Overloaded delete does not calls the destructor??

[rohits123]

I have an overload delete operator as below

//////////////////////////////////
void operator delete(void* mem,int head_type) {
mmHead local_Head = CPRMemory::GetMemoryHead(head_type);
mmFree(&local_Head,(char *)mem);
CPRMemory::SetMemoryHeadAs(local_Head,head_type);
}
/////////////////////
void* operator new(size_t sz, int head_Type) {
char *mem;
mmHead local_Head = CPRMemory::GetMemoryHead(head_Type);
mem = mmAlloc(&local_Head,sz);
CPRMemory::SetMemoryHeadAs(local_Head,head_Type);
if(!mem) cout<<"Out of Memory"<<endl;
return mem;
}
////////////////
and using it as

SmC* s1 = new(WORK_HEAD) SmC;
operator delete (s1,WORK_HEAD) ;

But the problem is overloaded delete operator is not calling the
destructor of class SmC.
Do I have to call the destructor explicitly?
Any suggestions please.

 

[Dave Rahardja]

I have an overload delete operator as below

//////////////////////////////////
void operator delete(void* mem,int head_type) {
mmHead local_Head = CPRMemory::GetMemoryHead(head_type);
mmFree(&local_Head,(char *)mem);
CPRMemory::SetMemoryHeadAs(local_Head,head_type);
}
/////////////////////
void* operator new(size_t sz, int head_Type) {
char *mem;
mmHead local_Head = CPRMemory::GetMemoryHead(head_Type);
mem = mmAlloc(&local_Head,sz);
CPRMemory::SetMemoryHeadAs(local_Head,head_Type);
if(!mem) cout<<"Out of Memory"<<endl;
return mem;
}
////////////////
and using it as

SmC* s1 = new(WORK_HEAD) SmC;
operator delete (s1,WORK_HEAD) ;

But the problem is overloaded delete operator is not calling the
destructor of class SmC.
Do I have to call the destructor explicitly?
Any suggestions please.

You've overridden placement delete, which is used only to deallocate memory in
case a constructor throws an exception. The destructor is not called if you
call placement delete.

What you need to do is to override placement new, placement delete, _and_
normal delete:


// Placement new
void* operator new(size_t sz, int) { /* ... */ }

// Placement delete
void operator delete(void*, int) { /* ... */ } // Note: no size_t parameter!

// Normal delete
void operator delete(void*) { /* ... */ }

then

SmC* s1 = new(WORK_HEAD) SmC; // Calls placement new
delete s1; // Calls normal delete, destructor called first.


If the constructor for SmC throws an exception, the placement delete function
will be called.

-dr

 

[Dave Rahardja]

I have an overload delete operator as below

//////////////////////////////////
void operator delete(void* mem,int head_type) {
mmHead local_Head = CPRMemory::GetMemoryHead(head_type);
mmFree(&local_Head,(char *)mem);
CPRMemory::SetMemoryHeadAs(local_Head,head_type);
}
/////////////////////
void* operator new(size_t sz, int head_Type) {
char *mem;
mmHead local_Head = CPRMemory::GetMemoryHead(head_Type);
mem = mmAlloc(&local_Head,sz);
CPRMemory::SetMemoryHeadAs(local_Head,head_Type);
if(!mem) cout<<"Out of Memory"<<endl;
return mem;
}
////////////////
and using it as

SmC* s1 = new(WORK_HEAD) SmC;
operator delete (s1,WORK_HEAD) ;

But the problem is overloaded delete operator is not calling the
destructor of class SmC.
Do I have to call the destructor explicitly?
Any suggestions please.

By the way, you should follow convention when overriding operator new:



void* operator new(size_t, int)
{
while (true)
{
if ( /* allocation successful? */ )
{
return /* ptr to memory */
}

std::new_handler handler = std::set_new_handler(0);
std::set_new_handler(handler);

if (handler)
{
(*handler)();
}
else
{
throw std::bad_alloc();
}
}
}

 

[rohits123]

You've overridden placement delete, which is used only to deallocate memory in
case a constructor throws an exception. The destructor is not called if you
call placement delete.

What you need to do is to override placement new, placement delete, _and_
normal delete:

// Placement new
void* operator new(size_t sz, int) { /* ... */ }

// Placement delete
void operator delete(void*, int) { /* ... */ } // Note: no size_t parameter!

// Normal delete
void operator delete(void*) { /* ... */ }

then

SmC* s1 = new(WORK_HEAD) SmC; // Calls placement new
delete s1; // Calls normal delete, destructor called first.

If the constructor for SmC throws an exception, the placement delete function
will be called.

-dr

HI Dave ,

I am trying for memory optimization .
I have a chunk of memory which will be divided in to smaller pools of
memory .
So, my overloaded new will allocate memory from a particular pool.
Now during delete I need to know from which pool I need to free the
memory.
Due to this I need to use placement delete so that I can pass the pool
related info to the
overloaded delete. But I want to delete to call destructor also.

Allocation and freeing here means getting the memory from a linked
list of free nodes and adding it to linked list of allocated
node .Deleting means adding the node back to the link list.
These two lists are maintained inside a pool.

