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event_monitor: Replace unsound static mut MONITOR

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See discussion in https://github.com/rust-lang/rust/issues/53639.
This came up during an internal review.

Signed-off-by: Christian Blichmann <cblichmann@google.com>
This commit is contained in:
Christian Blichmann
2023-09-14 11:19:12 +02:00
committed by Rob Bradford
parent f557aadb67
commit 88f3537b47
3 changed files with 13 additions and 13 deletions
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24
event_monitor/src/lib.rs
View File

@@ -3,6 +3,7 @@
// SPDX-License-Identifier: Apache-2.0
//
use once_cell::sync::OnceCell;
use serde::Serialize;
use std::borrow::Cow;
use std::collections::HashMap;
@@ -12,7 +13,7 @@ use std::os::unix::io::AsRawFd;
use std::sync::Arc;
use std::time::{Duration, Instant};
static mut MONITOR: Option<MonitorHandle> = None;
static MONITOR: OnceCell<MonitorHandle> = OnceCell::new();
#[derive(Serialize)]
struct Event<'a> {
@@ -69,8 +70,8 @@ fn set_file_nonblocking(file: &File) -> io::Result<()> {
/// This function must only be called once from the main thread before any threads
/// are created to avoid race conditions.
pub fn set_monitor(file: Option<File>) -> io::Result<Monitor> {
// SAFETY: there is only one caller of this function, so MONITOR is written to only once
assert!(unsafe { MONITOR.is_none() });
// There is only one caller of this function, so MONITOR is written to only once
assert!(MONITOR.get().is_none());
if let Some(ref file) = file {
set_file_nonblocking(file)?;
@@ -79,24 +80,21 @@ pub fn set_monitor(file: Option<File>) -> io::Result<Monitor> {
let (tx, rx) = flume::unbounded();
let monitor = Monitor::new(rx, file);
// SAFETY: MONITOR is None. Nobody else can hold a reference to it.
unsafe {
MONITOR = Some(MonitorHandle {
tx,
start: Instant::now(),
});
};
MONITOR.get_or_init(|| MonitorHandle {
tx,
start: Instant::now(),
});
Ok(monitor)
}
pub fn event_log(source: &str, event: &str, properties: Option<&HashMap<Cow<str>, Cow<str>>>) {
// SAFETY: `MONITOR` is always in a valid state (None or Some), because it
// is set only once before any threads are spawned, and it's not mutated
// `MONITOR` is always in a valid state (None or Some), because it is set
// only once before any threads are spawned, and it's not mutated
// afterwards. This function only creates immutable references to `MONITOR`.
// Because `MONITOR.tx` is `Sync`, it's safe to share `MONITOR` across
// threads, making this function thread-safe.
if let Some(monitor_handle) = unsafe { MONITOR.as_ref() } {
if let Some(monitor_handle) = MONITOR.get().as_ref() {
let event = Event {
timestamp: monitor_handle.start.elapsed(),
source,