[Feature request] more clear error hint when number of open files exceeds the OS limit

[msyyc]

There is a scenario we need to create many connection in Linux, but the error happens:

Here is simple code to reproduce:

import websocket

def create_client(idx):
    ws = websocket.create_connection(
        url="wss://xxxxxx",
        subprotocols=["xxx"],
    )
    print(f"{idx} done")
    return ws

ws_list = [create_client(i) for i in range(10000)]
for item in ws_list:
    item.close()

print("done")

The error hint is not clear so we don't know what's wrong. Finally, we infer that we may meet the file descriptor limit in Linux. Then we use ulimit -n xxx to increase the limit and the issue is fixed.

Here is aiohttp error hint in same scenario which is more clear:

So I expect websocket-client could promote the error hint in this scenario.

[engn33r]

This is a reasonable idea. I do not see this ulimit configuration in the docs but it has been mentioned in some past issues here and here.