Do not call TTree cache after an exception happens

IOPool/Input/src/RootDelayedReader.cc

@@ -11,6 +11,8 @@
 
 #include "IOPool/Common/interface/getWrapperBasePtr.h"
 
+#include "FWCore/Utilities/interface/EDMException.h"
+
 #include "TBranch.h"
 #include "TClass.h"
 
@@ -40,6 +42,9 @@ namespace edm {
 
   std::unique_ptr<WrapperBase>
   RootDelayedReader::getProduct_(BranchKey const& k, EDProductGetter const* ep) const {
+    if (lastException_) {
+      throw *lastException_;
+    }
     iterator iter = branchIter(k);
     if (!found(iter)) {
       if (nextReader_) {
@@ -59,6 +64,9 @@ namespace edm {
     }
 
     setRefCoreStreamer(ep);
+    //make code exception safe
+    std::shared_ptr<void> refCoreStreamerGuard(nullptr,[](void*){    setRefCoreStreamer(false);
+      ;});
     TClass* cp = branchInfo.classCache_;
     if(nullptr == cp) {
       branchInfo.classCache_ = TClass::GetClass(branchInfo.branchDescription_.wrappedName().c_str());
@@ -68,12 +76,17 @@ namespace edm {
     void* p = cp->New();
     std::unique_ptr<WrapperBase> edp = getWrapperBasePtr(p, branchInfo.offsetToWrapperBase_); 
     br->SetAddress(&p);
-    tree_.getEntry(br, tree_.entryNumberForIndex(ep->transitionIndex()));
+    try{
+      tree_.getEntry(br, tree_.entryNumberForIndex(ep->transitionIndex()));
+    } catch(const edm::Exception& exception) {
+      lastException_ = std::make_unique<Exception>(exception);
+      lastException_->addContext("Rethrowing an exception that happened on a different thread.");
+      throw exception;
+    }
     if(tree_.branchType() == InEvent) {
       // CMS-THREADING For the primary input source calls to this function need to be serialized
       InputFile::reportReadBranch(inputType_, std::string(br->GetName()));
     }
-    setRefCoreStreamer(false);
     return edp;
   }
 }

IOPool/Input/src/RootDelayedReader.h

@@ -21,6 +21,7 @@ namespace edm {
   class InputFile;
   class RootTree;
   class SharedResourcesAcquirer;
+  class Exception;
 
   //------------------------------------------------------------
   // Class RootDelayedReader: pretends to support file reading.
@@ -60,6 +61,10 @@ namespace edm {
     std::unique_ptr<SharedResourcesAcquirer> resourceAcquirer_;
     InputType inputType_;
     TClass* wrapperBaseTClass_;
+    //If a fatal exception happens we need to make a copy so we can
+    // rethrow that exception on other threads. This avoids TTree
+    // non-exception safety problems on later calls to TTree.
+    mutable std::unique_ptr<Exception> lastException_;
   }; // class RootDelayedReader
   //------------------------------------------------------------
 }