import mmap

import mmap

def basic_mmap_example():
    # 打開(kāi)文件
    with open('large_file.bin', 'r+b') as f:
        # 創(chuàng)建內(nèi)存映射
        with mmap.mmap(f.fileno(), 0, access=mmap.ACCESS_WRITE) as mm:
            # 現(xiàn)在可以通過(guò)mm對(duì)象訪問(wèn)文件內(nèi)容
            print(f"文件大小: {len(mm)} 字節(jié)")
            
            # 讀取前100字節(jié)
            data = mm[0:100]
            print(f"前100字節(jié): {data}")
            
            # 修改文件內(nèi)容
            mm[0:4] = b'TEST'
            
            # 搜索特定內(nèi)容
            position = mm.find(b'signature')
            if position != -1:
                print(f"找到簽名位置: {position}")

def partial_mmap_example():
    with open('huge_file.bin', 'r+b') as f:
        # 只映射文件的中間部分 (從1MB到2MB)
        offset = 1024 * 1024  # 1MB
        length = 1024 * 1024  # 1MB
        
        with mmap.mmap(f.fileno(), length, offset=offset, access=mmap.ACCESS_WRITE) as mm:
            # 處理映射的區(qū)域
            process_chunk(mm)

def mmap_with_memoryview():
    with open('data.bin', 'r+b') as f:
        with mmap.mmap(f.fileno(), 0, access=mmap.ACCESS_WRITE) as mm:
            # 創(chuàng)建memoryview以實(shí)現(xiàn)零拷貝訪問(wèn)
            mv = memoryview(mm)
            
            # 高效處理數(shù)據(jù)
            for i in range(0, len(mv), 1024):
                chunk = mv[i:i+1024]
                process_chunk(chunk)
                
            # 修改數(shù)據(jù)
            mv[0:4] = b'MODIFIED'

import struct

def process_structured_data():
    # 假設(shè)文件包含多個(gè)相同格式的記錄
    RECORD_FORMAT = 'I20sI'  # 4字節(jié)整數(shù) + 20字節(jié)字符串 + 4字節(jié)整數(shù)
    RECORD_SIZE = struct.calcsize(RECORD_FORMAT)
    
    with open('records.bin', 'r+b') as f:
        with mmap.mmap(f.fileno(), 0, access=mmap.ACCESS_WRITE) as mm:
            num_records = len(mm) // RECORD_SIZE
            
            for i in range(num_records):
                start = i * RECORD_SIZE
                end = start + RECORD_SIZE
                
                # 解包記錄
                record_data = mm[start:end]
                field1, field2, field3 = struct.unpack(RECORD_FORMAT, record_data)
                
                # 處理字符串字段（去除填充的空字節(jié)）
                field2_str = field2.decode('utf-8').rstrip('\x00')
                
                # 修改并寫(xiě)回
                new_field3 = field3 + 1
                new_data = struct.pack(RECORD_FORMAT, field1, field2, new_field3)
                mm[start:end] = new_data

class DatabaseIndex:
    def __init__(self, filename):
        self.filename = filename
        self.INDEX_ENTRY_SIZE = 16  # 每個(gè)索引項(xiàng)16字節(jié)
        self.file = open(filename, 'r+b')
        self.mm = mmap.mmap(self.file.fileno(), 0, access=mmap.ACCESS_WRITE)
        
    def get_index_entry(self, index):
        """獲取指定位置的索引項(xiàng)"""
        start = index * self.INDEX_ENTRY_SIZE
        end = start + self.INDEX_ENTRY_SIZE
        return self.mm[start:end]
    
    def update_index_entry(self, index, data):
        """更新指定位置的索引項(xiàng)"""
        start = index * self.INDEX_ENTRY_SIZE
        end = start + self.INDEX_ENTRY_SIZE
        self.mm[start:end] = data
        
    def find_index_entry(self, key):
        """查找包含特定鍵的索引項(xiàng)"""
        key_bytes = key.encode('utf-8')
        position = self.mm.find(key_bytes)
        if position != -1:
            # 計(jì)算索引項(xiàng)位置
            index = position // self.INDEX_ENTRY_SIZE
            return index, self.get_index_entry(index)
        return None
        
    def close(self):
        """關(guān)閉資源"""
        self.mm.close()
        self.file.close()
        
