linux C++ thread in class - c++

Question

Hi i want to do the class with method which will start in separate thread after creating class. That how i do that:
class Devemu {
int VarInc;
void Increm() {
for(;;) {
if (VarInc > 532) VarInc = 0;
else VarInc++;
}
}
public:
static void* IncWrapper(void* thisPtr) {
((Devemu*) thisPtr)->Increm();
return NULL;
}
Devemu() {
VarInc = 0;
}
int Var() {
return VarInc;
}
};
int main(int argc, char** argv) {
Devemu* em = new Devemu();
pthread_t thread_id;
pthread_create(&thread_id, NULL, &Devemu::IncWrapper, NULL);
for(int i = 0 ;i < 50; i++) {
printf("%d\n", em->Var());
}
return (EXIT_SUCCESS);
}
I unlike that pthread_create in main and IncWrapper method can i change that?

Answer 1

Yes, you can put it in the constructor if you like :
class Devemu {
int VarInc;
pthread_t thread_id;
void Increm() {
for(;;) {
if (VarInc > 532) VarInc = 0;
else VarInc++;
}
}
public:
static void* IncWrapper(void* thisPtr) {
((Devemu*) thisPtr)->Increm();
return NULL;
}
Devemu() {
VarInc = 0;
pthread_create(&thread_id, NULL, &Devemu::IncWrapper, NULL);
}
int Var() {
return VarInc;
}
};

Answer 2

I suppose it's better to put the thread creation in the separate member-function like that:
class Devemu {
...
void run()
{
pthread_create(&thread_id, NULL, &Devemu::IncWrapper, NULL);
}
...
};
Not actually in ctor, because sometimes you (or anyone who uses your code) can forget that thread created in the ctor and start coding like:
Devemu m;
...
Devemu m1;
...
creating unnecessary threads just like instances of the class.

Answer 3

If you want to get working source code you need make next changes:
--- so0.cpp 2019-11-04 11:26:11.101984795 +0000
+++ so1.cpp 2019-11-04 11:26:57.108501816 +0000
## -1,3 +1,7 ##
+#include "stdio.h"
+#include <pthread.h>
+#include <cstdlib>
+
class Devemu {
int VarInc;
## -24,7 +28,7 ##
Devemu* em = new Devemu();
pthread_t thread_id;
-pthread_create(&thread_id, NULL, &Devemu::IncWrapper, NULL);
+pthread_create(&thread_id, NULL, &Devemu::IncWrapper, em);
My variant for resolving your problem is :
#include "stdio.h"
#include <pthread.h>
#include <cstdlib>
#include <unistd.h>
class Devemu {
private:
int VarInc;
pthread_attr_t attr; /* отрибуты потока */
pthread_t thread_id;
void Increm();
public:
static void* IncWrapper (void* thisPtr);
Devemu();
~Devemu();
int Var();
};
void Devemu::Increm() {
while (true) {
if (VarInc > 532) { VarInc = 0; } else { VarInc++; }
}
}
void* Devemu::IncWrapper(void* thisPtr) {
((Devemu*) thisPtr)->Increm();
return NULL;
}
Devemu::~Devemu() {
pthread_cancel (thread_id);
}
Devemu::Devemu() {
VarInc = 0;
/// get default value of arrts
pthread_attr_init(&attr);
/// start thread
pthread_create(&thread_id, &attr, &Devemu::IncWrapper, this);
}
int Devemu::Var() {
return VarInc;
}
int main(int argc, char** argv) {
Devemu* em = new Devemu();
for(int i = 0 ; i < 100; i++) {
printf("%d\n", em->Var());
usleep (10);
}
delete em;
usleep (1000);
return (EXIT_SUCCESS);
}