151 lines
5.4 KiB
Python
151 lines
5.4 KiB
Python
"""POSIX shared-memory ring reader implementation."""
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from __future__ import annotations
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import mmap
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from pathlib import Path
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import struct
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import time
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from typing import Final
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from python_app.models.dataset_model import ResultCollection, SweepCollection
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from python_app.orchestration.shm.decoder import (
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PREPROC_MAGIC,
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RAW_MAGIC,
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decode_result_collection,
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decode_trace_collection,
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)
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_HEADER_SIZE: Final[int] = 64
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_SLOT_HEADER_SIZE: Final[int] = 16
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_MAGIC: Final[bytes] = b"RDRRING2"
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_VERSION: Final[int] = 1
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class ShmRingReader:
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"""Read binary payloads from a lock-free ring in `/dev/shm`."""
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def __init__(self, ring_name: str, open_timeout_s: float = 2.0, open_poll_s: float = 0.01) -> None:
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"""Open and validate ring by name, for example `/radar_results`."""
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if not ring_name.startswith("/"):
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raise ValueError("ring_name must start with '/'")
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self._ring_name = ring_name
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self._path = Path("/dev/shm") / ring_name[1:]
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self._wait_for_ring_file(timeout_s=open_timeout_s, poll_s=open_poll_s)
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self._file = self._path.open("r+b", buffering=0)
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self._mmap = mmap.mmap(self._file.fileno(), 0)
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self._validate_header_with_wait(timeout_s=1.0, poll_s=0.002)
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def close(self) -> None:
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"""Close mmap and file handle."""
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self._mmap.close()
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self._file.close()
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def pop_payload(self) -> bytes | None:
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"""Read next payload from ring, or `None` if no unread payload exists."""
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write_seq = self._read_u64(24)
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read_seq = self._read_u64(32)
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if read_seq >= write_seq:
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return None
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index = read_seq % self.capacity
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slot_offset = _HEADER_SIZE + index * (_SLOT_HEADER_SIZE + self.slot_size_bytes)
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payload_size = self._read_u32(slot_offset)
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sequence = self._read_u64(slot_offset + 8)
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if sequence != read_seq + 1:
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self._write_u64(32, write_seq)
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return None
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payload_offset = slot_offset + _SLOT_HEADER_SIZE
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payload = self._mmap[payload_offset : payload_offset + payload_size]
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self._write_u64(32, read_seq + 1)
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return bytes(payload)
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def pop_raw_collection(self) -> SweepCollection | None:
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"""Read next raw collection from ring."""
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payload = self.pop_payload()
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if payload is None:
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return None
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return decode_trace_collection(payload, RAW_MAGIC)
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def pop_preprocessed_collection(self) -> SweepCollection | None:
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"""Read next preprocessed collection from ring."""
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payload = self.pop_payload()
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if payload is None:
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return None
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return decode_trace_collection(payload, PREPROC_MAGIC)
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def pop_result_collection(self) -> ResultCollection | None:
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"""Read next processed result collection from ring."""
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payload = self.pop_payload()
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if payload is None:
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return None
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return decode_result_collection(payload)
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def drop_all(self) -> int:
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"""Mark all unread slots as consumed and return number of dropped payloads."""
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write_seq = self._read_u64(24)
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read_seq = self._read_u64(32)
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if read_seq >= write_seq:
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return 0
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dropped = int(write_seq - read_seq)
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self._write_u64(32, write_seq)
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return dropped
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@property
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def capacity(self) -> int:
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"""Number of slots in ring."""
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return self._read_u32(12)
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@property
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def slot_size_bytes(self) -> int:
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"""Maximum payload size per slot."""
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return self._read_u32(16)
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def _validate_header_with_wait(self, timeout_s: float, poll_s: float) -> None:
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"""Wait for ring header to contain expected magic and version."""
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deadline = time.monotonic() + timeout_s
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while True:
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magic = self._mmap[:8]
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version = self._read_u32(8)
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if magic == _MAGIC and version == _VERSION:
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return
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if time.monotonic() >= deadline:
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if magic != _MAGIC:
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got_magic = bytes(magic).hex()
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expected_magic = _MAGIC.hex()
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raise RuntimeError(
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f"Shared memory ring magic mismatch for {self._ring_name}: "
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f"got=0x{got_magic}, expected=0x{expected_magic}"
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)
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raise RuntimeError(
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f"Shared memory ring version mismatch for {self._ring_name}: "
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f"got={version}, expected={_VERSION}"
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)
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time.sleep(poll_s)
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def _wait_for_ring_file(self, timeout_s: float, poll_s: float) -> None:
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"""Wait until ring file appears in `/dev/shm`."""
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deadline = time.monotonic() + timeout_s
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while not self._path.exists():
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if time.monotonic() >= deadline:
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raise FileNotFoundError(f"Shared memory ring does not exist: {self._ring_name}")
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time.sleep(poll_s)
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def _read_u32(self, offset: int) -> int:
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"""Read little-endian u32 at mmap offset."""
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return struct.unpack_from("<I", self._mmap, offset)[0]
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def _read_u64(self, offset: int) -> int:
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"""Read little-endian u64 at mmap offset."""
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return struct.unpack_from("<Q", self._mmap, offset)[0]
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def _write_u64(self, offset: int, value: int) -> None:
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"""Write little-endian u64 at mmap offset."""
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struct.pack_into("<Q", self._mmap, offset, value)
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