From 3298ef52f19145d76bbaf6fbcc826cc21fd112d4 Mon Sep 17 00:00:00 2001
From: Tim Huang <tihuang@mozilla.com>
Date: Wed, 12 Mar 2025 07:34:39 +0000
Subject: [PATCH] Bug 1951017 - Dispatch
 nsRFPService::MaybeReportFontFingerprinter() to the main thread.  a=pascalc

Original Revision: https://phabricator.services.mozilla.com/D240306

Differential Revision: https://phabricator.services.mozilla.com/D241048
---
 .../resistfingerprinting/nsRFPService.cpp        | 16 +++++++++++++++-
 .../resistfingerprinting/nsRFPService.h          |  2 +-
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/toolkit/components/resistfingerprinting/nsRFPService.cpp b/toolkit/components/resistfingerprinting/nsRFPService.cpp
index 8f05998e684a..6459b7a987f2 100644
--- a/toolkit/components/resistfingerprinting/nsRFPService.cpp
+++ b/toolkit/components/resistfingerprinting/nsRFPService.cpp
@@ -1823,11 +1823,25 @@ static void MaybeCurrentCaller(nsACString& aFilename, uint32_t& aLineNum,
 }
 
 /* static */ void nsRFPService::MaybeReportFontFingerprinter(
-    nsIChannel* aChannel, nsACString& aOriginNoSuffix) {
+    nsIChannel* aChannel, const nsACString& aOriginNoSuffix) {
   if (!aChannel) {
     return;
   }
 
+  // The logging of the event will access nsLoadGroup which is main-thread only.
+  // So we need to dispatch the task to the main thread if we are reporting
+  // the event off-main-thread.
+  if (!NS_IsMainThread()) {
+    NS_DispatchToMainThread(NS_NewRunnableFunction(
+        "nsRFPService::MaybeReportFontFingerprinter",
+        [channel = nsCOMPtr{aChannel},
+         originNoSuffix = nsCString(aOriginNoSuffix)]() {
+          nsRFPService::MaybeReportFontFingerprinter(channel, originNoSuffix);
+        }));
+
+    return;
+  }
+
   if (MOZ_LOG_TEST(gFingerprinterDetection, LogLevel::Info)) {
     nsAutoCString filename;
     uint32_t lineNum = 0;
diff --git a/toolkit/components/resistfingerprinting/nsRFPService.h b/toolkit/components/resistfingerprinting/nsRFPService.h
index d45f4172c9f3..0ac097b3cc3f 100644
--- a/toolkit/components/resistfingerprinting/nsRFPService.h
+++ b/toolkit/components/resistfingerprinting/nsRFPService.h
@@ -358,7 +358,7 @@ class nsRFPService final : public nsIObserver, public nsIRFPService {
                                              nsACString& aOriginNoSuffix);
 
   static void MaybeReportFontFingerprinter(nsIChannel* aChannel,
-                                           nsACString& aOriginNoSuffix);
+                                           const nsACString& aOriginNoSuffix);
 
   // --------------------------------------------------------------------------