Methods for creating thread functions

1. Thread Functions

before starting a thread, you must write a global thread function for the thread that takes a 32-bit LPVOID as a parameter and returns a uint with the structure of the thread function:

UINT threadfunction (LPVOID pparam) { Thread-handling code Return0; }

The Thread processing code section usually includes a dead loop that waits for something to happen before processing the related work:

while (1) { WaitForSingleObject (...,...); /or WaitForMultipleObjects (...) Do something }

generally speaking, the class member function of C + + cannot be used as a thread function. This is because the member functions that are defined in the class are added by the compiler to this pointer. Please see the following procedure:

#include "Windows.h" #include Class Exampletask { Public void Taskmain (LPVOID param); void StartTask (); }; void Exampletask::taskmain (LPVOID param) {} void Exampletask::starttask () { _beginthread (Taskmain,0,null); } int main (int argc, char* argv[]) { Exampletask Realtimetask; Realtimetask.starttask (); return 0; }

The following error occurred while compiling the program:

Error C2664: ' _beginthread ': cannot convert parameter 1 from ' void (void *) ' to ' void (__cdecl *) (void *) ' None of the functions with this name in scope match the target type

then look at the following procedures:

#include" windows.h " #include   class exampletask  {  public:  void Taskmain (LPVOID param);   };  void Exampletask::taskmain (LPVOID param)   {}  int main (int argc, char* argv[]) { Exampletask realtimetask; _beginthread (Exampletask::taskmain,0,null); return 0;

The program compiles with an error:

Error C2664: ' _beginthread ': cannot convert parameter 1 from ' void (void *) ' to ' void (__cdecl *) (void *) ' None of the functions with this name in scope match the target type

If you must take a class member function as a thread function, there are usually the following solutions:

(1) Declare the member function as a static type,RemoveThis pointer;

We will change the above two programs to:

#include "Windows.h" #include Class Exampletask { Public void static taskmain (LPVOID param); void StartTask (); }; void Exampletask::taskmain (LPVOID param) {} void Exampletask::starttask () { _beginthread (Taskmain,0,null); } int main (int argc, char* argv[]) { Exampletask Realtimetask; Realtimetask.starttask (); return 0; } And #include "Windows.h" #include Class Exampletask { Public void static taskmain (LPVOID param); }; void Exampletask::taskmain (LPVOID param) {} int main (int argc, char* argv[]) { _beginthread (Exampletask::taskmain,0,null); return 0; }

are compiled and passed.

declaring a member function static can resolve a problem as a thread function, but it introduces a new problem, which is that the static member function can onlyAccessstatic member. One way to solve this problem is to pass the this pointer as a parameter when invoking a class static member function (thread function), and in a thread function to convert the this to a pointer to the class using the exponentially, which accesses the non-static member through that pointer.

(2) does not define a class member function as a thread function, but a threadfunction Definitiona friend function for the class. In this way, the thread function can also have the same permissions as the class member function;

We have modified the program to:

#include "Windows.h" #include Class Exampletask { Public friend void Taskmain (LPVOID param); void StartTask (); }; void Taskmain (LPVOID param) { Exampletask * Ptaskmain = (exampletask *) param; Referencing by Ptaskmain pointers } void Exampletask::starttask () { _beginthread (Taskmain,0,this); } int main (int argc, char* argv[]) { Exampletask Realtimetask; Realtimetask.starttask (); return 0; }

(3) You can implement callbacks on non-static member functions and access non-static members, which involves some advanced techniques that are no longer detailed here.

Methods for creating thread functions