Delete Raft Handle (facebookresearch#3435)

Summary:
Small Raft related modification to StandardGpuResources:
if the stream for a particular device is modified by a user, delete the Raft handle for that device. On any subsequent call to `getRaftHandle(device)`, a new raft handle with the updated stream will be created.
Closes facebookresearch#3424

Pull Request resolved: facebookresearch#3435

Reviewed By: ramilbakhshyiev

Differential Revision: D57640976

Pulled By: junjieqi

fbshipit-source-id: 41e2898a39250b7e52e920b71e819fc21ca9fc85

faiss/gpu/StandardGpuResources.cpp

@@ -257,6 +257,14 @@ void StandardGpuResourcesImpl::setDefaultStream(
         if (prevStream != stream) {
             streamWait({stream}, {prevStream});
         }
+#if defined USE_NVIDIA_RAFT
+        // delete the raft handle for this device, which will be initialized
+        // with the updated stream during any subsequent calls to getRaftHandle
+        auto it2 = raftHandles_.find(device);
+        if (it2 != raftHandles_.end()) {
+            raftHandles_.erase(it2);
+        }
+#endif
     }
 
     userDefaultStreams_[device] = stream;
@@ -275,6 +283,14 @@ void StandardGpuResourcesImpl::revertDefaultStream(int device) {
 
             streamWait({newStream}, {prevStream});
         }
+#if defined USE_NVIDIA_RAFT
+        // delete the raft handle for this device, which will be initialized
+        // with the updated stream during any subsequent calls to getRaftHandle
+        auto it2 = raftHandles_.find(device);
+        if (it2 != raftHandles_.end()) {
+            raftHandles_.erase(it2);
+        }
+#endif
     }
 
     userDefaultStreams_.erase(device);