vo001_AdoptOrOwnMemory.py File Reference

Detailed Description

In this tutorial we learn how the RVec class can be used to adopt existing memory or allocate some.

 
import ROOT
 
# We use this class for didactic purposes: upon copy, a line is printed to the terminal.
 
ROOT.gInterpreter.Declare('''
class UponCopyPrinter {
public:
   UponCopyPrinter() = default;
   UponCopyPrinter(UponCopyPrinter &&) = default;
   UponCopyPrinter(const UponCopyPrinter &) { std::cout << "Invoking copy c'tor!" << std::endl; }
};
''')
 
RVec_UponCopyPrinter = ROOT.ROOT.VecOps.RVec(ROOT.UponCopyPrinter)
 
# One of the essential features of RVec is its ability of adopting and owning memory.
 
# Let's create an RVec of UponCopyPrinter instances. We expect no printout:
v = RVec_UponCopyPrinter(3)
 
# Let's adopt the memory from v into v2. We expect no printout:
v2 = RVec_UponCopyPrinter(v.data(), v.size())
 
# OK, let's check the addresses of the memory associated to the two RVecs It is the same!
print("%s and %s" %(v.data(), v2.data()))
 
# Now, upon reallocation, the RVec stops adopting the memory and starts owning it. And yes,
# a copy is triggered. Indeed internally the storage of the RVec is an std::vector. Moreover,
# the interface of the RVec is very, very similar to the one of std::vector: you have already
# noticed it when the `data()` method was invoked, right?
v2.resize(4)
 
# Of course, now the addresses are different.
print("%s and %s" %(v.data(), v2.data()))

<cppyy.gbl.UponCopyPrinter object at 0x7ec86e0> and <cppyy.gbl.UponCopyPrinter object at 0x7ec86e0>
<cppyy.gbl.UponCopyPrinter object at 0x7ec86e0> and <cppyy.gbl.UponCopyPrinter object at 0x7dccfc0>

Date

May 2018

Author

Danilo Piparo

Definition in file vo001_AdoptOrOwnMemory.py.