Re: Desperation with Boost Threads

Johannes Bauer <>
Fri, 23 Jan 2009 23:12:42 +0100
Noah Roberts schrieb:

OK. What I'm trying to to: Create a thread (in C-terms speaking I'd like
to do a pthread_create). How do I do it in that constellation then?

The equivalent is the constructor for boost::thread. You can only call
that constructor once. It constructs and spawns a new thread. You will
have a handle to that thread through the boost::thread instance so long
as that instance survives. You can't, however, copy that instance.

Ah, okay, that makes perfect sense then. It seems I totally missed that
when reading the boost docs :-\

So I've changed it to employ your changes. So that I don't have to
fiddle with pointers I changed the behaviour of my Thread class to
behave just like boost::thread does. I threw out Work() and replaced it
by the operator(). Now the relevant parts look like this:

class Thread {
        boost::thread ThreadID;
        Thread(const Thread &Other);
        void operator=(const Thread &Other);

        virtual void operator()();
        virtual ~Thread();

include <iostream>

Thread::Thread() : ThreadID(*this) {

void Thread::operator()() {
    std::cerr << "NOWORK" << std::endl;

And an actual implementation:

Thread_Server::Thread_Server() : Thread() {

void Thread_Server::operator()() {
    std::cerr << "working" << std::endl;
    while (1) {
        std::cerr << "run" << std::endl;

This compiles and works. However the derived classes operator() is never
called, only the base classes. This means when I start a thread:

Thread_Server x = Thread_Server();

it only outputs "NOWORK" and terminates. However, as the Thread_Server()
constructor calls the Thread() constructor which creates the actual
boost::thread with *this I assumed that it would make a lookup in the
vtable (virtual operator()!) and start the derived classes working function.

It does not, however. It is my assumption that during the dereferencing
step of *this the Derived class somehow gets lost - but I do not
understnad why exactly.

Trying to follow your advice using pointers, I also tried:

Thread_Server::Thread_Server() : Thread(this) {

With a new constructor in Thread():

Thread::Thread(const Thread *Derived) : ThreadID(*Derived) {

Which yielded exactly the same result.

Could you elaborate on why this happens?

Kind regards,

"Meine Gegenklage gegen dich lautet dann auf bewusste Verlogenheit,
verl??sterung von Gott, Bibel und mir und bewusster Blasphemie."
         -- Prophet und Vision??r Hans Joss aka HJP in de.sci.physik

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