From 3964d1b8ece71516b1c4dc8708c69bec1c9a9334 Mon Sep 17 00:00:00 2001
From: Lee Salzman <lsalzman@mozilla.com>
Date: Thu, 1 Sep 2022 05:29:14 +0000
Subject: [PATCH] Bug 1786136 - Make UserData thread-safe. r=jrmuizel

Differential Revision: https://phabricator.services.mozilla.com/D155997
---
 gfx/2d/2D.h       |  4 +--
 gfx/2d/UserData.h | 84 ++++++++++++++++++++++++++++++++++++++++++++---
 2 files changed, 82 insertions(+), 6 deletions(-)

diff --git a/gfx/2d/2D.h b/gfx/2d/2D.h
index ce5bed6f20c7..f64872df0991 100644
--- a/gfx/2d/2D.h
+++ b/gfx/2d/2D.h
@@ -711,7 +711,7 @@ class SourceSurface : public SupportsThreadSafeWeakPtr<SourceSurface> {
  protected:
   friend class StoredPattern;
 
-  UserData mUserData;
+  ThreadSafeUserData mUserData;
 };
 
 class DataSourceSurface : public SourceSurface {
@@ -1241,7 +1241,7 @@ class ScaledFont : public SupportsThreadSafeWeakPtr<ScaledFont> {
   explicit ScaledFont(const RefPtr<UnscaledFont>& aUnscaledFont)
       : mUnscaledFont(aUnscaledFont), mSyntheticObliqueAngle(0.0f) {}
 
-  UserData mUserData;
+  ThreadSafeUserData mUserData;
   RefPtr<UnscaledFont> mUnscaledFont;
   Float mSyntheticObliqueAngle;
 
diff --git a/gfx/2d/UserData.h b/gfx/2d/UserData.h
index b5c5cc51c310..16a7db343ea8 100644
--- a/gfx/2d/UserData.h
+++ b/gfx/2d/UserData.h
@@ -10,6 +10,8 @@
 #include <stdlib.h>
 #include "Types.h"
 #include "mozilla/Assertions.h"
+#include "mozilla/Atomics.h"
+#include "mozilla/Mutex.h"
 
 namespace mozilla {
 namespace gfx {
@@ -20,14 +22,14 @@ struct UserDataKey {
 
 /* this class is basically a clone of the user data concept from cairo */
 class UserData {
-  typedef void (*destroyFunc)(void* data);
-
  public:
+  typedef void (*DestroyFunc)(void* data);
+
   UserData() : count(0), entries(nullptr) {}
 
   /* Attaches untyped userData associated with key. destroy is called on
    * destruction */
-  void Add(UserDataKey* key, void* userData, destroyFunc destroy) {
+  void Add(UserDataKey* key, void* userData, DestroyFunc destroy) {
     for (int i = 0; i < count; i++) {
       if (key == entries[i].key) {
         if (entries[i].destroy) {
@@ -109,6 +111,9 @@ class UserData {
   }
 
   void Destroy() {
+    if (!entries) {
+      return;
+    }
     for (int i = 0; i < count; i++) {
       if (entries[i].destroy) {
         entries[i].destroy(entries[i].userData);
@@ -125,13 +130,84 @@ class UserData {
   struct Entry {
     const UserDataKey* key;
     void* userData;
-    destroyFunc destroy;
+    DestroyFunc destroy;
   };
 
   int count;
   Entry* entries;
 };
 
+class ThreadSafeUserData {
+ protected:
+  struct LockedUserData : public UserData {
+    Mutex mLock;
+
+    LockedUserData() : mLock("LockedUserData::mLock") {}
+  };
+
+ public:
+  ~ThreadSafeUserData() {
+    if (LockedUserData* userData = mUserData.exchange(nullptr)) {
+      {
+        MutexAutoLock lock(userData->mLock);
+        userData->Destroy();
+      }
+      delete userData;
+    }
+  }
+
+  void Add(UserDataKey* key, void* value, UserData::DestroyFunc destroy) {
+    LockedUserData* userData = GetUserData();
+    MutexAutoLock lock(userData->mLock);
+    userData->Add(key, value, destroy);
+  }
+
+  void* Remove(UserDataKey* key) {
+    LockedUserData* userData = GetUserData();
+    MutexAutoLock lock(userData->mLock);
+    return userData->Remove(key);
+  }
+
+  void RemoveAndDestroy(UserDataKey* key) {
+    LockedUserData* userData = GetUserData();
+    MutexAutoLock lock(userData->mLock);
+    userData->RemoveAndDestroy(key);
+  }
+
+  void* Get(UserDataKey* key) const {
+    LockedUserData* userData = GetUserData();
+    MutexAutoLock lock(userData->mLock);
+    return userData->Get(key);
+  }
+
+  bool Has(UserDataKey* key) {
+    LockedUserData* userData = GetUserData();
+    MutexAutoLock lock(userData->mLock);
+    return userData->Has(key);
+  }
+
+ private:
+  LockedUserData* GetUserData() const {
+    LockedUserData* userData = mUserData;
+    if (!userData) {
+      userData = new LockedUserData;
+      if (!mUserData.compareExchange(nullptr, userData)) {
+        delete userData;
+        userData = mUserData;
+        MOZ_ASSERT(userData);
+      }
+    }
+    return userData;
+  }
+
+  // The Mutex class is quite large. For small, frequent classes (ScaledFont,
+  // SourceSurface, etc.) this can add a lot of memory overhead, especially if
+  // UserData is only infrequently used. To avoid this, we only allocate the
+  // LockedUserData if it is actually used. If unused, it only adds a single
+  // pointer as overhead.
+  mutable Atomic<LockedUserData*> mUserData;
+};
+
 }  // namespace gfx
 }  // namespace mozilla