From 9d54258570aff83255173ca9ee1639313fa823e0 Mon Sep 17 00:00:00 2001
From: Lester Hedges <lester.hedges@gmail.com>
Date: Mon, 21 Sep 2026 13:16:01 +0100
Subject: [PATCH] Backport fix from PR #484. [ci skip]

---
 src/sire/base/_progressbar.py |  7 +++++++
 src/sire/mol/_dynamics.py     | 38 ++++++++++++++++-------------------
 2 files changed, 24 insertions(+), 21 deletions(-)

diff --git a/src/sire/base/_progressbar.py b/src/sire/base/_progressbar.py
index 219c05781..870234fde 100644
--- a/src/sire/base/_progressbar.py
+++ b/src/sire/base/_progressbar.py
@@ -3,6 +3,7 @@
 from ..legacy.Base import ProgressBar as _ProgressBar
 
 _cached_in_notebook = None
+_is_silent = False
 
 
 def _in_notebook():
@@ -113,4 +114,10 @@ def set_theme(theme):
 
     @staticmethod
     def set_silent():
+        global _is_silent
+        _is_silent = True
         _ProgressBar.set_silent()
+
+    @staticmethod
+    def is_silent():
+        return _is_silent
diff --git a/src/sire/mol/_dynamics.py b/src/sire/mol/_dynamics.py
index 383300078..545d14090 100644
--- a/src/sire/mol/_dynamics.py
+++ b/src/sire/mol/_dynamics.py
@@ -1405,35 +1405,31 @@ class NeedsMinimiseError(Exception):
 
                 with ThreadPoolExecutor() as pool:
                     while completed < steps_to_run:
-                        block_size = 50
+                        # Each block ends at the next frame or energy save, or the end
+                        # of the run. Shorter blocks are only needed to update the
+                        # progress bar, and cost a GPU sync each.
+                        block_size = steps_to_run - completed
+                        if not ProgressBar.is_silent():
+                            block_size = min(block_size, 50)
 
                         steps_till_frame = self._next_save_frame - (
                             completed + nsteps_before_run
                         )
-                        if steps_till_frame <= 0 or (
-                            steps_till_frame <= block_size
-                            and steps_till_frame <= steps_to_run - completed
-                        ):
-                            save_frame = True
-                            self._next_save_frame += frame_frequency_steps
-                            if frame_frequency_steps < block_size:
-                                block_size = frame_frequency_steps
-                        else:
-                            save_frame = False
-
                         steps_till_energy = self._next_save_energy - (
                             completed + nsteps_before_run
                         )
-                        if steps_till_energy <= 0 or (
-                            steps_till_energy <= block_size
-                            and steps_till_energy <= steps_to_run - completed
-                        ):
-                            save_energy = True
+                        if 0 < steps_till_frame < block_size:
+                            block_size = steps_till_frame
+                        if 0 < steps_till_energy < block_size:
+                            block_size = steps_till_energy
+
+                        save_frame = steps_till_frame <= block_size
+                        if save_frame:
+                            self._next_save_frame += frame_frequency_steps
+
+                        save_energy = steps_till_energy <= block_size
+                        if save_energy:
                             self._next_save_energy += energy_frequency_steps
-                            if energy_frequency_steps < block_size:
-                                block_size = energy_frequency_steps
-                        else:
-                            save_energy = False
 
                         # save the last frame if we're about to exit and the user
                         # has requested it