Threading
Importance of enable_multithread
The enable_multithread
variable should be set to True
when
working with multiple threads. If enable_multithread
is not
set to True
, websocket-client will act asynchronously and
not be thread safe. This variable should be enabled by default
starting with the 1.1.0 release, but had a default value of False
in older versions. See issues
#591
and
#507
for related issues.
asyncio library usage
Issue #496 indicates that websocket-client is not compatible with asyncio. The engine-io project, which is used in a popular socket-io client, specifically uses websocket-client as a dependency only in places where asyncio is not used. If asyncio is an important part of your project, you might consider using another websockets library. However, some simple use cases, such as asynchronously receiving data, may be a place to use asyncio. Here is one snippet showing how asynchronous listening might be implemented.
async def mylisten(ws):
result = await asyncio.get_event_loop().run_in_executor(None, ws.recv)
return result
threading library usage
The websocket-client library has some built-in threading support
provided by the threading
library. You will see import threading
in some of this project’s code. The
echoapp_client.py example
is a good illustration of how threading
can be used in the websocket-client library.
Another example is found in
an external site’s documentation,
which demonstrates using the _thread library, which is lower level than
the threading library.
Possible issues with threading
Further investigation into using the threading
module is seen in
issue #612
which illustrates one situation where using the threading module can impact
the observed behavior of this library. The first code example below does
not trigger the on_close()
function, but the second code example does
trigger the on_close()
function. The highlighted rows show the lines added
exclusively in the second example. This threading approach is identical to the
echoapp_client.py example.
However, further testing found that some WebSocket servers, such as
ws://echo.websocket.events, do not trigger the on_close()
function.
NOT working on_close() example, without threading
import websocket
websocket.enableTrace(True)
def on_open(ws):
ws.send("hi")
def on_message(ws, message):
print(message)
ws.close()
print("Message received...")
def on_close(ws, close_status_code, close_msg):
print(">>>>>>CLOSED")
wsapp = websocket.WebSocketApp("wss://api.bitfinex.com/ws/1", on_open=on_open, on_message=on_message, on_close=on_close)
wsapp.run_forever()
Working on_close() example, with threading
import websocket
import threading
websocket.enableTrace(True)
def on_open(ws):
ws.send("hi")
def on_message(ws, message):
def run(*args):
print(message)
ws.close()
print("Message received...")
threading.Thread(target=run).start()
def on_close(ws, close_status_code, close_msg):
print(">>>>>>CLOSED")
wsapp = websocket.WebSocketApp("wss://api.bitfinex.com/ws/1", on_open=on_open, on_message=on_message, on_close=on_close)
wsapp.run_forever()
In part because threading is hard, but also because this project has (until recently) lacked any threading documentation, there are many issues on this topic, including: