python-smpplib
@@ -16,7 +16,7 @@
     url='https://github.com/python-smpplib/python-smpplib',
     description='SMPP library for python',
     packages=find_packages(),
-    install_requires=['six'],
+    install_requires=['six', 'monotonic'],
     extras_require=dict(
         tests=('typing; python_version < "3.5"', 'pytest', 'mock'),
     ),

@@ -19,12 +19,14 @@
 """SMPP client module"""
 
 import binascii
+import collections
 import logging
 import select
 import socket
 import struct
 import warnings
 
+from monotonic import monotonic
 from smpplib import consts, exceptions, smpp
 
 
@@ -91,7 +93,6 @@ def __init__(
         else:
             self.allow_unknown_opt_params = allow_unknown_opt_params
 
-
         self._socket = self._create_socket()
 
     def __enter__(self):
@@ -301,7 +302,7 @@ def set_message_received_handler(self, func):
     def set_message_sent_handler(self, func):
         """Set new function to handle message sent event"""
         self.message_sent_handler = func
-        
+
     def set_query_resp_handler(self, func):
         """Set new function to handle query resp event"""
         self.query_resp_handler = func
@@ -421,3 +422,73 @@ def query_message(self, **kwargs):
         qsm = smpp.make_pdu('query_sm', client=self, **kwargs)
         self.send_pdu(qsm)
         return qsm
+
+
+class ThreadSafeClient(Client):
+    should_stop = False
+
+    def __init__(self, *args, **kwargs):
+        # Socket polling period
+        select_timeout = kwargs.get('select_timeout', 1.0)
+
+        super(ThreadSafeClient, self).__init__(*args, **kwargs)
+
+        self._select_timeout = select_timeout
+
+        self._send_queue = collections.deque()
+        self._read_sock, self._send_sock = socket.socketpair()
+
+        # It will help not to spam the server
+        self._last_active_time = 0.0
+
+    def accept(self, obj):
+        """Accept an object"""
+        raise NotImplementedError('not implemented')
+
+    def send_pdu(self, pdu, send_later=False):
+        if send_later:
+            self._send_queue.append(pdu)
+            self._send_sock.send(b'\x00')
+            return True
+        else:
+            pdu_sent = super(ThreadSafeClient, self).send_pdu(pdu)
+            self._last_active_time = monotonic()
+            return pdu_sent
+
+    def send_message(self, send_later=True, **kwargs):
+        submit_sm_pdu = smpp.make_pdu('submit_sm', client=self, **kwargs)
+        self.send_pdu(submit_sm_pdu, send_later=send_later)
+        return submit_sm_pdu
+
+    def _should_prolong_session(self):
+        # We need some time to send enquire_link before the next `select` call comes
+        passed_from_last_message = monotonic() - self._last_active_time
+
+        return self.timeout - self._select_timeout <= passed_from_last_message
+
+    def observe(self, ignore_error_codes=None, auto_send_enquire_link=True):
+        while not self.should_stop:
+            rlist, _, _ = select.select(
+                [self._socket, self._read_sock], [], [], self._select_timeout,
+            )
+
+            if self.should_stop:
+                break
+
+            if not rlist:
+                if self._should_prolong_session():
+                    if not auto_send_enquire_link:
+                        raise exceptions.SessionProlongationDisabled()
+
+                    self.logger.debug('Sending enquire_link')
+                    pdu = smpp.make_pdu('enquire_link', client=self)
+                    self.send_pdu(pdu)
+            else:
+                for ready_socket in rlist:
+                    if ready_socket is self._socket:
+                        self.read_once(ignore_error_codes, auto_send_enquire_link)
+                    else:
+                        self._read_sock.recv(1)
+                        self.send_pdu(self._send_queue.pop())
+
+        self.logger.info('Finished observing...')
@@ -17,3 +17,7 @@ class PDUError(RuntimeError):
 
 class MessageTooLong(ValueError):
     """Text too long to fit 255 SMS"""
+
+
+class SessionProlongationDisabled(Exception):
+    """Server send nothing and we do not want to continue"""
@@ -1,11 +1,14 @@
+import time
 import warnings
+
 import pytest
-from mock import Mock, call
+from mock import call, Mock
+from monotonic import monotonic
 
-from smpplib.client import Client
-from smpplib.smpp import make_pdu
 from smpplib import consts
 from smpplib import exceptions
+from smpplib.client import Client, ThreadSafeClient
+from smpplib.smpp import make_pdu
 
 
 def test_client_construction_allow_unknown_opt_params_warning():
@@ -44,3 +47,13 @@ def test_client_error_pdu_custom_handler():
     client.read_once()
 
     assert mock_error_pdu_handler.mock_calls == [call(error_pdu)]
+
+
+def test_prolongation():
+    client = ThreadSafeClient("localhost", 5679)
+    client._last_active_time = monotonic()
+    assert not client._should_prolong_session()
+
+    time.sleep(client.timeout - client._select_timeout)
+
+    assert client._should_prolong_session()