diff --git a/alf/environments/dmc_gym_wrapper.py b/alf/environments/dmc_gym_wrapper.py
index 1c68cc090..ca33fa019 100644
--- a/alf/environments/dmc_gym_wrapper.py
+++ b/alf/environments/dmc_gym_wrapper.py
@@ -16,6 +16,43 @@
 """
 
 from functools import partial
+import ctypes
+import os
+import subprocess
+import sys
+
+# Preload GLFW library on macOS before importing dm_control/glfw
+if sys.platform == 'darwin':
+    glfw_lib_path = None
+    # Check common Homebrew locations
+    for lib_dir in ['/opt/homebrew/lib', '/usr/local/lib']:
+        candidate = os.path.join(lib_dir, 'libglfw.dylib')
+        if os.path.exists(candidate):
+            glfw_lib_path = candidate
+            break
+    # Fall back to brew --prefix
+    if glfw_lib_path is None:
+        try:
+            result = subprocess.run(['brew', '--prefix', 'glfw'],
+                                    capture_output=True,
+                                    text=True)
+            if result.returncode == 0:
+                candidate = os.path.join(result.stdout.strip(), 'lib',
+                                         'libglfw.dylib')
+                if os.path.exists(candidate):
+                    glfw_lib_path = candidate
+        except Exception:
+            pass
+    # Tell glfw Python package where to find the library
+    if glfw_lib_path is None:
+        raise ImportError(
+            "Could not find libglfw.dylib on macOS. "
+            "Install with: brew install glfw && pip install glfw")
+    os.environ['PYGLFW_LIBRARY'] = glfw_lib_path
+    try:
+        ctypes.CDLL(glfw_lib_path, mode=ctypes.RTLD_GLOBAL)
+    except OSError as e:
+        raise ImportError(f"Failed to load {glfw_lib_path}: {e}")
 
 import gym
 from gym import spaces
@@ -23,12 +60,12 @@
 import numpy as np
 from typing import Dict, Optional, Any
 
-try:
-    import dm_control
-    from dm_control import suite
-    import dm_env
-except ImportError:
-    dm_control = None
+# try:
+import dm_control
+from dm_control import suite
+import dm_env
+# except ImportError:
+#     dm_control = None
 
 
 def _dmc_spec_to_box(spec):
diff --git a/alf/environments/process_environment.py b/alf/environments/process_environment.py
index ef182caed..70cb513ab 100644
--- a/alf/environments/process_environment.py
+++ b/alf/environments/process_environment.py
@@ -23,6 +23,7 @@
 from functools import partial
 import multiprocessing
 import os
+import subprocess
 import sys
 import threadpoolctl
 import torch
@@ -39,12 +40,23 @@
 import pathlib
 
 DIR = pathlib.Path(__file__).parent.absolute()
+boost_include = os.path.join(os.path.expanduser('~'),
+                             'opt/homebrew/opt/boost/include')
+if not os.path.exists(boost_include):
+    brew_boost = subprocess.run(['brew', '--prefix', 'boost'],
+                                capture_output=True,
+                                text=True)
+    if brew_boost.returncode == 0:
+        boost_include = os.path.join(brew_boost.stdout.strip(), 'include')
+extra_cflags = [
+    '-O3', '-Wall', '-shared', '-std=c++17', '-fPIC', '-fvisibility=hidden'
+]
+if os.path.exists(boost_include):
+    extra_cflags.append(f'-I{boost_include}')
 _penv = lazy_load_extension(
     name="penv",
     sources=[os.path.join(DIR, "parallel_environment.cpp")],
-    extra_cflags=[
-        '-O3', '-Wall', '-shared', '-std=c++17', '-fPIC', '-fvisibility=hidden'
-    ],
+    extra_cflags=extra_cflags,
     verbose=True)
 
 FLAGS = flags.FLAGS
diff --git a/alf/networks/preprocessors.py b/alf/networks/preprocessors.py
index f61408c7b..21a524b6b 100644
--- a/alf/networks/preprocessors.py
+++ b/alf/networks/preprocessors.py
@@ -105,7 +105,7 @@ def forward(self, inputs, state=()):
             Tensor or TensorSpec: if ``Tensor``, the returned is the preprocessed
                 result; otherwise it's the tensor spec of the result.
         """
-        assert state is (), \
+        assert state == (), \
             "The preprocessor is assumed to be stateless currently."
 
         ret = self._preprocess(inputs)
diff --git a/alf/trainers/policy_trainer.py b/alf/trainers/policy_trainer.py
index 7454a2810..1f6ef080d 100644
--- a/alf/trainers/policy_trainer.py
+++ b/alf/trainers/policy_trainer.py
@@ -22,7 +22,6 @@
 import os
 from pathlib import Path
 import re
-import signal
 import threading
 import sys
 from typing import Callable
@@ -324,31 +323,7 @@ def train(self):
 
         self._checkpoint_requested = False
         self._evaluation_requested = False
-        if threading.current_thread() == threading.main_thread():
-            signal.signal(signal.SIGUSR2, self._request_checkpoint)
-            # kill -12 PID
-            logging.info(
-                "Use `kill -%s %s` to request checkpoint during training." %
-                (int(signal.SIGUSR2), self._pid))
-
         self._video_clip_requested = False
-        if threading.current_thread() == threading.main_thread():
-            signal.signal(signal.SIGRTMIN, self._request_video_clip)
-            # kill -34 PID
-            logging.info(
-                ("Use `kill -%s %s` to request video-clip during training. "
-                 f"The videos will be saved at `{self._train_dir}/train/video/"
-                 ) % (int(signal.SIGRTMIN), self._pid))
-
-        if (threading.current_thread() == threading.main_thread()
-                and PerProcessContext().ddp_rank <= 0):
-            # Debugging in subprocesses is not supported because they don't have
-            # stdin.
-            # kill -10 PID
-            signal.signal(signal.SIGUSR1, self._request_debug)
-            logging.info("Use `kill -%s %s` to request debugging." %
-                         (int(signal.SIGUSR1), self._pid))
-
         checkpoint_saved = False
         try:
             if self._config.profiling:
diff --git a/alf/utils/common.py b/alf/utils/common.py
index 3153a2cfd..d05d78157 100644
--- a/alf/utils/common.py
+++ b/alf/utils/common.py
@@ -16,6 +16,7 @@
 from absl import flags
 from absl import logging
 import contextlib
+import platform
 import copy
 import ctypes
 import ctypes.util
@@ -109,6 +110,8 @@ def allow_child_to_ptrace(child_pid: int) -> None:
 
         cat /proc/sys/kernel/yama/ptrace_scope
     """
+    if platform.system() != "Linux":
+        return
 
     libc = ctypes.CDLL(ctypes.util.find_library("c"), use_errno=True)