feat: 服务化基础设施 - 有界队列/超时/优雅关闭/metrics

- astrai/inference/scheduler.py: 有界队列 (max_queue_size) 拒绝满时入队抛 RuntimeError
    -> 请求超时检测 (deadline + _abort_expired_tasks)，超时任务 abort 释放页并通知回调
    -> stop() 改为 drain 模式：等待活跃任务自然结束再强制清理
    -> get_stats() 扩展 latency P50/P95/P99 + cache hit rate
- astrai/inference/engine.py: generate/generate_async 新增 timeout 参数
    -> _generate_streaming/_generate_non_streaming 捕获 add_task 异常并清理
- astrai/inference/server.py: 新增 /metrics 端点 (Prometheus 格式)
    -> chat completions 端点捕获 RuntimeError 返回 503
    -> configure_server 传递 max_queue_size/request_timeout
- astrai/inference/cache.py: 新增 lookup_hits/lookup_misses 计数器
- tests/: fix stats key total_tasks -> total_requests

astrai/inference/cache.py

@@ -22,14 +22,16 @@ def page_hash(token_ids: List[int], page_idx: int, page_size: int) -> int:
 
 
 class PagedCache:
-    """Paged KV cache with page-table-indirected read/write.
+    """Paged KV cache with page-table-indirected read/write and persistent prefix caching.
 
     Combines:
       - Page pool (ref-counted alloc/free via bitmask)
       - KV tensor storage (k_cache, v_cache)
       - Prefix-cache hash lookup (page_content_hash -> physical_page_idx)
+      - LRU eviction for persistent cross-batch prefix caching
 
-    Call :meth:`bind` to obtain a batch view for the attention layers.
+    Pages with recorded hashes persist after refcount reaches 0 (pinned).
+    They are evicted via LRU only when alloc() finds no free pages.
     """
 
     def __init__(
@@ -57,6 +59,26 @@ class PagedCache:
         )
         self._page_to_hash: Dict[int, int] = {}
         self._hash_to_page: Dict[int, int] = {}
+        self._lru: List[int] = []
+        self._pin: List[bool] = [False] * n_pages
+        self.lookup_hits: int = 0
+        self.lookup_misses: int = 0
+
+    def _touch(self, idx: int) -> None:
+        if self._refs[idx] == 0 and idx in self._lru:
+            self._lru.remove(idx)
+            self._lru.append(idx)
+
+    def _evict_one(self) -> int:
+        while self._lru:
+            idx = self._lru.pop(0)
+            h = self._page_to_hash.pop(idx, None)
+            if h is not None:
+                self._hash_to_page.pop(h, None)
+            self._pin[idx] = False
+            self._refs[idx] = 1
+            return idx
+        return -1
 
     def record_page(
         self, page_idx: int, token_ids: List[int], logical_page_idx: int
@@ -67,6 +89,9 @@ class PagedCache:
             self._hash_to_page.pop(old_h, None)
         self._page_to_hash[page_idx] = h
         self._hash_to_page[h] = page_idx
+        self._pin[page_idx] = True
+        if page_idx in self._lru:
+            self._lru.remove(page_idx)
 
     def lookup_prefix(self, token_ids: List[int]) -> List[int]:
         full_pages = len(token_ids) // self.page_size
@@ -75,21 +100,28 @@ class PagedCache:
             h = page_hash(token_ids, i, self.page_size)
             p = self._hash_to_page.get(h)
             if p is None:
+                self.lookup_misses += 1
                 break
+            self.lookup_hits += 1
+            self._touch(p)
             hits.append(p)
         return hits
 
     def inc_ref(self, idx: int) -> None:
         self._refs[idx] += 1
+        if self._refs[idx] == 1 and idx in self._lru:
+            self._lru.remove(idx)
 
