Print thread ID in panic message

[tgross35]

panic! does not print any identifying information for threads that are
unnamed. However, in many cases, the thread ID can be determined.

This changes the panic message from something like this:

thread '<unnamed>' panicked at src/main.rs:3:5:
explicit panic

To something like this:

thread '<unnamed>' (12345) panicked at src/main.rs:3:5:
explicit panic

Stack overflow messages are updated as well.

This change applies to both named and unnamed threads. The ID printed is
the OS integer thread ID rather than the Rust thread ID, which should
also be what debuggers print.

try-job: dist-x86_64-freebsd
try-job: dist-x86_64-linux
try-job: dist-x86_64-linux-alt
try-job: dist-x86_64-netbsd

[rustbot]

r? @davidtwco

(rustbot has picked a reviewer for you, use r? to override)

[tgross35]

I think this needs FCP since it's a visible change

@rustbot label -T-libs -T-compiler +T-libs-api
r? libs-api

[rustbot]

The Miri subtree was changed

cc @rust-lang/miri

[tgross35]

cc @m-ou-se since you recently did the formatting in #112849

[bjorn3]

Maybe

thread '<unnamed 2>' panicked at src/main.rs:3:5:
explicit panic

or

thread '<unnamed#2>' panicked at src/main.rs:3:5:
explicit panic

? That fits more with the way named threads are shown.

[the8472]

Note that this is a rust-internal thread ID, which isn't the OS thread ID which can be relevant if you're also logging from C code or looking at things with GDB. And as_u64() is unstable and there are questions about stabilizing it (#110738).

[tgross35]

Maybe

thread '<unnamed 2>' panicked at src/main.rs:3:5:
explicit panic

or

thread '<unnamed#2>' panicked at src/main.rs:3:5:
explicit panic

I just proposed the syntax as a demo, figured libs-api would make the final choice - though between those two, I like the first one better

Note that this is a rust-internal thread ID, which isn't the OS thread ID which can be relevant if you're also logging from C code or looking at things with GDB. And as_u64() is unstable and there are questions about stabilizing it (#110738).

It is kind of unfortunate that Rust and C won't use the same thread IDs. But this seems worthwhile still - Rust-only applications printing the thread ID in logs is common (tracing even has a builtin way to do this), probably more common than Rust thread IDs silently mixing with C thread IDs in logs. And even in that case, it still gives you something more concrete to trace than "something failed".

This is all inspired by the below failure I recently had in an highly threaded system. The entire backtrace uselessly displayed one repeated function, with no hints about which preceding log events were relevant:

thread '<unnamed>' panicked at src/scan.rs:101:55:
called `Result::unwrap()` on an `Err` value: ()
stack backtrace:
   0:        0x1009661d0 - __mh_execute_header
   1:        0x10088869b - __mh_execute_header
   2:        0x10093ba0e - __mh_execute_header
   4:        0x10096757c - __mh_execute_header
   5:        0x100968632 - __mh_execute_header
   6:        0x1009680f4 - __mh_execute_header
   7:        0x100968059 - __mh_execute_header
   8:        0x100968042 - __mh_execute_header
   9:        0x100bdd913 - __mh_execute_header

I don't think that stability of the thread ID is much of a concern since we will always have some integer ID for a thread, even if the semantics of that ID might change. The important thing is probably just that this panic message thread ID is the same as what shows up as Debug for ThreadId (or as_u64 as applicable) since that is what other libraries are directed to use. That is the case here

[tgross35]

Another display option - it looks a bit cleaner to not even call out that a thread is unnamed, and I don't think it adds much

thread with ID 2 panicked at src/main.rs:3:5:
explicit panic

Or we could use ThreadId's debug formatting which tracing and I think log do, but that seems unnecessarily clunky

thread with `ThreadId(2)` panicked at src/main.rs:3:5:
explicit panic

I also tried to poke some discussion at #67939

[bors]

☔ The latest upstream changes (presumably #115627) made this pull request unmergeable. Please resolve the merge conflicts.

