Recently I’m working on a project which needs to retrieve the edit operations of two strings. The latency requirement should be very low, so I use C++ and Cython to improve the efficiency. The repo link is here, it only provides a tiny function but personlly I think it is a good example of how to bridge C++ 11 and Python by Cython.
In the C++ code, I defined a struct type called EditOperations, and the major function EditOperations will return a vector of EditOperation object because there are maybe multi operations between two strings.
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struct EditOperation{
public:
const char* operation_type;
int index;
char x;
char y;
public:
EditOperation();
~EditOperation(){};
EditOperation(const char* operation_type, int index,
char x, char y){
this->operation_type = operation_type;
this->index = index;
this->x = x;
this->y = y;
}
};
vector<EditOperation> EditOperations(
const char* string1,
const char* string2,
int max_distance,
bool is_damerau);
But when I call the function through Cython and try to use the member of EditOperation, it will report the Segmentation Fault Error. After a number of trials, I avoid the error by returning vector of pointer of object instead of object itself.
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vector<EditOperation*> EditOperations(
const char* string1,
const char* string2,
int max_distance,
bool is_damerau);
I was happy that it was bugfree and was able to use the package without error, but when I benchmarked the efficiency of package by calling the function millions of times I found that the memory was increasing significantly.
There is a Memory Leak!!
The first reason that come into my mind is the EditOperation* pointer. The vector container will help to release the memory if the element type is object, but it will do nothing if the type is the pointer. If the project is written in pure C++ code, we could use delete function to release the memory by ourselves in the last. But right now the objects are being used in .pyx file. I tried to release the memory in cpdef function, but nothing works. The memory leak issue still exists.
In the last, I replaced the pointer by smart pointer, so that we could let C++ compiler release the memory by itself.
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typedef std::shared_ptr<EditOperation> EditOperationSharedPtr;
vector<EditOperationSharedPtr> EditOperations(
const char* string1,
const char* string2,
int max_distance,
bool is_damerau);