Re: What's the connection between objects and threads?

"Chris Thomasson" <>
Sun, 18 May 2008 23:54:22 -0700
"Szabolcs Ferenczi" <> wrote in message
On May 18, 3:23 pm, James Kanze <> wrote:

Except that, as Chris has already pointed out, it results in a
race condition. It's a serious design error.

Well, he did not point out anything but claimed something. He has
postings that he used to correct the next hour or the next day.

The pseudo-code I post over on 'comp.programming.threads' is all about the
__experimental__ synchronization algorihtms that I am brainstorming. We have
been over this before Szabolcs. If I come up with an idea, I try to make
sure to post it on c.p.t. If there is a typo in the pseudo-code, I promptly
document them and show the corrections. Anyway...

You better read carefully what I have written. I highlighted that one
needs discipline for it. It is hopless for you but at least you calm

I hope I could help though.

Unfortunately, wrt this thread, your so-called help is only going to lead
the OP down the wrong path. You don't seem to get it. AFAICT, the OP wanted
to create a thread base class for users to derive from. Something like:
class thread_base {
  pthread_t m_tid;
  virtual void on_entry() = 0;

  thread_base() {

  virtual ~thread_base() throw() = 0;

thread_base::~thread_base() throw() {}

The OP cannot start the thread from the constructor of the base class! This
is what I was referring to. When threads are involved there is a major
race-condition because the thread can be started and call the on_entry pure
virtual function which results in UB. Also, even in the absence of threads
there still can be a problem. Here is a VERY simple example:
#include <cstdio>
#include <cstdlib>

static void call_abstract_virtual_indirect(class base*);

class base {
  friend void call_abstract_virtual_indirect(class base*);
  virtual void on_action() = 0;

  base() {

  virtual ~base() throw() = 0;

base::~base() throw() {}

void call_abstract_virtual_indirect(base* _this) {

class derived : public base {
  int const m_ctor;

  derived() : m_ctor(123456789) {


  void on_action() {
    std::printf("(%p)::derived::on_action()\n", (void*)this);
    if (m_ctor != 123456789) {
      std::printf("(%p)::derived::on_action() - NOT CONSTRUCTED!\n",

int main() {
    derived d;

Press <ENTER> to exit...");
  return 0;


The above demonstrates one reason why its generally NOT a good idea to start
a thread in a constructor. Your failure to understand this is only going to
confuse the OP. Your advise is flawed in that respect. The problem produces
undefined-behavior. It can just seg-fault, or it might print "... NOT
CONSTRUCTED!", or whatever. Therefore, I guess the moral of the story is "Do
NOT call abstract virtual functions in constructors!"


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