From c15b9edd371baf25d5d886570f1d16f71ba49cd4 Mon Sep 17 00:00:00 2001
From: Jake Wharton <jw@squareup.com>
Date: Tue, 9 Apr 2024 18:04:08 -0400
Subject: [PATCH] Do not query guest version from UI thread (#1949)

I'm not sure how I ended up committing the previous version as I was making changes specifically to avoid this, but I did. Instead, read the version once on startup when the app lifecycle is first bound and cache its value for later access on the UI thread.
---
 CHANGELOG.md                                  |  1 +
 .../redwood/treehouse/ZiplineCodeSession.kt   | 23 +++++++++++--------
 2 files changed, 15 insertions(+), 9 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index cad7824381..6106d3ad26 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,6 +11,7 @@ Changed:
 
 Fixed:
 - Work around a problem with our memory-leak fix where our old LazyList code would crash when its placeholders were unexpectedly removed.
+- Avoid calling into the internal Zipline instance from the UI thread on startup. This would manifest as weird native crashes due to multiple threads mutating shared memory.
 
 
 ## [0.10.0] - 2024-04-05
diff --git a/redwood-treehouse-host/src/commonMain/kotlin/app/cash/redwood/treehouse/ZiplineCodeSession.kt b/redwood-treehouse-host/src/commonMain/kotlin/app/cash/redwood/treehouse/ZiplineCodeSession.kt
index e81621b586..43b3f70e77 100644
--- a/redwood-treehouse-host/src/commonMain/kotlin/app/cash/redwood/treehouse/ZiplineCodeSession.kt
+++ b/redwood-treehouse-host/src/commonMain/kotlin/app/cash/redwood/treehouse/ZiplineCodeSession.kt
@@ -20,6 +20,7 @@ import app.cash.zipline.Zipline
 import app.cash.zipline.ZiplineApiMismatchException
 import app.cash.zipline.ZiplineScope
 import app.cash.zipline.withScope
+import kotlin.concurrent.Volatile
 import kotlinx.coroutines.CoroutineScope
 import kotlinx.serialization.json.Json
 
@@ -37,22 +38,26 @@ internal class ZiplineCodeSession<A : AppService>(
   appService = appService,
 ) {
   private val ziplineScope = ZiplineScope()
-  private lateinit var appLifecycle: AppLifecycle
 
   override val json: Json
     get() = zipline.json
 
-  override val guestProtocolVersion: RedwoodVersion
-    get() {
-      return try {
-        appLifecycle.guestProtocolVersion
-      } catch (_: ZiplineApiMismatchException) {
-        RedwoodVersion.Unknown
-      }
+  @Volatile
+  private var _guestProtocolVersion: RedwoodVersion? = null
+
+  override val guestProtocolVersion: RedwoodVersion get() =
+    checkNotNull(_guestProtocolVersion) {
+      "Cannot access guest version before ziplineStart"
     }
 
   override fun ziplineStart() {
-    appLifecycle = appService.withScope(ziplineScope).appLifecycle
+    val appLifecycle = appService.withScope(ziplineScope).appLifecycle
+
+    _guestProtocolVersion = try {
+      appLifecycle.guestProtocolVersion
+    } catch (_: ZiplineApiMismatchException) {
+      RedwoodVersion.Unknown
+    }
 
     val host = RealAppLifecycleHost(
       appLifecycle = appLifecycle,