[tgross35]

@joshtriplett do you have any thoughts on this?

[timClicks]

Sorry to add bike shedding to the thread. Here is a slight derivative of the last suggestion, which omits a "with":

thread `ThreadId(2)` panicked at src/main.rs:3:5:
explicit panic

Although it's uglier than using the thread identifier in a sentence, using the Debug form makes it look like a Rust value rather than something else. It's also consistent with other output from Rust, although the case can definitely be made that thread IDs deserve a special case.

[tgross35]

I know Josh has a pretty busy queue, so perhaps it is best to reroll

r? libs-api

[dtolnay]

I think this needs FCP since it's a visible change

@​rustbot label -T-libs -T-compiler +T-libs-api

I think it wouldn't need one. T-libs-api FCP is primarily for any time a permanent API commitment is being made by the standard library, and deprecations. In contrast, anything that we can just change back with minimal effort or disruption would not warrant FCP.

#112849 had a T-libs FCP but I am not familiar with their criteria for that. @rust-lang/libs would you want to handle this PR?

In any case, this looks good to me.

[thomcc]

I don't know that this needs FCP. I'm not opposed and there is precedent for it, but OTOH we wouldn't FCP a panic message change somewhere in the stdlib. So I don't feel strongly.

In any case, I think this change is a good idea, and am in favor.

[tgross35]

For the remaining targets: @jclulow, @psumbera, @jethrogb, @jackpot51, do Illumos, Solaris, Fortanix, or Redox provide a way to get a current thread ID? I haven't been able to find anything documented.

[joshtriplett]

@rfcbot resolved ambiguous-non-os-thread-id

[rfcbot]

🔔 This is now entering its final comment period, as per the review above. 🔔

[jclulow]

For the remaining targets: @jclulow, @psumbera, @jethrogb, @jackpot51, do Illumos, Solaris, Fortanix, or Redox provide a way to get a current thread ID? I haven't been able to find anything documented.

Do you mean the name of the thread provided to the thread builder? If so, I believe you can read that from the lwpname file described in proc(5).

[cuviper]

Not the name -- we're looking for a numeric thread ID, like Linux's gettid().

[jclulow]

Oh, sorry. You probably want either the native thr_self(3C) then, or the pthread alias equivalent pthread_self(3C) which I believe is standard and I assume must be available anywhere you have pthreads support.

[tgross35]

I believe pthread_self is allowed to return an ID assigned by the threading library, whereas the functions we use here are an OS thread ID (at least to the best of my knowledge; gettid, getthrid, pthread_getthreadid_np, _lwp_self, pthread_threadid_np all return an integer or some pid_t rather than {p}thread_t). The downside of the pthread ID is that might not line up with the OS thread IDs from /proc or sysctl for debuggers or process viewers to use. But maybe those coincide on Illumos - any idea if that might be the case?

Admittedly I think it's probably to use pthread_self in any case if there isn't anything like described.

[jclulow]

I believe they all coincide on illumos, yes. Our threading model is 1:1, where a user visible (i.e., libc level) thread is directly equivalent to an LWP (light weight process) which is what the kernel uses to save and restore user register state. So the LWP/thread with ID 1 is the main thread, no matter where you look, and subsequent threads have higher ID numbers, etc. The same IDs are also used in /proc paths (for debuggers and process control tools) and DTrace and so on. Note that these IDs are scoped within a process (every process starts with an LWP 1), not globally unique like task IDs on Linux.

[tgross35]

That's easy then, thanks for confirming!

[psumbera]

That's easy then, thanks for confirming!

Solaris should be treated the same way as Illumos please.

[jethrogb]

For SGX: https://github.com/rust-lang/rust/blob/master/library/std/src/sys/pal/sgx/abi/thread.rs#L8

[bors]

☔ The latest upstream changes (presumably #143091) made this pull request unmergeable. Please resolve the merge conflicts.

[jackpot51]

@tgross35 Redox OS has gettid