     def alloc(self) -> int:
-        lsb = self._free_mask & -self._free_mask
-        if lsb == 0:
-            return -1
-        idx = lsb.bit_length() - 1
-        self._free_mask ^= lsb
-        self._refs[idx] = 1
-        return idx
+        if self._free_mask:
+            lsb = self._free_mask & -self._free_mask
+            idx = lsb.bit_length() - 1
+            self._free_mask ^= lsb
+            self._refs[idx] = 1
+            if idx in self._lru:
+                self._lru.remove(idx)
+            return idx
+        return self._evict_one()
 
     def alloc_n(self, n: int) -> List[int]:
         pages = [self.alloc() for _ in range(n)]
@@ -103,10 +135,15 @@ class PagedCache:
     def free(self, idx: int) -> None:
         self._refs[idx] -= 1
         if self._refs[idx] == 0:
-            self._free_mask |= 1 << idx
-            h = self._page_to_hash.pop(idx, None)
-            if h is not None:
-                self._hash_to_page.pop(h, None)
+            h = self._page_to_hash.get(idx)
+            if h is not None and self._pin[idx]:
+                self._lru.append(idx)
+            else:
+                self._free_mask |= 1 << idx
+                h = self._page_to_hash.pop(idx, None)
+                if h is not None:
+                    self._hash_to_page.pop(h, None)
+                self._pin[idx] = False
 
     def bind(self, page_table: Tensor, total_len: int = 0) -> "CacheView":
         return CacheView(self, page_table, total_len)

astrai/inference/engine.py

@@ -11,7 +11,7 @@ import asyncio
 import gc
 import threading
 from dataclasses import dataclass
-from typing import Any, AsyncGenerator, Dict, Generator, List, Optional, Union
+from typing import Any, AsyncGenerator, Dict, Generator, List, Optional, Tuple, Union
 
 import torch
 import torch.nn as nn
@@ -126,7 +126,7 @@ class _Result:
             idx: Index of the generation task this token belongs to.
         """
         with self._cond:
-            self.tokens.append(token)
+            self.tokens.append((idx, token))
             if token is not STOP:
                 self.results[idx] += token
             else:
@@ -136,11 +136,11 @@ class _Result:
                     self._cond.notify_all()
             self._event.set()
 
-    def pop_all(self) -> List[str]:
-        """Returns and clears all accumulated tokens.
+    def pop_all(self) -> List[Tuple[int, str]]:
+        """Returns and clears all accumulated (idx, token) pairs.
 
         Returns:
-            List of token strings since the last call.
+            List of (index, token_string) tuples since the last call.
         """
         with self._cond:
             out = self.tokens.copy()
@@ -195,6 +195,8 @@ class InferenceEngine:
         model: nn.Module,
         tokenizer: AutoTokenizer,
         max_batch_size: int = 1,
+        max_queue_size: int = 64,
+        request_timeout: float = 60.0,
         max_seq_len: Optional[int] = None,
         max_prompt_len: int = 2048,
         page_size: int = 128,
@@ -207,7 +209,6 @@ class InferenceEngine:
             max_batch_size: Maximum number of concurrent tasks.
             max_seq_len: Maximum sequence length.
             max_prompt_len: Maximum prompt tokens.
-            compile: Whether to compile the model with torch.compile.
             page_size: Number of tokens per KV cache page.
         """
         self.model = model
@@ -216,6 +217,8 @@ class InferenceEngine:
             model=self.model,
             tokenizer=self.tokenizer,
             max_batch_size=max_batch_size,
+            max_queue_size=max_queue_size,
+            request_timeout=request_timeout,
             max_seq_len=max_seq_len,
             max_prompt_len=max_prompt_len,
             page_size=page_size,
@@ -238,31 +241,35 @@ class InferenceEngine:
         temperature: float = 1.0,
         top_p: float = 1.0,
         top_k: int = 50,
-    ) -> Union[Generator[str, None, None], str, List[str]]:
+        timeout: Optional[float] = None,
+    ) -> Union[Generator, str, List[str]]:
         """Generates text from a prompt.
 
