"""POSIX shared-memory ring reader implementation.""" from __future__ import annotations import mmap from pathlib import Path import struct import time from typing import Final from python_app.models.dataset_model import ResultCollection, SweepCollection from python_app.orchestration.shm.decoder import ( PREPROC_MAGIC, RAW_MAGIC, decode_result_collection, decode_trace_collection, ) _HEADER_SIZE: Final[int] = 64 _SLOT_HEADER_SIZE: Final[int] = 16 _MAGIC: Final[bytes] = b"RDRRING2" _VERSION: Final[int] = 1 class ShmRingReader: """Read binary payloads from a lock-free ring in `/dev/shm`.""" def __init__(self, ring_name: str, open_timeout_s: float = 2.0, open_poll_s: float = 0.01) -> None: """Open and validate ring by name, for example `/radar_results`.""" if not ring_name.startswith("/"): raise ValueError("ring_name must start with '/'") self._ring_name = ring_name self._path = Path("/dev/shm") / ring_name[1:] self._wait_for_ring_file(timeout_s=open_timeout_s, poll_s=open_poll_s) self._file = self._path.open("r+b", buffering=0) self._mmap = mmap.mmap(self._file.fileno(), 0) self._validate_header_with_wait(timeout_s=1.0, poll_s=0.002) def close(self) -> None: """Close mmap and file handle.""" self._mmap.close() self._file.close() def pop_payload(self) -> bytes | None: """Read next payload from ring, or `None` if no unread payload exists.""" write_seq = self._read_u64(24) read_seq = self._read_u64(32) if read_seq >= write_seq: return None index = read_seq % self.capacity slot_offset = _HEADER_SIZE + index * (_SLOT_HEADER_SIZE + self.slot_size_bytes) # Seqlock read mirroring the C++ pop: a slot is valid for read_seq R only if # its sequence equals R+1 and is unchanged across the payload copy (i.e. the # producer did not overwrite this slot mid-copy). Sequence and payload_size # are read first; the slot is only accepted after the re-read confirms both. sequence = self._read_u64(slot_offset + 8) if sequence != read_seq + 1: # Producer overwrote this slot before we read it. Resync to latest. self._write_u64(32, write_seq) return None payload_size = self._read_u32(slot_offset) # Bound payload_size against the slot before slicing so a torn/garbage size # can never read out of the slot region; resync and skip on violation. if payload_size > self.slot_size_bytes: self._write_u64(32, write_seq) return None payload_offset = slot_offset + _SLOT_HEADER_SIZE payload = bytes(self._mmap[payload_offset : payload_offset + payload_size]) # Re-read the slot sequence after the copy; if it changed, the producer # overwrote this slot mid-copy and the payload is torn — discard and resync. if self._read_u64(slot_offset + 8) != read_seq + 1: self._write_u64(32, write_seq) return None self._write_u64(32, read_seq + 1) return payload def pop_raw_collection(self) -> SweepCollection | None: """Read next raw collection from ring.""" payload = self.pop_payload() if payload is None: return None return decode_trace_collection(payload, RAW_MAGIC) def pop_preprocessed_collection(self) -> SweepCollection | None: """Read next preprocessed collection from ring.""" payload = self.pop_payload() if payload is None: return None return decode_trace_collection(payload, PREPROC_MAGIC) def pop_result_collection(self) -> ResultCollection | None: """Read next processed result collection from ring.""" payload = self.pop_payload() if payload is None: return None return decode_result_collection(payload) def drop_all(self) -> int: """Mark all unread slots as consumed and return number of dropped payloads.""" write_seq = self._read_u64(24) read_seq = self._read_u64(32) if read_seq >= write_seq: return 0 dropped = int(write_seq - read_seq) self._write_u64(32, write_seq) return dropped @property def capacity(self) -> int: """Number of slots in ring.""" return self._read_u32(12) @property def slot_size_bytes(self) -> int: """Maximum payload size per slot.""" return self._read_u32(16) def _validate_header_with_wait(self, timeout_s: float, poll_s: float) -> None: """Wait for ring header to contain expected magic and version.""" deadline = time.monotonic() + timeout_s while True: magic = self._mmap[:8] version = self._read_u32(8) if magic == _MAGIC and version == _VERSION: return if time.monotonic() >= deadline: if magic != _MAGIC: got_magic = bytes(magic).hex() expected_magic = _MAGIC.hex() raise RuntimeError( f"Shared memory ring magic mismatch for {self._ring_name}: " f"got=0x{got_magic}, expected=0x{expected_magic}" ) raise RuntimeError( f"Shared memory ring version mismatch for {self._ring_name}: " f"got={version}, expected={_VERSION}" ) time.sleep(poll_s) def _wait_for_ring_file(self, timeout_s: float, poll_s: float) -> None: """Wait until ring file appears in `/dev/shm`.""" deadline = time.monotonic() + timeout_s while not self._path.exists(): if time.monotonic() >= deadline: raise FileNotFoundError(f"Shared memory ring does not exist: {self._ring_name}") time.sleep(poll_s) def _read_u32(self, offset: int) -> int: """Read little-endian u32 at mmap offset.""" return struct.unpack_from(" int: """Read little-endian u64 at mmap offset.""" return struct.unpack_from(" None: """Write little-endian u64 at mmap offset.""" struct.pack_into("