Auto merge of #12637 - asajeffrey:constellation-use-reentrant-logging-mutex, r=emilio

Replaced mutex in constellation logging by a reentrant mutex.

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The double-panic in #12553 may be caused by using a non-reentrant lock, which panics on reetry. This PR adds a reentrant lock type (slightly annoyingly, the implementation in std isn't exported) and uses it for logging. cc @jdm

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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #12619.
- [X] These changes do not require tests because they are designed to remove a class of intermittents.

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components/constellation/constellation.rs

@@ -54,8 +54,8 @@ use std::iter::once;
 use std::marker::PhantomData;
 use std::mem::replace;
 use std::process;
+use std::sync::Arc;
 use std::sync::mpsc::{Sender, channel, Receiver};
-use std::sync::{Arc, Mutex};
 use std::thread;
 use std::time::Instant;
 use style_traits::PagePx;
@@ -65,6 +65,7 @@ use timer_scheduler::TimerScheduler;
 use url::Url;
 use util::opts;
 use util::prefs::PREFS;
+use util::remutex::ReentrantMutex;
 use util::thread::spawn_named;
 use webrender_traits;
 
@@ -314,14 +315,14 @@ enum ExitPipelineMode {
 #[derive(Clone)]
 pub struct FromScriptLogger {
     /// A channel to the constellation
-    pub constellation_chan: Arc<Mutex<IpcSender<FromScriptMsg>>>,
+    pub constellation_chan: Arc<ReentrantMutex<IpcSender<FromScriptMsg>>>,
 }
 
 impl FromScriptLogger {
     /// Create a new constellation logger.
     pub fn new(constellation_chan: IpcSender<FromScriptMsg>) -> FromScriptLogger {
         FromScriptLogger {
-            constellation_chan: Arc::new(Mutex::new(constellation_chan))
+            constellation_chan: Arc::new(ReentrantMutex::new(constellation_chan))
         }
     }
 
@@ -352,14 +353,14 @@ impl Log for FromScriptLogger {
 #[derive(Clone)]
 pub struct FromCompositorLogger {
     /// A channel to the constellation
-    pub constellation_chan: Arc<Mutex<Sender<FromCompositorMsg>>>,
+    pub constellation_chan: Arc<ReentrantMutex<Sender<FromCompositorMsg>>>,
 }
 
 impl FromCompositorLogger {
     /// Create a new constellation logger.
     pub fn new(constellation_chan: Sender<FromCompositorMsg>) -> FromCompositorLogger {
         FromCompositorLogger {
-            constellation_chan: Arc::new(Mutex::new(constellation_chan))
+            constellation_chan: Arc::new(ReentrantMutex::new(constellation_chan))
         }
     }