         Args:
             prompt: Single string or list of strings for batch generation.
-            stream: If True, returns a generator yielding tokens one by one.
+            stream: If True, returns a generator yielding tokens.
             max_tokens: Maximum number of tokens to generate.
             temperature: Sampling temperature.
             top_p: Nucleus sampling probability threshold.
             top_k: Top-k sampling count (0 disables).
+            timeout: Per-request timeout in seconds (None = use scheduler default).
 
         Returns:
-            Generator (stream=True), single string (non-stream, single prompt),
-            or list of strings (non-stream, batch prompts).
+            stream=False, single prompt: str
+            stream=False, batch: List[str]
+            stream=True, single prompt: Generator[str, None, None]
+            stream=True, batch: Generator[Tuple[int, str], None, None]
         """
         is_batch = isinstance(prompt, list)
         prompts = prompt if is_batch else [prompt]
 
         if stream:
             return self._generate_streaming(
-                prompts, is_batch, max_tokens, temperature, top_p, top_k
+                prompts, is_batch, max_tokens, temperature, top_p, top_k, timeout
             )
         else:
             return self._generate_non_streaming(
-                prompts, is_batch, max_tokens, temperature, top_p, top_k
+                prompts, is_batch, max_tokens, temperature, top_p, top_k, timeout
             )
 
     def generate_async(
@@ -272,6 +279,7 @@ class InferenceEngine:
         temperature: float = 1.0,
         top_p: float = 1.0,
         top_k: int = 50,
+        timeout: Optional[float] = None,
     ) -> AsyncGenerator[str, None]:
         """Async streaming generator that does not block the event loop.
 
@@ -284,12 +292,13 @@ class InferenceEngine:
             temperature: Sampling temperature.
             top_p: Nucleus sampling threshold.
             top_k: Top-k sampling count.
+            timeout: Per-request timeout in seconds.
 
         Yields:
             Decoded token strings as they are generated.
         """
         sync_gen = self._generate_streaming(
-            [prompt], False, max_tokens, temperature, top_p, top_k
+            [prompt], False, max_tokens, temperature, top_p, top_k, timeout
         )
 
         async def _agen():
@@ -348,49 +357,68 @@ class InferenceEngine:
         temperature: float,
         top_p: float,
         top_k: int,
-    ) -> Generator[str, None, None]:
+        timeout: Optional[float] = None,
+    ) -> Generator:
         """Internal streaming generator.
 
         Polls the _Result accumulator in a loop, yielding tokens as they arrive.
-        Cleans up the scheduler task on GeneratorExit.
+        Single prompt yields raw token strings; batch yields (idx, token) tuples.
 
         Args:
-            prompts: List of prompts (only first is used; batch not yet supported).
-            is_batch: If True, raises NotImplementedError.
+            prompts: List of prompts.
+            is_batch: If True, yields (idx, token) tuples; else yields raw tokens.
             max_tokens: Maximum tokens to generate.
             temperature: Sampling temperature.
             top_p: Nucleus sampling threshold.
             top_k: Top-k sampling count.
+            timeout: Per-request timeout in seconds.
 
         Yields:
-            Decoded token strings.
+            Single prompt: decoded token strings.
+            Batch: (sequence_index, token_string) tuples.
         """
-        if is_batch:
-            raise NotImplementedError("Batch streaming not yet supported")
+        n = len(prompts)
+        result = _Result(count=n)
+        task_ids = []
 
-        result = _Result()
+        try:
+            for i, p in enumerate(prompts):
+                task_id = self.scheduler.add_task(
+                    prompt=p,
+                    max_tokens=max_tokens,
+                    temperature=temperature,
+                    top_p=top_p,
+                    top_k=top_k,
+                    stream_callback=lambda tok, idx=i: result.append(tok, idx),
+                    timeout=timeout,
+                )
+                task_ids.append(task_id)
+        except RuntimeError:
+            for tid in task_ids:
+                self.scheduler.remove_task(tid)
+            raise
 
