Bug 1595578 - Don't release the AutoIPCStream immediately when called from IPDLParamTraits, since we need it to outlive the message currently being serialized. r=baku,kmag

Differential Revision: https://phabricator.services.mozilla.com/D54867

--HG--
extra : moz-landing-system : lando

ipc/glue/IPCStreamUtils.cpp

@@ -441,7 +441,8 @@ Maybe<IPCStream>& AutoIPCStream::TakeOptionalValue() {
 void IPDLParamTraits<nsIInputStream*>::Write(IPC::Message* aMsg,
                                              IProtocol* aActor,
                                              nsIInputStream* aParam) {
-  mozilla::ipc::AutoIPCStream autoStream;
+  auto autoStream = MakeRefPtr<HoldIPCStream>();
+
   bool ok = false;
   bool found = false;
 
@@ -453,22 +454,22 @@ void IPDLParamTraits<nsIInputStream*>::Write(IPC::Message* aMsg,
     switch (actor->GetProtocolId()) {
       case PContentMsgStart:
         if (actor->GetSide() == mozilla::ipc::ParentSide) {
-          ok = autoStream.Serialize(
+          ok = autoStream->Serialize(
               aParam, static_cast<mozilla::dom::ContentParent*>(actor));
         } else {
           MOZ_RELEASE_ASSERT(actor->GetSide() == mozilla::ipc::ChildSide);
-          ok = autoStream.Serialize(
+          ok = autoStream->Serialize(
               aParam, static_cast<mozilla::dom::ContentChild*>(actor));
         }
         found = true;
         break;
       case PBackgroundMsgStart:
         if (actor->GetSide() == mozilla::ipc::ParentSide) {
-          ok = autoStream.Serialize(
+          ok = autoStream->Serialize(
               aParam, static_cast<mozilla::ipc::PBackgroundParent*>(actor));
         } else {
           MOZ_RELEASE_ASSERT(actor->GetSide() == mozilla::ipc::ChildSide);
-          ok = autoStream.Serialize(
+          ok = autoStream->Serialize(
               aParam, static_cast<mozilla::ipc::PBackgroundChild*>(actor));
         }
         found = true;
@@ -487,7 +488,13 @@ void IPDLParamTraits<nsIInputStream*>::Write(IPC::Message* aMsg,
   }
   MOZ_RELEASE_ASSERT(ok, "Failed to serialize nsIInputStream");
 
-  WriteIPDLParam(aMsg, aActor, autoStream.TakeOptionalValue());
+  WriteIPDLParam(aMsg, aActor, autoStream->TakeOptionalValue());
+
+  // Dispatch the autoStream to an async runnable, so that we guarantee it
+  // outlives this callstack, and doesn't shut down any actors we created
+  // until after we've finished sending the current message.
+  NS_ProxyRelease("IPDLParamTraits<nsIInputStream*>::Write::autoStream",
+                  NS_GetCurrentThread(), autoStream.forget(), true);
 }
 
 bool IPDLParamTraits<nsIInputStream*>::Read(const IPC::Message* aMsg,

ipc/glue/IPCStreamUtils.h

@@ -120,7 +120,7 @@ already_AddRefed<nsIInputStream> DeserializeIPCStream(
 //       with complex ipdl structures.  For example, you may want to create an
 //       array of RAII AutoIPCStream objects or build your own wrapping
 //       RAII object to handle other actors that need to be cleaned up.
-class AutoIPCStream final {
+class AutoIPCStream {
  public:
   // Implicitly create an Maybe<IPCStream> value.  Either
   // TakeValue() or TakeOptionalValue() can be used.
@@ -182,6 +182,14 @@ class AutoIPCStream final {
   const bool mDelayedStart;
 };
 
+class HoldIPCStream final : public AutoIPCStream {
+ public:
+  NS_INLINE_DECL_REFCOUNTING(HoldIPCStream)
+
+ private:
+  ~HoldIPCStream() = default;
+};
+
 template <>
 struct IPDLParamTraits<nsIInputStream*> {
   static void Write(IPC::Message* aMsg, IProtocol* aActor,