Backed out 2 changesets (bug 1720965) for causing bustages on nsContentUtils.cpp. CLOSED TREE

Backed out changeset 2ed56ddce45a (bug 1720965)
Backed out changeset 3531708ab54e (bug 1720965)

dom/canvas/ClientWebGLContext.cpp

@@ -903,10 +903,8 @@ RefPtr<gfx::SourceSurface> ClientWebGLContext::GetFrontBufferSnapshot(
     if (!child->SendGetFrontBufferSnapshot(&res)) {
       res = {};
     }
-    if (!res.shmem) return nullptr;
-
     const auto& surfSize = res.surfSize;
-    const webgl::RaiiShmem shmem{child, res.shmem.ref()};
+    const webgl::RaiiShmem shmem{child, res.shmem};
     const auto& shmemBytes = shmem.ByteRange();
     if (!surfSize.x) return nullptr;  // Zero means failure.
 

dom/canvas/WebGLIpdl.h

@@ -112,9 +112,9 @@ template <>
 struct IPDLParamTraits<mozilla::webgl::FrontBufferSnapshotIpc> final {
   using T = mozilla::webgl::FrontBufferSnapshotIpc;
 
-  static void Write(IPC::Message* const msg, IProtocol* actor, const T& in) {
+  static void Write(IPC::Message* const msg, IProtocol* actor, T& in) {
     WriteParam(msg, in.surfSize);
-    WriteIPDLParam(msg, actor, in.shmem);
+    WriteIPDLParam(msg, actor, std::move(in.shmem));
   }
 
   static bool Read(const IPC::Message* const msg, PickleIterator* const itr,
@@ -130,10 +130,10 @@ template <>
 struct IPDLParamTraits<mozilla::webgl::ReadPixelsResultIpc> final {
   using T = mozilla::webgl::ReadPixelsResultIpc;
 
-  static void Write(IPC::Message* const msg, IProtocol* actor, const T& in) {
+  static void Write(IPC::Message* const msg, IProtocol* actor, T& in) {
     WriteParam(msg, in.subrect);
     WriteParam(msg, in.byteStride);
-    WriteIPDLParam(msg, actor, in.shmem);
+    WriteIPDLParam(msg, actor, std::move(in.shmem));
   }
 
   static bool Read(const IPC::Message* const msg, PickleIterator* const itr,

dom/canvas/WebGLParent.cpp

@@ -100,16 +100,16 @@ IPCResult WebGLParent::RecvGetFrontBufferSnapshot(
       NS_WARNING("Failed to alloc shmem for RecvGetFrontBufferSnapshot.");
       return IPC_FAIL(this, "Failed to allocate shmem for result");
     }
-    const auto range = shmem.ByteRange();
-    *ret = {surfSize, Some(shmem.Extract())};
 
+    const auto range = shmem.ByteRange();
+    auto retSize = surfSize;
     if (!mHost->FrontBufferSnapshotInto(Some(range))) {
       gfxCriticalNote << "WebGLParent::RecvGetFrontBufferSnapshot: "
                          "FrontBufferSnapshotInto(some) failed after "
                          "FrontBufferSnapshotInto(none)";
-      // Zero means failure, as we still need to send any shmem we alloc.
-      ret->surfSize = {0, 0};
+      retSize = {0, 0};  // Zero means failure.
     }
+    *ret = {retSize, shmem.Extract()};
   }
   return IPC_OK();
 }

dom/canvas/WebGLTypes.h

@@ -740,7 +740,7 @@ struct GetUniformData final {
 
 struct FrontBufferSnapshotIpc final {
   uvec2 surfSize = {};
-  Maybe<mozilla::ipc::Shmem> shmem = {};
+  mozilla::ipc::Shmem shmem = {};
 };
 
 struct ReadPixelsResult {

gfx/ipc/GfxMessageUtils.h

@@ -1213,7 +1213,7 @@ struct IPDLParamTraits<gfx::PaintFragment> {
            aParam.mRecording.mLen);
 
     WriteParam(aMsg, aParam.mSize);
-    WriteIPDLParam(aMsg, aActor, shmem);
+    WriteIPDLParam(aMsg, aActor, std::move(shmem));
     WriteParam(aMsg, aParam.mDependencies);
   }
 

ipc/glue/Shmem.cpp

@@ -265,7 +265,7 @@ void Shmem::AssertInvariants() const {
   Unused << checkMappingBack;
 }
 