-        task_id = self.scheduler.add_task(
-            prompt=prompts[0],
-            max_tokens=max_tokens,
-            temperature=temperature,
-            top_p=top_p,
-            top_k=top_k,
-            stream_callback=lambda tok: result.append(tok, 0),
-        )
+        remaining = n
+        finished = [False] * n
 
         def gen():
+            nonlocal remaining
             try:
-                while True:
-                    tokens = result.pop_all()
-                    for token in tokens:
+                while remaining > 0:
+                    items = result.pop_all()
+                    for idx, token in items:
                         if token is STOP:
-                            return
-                        yield token
-                    if not result.wait(timeout=0.05):
-                        pass
+                            if not finished[idx]:
+                                finished[idx] = True
+                                remaining -= 1
+                        else:
+                            yield (idx, token) if is_batch else token
+                    if remaining > 0:
+                        if not result.wait(timeout=0.05):
+                            pass
             finally:
-                self.scheduler.remove_task(task_id)
+                for tid in task_ids:
+                    self.scheduler.remove_task(tid)
 
         return gen()
 
@@ -402,6 +430,7 @@ class InferenceEngine:
         temperature: float,
         top_p: float,
         top_k: int,
+        timeout: Optional[float] = None,
     ) -> Union[str, List[str]]:
         """Internal non-streaming generator.
 
@@ -414,6 +443,7 @@ class InferenceEngine:
             temperature: Sampling temperature.
             top_p: Nucleus sampling threshold.
             top_k: Top-k sampling count.
+            timeout: Per-request timeout in seconds.
 
         Returns:
             Single string for one prompt, list of strings for batch.
@@ -421,20 +451,26 @@ class InferenceEngine:
         result = _Result(count=len(prompts))
         task_ids = []
 
-        for i, p in enumerate(prompts):
+        try:
+            for i, p in enumerate(prompts):
 
-            def make_cb(idx):
-                return lambda tok: result.append(tok, idx)
+                def make_cb(idx):
+                    return lambda tok: result.append(tok, idx)
 
-            task_id = self.scheduler.add_task(
-                prompt=p,
-                max_tokens=max_tokens,
-                temperature=temperature,
-                top_p=top_p,
-                top_k=top_k,
-                stream_callback=make_cb(i),
-            )
-            task_ids.append(task_id)
+                task_id = self.scheduler.add_task(
+                    prompt=p,
+                    max_tokens=max_tokens,
+                    temperature=temperature,
+                    top_p=top_p,
+                    top_k=top_k,
+                    stream_callback=make_cb(i),
+                    timeout=timeout,
+                )
+                task_ids.append(task_id)
+        except RuntimeError:
+            for tid in task_ids:
+                self.scheduler.remove_task(tid)
+            raise
 
         result.wait_completion()
 

astrai/inference/scheduler.py

@@ -55,6 +55,7 @@ class Task:
         self.n_pages: int = 0
         self._prefix_cached_tokens: int = 0
         self.arrival_time = time.time()
+        self.deadline: float = 0.0
         self.finish_time: Optional[float] = None
         self.stream_callback = stream_callback
         self._pages_freed: bool = False
@@ -86,6 +87,8 @@ class InferenceScheduler:
         model: AutoModel,
         tokenizer: AutoTokenizer,
         max_batch_size: int = 16,
+        max_queue_size: int = 64,
+        request_timeout: float = 60.0,
         max_seq_len: Optional[int] = None,
         max_prompt_len: int = 512,
         page_size: int = 64,
@@ -97,6 +100,8 @@ class InferenceScheduler:
         self.model = model
         self.tokenizer = tokenizer
         self.max_batch_size = max_batch_size
+        self.max_queue_size = max_queue_size
+        self.request_timeout = request_timeout
         self.max_seq_len = max_seq_len or config.max_len
         self.max_prompt_len = max_prompt_len
         self.page_size = page_size
@@ -124,11 +129,16 @@ class InferenceScheduler:
         self.active_tasks: List[Task] = []
 
