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Homework

Pre-work

It will be useful for a post-work ;)

Post-work

  • shared_ptr (50 XP)
  • weak_ptr (25 XP) for volunteers
  • make_shared (40 XP) for volunteers

Bonuses

  • +3 XP for delivery of each task before 11.10.2020 23:59
  • +3 XP for cooperation for each person in the group

shared_ptr

(50 XP) Implement your own shared_ptr (simplified).

shared_ptr is a RAII class:

  • Holds a pointer to managed object (template class)
  • Holds a pointer to shared control block with 2 counters and a deleter:
    • shared_refs count (as std::atomic<size_t>)
    • weak_refs count (as std::atomic<size_t>)
    • deleter (function pointer)
  • Constructor copies a pointer and allocate the control block
  • Destructor decrease shared_refs and:
    • if shared_refs == 0 -> release the managed object
    • if shared_refs == 0 and weak_refs == 0 -> release the control block
  • Copying is allowed - it increments shared_refs
  • Moving is allowed and it means:
    • Copying original pointers to a new object
    • Setting source pointer to nullptr
  • Member functions: operator*(), operator->(), get(), reset(), use_count(), operator bool()

Do not forget about CI - UT + Valgrind / ASAN. Work in pairs.

Read the notes on cppreference.com

weak_ptr - for volunteers

(25 XP) Implement your own weak_ptr

  • Proper cooperation with above shared_ptr
  • Member functions: use_count(), expired(), lock(), reset()

Think about proper constructors / assignment operators or visit cppreference.com :)

make_shared - for volunteers (level hard)

(40 XP + achievement) Implement make_shared function.

It should:

  • create a shared_ptr of a given type
  • use variadic templates to take any number of parameters
  • first template parameter type is the underlying object type
  • other template parameters are passed via perfect forwarding to the constructor of a given type

Think about optimized memory layout of shared_ptr created by make_shared. How to achieve it?