mmap 行情数据读取器
Mmap Tick Reader
题目详情
高频交易系统常使用 mmap I/O 处理大型二进制行情文件，避免标准流缓冲和数据拷贝，最小化延迟。此技术将文件内容直接映射到虚拟地址空间，操作系统按需加载页面。
任务：实现 TickFileReader 类，使用 mmap() 将行情文件映射到内存。支持按时间范围快速跳转读取、解引用映射指针提取行情字段、munmap() 释放映射。处理大文件（>4GB）时使用 64 位偏移。
英文原题
High-frequency trading systems often utilize memory-mapped I/O (mmap) to process large binary market data files with minimal latency by avoiding standard stream buffering and data copying. This technique maps file contents directly into the virtual address space, allowing applications to access disk-resident data as if it were in-memory arrays while relying on the operating system for efficient page management.
Task
Implement the calculateTotalVolume method in the TickReader class to compute th
解析
问题分析
mmap 将文件直接映射到进程地址空间，实现零拷贝读取。在回测中，将历史行情文件 mmap 到内存后，可像访问数组一样直接读取行情记录，无需 read() 系统调用。
实现
class MmapTickReader {
void* addr_; size_t len_;
public:
MmapTickReader(const char* path) {
int fd = ::open(path, O_RDONLY);
len_ = ::lseek(fd, 0, SEEK_END);
addr_ = ::mmap(nullptr, len_, PROT_READ, MAP_PRIVATE, fd, 0);
::close(fd);
if (addr_ == MAP_FAILED) throw std::runtime_error("mmap failed");
}
const char* data() const { return static_cast<const char*>(addr_); }
size_t size() const { return len_; }
~MmapTickReader() { ::munmap(addr_, len_); }
};复杂度与边界
- 时间复杂度：构造 O(1)（映射而非读取），访问 O(1)
- 空间复杂度：O(文件大小) 虚拟内存，物理页按需加载
- 边界条件：(1) 文件大于地址空间时需分段映射 (2) 写入需 MAP_SHARED + msync (3) SIGBUS 在文件截断时触发
英文解析
Analysis
mmap maps files directly into the process address space, enabling zero-copy reads. In backtesting, historical market data files are mmap'd and tick records can be accessed like an array without read() system calls.
Solution
class MmapTickReader {
void* addr_; size_t len_;
public:
MmapTickReader(const char* path) {
int fd = ::open(path, O_RDONLY);
len_ = ::lseek(fd, 0, SEEK_END);
addr_ = ::mmap(nullptr, len_, PROT_READ, MAP_PRIVATE, fd, 0);
::close(fd);
if (addr_ == MAP_FAILED) throw std::runtime_error("mmap failed");
}
const char* data() const { return static_cast<const char*>(addr_); }
size_t size() const { return len_; }
~MmapTickReader() { ::munmap(addr_, len_); }
};Complexity & Edge Cases
- Time complexity: construct O(1) (maps not reads), access O(1)
- Space complexity: O(file size) virtual memory, physical pages loaded on demand
- Edge cases: (1) Files exceeding address space need segmented mapping (2) Writes require MAP_SHARED + msync (3) SIGBUS triggered on file truncation
Verification
Mmap a tick data file, verify random access performance matches array access. Test segmented mapping for large files. Confirm SIGBUS handling on truncation.
Key Considerations
mmap is the standard approach for backtest data access. Page-level lazy loading means only accessed time ranges consume physical memory. For multi-year tick datasets (terabytes), mmap provides O(1) access to any timestamp without loading the entire file - the OS manages page cache transparently.