I've implemented a Linked list using C++11 smart pointers. This implementation uses shared_ptr to store the internal data struct, which is used to implement implicit-sharing of it. I provide the relevant part of the source code bellow:
namespace Algos {
template <typename T>
struct LinkedListData{
struct Node {
std::unique_ptr<Node> next;
Node *prev = nullptr;
T data;
};
std::unique_ptr<Node> root;
Node *last = nullptr;
int size = 0;
LinkedListData() {
root = std::make_unique<Node>();
root->prev = nullptr; //last virtual element
root->next = std::make_unique<Node>();
last = root->next.get();
last->prev = root.get();
last->next = nullptr;
}
//deferr pointers manually to avoid stackoverflow due to
//recursion explosion
static void cleanup(LinkedListData<T> *data) {
#ifdef DEBUG_TXT
int nodeCount=0;
#endif
Node *n = data->last;
if(n==nullptr) { return; }
while(n) {
#ifdef DEBUG_TXT
if(n->next.get())
std::cout << "Release {n->next()} [" << ++nodeCount <<
"]: "<< n->next.get() << std::endl;
#endif
n->next.release();
ALGO_ASSERT(n->next.get() == nullptr, "Node reference not deferred");
n = n->prev;
}
data->size = 0;
#ifdef DEBUG_TXT
std::cout << "Release {Root} [" << ++nodeCount << "]: "<< data->root.get() << std::endl;
#endif
data->root.release();
}
};
template <class T>
class LinkedList {
typedef typename LinkedListData<T>::Node node_type;
std::shared_ptr<LinkedListData<T> > d;
public:
LinkedList() : d(new LinkedListData<T>(), LinkedListData<T>::cleanup){}
/* Code omitted .... */
};
}
The following code is triggering memory leak error on valgrind in the shared_pointer constructor due to the use of new:
#include "linked_list/linkedlist.h"
int main(int argv, char* argc[]) {
Data d;
Data::initDataSample(d);
Algos::LinkedList<DataTest> l1;
{
Algos::LinkedList<DataTest> l2;
l1 = l2;
}
sleep(2);
appendElements(l1, d);
int removeSize = l1.size()/2;
for(int i=0; i<removeSize; i++)
l1.takeFirst();
prependElements(l1, d);
removeSize = l1.size()/2;
for(int i=0; i<removeSize; i++)
l1.takeLast();
return 0;
}
This is the message I'm getting in the valgrind console:
> ==8897== HEAP SUMMARY:
==8897== in use at exit: 282,976 bytes in 3,757 blocks
==8897== total heap usage: 10,009 allocs, 6,252 frees, 633,040 bytes allocated
==8897==
==8897== 136 (24 direct, 112 indirect) bytes in 1 blocks are definitely lost in loss record 5 of 8
==8897== at 0x4C2E216: operator new(unsigned long) (vg_replace_malloc.c:334)
==8897== by 0x407C1C: Algos::LinkedList<DataTest>::LinkedList() (linkedlist.h:74)
==8897== by 0x4074B4: main (insert_delete_rounds.cpp:63)
==8897==
==8897== 210,136 (24 direct, 210,112 indirect) bytes in 1 blocks are definitely lost in loss record 8 of 8
==8897== at 0x4C2E216: operator new(unsigned long) (vg_replace_malloc.c:334)
==8897== by 0x407C1C: Algos::LinkedList<DataTest>::LinkedList() (linkedlist.h:74)
==8897== by 0x4074C3: main (insert_delete_rounds.cpp:65)
==8897==
==8897== LEAK SUMMARY:
==8897== definitely lost: 48 bytes in 2 blocks
==8897== indirectly lost: 210,224 bytes in 3,754 blocks
==8897== possibly lost: 0 bytes in 0 blocks
==8897== still reachable: 72,704 bytes in 1 blocks
==8897== suppressed: 0 bytes in 0 blocks
==8897== Reachable blocks (those to which a pointer was found) are not shown.
==8897== To see them, rerun with: --leak-check=full --show-leak-kinds=all
==8897==
==8897== For counts of detected and suppressed errors, rerun with: -v
==8897== ERROR SUMMARY: 2 errors from 2 contexts (suppressed: 0 from 0)
As far as I know there is no other way to initiate a shared_ptr with custom Deleter without using new in C++11. After reading the documentation and different threads on stackoverflow, I noticed that std::make_shared() doesn't support passing a custom Deleter. So, my question is: Is this memory leak warning legit ? If yes, is it possible to avoid it ?
Dev tools setup:
- gcc: 5.4.0
- Valgrind: 3.13.0
- OS: Linux Ubuntu 16.04
Aucun commentaire:
Enregistrer un commentaire