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Change Backtrace::enabled atomic from SeqCst to Relaxed#92139

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bors merged 1 commit intorust-lang:masterfrom
dtolnay:backtrace
Dec 23, 2021
Merged

Change Backtrace::enabled atomic from SeqCst to Relaxed#92139
bors merged 1 commit intorust-lang:masterfrom
dtolnay:backtrace

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@dtolnay
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@dtolnay dtolnay commented Dec 20, 2021

This atomic is not synchronizing anything outside of its own value, so we don't need the Acquire/Release guarantee that all memory operations prior to the store are visible after the subsequent load, nor the SeqCst guarantee of all threads seeing all of the sequentially consistent operations in the same order.

Using Relaxed reduces the overhead of Backtrace::capture() in the case that backtraces are not enabled.

Benchmark

#![feature(backtrace)]

use std::backtrace::Backtrace;
use std::sync::atomic::{AtomicUsize, Ordering};
use std::thread;
use std::time::Instant;

fn main() {
    let begin = Instant::now();
    let mut threads = Vec::new();
    for _ in 0..64 {
        threads.push(thread::spawn(|| {
            for _ in 0..10_000_000 {
                let _ = Backtrace::capture();
                static LOL: AtomicUsize = AtomicUsize::new(0);
                LOL.store(1, Ordering::Release);
            }
        }));
    }
    for thread in threads {
        let _ = thread.join();
    }
    println!("{:?}", begin.elapsed());
}

Before: 6.73 seconds
After: 5.18 seconds

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rust-highfive commented Dec 20, 2021

r? @m-ou-se

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@rust-highfive rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Dec 20, 2021
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m-ou-se commented Dec 21, 2021

@bors r+

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bors commented Dec 21, 2021

📌 Commit 984b10d has been approved by m-ou-se

@bors bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Dec 21, 2021
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bors commented Dec 21, 2021

⌛ Testing commit 984b10d with merge b0dcf2c76b3159084138c63b18bd31373c9e679b...

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bors commented Dec 21, 2021

💔 Test failed - checks-actions

@bors bors added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Dec 21, 2021
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rust-log-analyzer commented Dec 21, 2021

The job x86_64-msvc-1 failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot) 

failures:

---- process::tests::test_interior_nul_in_arg_is_error stdout ----
thread 'process::tests::test_interior_nul_in_arg_is_error' panicked at 'assertion failed: `(left == right)`
  left: `NotFound`,
 right: `InvalidInput`', library\std\src\process\tests.rs:309:19
---- process::tests::test_interior_nul_in_args_is_error stdout ----
thread 'process::tests::test_interior_nul_in_args_is_error' panicked at 'assertion failed: `(left == right)`
  left: `NotFound`,
  left: `NotFound`,
 right: `InvalidInput`', library\std\src\process\tests.rs:317:19
---- process::tests::test_interior_nul_in_current_dir_is_error stdout ----
thread 'process::tests::test_interior_nul_in_current_dir_is_error' panicked at 'assertion failed: `(left == right)`
  left: `NotFound`,
  left: `NotFound`,
 right: `InvalidInput`', library\std\src\process\tests.rs:325:19
---- sys::windows::process::tests::windows_exe_resolver stdout ----
---- sys::windows::process::tests::windows_exe_resolver stdout ----
thread 'sys::windows::process::tests::windows_exe_resolver' panicked at 'assertion failed: resolve_exe(OsStr::new(\"rustc\"), child_paths).is_ok()', library\std\src\sys\windows\process\tests.rs:174:5

failures:
    process::tests::test_interior_nul_in_arg_is_error
    process::tests::test_interior_nul_in_args_is_error
    process::tests::test_interior_nul_in_args_is_error
    process::tests::test_interior_nul_in_current_dir_is_error
    sys::windows::process::tests::windows_exe_resolver

test result: FAILED. 879 passed; 4 failed; 3 ignored; 0 measured; 0 filtered out; finished in 13.83s

error: test failed, to rerun pass '-p std --lib'


command did not execute successfully: "\\\\?\\D:\\a\\rust\\rust\\build\\x86_64-pc-windows-msvc\\stage0\\bin\\cargo.exe" "test" "--target" "x86_64-pc-windows-msvc" "-Zbinary-dep-depinfo" "-j" "8" "--release" "--locked" "--color" "always" "--features" "panic-unwind backtrace profiler compiler-builtins-c" "--manifest-path" "D:\\a\\rust\\rust\\library/test/Cargo.toml" "-p" "std" "--"


Build completed unsuccessfully in 0:40:00
Build completed unsuccessfully in 0:40:00
make: *** [Makefile:72: ci-subset-1] Error 1

AngelicosPhosphoros
AngelicosPhosphoros reviewed Dec 21, 2021
View reviewed changes
library/std/src/backtrace.rs
},
};
ENABLED.store(enabled as usize + 1, SeqCst);
ENABLED.store(enabled as usize + 1, Relaxed);
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How about storing boolean as is in atomic?
I managed to remove 1 branch and make code shorter by this:
godbolt

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ehuss commented Dec 22, 2021

The CI error was due to some infrastructure problem. I would retry, but do you want to respond to the comment at #92139 (comment) first?

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dtolnay commented Dec 22, 2021

That comment seems orthogonal to the change in this PR.

@bors retry

@bors bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Dec 22, 2021
@matthiaskrgr matthiaskrgr mentioned this pull request Dec 22, 2021
Merged
bors added a commit to rust-lang-ci/rust that referenced this pull request Dec 23, 2021
@bors
Auto merge of rust-lang#92216 - matthiaskrgr:rollup-luplvuc, r=matthi…
5aa0239 
…askrgr

Rollup of 7 pull requests

Successful merges:

 - rust-lang#88858 (Allow reverse iteration of lowercase'd/uppercase'd chars)
 - rust-lang#91544 (Fix duplicate derive clone suggestion)
 - rust-lang#92026 (Add some JSDoc comments to rustdoc JS)
 - rust-lang#92117 (kmc-solid: Add `std::sys::solid::fs::File::read_buf`)
 - rust-lang#92139 (Change Backtrace::enabled atomic from SeqCst to Relaxed)
 - rust-lang#92146 (Don't emit shared files when scraping examples from dependencies in Rustdoc)
 - rust-lang#92208 (Quote bat script command line)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup
@bors bors merged commit 12e4907 into rust-lang:master Dec 23, 2021
@rustbot rustbot added this to the 1.59.0 milestone Dec 23, 2021
@dtolnay dtolnay deleted the backtrace branch December 23, 2021 16:34
@dtolnay dtolnay mentioned this pull request Dec 23, 2021
Merged
@dtolnay dtolnay added T-libs Relevant to the library team, which will review and decide on the PR/issue. A-backtrace Area: Backtraces and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Jan 14, 2025
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