 

[=?iso-8859-1?q?Erik_Wikstr=F6m?=]

HI Dave ,

I am trying for memory optimization .
I have a chunk of memory which will be divided in to smaller pools of
memory .
So, my overloaded new will allocate memory from a particular pool.
Now during delete I need to know from which pool I need to free the
memory.
Due to this I need to use placement delete so that I can pass the pool
related info to the
overloaded delete. But I want to delete to call destructor also.

Allocation and freeing here means getting the memory from a linked
list of free nodes and adding it to linked list of allocated
node .Deleting means adding the node back to the link list.
These two lists are maintained inside a pool.

If each pool is a contiguous ranges of memory then you can figure out
which pool an object has been allocated in by checking the address
against the ranges.

 

[Kishore Yada]

HI Dave ,

I am trying for memory optimization .
I have a chunk of memory which will be divided in to smaller pools of
memory .
So, my overloaded new will allocate memory from a particular pool.
Now during delete I need to know from which pool I need to free the
memory.
Due to this I need to use placement delete so that I can pass the pool
related info to the
overloaded delete. But I want to delete to call destructor also.

Allocation and freeing here means getting the memory from a linked
list of free nodes and adding it to linked list of allocated
node .Deleting means adding the node back to the link list.
These two lists are maintained inside a pool.

Instead of using
operator delete (s1,WORK_HEAD) ;

call
delete s1;

That should call both the destructor and the overloaded delete. You
cannot pass any extra arguments to the destructor ( means also to your
delete function ).

However, be aware of inheritance nightmares while overloading new and
delete.
Also, instead of cluttering your class with memory allocation and
deallocation code, see if you can separate it to another class.

 

[Andrey Tarasevich]

...
and using it as

SmC* s1 = new(WORK_HEAD) SmC;
operator delete (s1,WORK_HEAD) ;

But the problem is overloaded delete operator is not calling the
destructor of class SmC.

'operator delete' is a raw memory deallocation function. It _never_ calls the
destructor and it's not supposed to do so.

When you destroy an object with delete-expression, which normally looks as follows

delete s1;

This is a delete-expression. It will do two things: 1) invoke the object's
destructor, 2) deallocate memory by selecting and calling 'operator delete'
function.

Note that 'operator delete' implements just a part of the functionality of
delete-expression. It is called when the destructor has already been called.

Do I have to call the destructor explicitly?

In your code you are not using delete-expression at all. This is fine, but that
means that you have to perform both of the aforementioned steps manually. I.e.
first you have to call the destructor manually and then you can deallocate the
memory by calling 'operator delete':

s1->SmC::~SmC();
operator delete(s1, WORK_HEAD);

 

[Ron Natalie]

You've overridden placement delete, which is used only to deallocate memory in
case a constructor throws an exception. The destructor is not called if you
call placement delete.

It's got squat to do with it being placement.

operator delete() is NOT the implementation of the delete operator
(despite it's unfortunately name), it is the memory deallocation
function that the delete operator uses.

Calling the deallocation function DOES not call the desructors
EVER, regardless of whether it is the normal or placement
version.

 

[Dave Rahardja]

It's got squat to do with it being placement.

operator delete() is NOT the implementation of the delete operator
(despite it's unfortunately name), it is the memory deallocation
function that the delete operator uses.

Calling the deallocation function DOES not call the desructors
EVER, regardless of whether it is the normal or placement
version.

You're right. What I meant was that the standard delete expression looks an
awful lot like a call to placement delete without the extra arguments.

-dr

 

[Dave Rahardja]

HI Dave ,

I am trying for memory optimization .
I have a chunk of memory which will be divided in to smaller pools of
memory .
So, my overloaded new will allocate memory from a particular pool.
Now during delete I need to know from which pool I need to free the
memory.
Due to this I need to use placement delete so that I can pass the pool
related info to the
overloaded delete. But I want to delete to call destructor also.

Allocation and freeing here means getting the memory from a linked
list of free nodes and adding it to linked list of allocated
node .Deleting means adding the node back to the link list.
These two lists are maintained inside a pool.

You've hit upon a classic design problem with C++ and memory allocation: The
fact that it's difficult to tell via during deletion how the memory was
allocated.

There are several solutions to the problem, but none of them are clean or
simple. Check out chapter 8 of Scott Meyers' Effective C++ (3rd Ed) for a
detailed look at the problem of customizing new and delete. Here are some
suggestions.

You can override new and delete for a class. This approach entangles the
problem domain of memory management with the problem domain your class was
intended to address.

You can override new and delete for a class, and then templatize the class to
use a memory manager class. This way the user of the class can choose (via the
template parameter) which memory manager will be used.

You can create a Factory that associates a class with a memory manager. You
call functions in the Factory (such as create() and destroy()) to perform
memory allocation and deallocation. In this scenario, the class is completely
disentangled from the memory allocation algorithm. However, you can no longer
use delete to destroy your class, or pass the pointers to other algorithms
that can delete your class for you.

You can override global new and delete. Each time new is called, allocate
memory that is slightly larger than needed. In the "spare" area of allocated
memory, store a pointer to the pool that you allocated the object from. During
deletion, peek at the pointer you stashed away to discover where the allocated
block came from. The downside to this is that your custom global new and
delete may be called to allocate _any_ class. It is difficult to restrict
allocation to a certain class or classes that are causing a bottleneck.

There are other solutions as well, but none of them are any cleaner or easier
to use.

-dr