Bug 1878199 - patch 1 - Don't create an additional Mutex in...

Bug 1878199 - patch 1 - Don't create an additional Mutex in FontFaceImpl::Entry, just use the base gfxFontEntry's existing RWLock.  a=dmeehan

No functional change here, just cleanup in preparation for the following patch.
We don't need FontFaceImpl to create a mutex, as there's already a lock (RWLock)
in its base class gfxFontEntry, and we can use that to guard the fields here.

Original Revision: https://phabricator.services.mozilla.com/D207295

Differential Revision: https://phabricator.services.mozilla.com/D208097

layout/style/FontFaceImpl.cpp

@@ -737,7 +737,7 @@ void FontFaceImpl::Entry::SetLoadState(UserFontLoadState aLoadState) {
 
   nsTArray<RefPtr<FontFaceImpl>> fontFaces;
   {
-    MutexAutoLock lock(mMutex);
+    AutoReadLock lock(mLock);
     fontFaces.SetCapacity(mFontFaces.Length());
     for (FontFaceImpl* f : mFontFaces) {
       fontFaces.AppendElement(f);
@@ -759,7 +759,7 @@ void FontFaceImpl::Entry::SetLoadState(UserFontLoadState aLoadState) {
 /* virtual */
 void FontFaceImpl::Entry::GetUserFontSets(
     nsTArray<RefPtr<gfxUserFontSet>>& aResult) {
-  MutexAutoLock lock(mMutex);
+  AutoReadLock lock(mLock);
 
   aResult.Clear();
 
@@ -784,7 +784,7 @@ void FontFaceImpl::Entry::GetUserFontSets(
 
 /* virtual */ already_AddRefed<gfxUserFontSet>
 FontFaceImpl::Entry::GetUserFontSet() const {
-  MutexAutoLock lock(mMutex);
+  AutoReadLock lock(mLock);
   if (mFontSet) {
     return do_AddRef(mFontSet);
   }
@@ -817,7 +817,7 @@ void FontFaceImpl::Entry::CheckUserFontSetLocked() {
 }
 
 void FontFaceImpl::Entry::FindFontFaceOwners(nsTHashSet<FontFace*>& aOwners) {
-  MutexAutoLock lock(mMutex);
+  AutoReadLock lock(mLock);
   for (FontFaceImpl* f : mFontFaces) {
     if (FontFace* owner = f->GetOwner()) {
       aOwners.Insert(owner);
@@ -826,13 +826,13 @@ void FontFaceImpl::Entry::FindFontFaceOwners(nsTHashSet<FontFace*>& aOwners) {
 }
 
 void FontFaceImpl::Entry::AddFontFace(FontFaceImpl* aFontFace) {
-  MutexAutoLock lock(mMutex);
+  AutoWriteLock lock(mLock);
   mFontFaces.AppendElement(aFontFace);
   CheckUserFontSetLocked();
 }
 
 void FontFaceImpl::Entry::RemoveFontFace(FontFaceImpl* aFontFace) {
-  MutexAutoLock lock(mMutex);
+  AutoWriteLock lock(mLock);
   mFontFaces.RemoveElement(aFontFace);
   CheckUserFontSetLocked();
 }

layout/style/FontFaceImpl.h

@@ -10,7 +10,7 @@
 #include "mozilla/dom/FontFaceBinding.h"
 #include "mozilla/FontPropertyTypes.h"
 #include "mozilla/Maybe.h"
-#include "mozilla/Mutex.h"
+#include "mozilla/RWLock.h"
 #include "mozilla/ServoStyleConsts.h"
 #include "gfxUserFontSet.h"
 #include "nsCSSPropertyID.h"
@@ -50,7 +50,6 @@ class FontFaceImpl final {
     Entry(gfxUserFontSet* aFontSet, nsTArray<gfxFontFaceSrc>&& aFontFaceSrcList,
           gfxUserFontAttributes&& aAttr)
         : gfxUserFontEntry(std::move(aFontFaceSrcList), std::move(aAttr)),
-          mMutex("FontFaceImpl::Entry::mMutex"),
           mFontSet(aFontSet) {}
 
     void SetLoadState(UserFontLoadState aLoadState) override;
@@ -58,13 +57,13 @@ class FontFaceImpl final {
     already_AddRefed<gfxUserFontSet> GetUserFontSet() const override;
 
     void CheckUserFontSet() {
-      MutexAutoLock lock(mMutex);
+      AutoWriteLock lock(mLock);
       CheckUserFontSetLocked();
     }
 
 #ifdef DEBUG
     bool HasUserFontSet(gfxUserFontSet* aFontSet) const {
-      MutexAutoLock lock(mMutex);
+      AutoReadLock lock(mLock);
       return mFontSet == aFontSet;
     }
 #endif
@@ -74,18 +73,16 @@ class FontFaceImpl final {
     void FindFontFaceOwners(nsTHashSet<FontFace*>& aOwners);
 
    protected:
-    void CheckUserFontSetLocked() MOZ_REQUIRES(mMutex);
-
-    mutable Mutex mMutex;
+    void CheckUserFontSetLocked() MOZ_REQUIRES(mLock);
 
     // Font set which owns this entry;
-    gfxUserFontSet* MOZ_NON_OWNING_REF mFontSet MOZ_GUARDED_BY(mMutex);
+    gfxUserFontSet* MOZ_NON_OWNING_REF mFontSet MOZ_GUARDED_BY(mLock);
 
     // The FontFace objects that use this user font entry.  We need to store
     // an array of these, not just a single pointer, since the user font
     // cache can return the same entry for different FontFaces that have
     // the same descriptor values and come from the same origin.
-    AutoTArray<FontFaceImpl*, 1> mFontFaces MOZ_GUARDED_BY(mMutex);
+    AutoTArray<FontFaceImpl*, 1> mFontFaces MOZ_GUARDED_BY(mLock);
   };
 
 #ifdef DEBUG