The document discusses new features in C++ 20 including coroutines, concepts and constraints, and multithreading. Coroutines allow for suspending and resuming functions using co_await, co_yield, and co_return. Concepts define requirements for templates and enable constraints. Multithreading features include std::jthread for auto-joinable threads and handling interrupt requests.

1. C++ 20
Features of the Modern C++ 20
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2. Agenda
• Coroutines
• Concepts and constraints
• Multithreading
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3. Coroutines
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4. Coroutines in C++
In C++ 20, coroutines are stackless: they suspend execution by
returning to the caller and the data that is required to resume
execution is stored separately from the stack.
A function is coroutine if its definition consists of any of the following:
• co_await
• co_yield
• co_return
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5. co_yield
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6. Number generator – co_yield
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7. Number generator – co_yield
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8. Number generator – co_yield
Output:
The coroutine int_generator creates an infinite data stream.
0 1 2 3 4 5 6 7 8 9
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9. Fibonacci generator using co_yield
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10. Fibonacci generator using co_yield
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11. Fibonacci generator using co_yield
Output:
0 1 1 2 3 5 8 13 21 34
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12. Sequence range – co_yeild
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13. Sequence range – co_yeild
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14. Sequence range – co_yeild
Output:
10 11 12 13 14
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15. co_await
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16. Disclaimer: slightly more complex
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17. Producer Consumer – co_await
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18. Producer Consumer – co_await
No need to suspend at the beginning or at the end
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19. Producer Consumer – co_await
Have to provide interface resumable interface
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20. Producer Consumer – co_await
Not going to control it via resumable interface
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21. Producer Consumer – co_await
Event that is used to organize communication
between producer and consumer
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22. Producer Consumer – co_await
Producer uses set() to resume consumer
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23. Producer Consumer – co_await
Consumer uses this operator to wait for
producer (suspend state)
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24. Producer Consumer – co_await
Describe behavior of Consumer
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25. Producer Consumer – co_await
Consumer stores pointer to awaiter
to be resumed by Producer
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26. Producer Consumer – co_await
Producer uses awaiter to resume Consumer
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27. Producer Consumer – co_await
Product that is produced by Producer
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28. Producer Consumer – co_await
Event to suspend and resume Consumer
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29. Producer Consumer – co_await
Producer’s thread
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30. Producer Consumer – co_await
Simulate long work to produce 1000
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31. Producer Consumer – co_await
Resume Consumer by the event
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32. Producer Consumer – co_await
Consumer’s coroutine
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33. Producer Consumer – co_await
Suspend Consumer until product
is ready
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34. Producer Consumer – co_await
Run Producer and Consumer
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35. Producer Consumer – co_await
Producer: Spend some time to produce a product.
Consumer: Wait for a product.
Main Thread: Consumer’s task is in progress.
Consumer: Product is consumed (value: 1000).
Producer: Product is produced.
Output of the program
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36. Constraints and
Concepts
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37. Constraints and concepts
A concept is a named set of requirements.
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38. Constraints and concepts
A concept is a named set of requirements.
Requirement to have a ‘size()’ method
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39. Constraints and concepts
A concept is a named set of requirements.
Concept usage
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40. Constraints and concepts
A concept is a named set of requirements.
Client code example
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41. Constraints and concepts
A concept is a named set of requirements.
Compilation error
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42. Constraints and concepts – Euclidean metric
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43. Constraints and concepts – Euclidean metric
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44. Constraints and concepts – Euclidean metric
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45. Constraints and concepts – Euclidean metric
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46. Constraints and concepts – Euclidean metric
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47. Constraints and concepts – Euclidean metric
Requirements for input
containers
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48. Multithreading
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49. Multithreading
std::jthread – auto-joinable thread.
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50. Multithreading
std::jthread – auto-joinable thread. Let’s take a look at the example:
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51. Multithreading
std::jthread – auto-joinable thread. Let’s take a look at the example:
terminate called without an active exception
I am a C++ thread.
Aborted (core dumped)
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52. Multithreading
std::jthread – auto-joinable thread. Let’s take a look at the example:
terminate called without an active exception
I am a C++ thread.
Aborted (core dumped) Rewrite using std::jthread
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53. Multithreading – std::jthread
std::jthread – auto-joinable thread. Let’s take a look at the example:
terminate called without an active exception
I am a C++ thread.
Aborted (core dumped)
Auto-joinable behaviorI am a C++ thread.
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54. Multithreading – std::jthread
std::jthread – interruptible thread.
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55. Multithreading – std::jthread
std::jthread – interruptible thread.
Alive during 5 seconds
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56. Multithreading – std::jthread
std::jthread – interruptible thread.
Interrupt after 1 second
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57. Multithreading – std::jthread
std::jthread – interruptible thread.
0 sec.: I am still exist.
Main Thread: interrupt jthread.
1 sec.: I am still exist.
2 sec.: I am still exist.
3 sec.: I am still exist.
4 sec.: I am still exist.
Actual output
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58. Multithreading – std::jthread
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59. Multithreading – std::jthread
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60. Multithreading – std::jthread
Check for stop request
Stop token is required to handle requests
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Send stop signal to the thread

61. Multithreading – std::jthread
0 sec.: I am still exist.
Main Thread: interrupt jthread.
Exit by request.
Thread is terminated after
1 second
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62. Thank you!
Enjoy C++ 20!
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