Hi,
I thought it'd be a better idea to start a new thread dealing directly
with my problem. Okay, here's again what's happening:
I'm storing boost::shared_p trS in an std::set. I supposed that on
program exit, when the set's dtor is called, the shared_ptrS would clean
up after themselves appropriately. What actually happens though is that
the program segfaults when the set is destructed.
I noticed that erasing the smart pointers from the std::set does not
work as expected. IIRC, std::set finds its elements by checking for
/equivalance/, right? That means, it would check for !less && !greater
right?
So, does that work with boost::shared_p tr at all? I know it features an
operator==, but that would only work if the container would check for
equality, which is not the case.
But then, even if my observation would be correct, I can't explain why
destroying the set would cause the program to segfault.
Any ideas?
Thanks,
Matthias 5 1711
Here are the relevant parts of my program code:
class Task {/* ... */}; // the definition is not relevant
// this class stores the set in question
class TaskManager
{
public:
void add_task(Task*) ;
void remove_task(Tas k*);
// ...
private:
std::set< boost::shared_p tr<Task> > tasks_;
// ...
};
void TaskManager::ad d_task(Task *task)
{
tasks_.insert(b oost::shared_pt r<Task>(task)) ;
// ...
task->start();
}
void TaskManager::re move_task(Task *task)
{
task->stop();
// ...
tasks_.erase(bo ost::shared_ptr <Task>(task)) ; // this does in fact
NOT erase anything
}
Tasks are added by calling TaskManager::ad d_task():
// in some other class:
taskmanager.add _task(new Task(...));
Hope that helps.
- Matthias
Matthias Kaeppler wrote: tasks_.erase(bo ost::shared_ptr <Task>(task)) ;*//*this*does*in*f act
You can't legally initialize a new shared_ptr with a given pointer, if
there are other shared_ptr's around pointing to the same object. You
probably could, if an intrusive reference counting technique were used,
which is not the case.
You should probably handle every 'task' object using a shared_ptr as it
gets instantiated, and change TaskManager's interface so that it accepts
shared_ptr arguments.
Max
"Matthias Kaeppler" <no*****@finite state.org> wrote in message
news:de******** *****@news.t-online.com...
[...] tasks_.erase(bo ost::shared_ptr <Task>(task)) ; // this does in fact NOT erase anything }
[...]
As it shouldn't. From the docs:
------
under the equivalence relation defined by operator<, !(a < b) && !(b < a),
two shared_ptr instances are equivalent if and only if they share ownership
or are both empty.
------
The shared_ptr in the set container doesn't share ownership with the
shared_ptr that you just created (they are unaware of each other's
existence), so they are not considered equivalent.
--
David Hilsee
Matthias Kaeppler wrote: Here are the relevant parts of my program code:
class Task {/* ... */}; // the definition is not relevant
// this class stores the set in question class TaskManager { public: void add_task(Task*) ; void remove_task(Tas k*); // ... private: std::set< boost::shared_p tr<Task> > tasks_; // ... };
This is getting you in trouble. You can't mix raw pointers and
shared_ptr. If you're going to use a shared_ptr to control a resource
you must initialize a shared_ptr object with the pointer to the resource
and then abandon the pointer. (It's not quite that drastic, but it's a
good rule of thumb when you're getting started):
shared_ptr<Task > sp(new Task);
And now your TaskManager's interface should traffic in shared_ptr<Task >s
rather than Task*'s.
--
Pete Becker
Dinkumware, Ltd. ( http://www.dinkumware.com)
Okay, thanks for all your input.
One more question:
When passing around a shared_ptr, is it better practice to do it by
reference or by value?
e.g.:
void foo(const shared_ptr<Bar> & ptr);
or
void foo(shared_ptr< Bar> ptr);
I mean, constructing a copy is certainly not that expensive I guess, but
if it's reference counted, it would imply a useless increment and
decrement of the reference counter right?
Right now, I pass it by reference to const, just to be safe, although
this looks kind of weird for a "pointer" (I usually try to keep my code
intuitive, and this would imply to pass it by value just like a raw
pointer).
Regards,
Matthias This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics |
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