fix: add async to direct_exp_gen avoid infinite loop (#992)

* refactor: convert direct_exp_gen to async and enforce parallel limit

* fix bug

* change coroutine function position

* fix fin_quant's direct_exp_gen

* format with isort

---------

Co-authored-by: Bowen Xian <xianbowen@outlook.com>
Co-authored-by: SunsetWolf <Lv.Linlang@hotmail.com>

rdagent/components/workflow/rd_loop.py

@@ -3,9 +3,11 @@ Model workflow with session control
 It is from `rdagent/app/qlib_rd_loop/model.py` and try to replace `rdagent/app/qlib_rd_loop/RDAgent.py`
 """
 
+import asyncio
 from typing import Any
 
 from rdagent.components.workflow.conf import BasePropSetting
+from rdagent.core.conf import RD_AGENT_SETTINGS
 from rdagent.core.developer import Developer
 from rdagent.core.proposal import (
     Experiment2Feedback,
@@ -55,10 +57,13 @@ class RDLoop(LoopBase, metaclass=LoopMeta):
         return exp
 
     # included steps
-    def direct_exp_gen(self, prev_out: dict[str, Any]):
-        hypo = self._propose()
-        exp = self._exp_gen(hypo)
-        return {"propose": hypo, "exp_gen": exp}
+    async def direct_exp_gen(self, prev_out: dict[str, Any]):
+        while True:
+            if self.get_unfinished_loop_cnt(self.loop_idx) < RD_AGENT_SETTINGS.get_max_parallel():
+                hypo = self._propose()
+                exp = self._exp_gen(hypo)
+                return {"propose": hypo, "exp_gen": exp}
+            await asyncio.sleep(1)
 
     def coding(self, prev_out: dict[str, Any]):
         exp = self.coder.develop(prev_out["direct_exp_gen"]["exp_gen"])