Custom member streamer for CalArray<o2::tpc::PadFlags>::mData

This commit expands on #14427
and fixes the issue brought up in https://its.cern.ch/jira/browse/O2-4671.

After debugging/testing it turns out that the approach taken via a customer streamer
for std::vector<o2::tpc::PadFlags> does not take effect in the ROOT/IO because
apparently ROOT still prefers to use the CollectionProxy for std::vector and does not
employ the custom streamer.

Instead, after discussion with @pcanal, this commit proposes to implement a
custom stream just for the mData data member of CalArray<o2::tpc::PadFlags>.
This is the only place where we use o2::tpc::PadFlags in IO and it fixes the problem
when reading CCDB objects containing such data.

I have verified that the following code
```
o2-ccdb-downloadccdbfile -p TPC/Calib/IDC_PadStatusMap_A -t 1731274461770 -d ./ -o tpc_idc.root --no-preserve-path
root tpc_idc.root
gFile->Get<o2::tpc::CalDet<o2::tpc::PadFlags>>("ccdb_object")
```
correctly executes the custom streamer function.

Note that there is also no need to make the code ROOT version dependent. We need to fix the reading in any
case and the writing will just stay the same.

Concerning situations, where future classes will write data containing std::vector<o2::tpc::PadFlags>
we should be protected by the fact that this bug has been fixed >= ROOT 6.36 in any case.

This commit relates also to

root-project/root#17009

The commit also re-enables dictionary creation of related classes
and adds a dictionary for CalArray<o2::tpc::PadFlags> previously missing.

Author: sawenzel

DataFormats/Detectors/TPC/CMakeLists.txt

@@ -40,7 +40,6 @@ o2_add_library(
 
 o2_target_root_dictionary(
   DataFormatsTPC
-  EXTRA_PATCH src/VectorPadflagsCustomStreamer.cxx
   HEADERS include/DataFormatsTPC/ClusterGroupAttribute.h
           include/DataFormatsTPC/ClusterNative.h
           include/DataFormatsTPC/ClusterNativeHelper.h

DataFormats/Detectors/TPC/src/DataFormatsTPCLinkDef.h

@@ -22,15 +22,15 @@
 #pragma link C++ class o2::tpc::ClusterHardwareContainerFixedSize < 8192> + ;
 #pragma link C++ class o2::tpc::ClusterNativeContainer + ;
 #pragma link C++ class o2::tpc::Digit + ;
-// pragma link C++ enum o2::tpc::PadFlags +;                // enum itself
+#pragma link C++ enum o2::tpc::PadFlags + ; // enum itself
 #pragma link C++ class o2::tpc::ZeroSuppressedContainer8kb + ;
 #pragma link C++ class std::vector < o2::tpc::ClusterNative> + ;
 #pragma link C++ class std::vector < o2::tpc::ClusterNativeContainer> + ;
 #pragma link C++ class std::vector < o2::tpc::ClusterHardware> + ;
 #pragma link C++ class std::vector < o2::tpc::ClusterHardwareContainerFixedSize < 8192>> + ;
 #pragma link C++ class std::vector < o2::tpc::ClusterHardwareContainer8kb> + ;
 #pragma link C++ class std::vector < o2::tpc::Digit> + ;
-// pragma link C++ class std::vector < o2::tpc::PadFlags> + ;
+#pragma link C++ class std::vector < o2::tpc::PadFlags> + ;
 #pragma link C++ class std::vector < o2::tpc::ZeroSuppressedContainer8kb> + ;
 #pragma link C++ class o2::tpc::TrackTPC + ;
 #pragma link C++ class o2::tpc::LaserTrack + ;

DataFormats/Detectors/TPC/src/VectorPadflagsCustomStreamer.cxx

@@ -43,6 +43,7 @@ o2_add_library(TPCBase
                                      O2::DetectorsRaw O2::CCDB FairRoot::Base)
 
 o2_target_root_dictionary(TPCBase
+                          EXTRA_PATCH src/TPCFlagsMemberCustomStreamer.cxx
                           HEADERS include/TPCBase/CalArray.h
                                   include/TPCBase/CalDet.h
                                   include/TPCBase/CDBInterface.h