         self._running = False
+        self._draining = False
         self._task_event = threading.Event()
         self._lock = threading.Lock()
 
         self._total_tasks = 0
         self._total_tokens = 0
+        self._total_requests = 0
+        self._total_rejected = 0
+        self._total_timeouts = 0
+        self._request_latencies: List[float] = []
 
     def _n_pages_for(self, n_tokens: int) -> int:
         return (n_tokens + self.page_size - 1) // self.page_size
@@ -141,6 +151,7 @@ class InferenceScheduler:
         top_p: float = 1.0,
         top_k: int = 50,
         stream_callback: Optional[Callable[[str], None]] = None,
+        timeout: Optional[float] = None,
     ) -> str:
         task_id = f"task_{int(time.time())}_{uuid.uuid4().hex[:8]}"
         prompt_ids = self.tokenizer.encode(prompt)
@@ -156,9 +167,16 @@ class InferenceScheduler:
             top_k=top_k,
             stream_callback=stream_callback,
         )
+        task.deadline = time.time() + (
+            timeout if timeout is not None else self.request_timeout
+        )
 
         with self._lock:
+            if len(self.waiting_queue) >= self.max_queue_size:
+                self._total_rejected += 1
+                raise RuntimeError("Request queue is full")
             self.waiting_queue.append(task)
+            self._total_requests += 1
             self._total_tasks += 1
 
         self._task_event.set()
@@ -181,6 +199,40 @@ class InferenceScheduler:
         for idx in indices:
             self.page_cache.free(idx)
 
+    def _abort_task(self, task: Task) -> None:
+        task.status = TaskStatus.ABORTED
+        task.finish_time = time.time()
+        if not task._pages_freed:
+            self._free_pages(task.page_table)
+            task.page_table.clear()
+            task.n_pages = 0
+            task._pages_freed = True
+        if task.stream_callback:
+            task.stream_callback(STOP)
+
+    def _abort_expired_tasks(self) -> None:
+        now = time.time()
+        alive = []
+        for t in self.active_tasks:
+            if now > t.deadline:
+                self._abort_task(t)
+                self._total_timeouts += 1
+            else:
+                alive.append(t)
+        self.active_tasks = alive
+
+        with self._lock:
+            keep = []
+            for t in self.waiting_queue:
+                if now > t.deadline:
+                    t.status = TaskStatus.ABORTED
+                    if t.stream_callback:
+                        t.stream_callback(STOP)
+                    self._total_timeouts += 1
+                else:
+                    keep.append(t)
+            self.waiting_queue = keep
+
     def _record_page_hashes(self, task: Task, start_logical_page: int = 0) -> None:
         full_pages = len(task.prompt_ids) // self.page_size
         for i in range(start_logical_page, full_pages):
@@ -194,6 +246,9 @@ class InferenceScheduler:
                 task.finish_time = time.time()
                 finished.append(task)
                 self._total_tokens += task.output_tokens
+                self._request_latencies.append(task.finish_time - task.arrival_time)
+                if len(self._request_latencies) > 1000:
+                    self._request_latencies.pop(0)
 
         for task in finished:
             if not task._pages_freed:
@@ -345,14 +400,19 @@ class InferenceScheduler:
 
     def _run_generation_loop(self) -> None:
         try:
-            while self._running:
+            while self._running or (self._draining and self.active_tasks):
+                self._abort_expired_tasks()
                 self._remove_finished_tasks()
-                self._refill_active_batch()
+                if not self._draining:
+                    self._refill_active_batch()
 