    def __enter__(self):
        return self
        
    def __exit__(self, exc_type, exc_val, exc_tb):
        self.close()

def process_large_image():
    # 假設(shè)是原始RGB圖像數(shù)據(jù)，無(wú)文件頭
    WIDTH = 4000
    HEIGHT = 3000
    CHANNELS = 3
    PIXEL_SIZE = CHANNELS  # 每個(gè)像素3字節(jié) (R, G, B)
    
    with open('large_image.raw', 'r+b') as f:
        with mmap.mmap(f.fileno(), 0, access=mmap.ACCESS_WRITE) as mm:
            # 創(chuàng)建memoryview以便高效訪問(wèn)
            mv = memoryview(mm)
            
            # 將圖像轉(zhuǎn)換為灰度
            for y in range(HEIGHT):
                for x in range(WIDTH):
                    # 計(jì)算像素偏移量
                    offset = (y * WIDTH + x) * PIXEL_SIZE
                    
                    # 獲取RGB值
                    r = mv[offset]
                    g = mv[offset + 1]
                    b = mv[offset + 2]
                    
                    # 計(jì)算灰度值
                    gray = int(0.299 * r + 0.587 * g + 0.114 * b)
                    
                    # 更新像素
                    mv[offset] = gray
                    mv[offset + 1] = gray
                    mv[offset + 2] = gray

def analyze_large_log_file(pattern):
    pattern_bytes = pattern.encode('utf-8')
    results = []
    
    with open('server.log', 'rb') as f:
        with mmap.mmap(f.fileno(), 0, access=mmap.ACCESS_READ) as mm:
            # 使用find方法查找所有匹配項(xiàng)
            pos = 0
            while True:
                pos = mm.find(pattern_bytes, pos)
                if pos == -1:
                    break
                
                # 提取匹配行
                line_start = mm.rfind(b'\n', 0, pos) + 1
                line_end = mm.find(b'\n', pos)
                if line_end == -1:
                    line_end = len(mm)
                
                line = mm[line_start:line_end].decode('utf-8')
                results.append((pos, line))
                
                pos = line_end + 1
    
    return results

def optimized_mmap_processing():
    CHUNK_SIZE = 1024 * 1024  # 1MB塊
    
    with open('large_data.bin', 'r+b') as f:
        file_size = os.path.getsize('large_data.bin')
        
        for offset in range(0, file_size, CHUNK_SIZE):
            # 計(jì)算當(dāng)前塊的實(shí)際大小
            chunk_length = min(CHUNK_SIZE, file_size - offset)
            
            with mmap.mmap(f.fileno(), chunk_length, offset=offset, 
                          access=mmap.ACCESS_WRITE) as mm:
                # 使用memoryview進(jìn)行高效處理
                mv = memoryview(mm)
                process_chunk(mv)

def safe_mmap_operation(filename):
    f = None
    mm = None
    try:
        f = open(filename, 'r+b')
        mm = mmap.mmap(f.fileno(), 0, access=mmap.ACCESS_WRITE)
        
        # 執(zhí)行操作
        process_data(mm)
        
    except FileNotFoundError:
        print(f"文件 {filename} 不存在")
    except PermissionError:
        print(f"沒(méi)有權(quán)限訪問(wèn)文件 {filename}")
    except Exception as e:
        print(f"處理文件時(shí)發(fā)生錯(cuò)誤: {e}")
    finally:
        # 確保資源被正確釋放
        if mm is not None:
            mm.close()
        if f is not None:
            f.close()

import multiprocessing as mp

def worker_process(offset, length, filename):
    """工作進(jìn)程函數(shù)"""
    with open(filename, 'r+b') as f:
        with mmap.mmap(f.fileno(), length, offset=offset, access=mmap.ACCESS_WRITE) as mm:
            # 處理分配的區(qū)域
            process_chunk(mm)

def parallel_mmap_processing(filename, num_processes=4):
    """并行處理大型文件"""
    file_size = os.path.getsize(filename)
    chunk_size = file_size // num_processes
    
    processes = []
    for i in range(num_processes):
        offset = i * chunk_size
        length = chunk_size if i < num_processes - 1 else file_size - offset
        
        p = mp.Process(target=worker_process, args=(offset, length, filename))
        processes.append(p)
        p.start()
    
    for p in processes:
        p.join()