TClass::GetBaseClassOffset is a 'often' used routine in the I/O.
In the fast path (looking up in a cache), rather than taking the
global read lock (which is not only global but also 'slower' than
a regular mutex), we are now use a instance specific mutex to
protect the cache.

Add new enum for TObject::Write: kOnlyPrepStep  = BIT(3)         ///< Just prepare the objects do not write them (i.e. call TTree::FlushBaskets)

If TBufferMerger can take the merge lock, then rather than queuing the input file, merge it immediately
and skip the Writing the TTree, doing a memcpy, Pushing to the queue then Reading and then deleting parts.

Currently only in the case where we have a Merge function and a dictionary.

For iteration over the list of baskets, the existing code try to reduce the range of the iteration
to stop as soon as all non-nullptr slot have been seen.
However to know the number of non-nullptr slot, the code (has to) call GetEntries which scan the
entire array anyway ...

TObjArray::GetEntries() counts the number of non-zero slots
while TObjArray::GetEntriesFast() return (in most case) the value of a high water mark (the slot over which all remaining slots
are empty).

In one use case (doing read a TTree and do many TTree cloning (via TBufferMerger), TObjArray::GetEntries was taking 8% of the
running time (compression was disabled)

Note: TObjArray::IsEmpty use GetEntriesFast rather than GetEntries.

Limited to TTree and Histogram.

We do not apply the same to CloneTree as the addresses copying
is a side-effect (no reset at the end) that is relied upon by
user code.g

This can be used to monitor the queue size in bytes rather than number of files

This can now be safely use to avoid overloading the queue.

This speeds up the first step of merging (hadd)

This allow the fast cloning of the first tree in the list when using TTree::MergeTrees (rare)

When fMother is not set, first try to use fParent rather than iterate through
the TTree's list of top level branches

fParent was already set during the usual branch creation (TTree::Branch and friends) but
might still be not set if the user create a hierarchy by hand

... instead of just always ignoring it

apply this:
https://github.com/root-project/root/pull/7193#discussion_r585660675

change test limits taken from:
https://github.com/root-project/root/commit/fe5c74b5ed6045eb72091bad693f7af1fdf2266e

Cloned histogram should not be assign to current directory

Adding them in the MT tutorial list should make them run serially

Fixes issue #7115.

Some characters need to be escaped before using variable names in std::regex
expressions formed in RooFormula::processForumla.

Both [ and ] were already considered; this commit adds { and } to the list.

In such case gPad can be set to nullptr and function fails
Solving https://root-forum.cern.ch/t/43560

This modification was done in the old (legacy) JupyROOT, but not
in the new one that was separated from the new PyROOT.

This fixes the display of JSROOT graphics in SWAN.

* Allow for dynamic switching of system of units between Geant4 units and Root units

* Add README file for dynamic switching of system of units between Geant4 units and Root units

* Add README file for dynamic switching of system of units between Geant4 units and Root units

* Fix geom warnings on windows

* Fix to PR 7165: Remove inline access to static class member

(cherry picked from commit 60890d891df3e18c33d321015966916998680a0b)

* Allow for dynamic switching of system of units between Geant4 units and Root units

* Add README file for dynamic switching of system of units between Geant4 units and Root units

* Add README file for dynamic switching of system of units between Geant4 units and Root units

* Fix geom warnings on windows

(cherry picked from commit 3d545273d7763e09aa85449ba86be5d2493f7f13)

Avoid misinterpretation of parameter if after SetBinary
SetNull is set. Also check memory allocation.

It does not return size of allocated memory,
therefore just reallocate buffer if maxsize bigger than standard buffer