Workaround for ROOT6 limitation

[wmtan]

ROOT6 uses a version of the llvm just in time compiler that cannot handle embedded assembler code.
boost/shared_ptr.hpp contains (indirectly) two headers that contain assembler. This breaks many framework unit tests.
This workaround sets preprocessor variables recognized by boost that are used if and only if ROOTCLING is defined. These preprocessor definitions cause the assembler code to not be included. This fixes the unit test errors.
The final fix for this problem should be either that ROOT6 is fixed to handle assembler, OR that CMSSW replaces with std::shared_ptr those uses of boost::shared_ptr that cause problems

[cmsbuild]

A new Pull Request was created by @wmtan for CMSSW_7_0_ROOT6_X.

Workaround for ROOT6 limitation

It involves the following packages:

DataFormats/Common
DataFormats/FWLite
DataFormats/Provenance
DataFormats/Streamer
DataFormats/TestObjects
DataFormats/WrappedStdDictionaries
FWCore/Common
FWCore/MessageLogger
FWCore/TFWLiteSelector
FWCore/TFWLiteSelectorTest
FWCore/Utilities

@cmsbuild, @Dr15Jones, @ktf, @nclopezo can you please review it and eventually sign? Thanks.
You can sign-off by replying to this message having '+1' in the first line of your reply.
You can reject by replying to this message having '-1' in the first line of your reply.

[davidlt]

I thought I fixed it [1] by forcing boost to use spinlocks instead of self-implemented atomics.

As I recall this limitation for inline assembly should be gone before the final ROOT6 release and we should look into refactoring code to use std::shared_ptr as we already have discussed (Maybe CMSSW_7_1_X?)

[1] https://github.com/cms-sw/cmsdist/blob/IB/CMSSW_7_0_X/root6/boost-1.51.0-define-BOOST_SP_USE_SPINLOCK.patch

[wmtan]

Unfortunately, contrary to what the ROOT team says, using BOOST_SP_USE_SPINLOCK does not fix the problem, for two separate reasons: 1) the headers pulled in by spinlock also contain assembler, AND 2) boost/shared_ptr contains (indirectly) a second header that includes assembler that is unaffected by spinlock.
A separate #defe
Refactoring the code to use std::shared ptr is a good idea but far from easy, because the framework uses many other boost constructs that require boost::shared_ptr.

[wmtan]

Help! I closed this accidentally! Please reopen!!!

[davidlt]

Usually there should "reopen" button.

[wmtan]

I've been through this before. I don't have the authority for a reopen button. None on my screen/
Anyway, I opened 1843 as a duplicate. Close one and merge the other.

[wmtan]

The forcing of boost to use spinlocks should now be removed. It could cause other problems.

[davidlt]

I only noticed performance regressions with spinlocks, which is fully expected for my eyes. Once we have the IB we could re-test if it fixes all boost related inline assembly cases.