[Bugfix] Fix pooling models on CPU backend (#23392)

Signed-off-by: jiang1.li <jiang1.li@intel.com>

vllm/utils/__init__.py

@@ -1440,6 +1440,12 @@ def _patched_set_stream(stream: torch.cuda.Stream) -> None:
 torch.cuda.set_stream = _patched_set_stream
 
 
+class _StreamPlaceholder:
+
+    def __init__(self):
+        self.synchronize = lambda: None
+
+
 def current_stream() -> torch.cuda.Stream:
     """
     replace `torch.cuda.current_stream()` with `vllm.utils.current_stream()`.
@@ -1459,8 +1465,18 @@ def current_stream() -> torch.cuda.Stream:
         # On ROCm using the default 0 stream in combination with RCCL
         # is hurting performance. Therefore creating a dedicated stream
         # per process
-        _current_stream_tls.value = torch.cuda.Stream(
-        ) if current_platform.is_rocm() else torch.cuda.current_stream()
+        if current_platform.is_rocm():
+            _current_stream_tls.value = torch.cuda.Stream()
+        elif current_platform.is_cpu():
+            _current_stream_tls.value = _StreamPlaceholder()
+        else:
+            current_stream = current_platform.current_stream
+            if current_stream is not None:
+                _current_stream_tls.value = current_stream()
+            else:
+                raise ValueError(
+                    "Fail to set current stream, current platform "
+                    "may not support current_stream with torch API")
     return _current_stream_tls.value