pthread function from a class

Question

Let s say I have a class such as  class c                   void  print void     cout  lt  lt   Hello         And then I have a vector of c  vector lt c gt  classes  pthread t t1  classes push back c     classes push back c       Now  I want to create a thread on c print     And the following is giving me the problem below  pthread create  amp t1  NULL   amp c 0  print  NULL       Error Ouput  cannot convert    void   tree item    void     to    void       void      for argument    3    to    int pthread create pthread t   const   pthread attr t   void     void   void

User · Answer

My guess would be this is b c its getting mangled up a bit by C   b c your sending it a C   pointer  not a C function pointer  There is a difference apparently  Try doing a    void   p  void      void    void    amp c 0  print     check my syntax on that cast    and then sending p    I ve done what your doing with a member function also  but i did it in the class that was using it  and with a static function - which i think made the difference

User · Answer

Too many times I ve found ways to solve what you are asking for that  in my opinion are too complicated   For instance you have to define new class types  link library etc   So I decided to write a few lines of code that allow the end user  to basically be able to  thread-ize  a  void   method void   of whatever class  For sure this solution I implemented can be extended  improved etc  so   if you need more specific methods or features  add them and please be so kind to keep me in the loop   Here are 3 files that show what I did          A basic mutex class  I called this file Mutex h  ifndef MUTEXCONDITION H   define MUTEXCONDITION H    include  lt pthread h gt   include  lt stdio h gt   class MutexCondition   private      bool init               printf  MutexCondition  init called n            pthread mutex init  amp m mut  NULL           pthread cond init  amp m con  NULL           return true             bool destroy             pthread mutex destroy  amp m mut           pthread cond destroy  amp 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  amp m mut           return true             bool unlock             pthread mutex unlock  amp m mut           return true             bool wait             lock            pthread cond wait  amp m con   amp m mut           unlock            return true             bool signal             pthread cond signal  amp m con           return true            endif    End of Mutex h      The class that incapsulates all the work to thread-ize a method  test h     ifndef   THREAD HANDLER     define   THREAD HANDLER      include  lt pthread h gt   include  lt vector gt   include  lt iostream gt   include  Mutex h   using namespace std   template  lt class T gt   class CThreadInfo     public      typedef void  T   MHT PTR   void       vector lt MHT PTR gt   threaded methods      vector lt bool gt   status flags      T   data      MutexCondition  mutex      int  idx      bool  status       CThreadInfo T  p1   data p1    idx 0         void setThreadedMethods vector lt MHT PTR gt   amp  pThreadedMethods                 threaded methods   pThreadedMethods         status flags resize  threaded methods size    false             template  lt class T gt   class CSThread     protected      typedef void  T   MHT PTR   void       vector lt MHT PTR gt   threaded methods      vector lt string gt   thread labels      MHT PTR  stop f pt      vector lt T  gt   elements      vector lt T  gt   performDelete      vector lt CThreadInfo lt T gt   gt   threadlds      vector lt pthread t  gt   threads      int  totalRunningThreads       static void   gencker  void   pArg              CThreadInfo lt T gt   vArg    CThreadInfo lt T gt     pArg        vArg- gt  mutex lock          int vIndex   vArg- gt  idx          vArg- gt  mutex unlock           vArg- gt  status flags vIndex  true         MHT PTR mhtCalledOne   vArg- gt  threaded methods vIndex          vArg- gt  data- gt  mhtCalledOne           vArg- gt  status flags vIndex  false          return NULL           public      CSThread     stop f pt NULL    totalRunningThreads 0           CSThread               for  int i  threads size   -1  i  gt   0  --i            pthread detach   threads i           for  int i  threadlds size   -1  i  gt   0  --i          delete  threadlds i          for  int i  elements size   -1  i  gt   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  gt   elements size    return false        return  threadlds  elementIndex - gt  status flags pMethodIndex              bool run unsigned int pIdx               T   myElem    elements pIdx          threadlds push back new CThreadInfo lt T gt  myElem           threadlds  threadlds size  -1 - gt setThreadedMethods  threaded methods          int vStart    threads size          for  int hhh 0  hhh lt  threaded methods size      hhh             threads push back new pthread t          for  int currentCount  0  currentCount  lt   threaded methods size      