Q81. How does copy-on-write work for Swift collections?
Swift collections such as `Array`, `Dictionary` and `String` are value types with copy-on-write. Copying a variable is cheap because both copies share the same buffer unt...
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Q82. Explain declaration-site variance with in and out.
Variance describes how generic types relate when their type arguments are related. `out T` (covariant) means `Producer` can be used where `Producer` is expected. `in T` (...
Q83. What causes async deadlocks and how does ConfigureAwait help?
A classic deadlock happens in UI applications and classic ASP.NET when you block synchronously on async code with `.Result` or `.Wait()`. The awaited task wants to resume...
Q84. Explain the rule of three, five and zero, plus undefined behaviour.
The rule of three: if a class needs a custom destructor, copy constructor or copy assignment operator, it probably needs all three, because they manage the same resource....
Q85. How do async/await, futures, Send and Sync fit together?
An `async fn` returns a `Future`, a state machine that does nothing until polled. An executor such as Tokio drives it. `.await` yields control while the future is pending...
Q86. How do you choose between mutexes and channels for concurrency?
Go's advice is "do not communicate by sharing memory; share memory by communicating", but both tools are legitimate. - Use a mutex when protecting a small piece of shared...
Q87. How do you add tests to legacy code that has none?
Legacy code is often defined as code without tests, which makes changing it risky. The core technique is to introduce a seam, a place where behaviour can be substituted w...
Q88. Explain two-phase commit and its drawbacks.
Two-phase commit, 2PC, is an atomic commit protocol for transactions spanning multiple databases or resource managers. Phase one, prepare: the coordinator asks every part...
Q89. Explain TCP congestion control.
TCP congestion control keeps the sender from overwhelming the network. The sender maintains a congestion window, cwnd, and sends at most the minimum of cwnd and the recei...
Q90. Explain the Banker's algorithm for deadlock avoidance.
The Banker's algorithm grants a resource request only if the resulting state is safe, meaning some order exists in which all processes can finish. Inputs are the maximum ...