diff --git a/functioncall/code/local_verify.py b/functioncall/code/local_verify.py
index d8c9ff6..a174ebb 100644
--- a/functioncall/code/local_verify.py
+++ b/functioncall/code/local_verify.py
@@ -95,7 +95,7 @@ def call_verify(problem, generation, debug, timeout=SINGLE_CASE_EXEC_TIMEOUT):
     return result["result"], result["info"]
 
 
-def code_verify(id2info, generateds, query_ids, debug=False):
+def code_verify(id2info, generateds, query_ids, max_workers=None, debug=False):
     assert len(generateds) == len(query_ids)
     problems = [id2info[qid] for qid in query_ids]
 
@@ -106,8 +106,10 @@ def code_verify(id2info, generateds, query_ids, debug=False):
         infer_args.append((problem, generated, debug, SINGLE_CASE_EXEC_TIMEOUT))
 
     run_results = []
-    num_process = max(1, os.cpu_count() // 8)
-    with concurrent.futures.ProcessPoolExecutor(num_process) as executor:
+    if max_workers is None:
+        max_workers = max(1, os.cpu_count() // 8)
+
+    with concurrent.futures.ProcessPoolExecutor(max_workers) as executor:
         run_results = executor.map(call_verify, *zip(*infer_args))
 
     for run_result in run_results:
diff --git a/realhf/impl/dataset/math_parser.py b/realhf/impl/dataset/math_parser.py
index 5189c5d..30e8bd1 100644
--- a/realhf/impl/dataset/math_parser.py
+++ b/realhf/impl/dataset/math_parser.py
@@ -7,7 +7,7 @@ from typing import List, Union
 
 import regex
 from latex2sympy2 import latex2sympy
-from pebble import ProcessPool
+from pebble import ProcessExpired, ProcessPool
 from sympy import N, simplify
 from sympy.parsing.latex import parse_latex
 from sympy.parsing.sympy_parser import parse_expr
@@ -289,6 +289,7 @@ def strip_string(string, skip_unit=False):
 
     # remove percentage
     string = string.replace("\\%", "")
+    string = string.replace("\%", "")
     string = string.replace("%", "")
 
     # " 0." equivalent to " ." and "{0." equivalent to "{." Alternatively, add "0" if "." is the start of the string
@@ -398,7 +399,7 @@ def extract_answer(pred_str, data_name, use_last_number=True):
         pred = pred_str.split("答案是")[1].strip().split("\n\n")[0].strip()
     else:  # use the last number
         if use_last_number:
-            pattern = r"-?\d*\.?\d+"
+            pattern = "-?\d*\.?\d+"
             pred = re.findall(pattern, pred_str.replace(",", ""))
             if len(pred) >= 1:
                 pred = pred[-1]
@@ -836,6 +837,12 @@ def parse_lines_in_parallel(
                 # print("[debug: timeout]")
                 logger.warning(f"Timeout occurred while justifying the math answer.")
                 x = (0, "timeout", "timeout")
+            except ProcessExpired as e:
+                logger.warning(f"Process terminated abnormally: {e}")
+                x = (0, "error", "error")
+            except Exception as e:
+                logger.warning(f"Other error occurred: {e.__class__.__name__}, {e}")
+                x = (0, "error", "error")
             label = label or x[0]
         labels.append(label)
     return labels
diff --git a/realhf/impl/environment/math_code_single_step_env.py b/realhf/impl/environment/math_code_single_step_env.py
index c07278f..ce9061e 100644
--- a/realhf/impl/environment/math_code_single_step_env.py
+++ b/realhf/impl/environment/math_code_single_step_env.py
@@ -57,6 +57,7 @@ class MathCodeSingleStepEnv(EnvironmentService):
                 self.id2info,
                 answers,
                 [qid for _ in range(group_size)],
+                max_workers=1,
             )
         elif cur_task == "code":
             answers = [extract_code(x) for x in answers]
@@ -65,6 +66,7 @@ class MathCodeSingleStepEnv(EnvironmentService):
                 self.id2info,
                 answers,
                 [qid for _ in range(group_size)],
+                max_workers=1,
             )
         else:
             raise NotImplementedError()