Bug 1458246 - Use Shmem to pass the profiler data to be able to send large profiler data r=mstange

We were using nsCString to pass the profiler data between processes. But it was
failing to send because there is a ~256MB limit for the string data. So we
changed it to use Shmem instead. Shmem creates a shared memory and passes the
weak reference. With it, we can send larger data without having a problem.

MozReview-Commit-ID: 1kj57fZDXVF

--HG--
extra : rebase_source : 25a8ab57bcae8012fee1cdd9d4b767036db192d7

tools/profiler/gecko/PProfiler.ipdl

@@ -23,7 +23,7 @@ child:
   async Pause();
   async Resume();
 
-  async GatherProfile() returns (nsCString profile);
+  async GatherProfile() returns (Shmem profile);
 };
 
 } // namespace mozilla

tools/profiler/gecko/ProfilerChild.cpp

@@ -88,10 +88,26 @@ CollectProfileOrEmptyString(bool aIsShuttingDown)
   return profileCString;
 }
 
+Shmem
+ProfilerChild::ConvertProfileStringToShmem(const nsCString& aProfileCString) {
+  Shmem shmem;
+  if (!AllocShmem(aProfileCString.Length(),
+                  SharedMemory::TYPE_BASIC,
+                  &shmem)) {
+    return shmem;
+  }
+
+  PodCopy(shmem.get<char>(),
+          aProfileCString.BeginReading(),
+          aProfileCString.Length());
+  return shmem;
+}
+
 mozilla::ipc::IPCResult
 ProfilerChild::RecvGatherProfile(GatherProfileResolver&& aResolve)
 {
-  aResolve(CollectProfileOrEmptyString(/* aIsShuttingDown */ false));
+  nsCString profile = CollectProfileOrEmptyString(/* aIsShuttingDown */ false);
+  aResolve(ConvertProfileStringToShmem(profile));
   return IPC_OK();
 }
 

tools/profiler/gecko/nsProfiler.cpp

@@ -618,8 +618,10 @@ nsProfiler::StartGathering(double aSinceTime)
   RefPtr<nsProfiler> self = this;
   for (auto profile : profiles) {
     profile->Then(GetMainThreadSerialEventTarget(), __func__,
-      [self](const nsCString& aResult) {
-        self->GatheredOOPProfile(aResult);
+      [self](const mozilla::ipc::Shmem& aResult) {
+        const nsDependentCString profileString(aResult.get<char>(),
+                                               aResult.Size<char>());
+        self->GatheredOOPProfile(profileString);
       },
       [self](ipc::ResponseRejectReason aReason) {
         self->GatheredOOPProfile(NS_LITERAL_CSTRING(""));

tools/profiler/public/ProfilerChild.h

@@ -18,7 +18,8 @@ namespace mozilla {
 // process. The corresponding ProfilerParent actor is created in the main
 // process, and it will notify us about profiler state changes and request
 // profiles from us.
-class ProfilerChild final : public PProfilerChild
+class ProfilerChild final : public PProfilerChild,
+                            public mozilla::ipc::IShmemAllocator
 {
   NS_INLINE_DECL_REFCOUNTING(ProfilerChild)
 
@@ -43,6 +44,9 @@ private:
   mozilla::ipc::IPCResult RecvGatherProfile(GatherProfileResolver&& aResolve) override;
 
   void ActorDestroy(ActorDestroyReason aActorDestroyReason) override;
+  Shmem ConvertProfileStringToShmem(const nsCString& profile);
+
+  FORWARD_SHMEM_ALLOCATOR_TO(PProfilerChild)
 
   nsCOMPtr<nsIThread> mThread;
   bool mDestroyed;

tools/profiler/public/ProfilerParent.h

@@ -35,7 +35,7 @@ public:
 
   static mozilla::ipc::Endpoint<PProfilerChild> CreateForProcess(base::ProcessId aOtherPid);
 
-  typedef MozPromise<nsCString, ResponseRejectReason, false> SingleProcessProfilePromise;
+  typedef MozPromise<Shmem, ResponseRejectReason, true> SingleProcessProfilePromise;
 
   // The following static methods can be called on any thread, but they are
   // no-ops on anything other than the main thread.