SberTech ♥ Open Source, concurrency and reliable banking operations - problem analysis with Joker 2018

This weekend passed Joker 2018 , it was interesting! But not only by speeches was the conference rich. All sponsoring companies tried to stand out against the “competitors” and we are no exception.

There was a lot of interesting things on the Sberbank-Technologies stand, but I want to tell you about how we stood out. Our Apache Ignite development team at SberTech prepared tasks and conducted a rally for those who dared to solve them.

Under the cat you expect the problem, the analysis of solutions and the ability to justify your own solution in the comments.
')

Woe-committers

Petya and Kolya commit in Apache Ignite one feature per day.

Masha promptly tests every feature and rolls back commits containing errors.
Every third initial commit from Petit and the fifth from Kolya contain an error.
Petya spends an additional 2 days on correcting the error, Kolya 3, and they again do
commit

How many features will be committed in 86 working days, if Masha likes Peter,
and she notices his mistake only on the day when only he is mistaken?

Villaribo and Villabaggio

Processing an unreliable bank in a group of accounts locks keys
accounts in the order of their announcement in the operation, i.e. from left to right.
Each deadlock is solved manually by bank specialists and takes 10 times more.
time than usual operation.
Processing a reliable bank always blocks keys in ascending order, but spends 2
times longer than a normal operation in an unreliable bank.
In both banks there are 10 accounts, the keys of the accounts are numbers from 1 to 10.
The processing of each bank requires 12 operations.
Operations are carried out in parallel, two at a time. Each operation affects up to 3
accounts:
- operation №1 (accounts: A, B, C), where A = i, B = A + 1, C = (A + B)% 10,
- operation №2 (accounts: D, E, F), where D = 11-i, E = D-1, F = (D + E)% 10,
i varies from 1 to 6.
The execution of the next pair of operations begins only after full completion.
previous.
Keys are locked according to bank policy, one in each of the operations, starting
from operation №1.
If the key is already locked in one of the operations, but is required to perform another,
first the first operation is completed, then the second one continues.
Forced execution of a pair of operations in sequential mode, as expected, occurs 2 times slower than in parallel.
What bank and how many times faster will complete operations?

Risks of public repositories

Serezha is a very experienced programmer, extremely reckless and infinitely greedy.
Once he found the source code of his favorite tote on a githaba.
What is the minimum bet that Serezha can win?

A simplified tote listing is attached:

class Bid { //  int amount; boolean checked; boolean restricted; Bid(int amount) {this.amount = amount;} } ~~~ AtomicReference<Bid> ref = new AtomicReference<>(); volatile boolean winner = false; ~~~ Thread validator = new Thread(() -> { //  ! while (true) { Bid bid = ref.get(); if (bid == null) continue; if ((((bid.amount << 5) ^ 1_000_000) >>> 6) < (2 << 15)) bid.restricted = true; bid.checked = true; } }); Thread payer = new Thread(() -> { //  ! while (true) { Bid bid = ref.get(); if (bid == null) continue; if (bid.checked) { if (!bid.restricted) winner = true; // ! ref.set(null); } } }); ~~~ synchronized boolean makeMeRich(int amount){ //    ? if (winner) return false; //    -    ref.set(new Bid(amount)); while(ref.get() != null) sleep(1); return winner; //   "true" -     } 

Winners

Best tasks solved
- Yevgeny Zubenko
- Alexander Novikov
- Andrey Golikov

The guys got branded backpacks, t-shirts and, of course, books.