Derive Hash for ThreadId + better example

[sagebind]

Derive Hash for ThreadId (see comments in #21507). Useful for making maps based on thread, e.g. HashMap<ThreadId, ?>. Also update example code for thread IDs to be more useful.

[rust-highfive]

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[sfackler]

Looks like the doctests are failing:

failures:
[01:02:27] 
[01:02:27] ---- thread/mod.rs - thread::Thread::id (line 791) stdout ----
[01:02:27] 	error: no method named `unwrap` found for type `std::thread::JoinHandle<std::thread::ThreadId>` in the current scope
[01:02:27]   --> <anon>:10:4
[01:02:27]    |
[01:02:27] 10 | }).unwrap();
[01:02:27]    |    ^^^^^^
[01:02:27] 
[01:02:27] error: aborting due to previous error(s)
[01:02:27] 
[01:02:27] thread 'rustc' panicked at 'Box<Any>', /checkout/src/librustc/session/mod.rs:203
[01:02:27] note: Run with `RUST_BACKTRACE=1` for a backtrace.
[01:02:27] 
[01:02:27] ---- thread/mod.rs - thread::ThreadId (line 660) stdout ----
[01:02:27] 	error: no method named `unwrap` found for type `std::thread::JoinHandle<std::thread::ThreadId>` in the current scope
[01:02:27]   --> <anon>:10:4
[01:02:27]    |
[01:02:27] 10 | }).unwrap();
[01:02:27]    |    ^^^^^^
[01:02:27] 
[01:02:27] error: aborting due to previous error(s)
[01:02:27] 
[01:02:27] thread 'rustc' panicked at 'Box<Any>', /checkout/src/librustc/session/mod.rs:203
[01:02:27] 
[01:02:27] 
[01:02:27] failures:
[01:02:27]     thread/mod.rs - thread::Thread::id (line 791)
[01:02:27]     thread/mod.rs - thread::ThreadId (line 660)
[01:02:27] 
[01:02:27] test result: FAILED. 776 passed; 2 failed; 22 ignored; 0 measured
[01:02:27] 
[01:02:27] error: test failed

Could you add Debug into the derive list while you're in there?

[nrc]

Could you add Debug into the derive list while you're in there?

Note that there is already a Debug impl, it just prints ThreadId { .. } rather than the more useful, obvious solution. If we do want to derive Debug, then we would need to remove the explicit impl.

[sfackler]

Oh, that's weird. I have no problem with a derived implementation that actually shows the value.

[sagebind]

I think we originally did not derive Debug because we did not want to expose the actual value in any way, even for debugging. I see no issue with displaying it though, for debugging purposes anyway. Would probably be really helpful for identifying threads for logs, etc.

[alexcrichton]

Yeah hiding the value from the Debug impl seems like it's trying to hard to me, I'd also expect #[derive(Debug)] here (and would be ok with it)

[nrc]

hiding the value from the Debug impl seems like it's trying to hard to me

it is irritating but also useless - you can always just transmute

[sfackler]

You monster!

[alexcrichton]

@rfcbot fcp merge

[rfcbot]

Team member @alexcrichton has proposed to merge this. The next step is review by the rest of the tagged teams:

• @BurntSushi
• @GuillaumeGomez
• @Kimundi
• @alexcrichton
• @aturon
• @brson
• @frewsxcv
• @jonathandturner
• @peschkaj
• @sfackler
• @steveklabnik

No concerns currently listed.

Once these reviewers reach consensus, this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

See this document for info about what commands tagged team members can give me.

[frewsxcv]

I don't remember why I tagged this T-doc, but here's my checkmark anyways.

[sagebind]

@frewsxcv Perhaps because the example code is updated for the ThreadId type?

[peschkaj]

@rfcbot reviewed

[sophiajt]

@rfcbot reviewed

[GuillaumeGomez]

@rfcbot reviewed

[alexcrichton]

@bors: r+

[bors]

📌 Commit cd14a32 has been approved by alexcrichton

[bors]

⌛ Testing commit cd14a32 with merge d62179c...

[bors]

💔 Test failed - status-appveyor

[TimNN]

@bors retry

• Spurious failures on AppVeyor due to ar.exe errors #40546

[bors]

⌛ Testing commit cd14a32 with merge 4a78fc0...

[bors]

💔 Test failed - status-appveyor

[TimNN]

@bors retry

• Spurious failures on AppVeyor due to ar.exe errors #40546

[bors]

⌛ Testing commit cd14a32 with merge 14481f7...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: alexcrichton
Pushing 14481f7 to master...