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Large pending connections bug

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I have used BitComet for many years, and I didn't bother to report this bug, but I have decided to report this today. BitComet has an unsustainable bug in which you cannot let it run for a long time. I think this bug related to a few other issues that users are experiencing slow uploads after turning on BitComet for a few days.

I get disconnection once in a while, when I get disconnected, the "pending connections" becomes insanely large. However, these are not actual connections, in which I have already set a sensible limit on the total connections. When this happens, BitComet becomes extremely lagging, and network speed dropped to less than half due to BitComet becoming lagging.

This is not related to hardware or anything, as doing other stuff on the machine is fine. You can also see my machine specs below.

It would be great if the developer can check why the program lags so much when there are a large number of pending connections, is there a bug somewhere?

My machine specs are: 128GB DDR5 RAM, Samsung EVO 990 Pro SSD, i9 14900K CPU.


Screenshot 2024-01-12 172845.png

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There are 2 ways that you can reproduce this:

1. Have 200+ tasks sitting in the stopped state. Then start them all in one go, this will immediately blow up the pending connections.

2. Have 200+ tasks running for a while, then power off your router, this will also blow up the pending connections.

As soon as pending connections reach around 100,000, BitComet UI will start to lag, and network throughput is greatly reduced.

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Suggested fix:

  • New advanced option to limit number of pending connections, with a default value of 5000. 5000 would not cause an issue from my usage experience in BitComet even with slower machines.
  • Look into program source code, locate and fix the bug by ensuring large amount of pending connections does not cause a UI lag. However, it may not be trivial.
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Thanks for your comments.

  • 2.05 is already the latest, see screenshot
  • I don't know what to say for the suggestions of connecting one by one or reboot, but thanks anyway

Please see screenshot carefully, I am talking about "pending" connections, not established / half opened connections, currently there is no way to limit pending connections. Pending connections is the one causing the issue. As far as I'm aware, pending connections are not opened connections, from my network monitoring. If they are, then there is a flaw in the program because you cannot limit this number.

Is it possible to add an advanced option to limit "pending" connections?

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If you click on the connection, you can stop it (if the left hand icon is an arrow, it's running - a circle means it's stopped except for Long term seeding)

You could try disabling LTS and see if that helps

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Thanks @Rhubarb,

However, I don't think stopping LTS is a long term solution.

I have a few questions:

  • Why do you think disabling LTS would solve the pending connections issue that is causing the program to lag?
  • Can you explain what are pending connections? What does it do? Does it require system resources? If so, why pending connections need system resources?
  • Why there is no Advanced option to limit pending connections, obviously it gets out of control when it blows up and the program gets into an unusable state. The screenshot above is showing 300,000+ pending connections and the UI lags so much, while i have a good limit in place for global maximum number of connections and half open connections

If you still cannot see what the issue here is, let me explain a bit more by giving you a scenario.

  • network.max_connections set to 1
  • network.max_connecting_connections set to 1
  • bittorrent.max_connections_per task set to 1

Now, let's say your pending connections is 300,000+ and BitComet UI starts to lag and leads to an unusable state.

This tells me there is a potential unintended bug in pending connections that is causing hogging/UI lag in the program. Pending connections are supposed to be waiting to be connected and not supposed to cause hogging/UI lag.

If the program gives us the flexibility to limit the maximum number of "pending" connections, it should solve the issue.


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I did suggest that you TRY it and see if it helps.

Unfortunately I can't sit at your computer and diagnose what's happening - all I can do is make suggestions.

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Hi, I'm sorry if theres a misunderstanding. But I'm not asking for diagnosing, i'm kindly asking you to file this bug with the developer.

I have already pin point exactly what the bug is, so please file this bug with the developer, unless you dont want to make the program better and more robust? 

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We don't file reports - the devs keep an eye on the forum. However, if it actually IS a 'bug', normally we would have a flood of 'me too' posts. One off problems tend to be overlooked unless it happens to a lot of people

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