Concurrency & Multithreading Interview Questions

Swift Concurrency introduces: 1) async/await for asynchronous code, 2) Structured concurrency with tasks, 3) Actor model for state isolation, 4) Improved error handling, 5) Better code readability compared to completion handlers, 6) Built-in deadlock prevention. Unlike GCD, it provides compile-time checking and safer concurrency patterns.

Actors provide: 1) Data race protection through isolation, 2) Synchronized access to mutable state, 3) Serial execution of methods, 4) Async interface for external access, 5) Safe state management across tasks, 6) Reference type semantics. Use actors when shared mutable state needs thread-safe access.

async/await provides: 1) Structured approach to asynchronous code, 2) Elimination of completion handler pyramids, 3) Linear code flow for async operations, 4) Automatic error propagation, 5) Integration with throwing functions, 6) Better stack traces. Solves callback hell and improves code readability.

Tasks represent: 1) Units of asynchronous work, 2) Structured task hierarchies, 3) Cancellation support, 4) Priority management, 5) Task-local storage, 6) Task groups for parallel execution. Tasks provide structured approach to managing concurrent operations.

GCD features: 1) Queue-based task execution, 2) Serial and concurrent queues, 3) Quality of service levels, 4) Dispatch groups for synchronization, 5) Barrier flags for synchronization, 6) Semaphores for resource management. Provides low-level concurrency primitives.

AsyncSequence/AsyncStream provide: 1) Asynchronous iteration over values, 2) Back-pressure handling, 3) Cancellation support, 4) Integration with for-await-in loops, 5) Buffer control, 6) Continuation handling. Used for handling streams of asynchronous values.

Task cancellation involves: 1) Checking cancellation status, 2) Responding to cancellation, 3) Propagating cancellation to child tasks, 4) Implementing cleanup code, 5) Handling cancellation errors, 6) Setting up cancellation handlers. Ensures graceful task termination.

@MainActor ensures: 1) Code runs on main thread, 2) UI updates are safe, 3) State isolation for main thread, 4) Automatic thread switching, 5) Compile-time checking, 6) Integration with async/await. Use for UI-related code and main thread operations.

Concurrent data access patterns: 1) Using actors for isolation, 2) Implementing thread-safe properties, 3) Queue-based synchronization, 4) Read-write patterns, 5) Lock mechanisms, 6) Copy-on-write for value types. Ensures thread-safe data access.

Task Groups enable: 1) Parallel task execution, 2) Dynamic task creation, 3) Result collection, 4) Error handling, 5) Cancellation propagation, 6) Resource limiting. Used for managing multiple concurrent tasks with similar purpose.

Async testing includes: 1) Using async test methods, 2) Implementing expectations, 3) Testing actor isolation, 4) Simulating delays, 5) Testing cancellation, 6) Verifying async sequences. Ensures proper testing of concurrent code.

Sendable protocol ensures: 1) Safe cross-actor data transfer, 2) Value type conformance, 3) Thread-safe reference types, 4) Compile-time checking, 5) Actor isolation preservation, 6) Concurrent data safety. Used for safe data sharing between concurrent contexts.

Concurrent collections require: 1) Thread-safe access methods, 2) Atomic operations, 3) Lock-free algorithms, 4) Copy-on-write optimization, 5) Consistency guarantees, 6) Performance considerations. Ensures safe concurrent access to collection data.

AsyncThrowingStream provides: 1) Asynchronous error handling, 2) Cancellation support, 3) Back-pressure management, 4) Buffer control, 5) Continuation handling, 6) Integration with async/await. Used for error-throwing asynchronous sequences.

Deadlock prevention includes: 1) Using structured concurrency, 2) Implementing proper lock ordering, 3) Avoiding nested locks, 4) Using actors for isolation, 5) Implementing timeouts, 6) Proper resource release. Prevents concurrent access issues.

Concurrent error handling: 1) Using async throws functions, 2) Implementing error propagation, 3) Handling task cancellation, 4) Managing timeouts, 5) Implementing retry logic, 6) Proper cleanup on errors. Ensures robust error management.

Custom executors require: 1) Conforming to Executor protocol, 2) Managing task scheduling, 3) Implementing priority handling, 4) Resource management, 5) Queue management, 6) Performance optimization. Used for specialized execution contexts.

Task priority management: 1) Setting priority levels, 2) Priority inheritance, 3) Priority escalation, 4) QoS integration, 5) Task scheduling impact, 6) Priority propagation. Ensures proper resource allocation for tasks.

Async properties require: 1) Using async get keyword, 2) Managing property dependencies, 3) Handling cancellation, 4) Implementing caching, 5) Error handling, 6) Actor isolation consideration. Used for properties requiring async computation.

Background task patterns: 1) Task prioritization, 2) Resource management, 3) State preservation, 4) Background execution limits, 5) Task completion handling, 6) System integration. Ensures efficient background processing.

Concurrent networking: 1) Using async URLSession, 2) Implementing request grouping, 3) Managing timeouts, 4) Handling cancellation, 5) Error handling, 6) Response processing. Ensures efficient network operations.

AsyncLetBinding enables: 1) Parallel async operations, 2) Result dependency management, 3) Structured concurrency, 4) Error propagation, 5) Cancellation handling, 6) Resource optimization. Used for concurrent independent operations.

Rate limiting implementation: 1) Token bucket algorithm, 2) Time-based limiting, 3) Queue-based throttling, 4) Semaphore usage, 5) BackPressure handling, 6) Overflow management. Prevents resource exhaustion.

Concurrent memory management: 1) Weak reference usage, 2) Proper closure capture, 3) Resource cleanup, 4) Cycle prevention, 5) Buffer management, 6) Leak detection. Ensures proper resource handling.

