Change logging so that the messages appear once on thread status change

example.py

@@ -8,11 +8,19 @@ def sleep(t):
 if __name__ == '__main__':
     print("Starting the deadlocks monitoring")
     monitoring_thread = start_monitoring(seconds_frozen=1)
+    print("Sleep 3 seconds in custom func")
     sleep(3)
-    time.sleep(2)
+    print("Sleep 3 seconds")
+    time.sleep(3)
+    print("Sleep 3 seconds")
+    time.sleep(3)
+
     print("Stopping the deadlocks monitoring")
     # This may be useful when working in shell.
     monitoring_thread.stop()
+    print("Sleep 3 seconds")
+    time.sleep(3)
+    print("Sleep 3 seconds")
     time.sleep(3)
 
     print("Exiting")

hanging_threads.py

@@ -53,6 +53,14 @@ def is_stopped(self):
         return self._stopped
 
 
+def get_current_frames():
+    """Return current threads prepared for further processing"""
+    return dict(
+        (thread_id, {'frame': thread2list(frame), 'time': None})
+        for thread_id, frame in sys._current_frames().items()
+    )
+
+
 def frame2string(frame):
     """Return info about frame
 
@@ -75,7 +83,7 @@ def frame2string(frame):
 
 
 def thread2list(frame):
-    """Return list with string frame representation of each fame of thread"""
+    """Return list with string frame representation of each frame of thread"""
     l = []
     while frame:
         l.insert(0, frame2string(frame))
@@ -91,35 +99,65 @@ def monitor(seconds_frozen, tests_per_second):
     of test_per_second parameter
     """
     current_thread = threading.current_thread()
-    self = get_ident()
-    old_threads = {}
+    hanging_threads = set()
+    old_threads = {}  # Threads found on previous iteration.
+
     while not current_thread.is_stopped():
+        new_threads = get_current_frames()
+
+        # Report died threads.
+        for thread_id in old_threads.keys():
+            if thread_id not in new_threads and thread_id in hanging_threads:
+                log_died_thread(thread_id)
+
+        # Process live threads.
         time.sleep(1. / tests_per_second)
         now = time.time()
         then = now - seconds_frozen
-        frames = sys._current_frames()
-        new_threads = {}
-        for frame_id, frame in frames.items():
-            new_threads[frame_id] = thread2list(frame)
-        for thread_id, frame_list in new_threads.items():
-            if thread_id == self: continue
-            if thread_id not in old_threads or \
-               frame_list != old_threads[thread_id][0]:
-                new_threads[thread_id] = (frame_list, now)
-            elif old_threads[thread_id][1] < then:
-                print_frame_list(frame_list, thread_id)
+        for thread_id, thread_data in new_threads.items():
+            # Don't report the monitor thread.
+            if thread_id == current_thread.ident:
+                continue
+            frame = thread_data['frame']
+            # If thread is new or it's stack is changed then update time.
+            if (thread_id not in old_threads or
+                    frame != old_threads[thread_id]['frame']):
+                thread_data['time'] = now
+                # If the thread was hanging then report awaked thread.
+                if thread_id in hanging_threads:
+                    hanging_threads.remove(thread_id)
+                    log_awaked_thread(thread_id)
             else:
-                new_threads[thread_id] = old_threads[thread_id]
+                # If stack is not changed then keep old time.
+                last_change_time = old_threads[thread_id]['time']
+                thread_data['time'] = last_change_time
+                # Check if this is a new hanging thread.
+                if (thread_id not in hanging_threads and
+                        last_change_time < then):
+                    # Gotcha!
+                    hanging_threads.add(thread_id)
+                    # Report the hanged thread.
+                    log_hanged_thread(thread_id, frame)
         old_threads = new_threads
 
 
-def print_frame_list(frame_list, frame_id):
+def log_hanged_thread(thread_id, frame):
     """Print the stack trace of the deadlock after hanging `seconds_frozen`"""
-    sys.stderr.write('-' * 20 + 
-                     'Thread {0}'.format(frame_id).center(20) +
-                     '-' * 20 +
-                     '\n' + 
-                     ''.join(frame_list))
+    write_log('Thread {0} hangs '.format(thread_id), ''.join(frame))
+
+
+def log_awaked_thread(thread_id):
+    write_log('Thread {0} awaked'.format(thread_id))
+
+
+def log_died_thread(thread_id):
+    write_log('Thread {0} died  '.format(thread_id))
+
+
+def write_log(title, message=''):
+    sys.stderr.write(''.join([
+        title.center(40).center(60, '-'), '\n', message
+    ]))
 
 
 def start_monitoring(seconds_frozen=SECONDS_FROZEN,