Repository: opencv
Issue: OpenCV: Using setDefaultAllocator() with custom allocator calls allocate() but not deallocate() - why?
Labels: bug

### System Information

I am trying to use a custom allocator with opencv. I tried to test it but the beahvior doesn’t make sense to me. I created a CV mat inside some scope. I can see the print inside the allocate() but don’t see the print inside the deallocate().

Any explanation?

### Detailed description

```


#include "gtest/gtest.h"
#include "opencv2/opencv.hpp"
 
 
class CvMatAllocatorTest : public ::testing::Test
{
protected:
};
 
 
class UserMatDebugAllocator : public cv::MatAllocator
    {
    public:
        UserMatDebugAllocator()
        {
            m_defaultAllocator = cv::Mat::getDefaultAllocator();
            m_stdAllocator = cv::Mat::getStdAllocator();
            std::cout << "UserMatDebugAllocator: constructor" << std::endl;
        }
 
        ~UserMatDebugAllocator() override
        {
            std::cout << "UserMatDebugAllocator: destructor" << std::endl;
        }
 
        cv::UMatData* allocate(int dims, const int* sizes, int type,
            void* data, size_t* step, cv::AccessFlag flags, cv::UMatUsageFlags usageFlags) const override
        {
            std::cout << "UserMatDebugAllocator: allocate" << std::endl;
            return m_defaultAllocator->allocate(dims, sizes, type, data, step, flags, usageFlags);
        }
 
        bool allocate(cv::UMatData* data, cv::AccessFlag accessflags, cv::UMatUsageFlags usageFlags) const override
        {
            std::cout << "UserMatDebugAllocator: allocate2" << std::endl;
            return m_defaultAllocator->allocate(data, accessflags, usageFlags);
        }
 
        void deallocate(cv::UMatData* data) const override
        {
 
            std::cout << "UserMatDebugAllocator: deallocate" << std::endl;
            return m_defaultAllocator->deallocate(data);
        }
 
        void map(cv::UMatData* data, cv::AccessFlag accessflags) const override
        {
            std::cout << "UserMatDebugAllocator: map" << std::endl;
            return m_defaultAllocator->map(data, accessflags);
        }
 
        void unmap(cv::UMatData* data) const override
        {
            std::cout << "UserMatDebugAllocator: unmap" << std::endl;
            return m_defaultAllocator->unmap(data);
        }
 
        void download(cv::UMatData* data, void* dst, int dims, const size_t sz[],
            const size_t srcofs[], const size_t srcstep[],
            const size_t dststep[]) const override
        {
            std::cout << "UserMatDebugAllocator: download" << std::endl;
            return m_defaultAllocator->download(data, dst, dims, sz, srcofs, srcstep, dststep);
        }
 
        void upload(cv::UMatData* data, const void* src, int dims, const size_t sz[],
            const size_t dstofs[], const size_t dststep[],
            const size_t srcstep[]) const override
        {
            std::cout << "UserMatDebugAllocator: upload" << std::endl;
            return m_defaultAllocator->upload(data, src, dims, sz, dstofs, dststep, srcstep);
        }
 
        void copy(cv::UMatData* srcdata, cv::UMatData* dstdata, int dims, const size_t sz[],
            const size_t srcofs[], const size_t srcstep[],
            const size_t dstofs[], const size_t dststep[], bool sync) const override
        {
            std::cout << "UserMatDebugAllocator: copy" << std::endl;
            return m_defaultAllocator->copy(srcdata, dstdata, dims, sz, srcofs, srcstep, dstofs, dststep, sync);
        }
 
        cv::BufferPoolController* getBufferPoolController(const char* id = NULL) const override
        {
            std::cout << "UserMatDebugAllocator: getBufferPoolController" << std::endl;
            return m_defaultAllocator->getBufferPoolController(id);
        }
 
        cv::MatAllocator* m_defaultAllocator;
        cv::MatAllocator* m_stdAllocator;
    };

TEST_F(CvMatAllocatorTest, cvMatAllocatorTest)
{
    std::cout << "test start" << std::endl;
 
    UserMatDebugAllocator userAllocator;
    cv::Mat::setDefaultAllocator(&userAllocator);

    {
        cv::Mat mat(1000, 1000, CV_8UC3);
        mat.at<cv::Vec3b>(500, 500) = cv::Vec3b(255, 0, 0);
    }
 
    sleep(3);
    std::cout << "test end" << std::endl;
}

```
Output:

test start

UserMatDebugAllocator: constructor

UserMatDebugAllocator: allocate

test end

UserMatDebugAllocator: destructor

[ OK ] CvMatAllocatorTest.cvMatAllocatorTest (3000 ms)

### Steps to reproduce

Run the test

### Issue submission checklist

- [X] I report the issue, it's not a question
- [X] I checked the problem with documentation, FAQ, open issues, forum.opencv.org, Stack Overflow, etc and have not found any solution
- [X] I updated to the latest OpenCV version and the issue is still there
- [X] There is reproducer code and related data files (videos, images, onnx, etc)