From a905439d9cf5eb4c9f523d7858e44b9e7235113f Mon Sep 17 00:00:00 2001
From: Nolan Darilek <nolan@thewordnerd.info>
Date: Mon, 7 Dec 2020 14:58:59 -0600
Subject: [PATCH] Add strategic backoff in WinRT backend to (hopefully)
 eliminate a deadlock.

---
 Cargo.toml            |  1 +
 src/backends/winrt.rs | 30 ++++++++++++++++++++++--------
 src/lib.rs            |  8 ++++++++
 3 files changed, 31 insertions(+), 8 deletions(-)

diff --git a/Cargo.toml b/Cargo.toml
index 7d4f78b..6e1eb71 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -16,6 +16,7 @@ crate-type = ["lib", "cdylib", "staticlib"]
 use_tolk = ["tolk"]
 
 [dependencies]
+backoff = "0.2"
 dyn-clonable = "0.9"
 lazy_static = "1"
 log = "0.4"
diff --git a/src/backends/winrt.rs b/src/backends/winrt.rs
index 512eba4..4e60abe 100644
--- a/src/backends/winrt.rs
+++ b/src/backends/winrt.rs
@@ -1,7 +1,8 @@
-#[cfg(windows)]
-use std::collections::HashMap;
 use std::sync::Mutex;
+#[cfg(windows)]
+use std::{collections::HashMap, time::Duration};
 
+use backoff::{ExponentialBackoff, Operation};
 use lazy_static::lazy_static;
 use log::{info, trace};
 use winrt::*;
@@ -133,6 +134,13 @@ impl WinRT {
             playback_list,
         })
     }
+
+    fn backoff(&self) -> ExponentialBackoff {
+        ExponentialBackoff {
+            initial_interval: Duration::from_millis(3),
+            ..Default::default()
+        }
+    }
 }
 
 impl Backend for WinRT {
@@ -167,12 +175,18 @@ impl Backend for WinRT {
         if self.player.playback_session()?.playback_state()? != MediaPlaybackState::Playing {
             self.player.play()?;
         }
-        let mut uid = NEXT_UTTERANCE_ID.lock().unwrap();
-        let utterance_id = UtteranceId::WinRT(*uid);
-        *uid += 1;
-        drop(uid);
-        let mut mappings = UTTERANCE_MAPPINGS.lock().unwrap();
-        mappings.push((self.id, item, utterance_id));
+        let mut op = || {
+            let mut uid = NEXT_UTTERANCE_ID.try_lock()?;
+            let utterance_id = UtteranceId::WinRT(*uid);
+            *uid += 1;
+            Ok(utterance_id)
+        };
+        let mut backoff = self.backoff();
+        let utterance_id = op.retry(&mut backoff)?;
+        {
+            let mut mappings = UTTERANCE_MAPPINGS.lock().unwrap();
+            mappings.push((self.id, item, utterance_id));
+        }
         Ok(Some(utterance_id))
     }
 
diff --git a/src/lib.rs b/src/lib.rs
index 820ccd3..15504f6 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -99,6 +99,8 @@ impl Default for Features {
 pub enum Error {
     #[error("IO error: {0}")]
     IO(#[from] std::io::Error),
+    #[error("Backoff error")]
+    Backoff,
     #[error("Value not received")]
     NoneError,
     #[cfg(target_arch = "wasm32")]
@@ -113,6 +115,12 @@ pub enum Error {
     OutOfRange,
 }
 
+impl<E> From<backoff::Error<E>> for Error {
+    fn from(_: backoff::Error<E>) -> Self {
+        Error::Backoff
+    }
+}
+
 #[clonable]
 trait Backend: Clone + std::fmt::Debug {
     fn id(&self) -> Option<BackendId>;