* Fix inference stall during prefill by removing retry storm
The _stream_with_retry method used a 0.5s read timeout and retried by
sending a brand new POST request each time. During prompt prefill (which
can take 5-30+ seconds for long contexts or reasoning models), this
caused 10-60 duplicate requests that forced llama-server to restart
processing from scratch each time, resulting in 10-20s stalls visible
as "Generating" with no progress in the UI.
Fix: send the request ONCE with a 120s read timeout for the initial
response headers. Cancel support during the prefill wait is handled by
a background thread that monitors cancel_event (checked every 0.3s)
and closes the response to unblock the httpx read immediately. This
preserves the ability to stop/cancel/refresh during generation.
The existing 0.5s timeout on the httpx.Client is still used by
_iter_text_cancellable for per-token cancel checking during streaming
(after prefill), which is unaffected by this change.
* Fix race in cancel watcher when response is not yet created
When cancel_event fires before client.stream() returns (response is
still None), the watcher would hit return and exit without closing
anything. The main thread stays blocked for up to 120s.
Fix: after cancel is requested, keep polling _response_ref every 0.1s
until the response object appears (then close it) or _cancel_closed
is set (main thread finished on its own).
* Minor cleanup: remove redundant None check, add debug logging in cancel watcher
Address Gemini review: cancel_event is guaranteed non-None when the
watcher thread runs, and logging the close exception aids debugging.
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* Retry r.close() on failure instead of giving up
If r.close() raises, stay in the polling loop and retry rather than
returning and leaving the main thread blocked for up to 120s.
* fix: keep short read timeout during token streaming
The prefill_timeout (read=120s) was passed to client.stream(), which
applied to ALL reads -- not just the initial response headers. This
meant _iter_text_cancellable's ReadTimeout-based cancel checking was
broken during token streaming: the Stop button could take up to 120s
to respond instead of 0.5s.
Fix: keep the client's short read timeout (0.5s) for the stream call.
During prefill, catch ReadTimeout in a loop and re-check cancel_event
instead of re-sending the POST (which was the original retry storm).
Once the first bytes arrive, yield the response with a PrependStream
wrapper so iter_text() sees the buffered first chunk.
This preserves both:
- Fast cancel during prefill (via cancel watcher + ReadTimeout loop)
- Fast cancel during streaming (via _iter_text_cancellable's 0.5s
ReadTimeout, which now fires correctly again)
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* fix: swap to short-timeout stream after prefill completes
Address two review issues:
1. _PrependStream did not inherit from httpx.SyncByteStream, so
Response.iter_raw() would raise RuntimeError. Replaced with a
_ShortTimeoutStream that inherits SyncByteStream properly.
2. client.stream() entry itself raises ReadTimeout during slow prefill
(before headers arrive). The previous fix tried to catch this at
the body-read level but missed the connection-level timeout.
New approach: keep the 120s read timeout for client.stream() so the
connection survives long prefills. Once headers arrive, replace the
response stream with _ShortTimeoutStream -- a wrapper that uses a
background reader thread and a Queue with a short get() timeout to
re-raise ReadTimeout at the original 0.5s interval. This way
_iter_text_cancellable's cancel-checking remains responsive during
token streaming while prefill gets the long timeout it needs.
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* fix: move _ShortTimeoutStream before LlamaCppBackend class
The class was placed inside LlamaCppBackend's body, splitting the
class in two and making _codec_mgr and other attributes unreachable.
Move it to module level before LlamaCppBackend.
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* fix: remove _ShortTimeoutStream, use watcher for all cancel
_ShortTimeoutStream had two critical issues:
1. Raising ReadTimeout from a generator kills it -- Python finalizes
generators after an uncaught exception, so the next next() call
hits StopIteration and streaming ends mid-response.
2. The unbounded Queue in the background reader loses backpressure,
causing memory spikes with slow clients.
Simpler approach: use the 120s read timeout for the entire stream and
rely on the cancel watcher thread for all cancellation (both prefill
and streaming). The watcher closes the response on cancel_event,
which unblocks any blocking httpx read within ~0.3s. This eliminates
the need for short timeout tricks entirely.
Cancel latency:
- Prefill: ~0.3s (watcher polls cancel_event every 0.3s)
- Streaming: ~0.3s (same watcher mechanism)
- Both faster than the old 0.5s ReadTimeout approach
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* docs: clarify cancel limitations in _stream_with_retry
The docstrings claimed ~0.3s cancel in all cases, but httpx cannot
interrupt a blocked read before the response object exists. Update
the docstrings to accurately describe the behavior:
- Cancel during prefill (header wait) is deferred until headers arrive
- Cancel during streaming works via response.close() from the watcher
- _iter_text_cancellable docstring updated to reflect the watcher-based
cancel mechanism instead of the old ReadTimeout polling
---------
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
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