77 lines
2.1 KiB
Python
77 lines
2.1 KiB
Python
"""
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ChunkQueue — bounded, thread-safe queue with sentinel-based shutdown.
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Demonstrates: Core data structures — queue.Queue (Interview Topic 5).
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"""
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import queue
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from typing import Optional
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from .models import Chunk
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# Sentinel value to signal workers to stop
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_SENTINEL = object()
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class ChunkQueue:
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"""
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Thread-safe bounded queue for chunks.
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Provides backpressure: producers block when the queue is full,
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preventing unbounded memory usage.
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Args:
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maxsize: Maximum number of chunks in the queue (default: 10)
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"""
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def __init__(self, maxsize: int = 10):
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self._queue: queue.Queue = queue.Queue(maxsize=maxsize)
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self._closed = False
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self.maxsize = maxsize
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def put(self, chunk: Chunk, timeout: Optional[float] = None) -> None:
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"""
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Add a chunk to the queue. Blocks if full (backpressure).
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Args:
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chunk: The chunk to enqueue
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timeout: Max seconds to wait (None = block forever)
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Raises:
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queue.Full: If timeout expires while queue is full
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"""
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self._queue.put(chunk, timeout=timeout)
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def get(self, timeout: Optional[float] = None) -> Optional[Chunk]:
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"""
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Get next chunk from queue. Returns None if queue is closed.
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Args:
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timeout: Max seconds to wait (None = block forever)
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Returns:
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Chunk or None (if sentinel received, meaning queue is closed)
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Raises:
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queue.Empty: If timeout expires while queue is empty
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"""
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item = self._queue.get(timeout=timeout)
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if item is _SENTINEL:
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# Re-put sentinel so other workers also see it
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self._queue.put(_SENTINEL)
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return None
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return item
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def close(self) -> None:
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"""Signal all consumers to stop by inserting a sentinel."""
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self._closed = True
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self._queue.put(_SENTINEL)
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@property
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def is_closed(self) -> bool:
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return self._closed
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def qsize(self) -> int:
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"""Current number of items in the queue (approximate)."""
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return self._queue.qsize()
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