Re: [Boost-users] Boost shared pointers, PThreads and void* casts

19 Dec 2007


      Andrew Holden [aholden@charteroaksystems.com] wrote:
...
STenyaK (Bruno Gonzalez) [stenyak@gmail.com] wrote:
...
Ok. This is how my code structure looks:
----------------------------
typedef shared_ptr<MyClass> pMyClass;
void* MyClass::actionThread(void *objectPointer) {
    pMyClass * _obj = static_cast(objectPointer);    
    pMyClass obj = *_obj; obj->action(false);
    delete _obj;
}
void MyClass::action(bool threaded)
{
    if (threaded)
    {
        pthread_t tid;
        pthread_create(&tid, 0, actionThread, new pMyClass(this))
    } else {
           //TODO: actually perform the action
    }
}
----------------------------
----------------------------
typedef shared_ptr<MyClass> pMyClass;
void* MyClass::actionThread(void *objectPointer) {
    MyClass * _obj = static_cast(objectPointer);
    pMyClass obj = _obj->shared_from_this();
    obj->action(false);
}
void MyClass::action(bool threaded)
{
    if (threaded)
    {
        pthread_t tid;
        pthread_create(&tid, 0, actionThread, this)     } else {
        //TODO: actually perform the action
    }
}
----------------------------
I just realized you should ignore this implementation because it
contains a race condition (main thread may delete the object before
actionThread can call shared_from_this.  Here is a tweak for your
version that uses shared_from_this:

----------------------------
typedef shared_ptr<MyClass> pMyClass;
void* MyClass::actionThread(void *objectPointer) {
    pMyClass * _obj = static_cast(objectPointer);
    pMyClass obj = *_obj;
    delete _obj;
    obj->action(false);
}
void MyClass::action(bool threaded)
{
    if (threaded)
    {
        pthread_t tid;

//Change next line:
        pthread_create(&tid, 0, actionThread, new
pMyClass(shared_from_this()))
    } else {
        //TODO: actually perform the action
    }
}
----------------------------