diff --git a/bind/G4Calo.py b/bind/G4Calo.py
index 2a2c601..ce471c6 100644
--- a/bind/G4Calo.py
+++ b/bind/G4Calo.py
@@ -170,7 +170,8 @@ def run_batch(
         particleSpec: str,
         minEnergy_GeV: float,
         maxEnergy_GeV: float = -1.0,
-        filename: str = ""):
+        filename: str = "",
+        threading_lock = None):
     '''
     splits the batch in jobs depending on how many cores are available and runs mini batches in parallel
     '''
@@ -188,15 +189,15 @@ def run_batch(
     
     nevents = [nEventsPerCore if i < nCores - 1 else nEventsLastCore for i in range(nCores)]
 
-    #the used seeds are stored in the home directory in a file called .seeds.txt
-    # check if file exists, if so, read last seed. If not create it
-    if os.path.exists(os.path.expanduser("~/.g4calo_seeds.txt")):
-        with open(os.path.expanduser("~/.g4calo_seeds.txt"), "r") as f:
-            seed = int(f.read())
-    else:
-        seed = 0
-    with open(os.path.expanduser("~/.g4calo_seeds.txt"), "w") as f:
-        f.write(str(seed + nCores))
+    with threading_lock if threading_lock is not None else contextlib.nullcontext():
+        # check if file exists, if so, read last seed. If not create it
+        if os.path.exists(os.path.expanduser("~/.g4calo_seeds.txt")):
+            with open(os.path.expanduser("~/.g4calo_seeds.txt"), "r") as f:
+                seed = int(f.read())
+        else:
+            seed = 0
+        with open(os.path.expanduser("~/.g4calo_seeds.txt"), "w") as f:
+            f.write(str(seed + nCores))
 
     seed += 1
     print(f"Batch seed: {seed}")