204 lines
6.0 KiB
Python
204 lines
6.0 KiB
Python
#!/usr/bin/env python3
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"""
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read_shm_image_mmap_only.py
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仅使用 mmap 读取共享内存的 reader：
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- 共享内存 /dev/shm/debug_frame 前 4 bytes = uint32 jpg_size (little endian)
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紧随其后的是 jpg_bytes (jpg_size bytes)
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- 不再回退到文件读取；若 mmap 不可用则按 MMAP_RETRY_SECONDS 重试打开
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- 原子写入 out_path.tmp -> out_path
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- 支持环境变量覆盖： SHM_PATH, SHM_SIZE, OUT_PATH, FPS, DEBUG, MMAP_RETRY_SECONDS
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"""
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import os
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import sys
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import time
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import struct
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import hashlib
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import signal
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try:
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import mmap as _mmap
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except Exception:
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_mmap = None
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from io import BytesIO
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# ---------- 配置（环境变量覆盖） ----------
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SHM_PATH = os.environ.get("SHM_PATH", "/dev/shm/debug_frame")
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SHM_SIZE = int(os.environ.get("SHM_SIZE", str(2 * 1024 * 1024))) # bytes
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OUT_PATH = os.environ.get("OUT_PATH", "/dev/shm/frame_preview.jpg")
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FPS = float(os.environ.get("FPS", "10.0"))
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DEBUG = os.environ.get("DEBUG", "0") != "0"
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MMAP_RETRY_SECONDS = float(os.environ.get("MMAP_RETRY_SECONDS", "5.0"))
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# -------------------------------------------------------------------
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sleep_interval = 1.0 / max(1.0, FPS)
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def log(*a, **k):
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if DEBUG:
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print(*a, **k)
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def is_valid_image_bytes(b: bytes) -> bool:
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"""尝试用 Pillow 验证图像是否完整（若 Pillow 不存在，返回 True 以不阻塞）"""
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try:
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from PIL import Image
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im = Image.open(BytesIO(b))
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im.verify()
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return True
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except ImportError:
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log("Pillow not installed; skipping image verify")
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return True
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except Exception as e:
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log("image verify failed:", e)
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return False
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def open_mmap():
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"""尝试打开并返回 (fd, mmap_obj) 或 (None, None)"""
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if _mmap is None:
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return None, None
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try:
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fd = os.open(SHM_PATH, os.O_RDONLY)
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mm = _mmap.mmap(fd, SHM_SIZE, access=_mmap.ACCESS_READ)
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log("mmap opened:", SHM_PATH, "size", SHM_SIZE)
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return fd, mm
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except Exception as e:
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log("open_mmap failed:", e)
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try:
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if 'fd' in locals() and fd:
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os.close(fd)
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except:
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pass
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return None, None
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def close_mmap(fd, mm):
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try:
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if mm:
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mm.close()
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except:
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pass
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try:
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if fd:
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os.close(fd)
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except:
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pass
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def read_from_mmap(mm):
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"""
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从 mmap 读取一帧：
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结构: [uint32 little-endian jpg_size][jpg_bytes...]
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返回 bytes 或 None
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"""
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try:
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mm.seek(0)
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hdr = mm.read(4)
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if len(hdr) < 4:
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return None
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jpg_size = struct.unpack("<I", hdr)[0]
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if jpg_size <= 0 or jpg_size > (SHM_SIZE - 4):
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log("invalid jpg_size:", jpg_size)
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return None
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jpg_bytes = mm.read(jpg_size)
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if len(jpg_bytes) != jpg_size:
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log(f"mmap truncated: expected {jpg_size} got {len(jpg_bytes)}")
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return None
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# quick header check
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if not (jpg_bytes.startswith(b"\xff\xd8\xff")):
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log("jpg header mismatch")
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return None
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return jpg_bytes
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except ValueError as e:
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log("mmap read ValueError:", e)
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return None
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except Exception as e:
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log("mmap read exception:", e)
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raise
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def atomic_write(out_path, data):
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tmp = out_path + ".tmp"
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with open(tmp, "wb") as f:
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f.write(data)
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os.replace(tmp, out_path)
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def loop():
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if _mmap is None:
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print("ERROR: mmap module not available in this Python environment. Exiting.", file=sys.stderr)
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sys.exit(2)
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fd = None
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mm = None
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last_hash = None
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last_mmap_try = 0.0
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# 初始尝试打开 mmap（若失败则进入重试循环）
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fd, mm = open_mmap()
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print(f"watching (mmap_only) '{SHM_PATH}' -> '{OUT_PATH}' @ {FPS} fps")
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while True:
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try:
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jpg_bytes = None
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# 尝试 mmap 读取（若 mm 为 None 则尝试重建）
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if mm is not None:
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try:
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jpg_bytes = read_from_mmap(mm)
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if jpg_bytes is None:
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# 写端可能尚未写入完整帧，短暂等待
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pass
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else:
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log("read frame from mmap, len=", len(jpg_bytes))
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except Exception as e:
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log("mmap error, closing and will retry:", e)
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close_mmap(fd, mm)
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fd, mm = None, None
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last_mmap_try = time.time()
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# 如果没有读到数据并且 mmap 不可用或不可读，则重试打开 mmap（按间隔）
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if jpg_bytes is None:
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now = time.time()
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if mm is None and (now - last_mmap_try) >= MMAP_RETRY_SECONDS:
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fd, mm = open_mmap()
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last_mmap_try = now
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time.sleep(sleep_interval)
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continue
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# 校验完整性（PIL verify）
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if not is_valid_image_bytes(jpg_bytes):
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log("image bytes failed verify, skipping")
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time.sleep(sleep_interval)
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continue
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# 内容哈希，避免重复写磁盘
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h = hashlib.sha256(jpg_bytes).hexdigest()
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if h != last_hash:
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atomic_write(OUT_PATH, jpg_bytes)
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last_hash = h
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log("wrote", OUT_PATH, "len=", len(jpg_bytes))
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# else: skip (no change)
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time.sleep(sleep_interval)
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except KeyboardInterrupt:
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print("terminated by user")
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break
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except Exception as e:
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log("unexpected error:", e)
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try:
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if mm is not None:
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close_mmap(fd, mm)
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except:
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pass
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fd, mm = None, None
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time.sleep(1.0)
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# 退出前清理
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close_mmap(fd, mm)
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def _handle_sigterm(signum, frame):
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print("terminated", file=sys.stderr)
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sys.exit(0)
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if __name__ == "__main__":
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signal.signal(signal.SIGINT, _handle_sigterm)
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signal.signal(signal.SIGTERM, _handle_sigterm)
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loop()
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