[Sampler] Vectorized sampling (simplified) (#1048)

Co-authored-by: Antoni Baum <antoni.baum@protonmail.com>

vllm/sampling_params.py

@@ -1,9 +1,17 @@
 """Sampling parameters for text generation."""
+from enum import IntEnum
+from functools import cached_property
 from typing import List, Optional, Union
 
 _SAMPLING_EPS = 1e-5
 
 
+class SamplingType(IntEnum):
+    GREEDY = 0
+    RANDOM = 1
+    BEAM = 2
+
+
 class SamplingParams:
     """Sampling parameters for text generation.
 
@@ -166,6 +174,14 @@ class SamplingParams:
         if self.top_k != -1:
             raise ValueError("top_k must be -1 when using greedy sampling.")
 
+    @cached_property
+    def sampling_type(self) -> SamplingType:
+        if self.use_beam_search:
+            return SamplingType.BEAM
+        if self.temperature < _SAMPLING_EPS:
+            return SamplingType.GREEDY
+        return SamplingType.RANDOM
+
     def __repr__(self) -> str:
         return (f"SamplingParams(n={self.n}, "
                 f"best_of={self.best_of}, "