diff --git a/.gitignore b/.gitignore
index c78b060c4a06e8597917b39f67d90fb53f466a29..27ab66f9ec8071c47b818c68404a9b73c924108d 100644
--- a/.gitignore
+++ b/.gitignore
@@ -9,3 +9,4 @@ mace/codegen/opencl_bin/
 mace/codegen/tuning/
 mace/codegen/version/
 build/
+docs/_build/
diff --git a/tools/bazel_adb_run.py b/tools/bazel_adb_run.py
index 88d8c1814b84aaa36e178f2c844ce3675a279d58..2698a9eadf3e28e24b6b5fc851f52ca2eb8516d4 100644
--- a/tools/bazel_adb_run.py
+++ b/tools/bazel_adb_run.py
@@ -86,7 +86,12 @@ def main(unused_args):
         target_socs = set(FLAGS.target_socs.split(','))
     target_devices = sh_commands.adb_devices(target_socs=target_socs)
     if FLAGS.target_socs == "random":
-        target_devices = [random.choice(target_devices)]
+        unlocked_devices = \
+            [d for d in target_devices if not sh_commands.is_device_locked(d)]
+        if len(unlocked_devices) > 0:
+            target_devices = [random.choice(unlocked_devices)]
+        else:
+            target_devices = [random.choice(target_devices)]
 
     target = FLAGS.target
     host_bin_path, bin_name = sh_commands.bazel_target_to_bin(target)
diff --git a/tools/sh_commands.py b/tools/sh_commands.py
index 4c3d16a2b09fdd62f60d00e81f5eab020fcd825b..40cc932a33977fa34c0c3b3b75156001966e871c 100644
--- a/tools/sh_commands.py
+++ b/tools/sh_commands.py
@@ -20,6 +20,22 @@ def make_output_processor(buff):
     return process_output
 
 
+def device_lock_path(serialno):
+    return "/tmp/device-lock-%s" % serialno
+
+
+def device_lock(serialno, timeout=3600):
+    return filelock.FileLock(device_lock_path(serialno), timeout=timeout)
+
+
+def is_device_locked(serialno):
+    try:
+        with device_lock(serialno, timeout=0.000001):
+            return False
+    except filelock.Timeout:
+        return True
+
+
 ################################
 # adb commands
 ################################
@@ -90,12 +106,11 @@ def adb_run(serialno,
     print(
         "====================================================================="
     )
-    lock_path = "/tmp/device-lock-%s" % serialno
-    print("Try to lock ", lock_path)
-    with filelock.FileLock(lock_path, timeout=3600):
-        print("Run on device: %s, %s, %s" % (serialno,
-                                             props["ro.board.platform"],
-                                             props["ro.product.model"]))
+    print("Trying to lock device", serialno)
+    with device_lock(serialno):
+        print("Run on device: %s, %s, %s" %
+              (serialno, props["ro.board.platform"],
+               props["ro.product.model"]))
         sh.adb("-s", serialno, "shell", "rm -rf %s" % device_bin_path)
         sh.adb("-s", serialno, "shell", "mkdir -p %s" % device_bin_path)
         print("Push %s to %s" % (host_bin_full_path, device_bin_full_path))
@@ -111,7 +126,7 @@ def adb_run(serialno,
             "MACE_OUT_OF_RANGE_CHECK=%d MACE_OPENCL_PROFILING=%d "
             "MACE_CPP_MIN_VLOG_LEVEL=%d %s %s" %
             (out_of_range_check, opencl_profiling, vlog_level,
-                device_bin_full_path, args),
+             device_bin_full_path, args),
             _out=process_output,
             _bg=True,
             _err_to_out=True)