vStart    currentCount                          if  pthread create  threads vStart   NULL  gencker    void    threadlds  threadlds size  -1      0                               cout  lt  lt   t tThread    lt  lt  currentCount  lt  lt    creation FAILED for element     lt  lt  pIdx  lt  lt  endl                      return false                            else                          totalRunningThreads                  cout  lt  lt   t tThread    lt  lt  currentCount  lt  lt    creation SUCCEDED for element     lt  lt  pIdx  lt  lt  endl                                  return true             bool run                      for  int vI   0  vI  lt   elements size      vI               if  run vI     false  return false               cout  lt  lt  Number of currently running threads     lt  lt   totalRunningThreads  lt  lt  endl          return true             T   addElement void              int vId -1        return addElement vId              T   addElement int  amp  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  amp  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 - gt   stop f pt                    pthread detach   threads i          -- totalRunningThreads             void stopAll                 if   stop f pt    NULL           for  int i 0  i lt  elements size      i                          elements i - gt   stop f pt                       totalRunningThreads 0            endif    end of test h      A usage example file  test cc  that on linux I ve compiled with  The class that incapsulates all the work to thread-ize a method  g   -o mytest exe test cc -I  -lpthread -lstdc     include  lt test h gt   include  lt vector gt   include  lt iostream gt   include  lt Mutex h gt   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  lt  lt  super    lt  lt  vc  lt  lt  endl              sleep 2                    cout  lt  lt  end of super    lt  lt  vc  lt  lt  endl           void vusss             while   go               cout  lt  lt  vusss    lt  lt  vc  lt  lt  endl        sleep 2                cout  lt  lt  end of vusss    lt  lt  vc  lt  lt  endl           void fazz             static int vcount  0       vc   vcount         cout  lt  lt  Puck create instance     lt  lt  vc  lt  lt  endl       while   go                cout  lt  lt  fazz    lt  lt  vc  lt  lt  endl         sleep 2               cout  lt  lt  Completed TPuck  fazz instance   lt  lt   vc  lt  lt  endl           void stop               go false        cout  lt  lt  endl  lt  lt   Stopping TPuck       lt  lt  vc  lt  lt  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 lt TPuck gt  PuckThreadMaker            Hera I m telling which methods should be threaded   PuckThreadMaker addThread  amp TPuck  fazz   fazz1      PuckThreadMaker addThread  amp TPuck  fazz   fazz2      PuckThreadMaker addThread  amp TPuck  fazz   fazz3      PuckThreadMaker addThread  amp TPuck  vusss   vusss      PuckThreadMaker addThread  amp TPuck  super   super       PuckThreadMaker addStopMethod  amp TPuck  stop      for  int ii 0  ii lt 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  amp myinstance        TPuck   vOne   PuckThreadMaker addElement           if  PuckThreadMaker run      true          cout  lt  lt  All running    lt  lt  endl        else         cout  lt  lt  Error  not all threads running    lt  lt  endl         sleep 1     cout  lt  lt  Totale threads creati     lt  lt  PuckThreadMaker runningThreadsCount     lt  lt  endl    for  unsigned int ii 0  ii lt vN    ii          unsigned int kk 0      cout  lt  lt  status for element    lt  lt  ii  lt  lt    is    lt  lt  PuckThreadMaker getStatusStr ii  kk     lt  lt  endl       cout  lt  lt  status for element    lt  lt  ii  lt  lt    is    lt  lt  PuckThreadMaker getStatusStr ii  kk     lt  lt  endl       cout  lt  lt  status for element    lt  lt  ii  lt  lt    is    lt  lt  PuckThreadMaker getStatusStr ii  kk     lt  lt  endl       cout  lt  lt  status for element    lt  lt  ii  lt  lt    is    lt  lt  PuckThreadMaker getStatusStr ii  kk     lt  lt  endl       cout  lt  lt  status for element    lt  lt  ii  lt  lt    is    lt  lt  PuckThreadMaker getStatusStr ii  kk     lt  lt  endl          sleep 2     PuckThreadMaker stopAll      cout  lt  lt   n nAfter the stop       lt  lt  endl    sleep 2      for  int ii 0  ii lt vN    ii          int kk 0      cout  lt  lt  status for element    lt  lt  ii  lt  lt    is    lt  lt  PuckThreadMaker getStatusStr ii  kk     lt  lt  endl       cout  lt  lt  status for element    lt  lt  ii  lt  lt    is    lt  lt  PuckThreadMaker getStatusStr ii  kk     lt  lt  endl       cout  lt  lt  status for element    lt  lt  ii  lt  lt    is    lt  lt  PuckThreadMaker getStatusStr ii  kk     lt  lt  endl       cout  lt  lt  status for element    lt  lt  ii  lt  lt    is    lt  lt  PuckThreadMaker getStatusStr ii  kk     lt  lt  endl       cout  lt  lt  status for element    lt  lt  ii  lt  lt    is    lt  lt  PuckThreadMaker getStatusStr ii  kk     lt  lt  endl          sleep 5     return 0        End of test cc