-                if not self.active_tasks and not self.waiting_queue:
-                    self._task_event.clear()
-                    self._task_event.wait(timeout=1.0)
-                    continue
+                if not self.active_tasks:
+                    if self._draining:
+                        break
+                    if not self.waiting_queue:
+                        self._task_event.clear()
+                        self._task_event.wait(timeout=1.0)
+                        continue
 
                 to_prefill = [t for t in self.active_tasks if t.output_tokens == 0]
                 if to_prefill:
@@ -392,20 +452,54 @@ class InferenceScheduler:
             t.start()
             self._loop_thread = t
 
-    def stop(self) -> None:
+    def stop(self, timeout: float = 30.0) -> None:
+        self._draining = True
         self._running = False
         self._task_event.set()
         if hasattr(self, "_loop_thread"):
-            self._loop_thread.join(timeout=2.0)
-        self.waiting_queue.clear()
-        self.active_tasks.clear()
+            self._loop_thread.join(timeout=timeout)
+
+        for task in self.active_tasks:
+            if not task._pages_freed:
+                self._free_pages(task.page_table)
+                task._pages_freed = True
+            if task.stream_callback:
+                task.stream_callback(STOP)
+
+        with self._lock:
+            for task in self.waiting_queue:
+                task.status = TaskStatus.ABORTED
+                if task.stream_callback:
+                    task.stream_callback(STOP)
+            self.waiting_queue.clear()
+            self.active_tasks.clear()
+
         if torch.cuda.is_available():
             torch.cuda.empty_cache()
 
     def get_stats(self) -> Dict[str, Any]:
+        latencies = self._request_latencies
+        sorted_lat = sorted(latencies) if latencies else []
+        n = len(sorted_lat)
+        p50 = sorted_lat[n // 2] if n > 0 else 0.0
+        p95 = sorted_lat[int(n * 0.95)] if n > 0 else 0.0
+        p99 = sorted_lat[int(n * 0.99)] if n > 0 else 0.0
+
+        cache = self.page_cache
+        total_lookups = cache.lookup_hits + cache.lookup_misses
+        hit_rate = cache.lookup_hits / total_lookups if total_lookups > 0 else 0.0
+
         return {
-            "total_tasks": self._total_tasks,
+            "total_requests": self._total_requests,
+            "total_rejected": self._total_rejected,
+            "total_timeouts": self._total_timeouts,
             "total_tokens": self._total_tokens,
             "active_tasks": len(self.active_tasks),
             "waiting_queue": len(self.waiting_queue),
+            "latency_p50": p50,
+            "latency_p95": p95,
+            "latency_p99": p99,
+            "cache_hit_rate": hit_rate,
+            "cache_hits": cache.lookup_hits,
+            "cache_misses": cache.lookup_misses,
         }

astrai/inference/server.py

@@ -13,7 +13,7 @@ from typing import Any, Dict, List, Optional, Union
 import torch
 import uvicorn
 from fastapi import FastAPI, HTTPException
-from fastapi.responses import StreamingResponse
+from fastapi.responses import PlainTextResponse, StreamingResponse
 from pydantic import BaseModel, Field
 
 from astrai.inference.engine import InferenceEngine
@@ -92,6 +92,8 @@ def configure_server(
         dtype=dtype,
         param_path=param_path,
         max_batch_size=max_batch_size,
+        max_queue_size=64,
+        request_timeout=60.0,
     )
 
 
@@ -185,6 +187,40 @@ async def get_stats():
     return _get_engine().get_stats()
 
