release initial code

Co-authored-by: Ying Sheng <sqy1415@gmail.com>
Co-authored-by: Liangsheng Yin <hnyls2002@gmail.com>
Co-authored-by: Zhiqiang Xie <xiezhq@stanford.edu>
Co-authored-by: parasol-aser <3848358+parasol-aser@users.noreply.github.com>
Co-authored-by: LiviaSun <33578456+ChuyueSun@users.noreply.github.com>
Co-authored-by: Cody Yu <hao.yu.cody@gmail.com>

python/sglang/srt/constrained/fsm_cache.py

@@ -0,0 +1,41 @@
+import threading
+
+from sglang.srt.constrained.fsm import RegexFSM
+from sglang.srt.constrained.tokenizer import TransformerTokenizer
+
+
+def get_fsm(regex, tokenizer, fsm_cache_entry):
+    outlines_tokenizer = TransformerTokenizer(tokenizer)
+    fsm = RegexFSM(regex, outlines_tokenizer)
+    fsm_cache_entry.fsm = fsm
+    fsm_cache_entry.event.set()
+
+
+class FSMCacheEntry:
+    def __init__(self):
+        self.fsm = None
+        self.event = threading.Event()
+
+
+class FSMCache:
+    def __init__(self, tokenizer):
+        self.cache = {}
+        self.tokenizer = tokenizer
+
+    def init_fsm_in_background(self, regex):
+        if regex not in self.cache:
+            self.cache[regex] = FSMCacheEntry()
+            threading.Thread(
+                target=get_fsm,
+                args=(
+                    regex,
+                    self.tokenizer,
+                    self.cache[regex],
+                ),
+            ).start()
+
+    def get_fsm(self, regex):
+        self.init_fsm_in_background(regex)
+        entry = self.cache[regex]
+        entry.event.wait()
+        return entry.fsm