-void Shmem::RevokeRights(PrivateIPDLCaller) const {
+void Shmem::RevokeRights(PrivateIPDLCaller) {
   AssertInvariants();
 
   size_t pageSize = SharedMemory::SystemPageSize();
@@ -437,11 +437,11 @@ UniquePtr<IPC::Message> Shmem::UnshareFrom(PrivateIPDLCaller,
 }
 
 void IPDLParamTraits<Shmem>::Write(IPC::Message* aMsg, IProtocol* aActor,
-                                   const Shmem& aParam) {
-  MOZ_ASSERT(aParam.IsReadable());
+                                   Shmem&& aParam) {
   WriteIPDLParam(aMsg, aActor, aParam.mId);
 
   aParam.RevokeRights(Shmem::PrivateIPDLCaller());
+  aParam.forget(Shmem::PrivateIPDLCaller());
 }
 
 bool IPDLParamTraits<Shmem>::Read(const IPC::Message* aMsg,

ipc/glue/Shmem.h

@@ -138,9 +138,9 @@ class Shmem final {
   SharedMemory* Segment(PrivateIPDLCaller) const { return mSegment; }
 
 #ifndef DEBUG
-  void RevokeRights(PrivateIPDLCaller) const {}
+  void RevokeRights(PrivateIPDLCaller) {}
 #else
-  void RevokeRights(PrivateIPDLCaller) const;
+  void RevokeRights(PrivateIPDLCaller);
 #endif
 
   void forget(PrivateIPDLCaller) {

ipc/glue/ShmemMessageUtils.h

@@ -18,20 +18,7 @@ template <>
 struct IPDLParamTraits<Shmem> {
   typedef Shmem paramType;
 
-  // NB: std::move(Shmem) is a /copy/.
-  // It would be nice to make a Shmem a move-only class, but the ipdlh
-  // generator can't handle those yet. One solution would be to use a dumb
-  // struct/descriptor for ipdlh purposes. Arguably this dumb non-move-only
-  // struct *is* Shmem.
-  // Because Shmem is not move-only, when previous versions of this code
-  // required Shmem&& here, it caused devs to assume that Shmem was move-aware,
-  // when it is not. People would then cargo-cult std::move(shmem), even though
-  // that's a copy. This can be a sign that people are getting the wrong idea
-  // about how to use it, and when things happen. In particular,
-  // `std::move(shmem)` leaves the strong references in `shmem` intact, and we
-  // should avoid causing readers to believe otherwise.
-  static void Write(IPC::Message* aMsg, IProtocol* aActor,
-                    const paramType& aParam);
+  static void Write(IPC::Message* aMsg, IProtocol* aActor, paramType&& aParam);
   static bool Read(const IPC::Message* aMsg, PickleIterator* aIter,
                    IProtocol* aActor, paramType* aResult);
 

ipc/ipdl/ipdl/lower.py

@@ -559,6 +559,9 @@ def _cxxConstRefType(ipdltype, side):
     t = _cxxBareType(ipdltype, side)
     if ipdltype.isIPDL() and ipdltype.isActor():
         return t
+    if ipdltype.isIPDL() and ipdltype.isShmem():
+        t.ref = True
+        return t
     if ipdltype.isIPDL() and ipdltype.isByteBuf():
         t.ref = True
         return t
@@ -610,7 +613,8 @@ def _cxxTypeNeedsMoveForSend(ipdltype):
         if ipdltype.hasBaseType():
             return _cxxTypeNeedsMove(ipdltype.basetype)
         return (
-            ipdltype.isByteBuf()
+            ipdltype.isShmem()
+            or ipdltype.isByteBuf()
             or ipdltype.isEndpoint()
             or ipdltype.isManagedEndpoint()
         )
@@ -845,6 +849,8 @@ class _StructField(_CompoundTypeComponent):
     def constRefExpr(self, thisexpr=None):
         # sigh, gross hack
         refexpr = self.refExpr(thisexpr)
+        if "Shmem" == self.ipdltype.name():
+            refexpr = ExprCast(refexpr, Type("Shmem", ref=True), const=True)
         if "ByteBuf" == self.ipdltype.name():
             refexpr = ExprCast(refexpr, Type("ByteBuf", ref=True), const=True)
         if "FileDescriptor" == self.ipdltype.name():
@@ -1024,6 +1030,8 @@ class _UnionMember(_CompoundTypeComponent):
         # sigh
         if "ByteBuf" == self.ipdltype.name():
             v = ExprCast(v, Type("ByteBuf", ref=True), const=True)
+        if "Shmem" == self.ipdltype.name():
+            v = ExprCast(v, Type("Shmem", ref=True), const=True)
         if "FileDescriptor" == self.ipdltype.name():
             v = ExprCast(v, Type("FileDescriptor", ref=True), const=True)
         return v