Concurrent state machines: 1) Actor-based state management, 2) Thread-safe transitions, 3) Event handling, 4) State validation, 5) Error handling, 6) State observation. Ensures safe state management.

Actors provide: 1) Data race protection through isolation, 2) Synchronized access to mutable state, 3) Serial execution of methods, 4) Async interface for external access, 5) Safe state management across tasks, 6) Reference type semantics. Use actors when shared mutable state needs thread-safe access.

async/await provides: 1) Structured approach to asynchronous code, 2) Elimination of completion handler pyramids, 3) Linear code flow for async operations, 4) Automatic error propagation, 5) Integration with throwing functions, 6) Better stack traces. Solves callback hell and improves code readability.

Tasks represent: 1) Units of asynchronous work, 2) Structured task hierarchies, 3) Cancellation support, 4) Priority management, 5) Task-local storage, 6) Task groups for parallel execution. Tasks provide structured approach to managing concurrent operations.

GCD features: 1) Queue-based task execution, 2) Serial and concurrent queues, 3) Quality of service levels, 4) Dispatch groups for synchronization, 5) Barrier flags for synchronization, 6) Semaphores for resource management. Provides low-level concurrency primitives.

AsyncSequence/AsyncStream provide: 1) Asynchronous iteration over values, 2) Back-pressure handling, 3) Cancellation support, 4) Integration with for-await-in loops, 5) Buffer control, 6) Continuation handling. Used for handling streams of asynchronous values.

Task cancellation involves: 1) Checking cancellation status, 2) Responding to cancellation, 3) Propagating cancellation to child tasks, 4) Implementing cleanup code, 5) Handling cancellation errors, 6) Setting up cancellation handlers. Ensures graceful task termination.

@MainActor ensures: 1) Code runs on main thread, 2) UI updates are safe, 3) State isolation for main thread, 4) Automatic thread switching, 5) Compile-time checking, 6) Integration with async/await. Use for UI-related code and main thread operations.

Concurrent data access patterns: 1) Using actors for isolation, 2) Implementing thread-safe properties, 3) Queue-based synchronization, 4) Read-write patterns, 5) Lock mechanisms, 6) Copy-on-write for value types. Ensures thread-safe data access.

Task Groups enable: 1) Parallel task execution, 2) Dynamic task creation, 3) Result collection, 4) Error handling, 5) Cancellation propagation, 6) Resource limiting. Used for managing multiple concurrent tasks with similar purpose.

Async testing includes: 1) Using async test methods, 2) Implementing expectations, 3) Testing actor isolation, 4) Simulating delays, 5) Testing cancellation, 6) Verifying async sequences. Ensures proper testing of concurrent code.

Sendable protocol ensures: 1) Safe cross-actor data transfer, 2) Value type conformance, 3) Thread-safe reference types, 4) Compile-time checking, 5) Actor isolation preservation, 6) Concurrent data safety. Used for safe data sharing between concurrent contexts.

Concurrent collections require: 1) Thread-safe access methods, 2) Atomic operations, 3) Lock-free algorithms, 4) Copy-on-write optimization, 5) Consistency guarantees, 6) Performance considerations. Ensures safe concurrent access to collection data.

AsyncThrowingStream provides: 1) Asynchronous error handling, 2) Cancellation support, 3) Back-pressure management, 4) Buffer control, 5) Continuation handling, 6) Integration with async/await. Used for error-throwing asynchronous sequences.

Deadlock prevention includes: 1) Using structured concurrency, 2) Implementing proper lock ordering, 3) Avoiding nested locks, 4) Using actors for isolation, 5) Implementing timeouts, 6) Proper resource release. Prevents concurrent access issues.

Concurrent error handling: 1) Using async throws functions, 2) Implementing error propagation, 3) Handling task cancellation, 4) Managing timeouts, 5) Implementing retry logic, 6) Proper cleanup on errors. Ensures robust error management.

Custom executors require: 1) Conforming to Executor protocol, 2) Managing task scheduling, 3) Implementing priority handling, 4) Resource management, 5) Queue management, 6) Performance optimization. Used for specialized execution contexts.

Task priority management: 1) Setting priority levels, 2) Priority inheritance, 3) Priority escalation, 4) QoS integration, 5) Task scheduling impact, 6) Priority propagation. Ensures proper resource allocation for tasks.

Async properties require: 1) Using async get keyword, 2) Managing property dependencies, 3) Handling cancellation, 4) Implementing caching, 5) Error handling, 6) Actor isolation consideration. Used for properties requiring async computation.

Background task patterns: 1) Task prioritization, 2) Resource management, 3) State preservation, 4) Background execution limits, 5) Task completion handling, 6) System integration. Ensures efficient background processing.

Concurrent networking: 1) Using async URLSession, 2) Implementing request grouping, 3) Managing timeouts, 4) Handling cancellation, 5) Error handling, 6) Response processing. Ensures efficient network operations.

AsyncLetBinding enables: 1) Parallel async operations, 2) Result dependency management, 3) Structured concurrency, 4) Error propagation, 5) Cancellation handling, 6) Resource optimization. Used for concurrent independent operations.

Rate limiting implementation: 1) Token bucket algorithm, 2) Time-based limiting, 3) Queue-based throttling, 4) Semaphore usage, 5) BackPressure handling, 6) Overflow management. Prevents resource exhaustion.

Concurrent memory management: 1) Weak reference usage, 2) Proper closure capture, 3) Resource cleanup, 4) Cycle prevention, 5) Buffer management, 6) Leak detection. Ensures proper resource handling.

Concurrent state machines: 1) Actor-based state management, 2) Thread-safe transitions, 3) Event handling, 4) State validation, 5) Error handling, 6) State observation. Ensures safe state management.