Cargo stuck for hours, taking 100% of the CPU

[paulrouget]

While working on Servo, on a regular basis, Cargo gets stuck on Updating git repository or Updating registry.

I usually have to wait few hours until it finishes. Sometimes with no error (compilation went through). Sometimes with an error (conflict of version with a dependency in my Cargo.toml and Servo's Cargo.toml).

I guess #4502 is related.

Is there anything I can do to help diagnose this problem?

[paulrouget]

I don't know if it's easily reproducible, but cargo check freeze with this: https://github.com/paulrouget/cargo-issue-4604

[paulrouget]

By freeze, I mean, get stuck on Updating git repository https://github.com/servo/servo.

[paulrouget]

After few hours (I think 3 or 4 hours), this is what the Cargo.lock looks like: https://gist.github.com/paulrouget/385dd3d86028c698c98776d8d198e61a

The difference is the move from a local checkout of servo, webrender and webrender_api to the github repo.

[alexcrichton]

This is likely an unfortunate instance of #4066, although I'd have to dig in to be sure

[paulrouget]

This is likely an unfortunate instance of #4066, although I'd have to dig in to be sure

In this issue, you say:

We should have a hard limit for the number of steps the resolution algorithm can take before it just hard aborts and exits saying "this probably isn't gonna work".

But in this case, it works. But it takes 4 hours.

[paulrouget]

Is there any workaround?

Because every time I need to update servo in my projects, I have to run Cargo for hours before being able to do anything.

[alexcrichton]

I don't think I understand what's going on enough to recommend a workaround or know how to fix it. If it's not #4066 then Cargo may just need a tweak to a heuristic or something like that. I do not have time to investigate right now, but I can try to get around to this soon.

[carols10cents]

Could this be a slow libgit operation? That is, #4261 ?

[paulrouget]

I tried to reproduce today with: #4604 (comment)

But suddenly it's fast.

What changed since last week:

• I have a faster connection
• maybe the content of ~/.cargo/

[paulrouget]

This is still happening.

Stuck on:

    Updating git repository `https://github.com/servo/servo`
DEBUG:cargo::sources::git::utils: skipping gc as there's only 35 pack files
DEBUG:cargo::sources::git::utils: doing a fetch for https://github.com/servo/servo
DEBUG:cargo::sources::git::utils: initiating fetch of refs/heads/*:refs/heads/* from https://github.com/servo/servo
INFO:cargo::sources::git::utils: fetch /Users/paul/.cargo/git/checkouts/servo-12bfca331f128de3/43a4f01/.git/
DEBUG:cargo::sources::git::utils: skipping gc as there's only 3 pack files
DEBUG:cargo::sources::git::utils: doing a fetch for file:///Users/paul/.cargo/git/db/servo-12bfca331f128de3
DEBUG:cargo::sources::git::utils: initiating fetch of refs/heads/*:refs/heads/* from file:///Users/paul/.cargo/git/db/servo-12bfca331f128de3

[paulrouget]

Would it be possible to work around the issue by pulling manually?

I checkout-ed commit #43a4f01 in /Users/paul/.cargo/git/checkouts/servo-12bfca331f128de3/43a4f01/ - but still, it gets stuck exactly the same way.

[paulrouget]

I attached lldb to the process and dumped the backtrace:

https://gist.github.com/paulrouget/d6e3d62c5fd03af96b3338cf9414335d

[alexcrichton]

@paulrouget it looks like it's stuck in libgit2 fetching? If that's the case I'm not sure how to debug... You could try out #4646 locally and perhaps see if progress is being made?

[paulrouget]

it looks like it's stuck in libgit2 fetching? If that's the case I'm not sure how to debug... You could try out #4646 locally and perhaps see if progress is being made?

Now this has landed, I see that it's progressing, but very very slowly. It's apparently stagnating at 1 minute per percent. The network monitor tells me it's downloading at 2 to 7 kb/s.