2);
PuckThreadMaker.stopAll();
cout <<"\n\nAfter the stop!!!!" << endl;
sleep(2);
for (int ii=0; ii<vN; ++ii)
{
int kk=0;
cout <<"status for element " << ii << " is " << PuckThreadMaker.getStatusStr(ii, kk++) << endl;
cout <<"status for element " << ii << " is " << PuckThreadMaker.getStatusStr(ii, kk++) << endl;
cout <<"status for element " << ii << " is " << PuckThreadMaker.getStatusStr(ii, kk++) << endl;
cout <<"status for element " << ii << " is " << PuckThreadMaker.getStatusStr(ii, kk++) << endl;
cout <<"status for element " << ii << " is " << PuckThreadMaker.getStatusStr(ii, kk++) << endl;
}
sleep(5);
return 0;
}
// End of test.cc
答案 6 :(得分：0)
这是一个有点老的问题，但很多人都面临一个非常普遍的问题。 以下是使用std :: thread
的一种简单而优雅的方法来处理此问题#include <iostream>
#include <utility>
#include <thread>
#include <chrono>
class foo
{
public:
void bar(int j)
{
n = j;
for (int i = 0; i < 5; ++i) {
std::cout << "Child thread executing\n";
++n;
std::this_thread::sleep_for(std::chrono::milliseconds(10));
}
}
int n = 0;
};
int main()
{
int n = 5;
foo f;
std::thread class_thread(&foo::bar, &f, n); // t5 runs foo::bar() on object f
std::this_thread::sleep_for(std::chrono::milliseconds(20));
std::cout << "Main Thread running as usual";
class_thread.join();
std::cout << "Final value of foo::n is " << f.n << '\n';
}
以上代码还负责将参数传递给线程函数。
有关更多详细信息，请参见std::thread文档。
答案 7 :(得分：-1)
我的猜测是这是b / c它被C ++ b / c稍微破坏了你发送它的C ++指针，而不是C函数指针。显然有一个difference。尝试做一个
(void)(*p)(void) = ((void) *(void)) &c[0].print; //(check my syntax on that cast)
然后发送p。
我已经完成了你对成员函数所做的事情，但是我在使用它的类中做了这个，并且使用了静态函数 - 我认为这有所不同。
答案 8 :(得分：-1)
<强> C++ : How to pass class member function to pthread_create()?
http://thispointer.com/c-how-to-pass-class-member-function-to-pthread_create/
typedef void * (*THREADFUNCPTR)(void *);
class C {
// ...
void *print(void *) { cout << "Hello"; }
}
pthread_create(&threadId, NULL, (THREADFUNCPTR) &C::print, NULL);