User · Answer

You ll have to give pthread create a function that matches the signature it s looking for  What you re passing won t work   You can implement whatever static function you like to do this  and it can reference an instance of c and execute what you want in the thread  pthread create is designed to take not only a function pointer  but a pointer to  context   In this case you just pass it a pointer to an instance of c   For instance   static void  execute print void  ctx        c  cptr    c  ctx      cptr- gt print        return NULL      void func                   pthread create  amp t1  NULL  execute print   amp c 0

User · Answer

My favorite way to handle a thread is to encapsulate it inside a C   object   Here s an example   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  amp  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 - gt InternalThreadEntry    return NULL       pthread t  thread       To use it  you would just create a subclass of MyThreadClass with the InternalThreadEntry   method implemented to contain your thread s event loop   You d need to call WaitForInternalThreadToExit   on the thread object before deleting the thread object  of course  and have some mechanism to make sure the thread actually exits  otherwise WaitForInternalThreadToExit   would never return

User · Answer

This is a bit old question but a very common issue which many face  Following is a simple and elegant way to handle this by using std  thread    include  lt iostream gt   include  lt utility gt   include  lt thread gt   include  lt chrono gt   class foo       public          void bar int j                        n   j              for  int i   0  i  lt  5    i                    std  cout  lt  lt   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  amp foo  bar   amp f  n      t5 runs foo  bar   on object f     std  this thread  sleep for std  chrono  milliseconds 20        std  cout  lt  lt   Main Thread running as usual       class thread join        std  cout  lt  lt   Final value of foo  n is    lt  lt  f n  lt  lt    n       Above code also takes care of passing argument to the thread function   Refer std  thread document for more details

User · Answer

The above answers are good  but in my case  1st approach that converts the function to be a static didn t work  I was trying to convert exiting code to move into thread function but that code had lots to references to non-static  class members already  The second solution of encapsulating into C   object works  but has 3-level wrappers to run a thread   I had an alternate solution that uses existing C   construct -  friend  function  and it worked perfect for my case  An example of how I used  friend   will use the above same example for names showing how it can be converted into a compact form using friend       class MyThreadClass           public         MyThreadClass       empty            virtual  MyThreadClass       empty             bool Init                      return  pthread create  amp  thread  NULL   amp 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- gt       return NULL          Ofcourse  we can use boost  thread and avoid all these  but I was trying to modify the C   code to not use boost  the code was linking against boost just for this purpose

User · Answer

My first answer ever in the hope that it ll be usefull to someone   I now this is an old question but I encountered exactly the same error as the above question as I m writing a TcpServer class and I was trying to use pthreads  I found this question and I understand now why it was happening  I ended up doing this    include  lt thread gt    method to run threaded -  void  TcpServer  sockethandler void  lp     code here     and I call it with a lambda -  std  thread        sockethandler  void  csock       detach     that seems a clean approach to me

User · Answer

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  lt  lt   Hello        pthread create  amp threadId  NULL   THREADFUNCPTR   amp C  print  NULL

User · Answer

You can t do it the way you ve written it because C   class member functions have a hidden this parameter passed in   pthread create   has no idea what value of this to use  so if you try to get around the compiler by casting the method to a function pointer of the appropriate type  you ll get a segmetnation fault   You have to use a static class method  which has no this parameter   or a plain ordinary function to bootstrap the class   class C   public      void  hello void                std  cout  lt  lt   Hello  world    lt  lt  std  endl          return 0             static void  hello helper void  context                return   C   context - gt hello                 C c  pthread t t  pthread create  amp t  NULL   amp C  hello helper   amp c

[c++] pthread function from a class

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