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Fix self profiler ICE on Windows #56170

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merged 2 commits into from
Nov 25, 2018
Merged

Fix self profiler ICE on Windows #56170

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b319715
Disable the self-profiler unless the `-Z self-profile` flag is set
wesleywiser Nov 22, 2018
dce1c45
[Windows] Work around non-monotonic clocks in the self-profiler
wesleywiser Nov 22, 2018
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6 changes: 4 additions & 2 deletions src/librustc/session/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -826,8 +826,10 @@ impl Session {
}

pub fn profiler<F: FnOnce(&mut SelfProfiler) -> ()>(&self, f: F) {
let mut profiler = self.self_profiling.borrow_mut();
f(&mut profiler);
if self.opts.debugging_opts.self_profile {
let mut profiler = self.self_profiling.borrow_mut();
f(&mut profiler);
}
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Was this change needed? (Not that it's wrong, just surprised it wasn't already the case).

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Not needed per se. It wasn't already the case because we showed a very small amount of overhead from turning on the profiler. I think it's probably best to make it opt-in though.

}

pub fn print_profiler_results(&self) {
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17 changes: 15 additions & 2 deletions src/librustc/util/profiling.rs
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Expand Up @@ -12,7 +12,7 @@ use session::config::Options;

use std::fs;
use std::io::{self, StdoutLock, Write};
use std::time::Instant;
use std::time::{Duration, Instant};

macro_rules! define_categories {
($($name:ident,)*) => {
Expand Down Expand Up @@ -197,7 +197,20 @@ impl SelfProfiler {
}

fn stop_timer(&mut self) -> u64 {
let elapsed = self.current_timer.elapsed();
let elapsed = if cfg!(windows) {
// On Windows, timers don't always appear to be monotonic (see #51648)
// which can lead to panics when calculating elapsed time.
// Work around this by testing to see if the current time is less than
// our recorded time, and if it is, just returning 0.
let now = Instant::now();
if self.current_timer >= now {
Duration::new(0, 0)
} else {
self.current_timer.elapsed()
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Shouldn't this line (209) be changed to do now - self.current_timer instead? I think right now it's susceptible to the same error the workaround is meant to prevent. Since Instant::elapsed will call Instant::now again, which could be inaccurate and won't be double-checked like the variable now just was.

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That seems like a reasonable change to me

}
} else {
self.current_timer.elapsed()
};

self.current_timer = Instant::now();

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