使用mmap地址複製構造函數

Question

當類具有mmap地址指針時，是否可以使用複製構造函數？我在想，mmap只被調用過一次，所以只有一個引用已經在內核中註冊了。現在兩個對象共享該地址，當刪除1時，該地址會發生什麼？我想這是清理。如果可能的話，mmap文件會爲我處理同步嗎？

Answer 1

shared_ptr是你的朋友在這裏：

#include <sys/mman.h> 
#include <memory> 


std::shared_ptr<void> map_some_memory(void *addr, size_t length, 
             int prot, int flags, 
             int fd, off_t offset) 
{ 
    auto deleter = [length](void* p) { 
    munmap(p, length); 
    }; 

    // use of a custom deleter ensures that the mmap call is undone 
    // when the last reference to the memory goes away. 

    return { mmap(addr, length, prot, flags, fd, offset), deleter }; 

} 

// some function that gets you a file descriptor 
extern int alloc_fd(); 

int main() 
{ 
    int some_file = alloc_fd(); 

    // allocate a shared mapping 
    auto my_mapped_ptr = map_some_memory(nullptr, 100, PROT_READ | PROT_WRITE, 
             MAP_SHARED, some_file, 0); 

    // cast it to sometthing else 

    auto shared_ints = std::shared_ptr<int>(my_mapped_ptr, 
              reinterpret_cast<int*>(my_mapped_ptr.get())); 

    // another shared pointer pointing to the shared ints 
    auto another_share = shared_ints; 

}