From 7d396ff5b4c8d39f1c2c0dd18d7a90bf8496e360 Mon Sep 17 00:00:00 2001
From: Jonathan Kew <jkew@mozilla.com>
Date: Wed, 1 Oct 2025 23:53:56 +0000
Subject: [PATCH] Bug 1988244 - Guard the space-features bit vectors with the
 feature-info mutex.  a=RyanVM DONTBUILD

Original Revision: https://phabricator.services.mozilla.com/D266136

Differential Revision: https://phabricator.services.mozilla.com/D267025
---
 gfx/thebes/gfxFont.cpp    | 10 ++++++++--
 gfx/thebes/gfxFontEntry.h |  7 ++++---
 2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/gfx/thebes/gfxFont.cpp b/gfx/thebes/gfxFont.cpp
index 5f738195c725..f9dccee78841 100644
--- a/gfx/thebes/gfxFont.cpp
+++ b/gfx/thebes/gfxFont.cpp
@@ -1427,6 +1427,7 @@ void gfxFont::CheckForFeaturesInvolvingSpace() const {
         flags = flags | gfxFontEntry::SpaceFeatures::HasFeatures;
         uint32_t index = static_cast<uint32_t>(s) >> 5;
         uint32_t bit = static_cast<uint32_t>(s) & 0x1f;
+        MutexAutoLock lock(mFontEntry->mFeatureInfoLock);
         if (isDefaultFeature) {
           mFontEntry->mDefaultSubSpaceFeatures[index] |= (1 << bit);
         } else {
@@ -1440,8 +1441,11 @@ void gfxFont::CheckForFeaturesInvolvingSpace() const {
   // spaces in default features of default script?
   // ==> can't use word cache, skip GPOS analysis
   bool canUseWordCache = true;
-  if (HasSubstitution(mFontEntry->mDefaultSubSpaceFeatures, Script::COMMON)) {
-    canUseWordCache = false;
+  {
+    MutexAutoLock lock(mFontEntry->mFeatureInfoLock);
+    if (HasSubstitution(mFontEntry->mDefaultSubSpaceFeatures, Script::COMMON)) {
+      canUseWordCache = false;
+    }
   }
 
   // GPOS lookups - distinguish kerning from non-kerning features
@@ -1460,6 +1464,7 @@ void gfxFont::CheckForFeaturesInvolvingSpace() const {
   }
 
   if (MOZ_UNLIKELY(log)) {
+    MutexAutoLock lock(mFontEntry->mFeatureInfoLock);
     TimeDuration elapsed = TimeStamp::Now() - start;
     LOG_FONTINIT((
         "(fontinit-spacelookups) font: %s - "
@@ -1494,6 +1499,7 @@ bool gfxFont::HasSubstitutionRulesWithSpaceLookups(Script aRunScript) const {
   }
 
   // default features have space lookups ==> true
+  MutexAutoLock lock(mFontEntry->mFeatureInfoLock);
   if (HasSubstitution(mFontEntry->mDefaultSubSpaceFeatures, Script::COMMON) ||
       HasSubstitution(mFontEntry->mDefaultSubSpaceFeatures, aRunScript)) {
     return true;
diff --git a/gfx/thebes/gfxFontEntry.h b/gfx/thebes/gfxFontEntry.h
index f67f0c8c451e..b49a8cbce300 100644
--- a/gfx/thebes/gfxFontEntry.h
+++ b/gfx/thebes/gfxFontEntry.h
@@ -606,9 +606,10 @@ class gfxFontEntry {
 
   // bitvector of substitution space features per script, one each
   // for default and non-default features
-  uint32_t mDefaultSubSpaceFeatures[(int(Script::NUM_SCRIPT_CODES) + 31) / 32];
-  uint32_t
-      mNonDefaultSubSpaceFeatures[(int(Script::NUM_SCRIPT_CODES) + 31) / 32];
+  uint32_t mDefaultSubSpaceFeatures[(int(Script::NUM_SCRIPT_CODES) + 31) /
+                                    32] MOZ_GUARDED_BY(mFeatureInfoLock);
+  uint32_t mNonDefaultSubSpaceFeatures[(int(Script::NUM_SCRIPT_CODES) + 31) /
+                                       32] MOZ_GUARDED_BY(mFeatureInfoLock);
 
   mozilla::Atomic<uint32_t> mUVSOffset;