Detectors/TPC/base/CMakeLists.txt

@@ -21,6 +21,7 @@
 #pragma link C++ class o2::tpc::CalArray < unsigned> + ;
 #pragma link C++ class o2::tpc::CalArray < short> + ;
 #pragma link C++ class o2::tpc::CalArray < bool> + ;
+#pragma link C++ class o2::tpc::CalArray < o2::tpc::PadFlags> + ;
 #pragma link C++ class o2::tpc::CalDet < float> + ;
 #pragma link C++ class o2::tpc::CalDet < double> + ;
 #pragma link C++ class o2::tpc::CalDet < int> + ;

Detectors/TPC/base/src/TPCBaseLinkDef.h

@@ -0,0 +1,79 @@
+// Copyright 2019-2020 CERN and copyright holders of ALICE O2.
+// See https://alice-o2.web.cern.ch/copyright for details of the copyright holders.
+// All rights not expressly granted are reserved.
+//
+// This software is distributed under the terms of the GNU General Public
+// License v3 (GPL Version 3), copied verbatim in the file "COPYING".
+//
+// In applying this license CERN does not waive the privileges and immunities
+// granted to it by virtue of its status as an Intergovernmental Organization
+// or submit itself to any jurisdiction.
+
+#include "TPCBase/CalArray.h"
+#include <TMemberStreamer.h>
+#include <TBuffer.h>
+#include <DataFormatsTPC/Defs.h>
+#include <iostream>
+
+// to enable assert statements
+#ifdef NDEBUG
+#undef NDEBUG
+#include <cassert>
+#endif
+
+// The following code provides a specific ROOT I/O streaming method
+// for the mData member of CalArray<o2::tpc::PadFlags>
+// This member was written incorrectly to the TFile in ROOT versions < 6.36, causing
+// segfaults when reading on ARM64 (occassionally).
+// We continue to write it in the incorrect format and fix the reading back.
+
+// See also:
+// - https://github.com/root-project/root/pull/17009
+// - https://its.cern.ch/jira/browse/O2-4671
+
+void MemberVectorPadFlagsStreamer(TBuffer& R__b, void* objp, int n)
+{
+  if (n != 1) {
+    std::cerr << "Error in MemberVectorPadFlagsStreamer : Unexpected n " << n << std::endl;
+    return;
+  }
+  std::vector<o2::tpc::PadFlags>* obj = static_cast<std::vector<o2::tpc::PadFlags>*>(objp);
+  if (R__b.IsReading()) {
+    std::vector<int> R__stl;
+    R__stl.clear();
+    int R__n;
+    R__b >> R__n;
+    R__stl.reserve(R__n);
+    for (int R__i = 0; R__i < R__n; R__i++) {
+      Int_t readtemp;
+      R__b >> readtemp;
+      R__stl.push_back(readtemp);
+    }
+    auto data = reinterpret_cast<unsigned short*>(R__stl.data());
+    for (int i = 0; i < R__n; ++i) {
+      obj->push_back(static_cast<o2::tpc::PadFlags>(data[i]));
+    }
+  } else {
+    // We always save things with the old format.
+    R__b << (int)obj->size() / 2;
+    for (size_t i = 0; i < obj->size(); i++) {
+      R__b << (short)obj->at(i);
+    }
+  }
+}
+
+// register the streamer via static global initialization (on library load)
+namespace ROOT
+{
+static __attribute__((used)) int _R__dummyStreamer_3 =
+  ([]() {
+    auto cl = TClass::GetClass<o2::tpc::CalArray<o2::tpc::PadFlags>>();
+    if (cl) {
+      cl->AdoptMemberStreamer("mData", new TMemberStreamer(MemberVectorPadFlagsStreamer));
+    } else {
+      // we should never come here ... and if we do we should assert/fail
+      assert(false);
+    }
+    return 0;
+  })();
+} // namespace ROOT