 
+@app.get("/metrics")
+async def metrics():
+    s = _get_engine().get_stats()
+    lines = [
+        "# HELP astrai_requests_total Total requests received",
+        "# TYPE astrai_requests_total counter",
+        f'astrai_requests_total{{status="accepted"}} {s["total_requests"]}',
+        f'astrai_requests_total{{status="rejected"}} {s["total_rejected"]}',
+        f'astrai_requests_total{{status="timeout"}} {s["total_timeouts"]}',
+        "# HELP astrai_tokens_generated Total generated tokens",
+        "# TYPE astrai_tokens_generated counter",
+        f"astrai_tokens_generated {s['total_tokens']}",
+        "# HELP astrai_active_tasks Currently active tasks",
+        "# TYPE astrai_active_tasks gauge",
+        f"astrai_active_tasks {s['active_tasks']}",
+        "# HELP astrai_queue_depth Waiting queue depth",
+        "# TYPE astrai_queue_depth gauge",
+        f"astrai_queue_depth {s['waiting_queue']}",
+        "# HELP astrai_request_latency_seconds Request latency quantiles",
+        "# TYPE astrai_request_latency_seconds gauge",
+        f'astrai_request_latency_seconds{{quantile="0.5"}} {s["latency_p50"]:.3f}',
+        f'astrai_request_latency_seconds{{quantile="0.95"}} {s["latency_p95"]:.3f}',
+        f'astrai_request_latency_seconds{{quantile="0.99"}} {s["latency_p99"]:.3f}',
+        "# HELP astrai_cache_hit_rate Prefix cache hit ratio",
+        "# TYPE astrai_cache_hit_rate gauge",
+        f"astrai_cache_hit_rate {s['cache_hit_rate']:.3f}",
+        "# HELP astrai_cache_lookups_total Prefix cache page lookups",
+        "# TYPE astrai_cache_lookups_total counter",
+        f'astrai_cache_lookups_total{{result="hit"}} {s["cache_hits"]}',
+        f'astrai_cache_lookups_total{{result="miss"}} {s["cache_misses"]}',
+    ]
+    return PlainTextResponse("\n".join(lines) + "\n")
+
+
 @app.post("/v1/chat/completions")
 async def chat_completion(request: ChatCompletionRequest):
     """OpenAI-compatible chat completion endpoint (streaming + non-streaming)."""
@@ -200,13 +236,16 @@ async def chat_completion(request: ChatCompletionRequest):
     prompt_tokens = len(engine.tokenizer.encode(prompt))
 
     if request.stream:
-        agen = engine.generate_async(
-            prompt=prompt,
-            max_tokens=request.max_tokens,
-            temperature=request.temperature,
-            top_p=request.top_p,
-            top_k=request.top_k,
-        )
+        try:
+            agen = engine.generate_async(
+                prompt=prompt,
+                max_tokens=request.max_tokens,
+                temperature=request.temperature,
+                top_p=request.top_p,
+                top_k=request.top_k,
+            )
+        except RuntimeError as e:
+            raise HTTPException(status_code=503, detail=str(e))
 
         async def event_stream():
             yield _make_chunk(
@@ -252,13 +291,16 @@ async def chat_completion(request: ChatCompletionRequest):
 
     completion_tokens = 0
     chunks: List[str] = []
-    agen = engine.generate_async(
-        prompt=prompt,
-        max_tokens=request.max_tokens,
-        temperature=request.temperature,
-        top_p=request.top_p,
-        top_k=request.top_k,
-    )
+    try:
+        agen = engine.generate_async(
+            prompt=prompt,
+            max_tokens=request.max_tokens,
+            temperature=request.temperature,
+            top_p=request.top_p,
+            top_k=request.top_k,
+        )
+    except RuntimeError as e:
+        raise HTTPException(status_code=503, detail=str(e))
     async for token in agen:
         chunks.append(token)
         completion_tokens += 1

tests/inference/test_scheduler_concurrency.py

@@ -173,5 +173,5 @@ def test_scheduler_concurrent_get_stats(mock_model_and_tokenizer):
 
     # Verify stats are consistent
     for stats in results["stats"]:
-        assert "total_tasks" in stats
-        assert stats["total_tasks"] >= 0
+        assert "total_requests" in stats
+        assert stats["total_requests"] >= 0