Introduction

This 10-day intensive drill is designed for candidates preparing for Meta OS/Frameworks interviews. Each day focuses on a critical area with specific goals, study materials, hands-on exercises, and mock interview questions. This drill assumes you have foundational knowledge and are polishing for the interview.

How to Use This Drill:

  • Dedicate 4-6 hours per day
  • Complete all exercises and mock questions
  • Practice drawing diagrams and explaining designs
  • Time yourself on mock questions (40-50 minutes)

Day 1: Android Frameworks & System Architecture

Goals: Understand Android OS architecture, Binder, system services, and framework modules.

Study:

  • Android system architecture (AOSP)
    • Application layer → Framework layer → Native layer → Kernel
    • System server architecture
    • Zygote process and app spawning
  • Binder IPC mechanism
    • How Binder ensures inter-process communication
    • Binder driver implementation
    • Transaction flow and thread safety
  • Looper & Handler pattern
    • Message queues and message handling
    • Thread communication in Android
  • Lifecycle of system services
    • Service initialization and startup
    • Service binding and connection management
    • Service lifecycle callbacks

Exercises:

  1. Draw diagram: App → System Service → Native/Driver layer
    • Show data flow for a Camera service request
    • Include Binder IPC in the diagram
    • Mark thread boundaries
  2. Explain how Binder ensures thread safety
    • Binder’s thread pool model
    • Transaction serialization
    • Deadlock prevention mechanisms
  3. Design a simple system service
    • Define the service interface
    • Show how clients connect
    • Handle concurrent requests

Mock Question:

“Explain how Android handles multiple apps sending requests to the Camera service simultaneously. How is concurrency managed?”

Key Points to Cover:

  • Binder’s thread pool mechanism
  • Transaction queuing and serialization
  • Service-side thread management
  • Synchronization within the service
  • Resource contention handling

Resources:

  • AOSP source code: frameworks/base/services
  • Android Developer documentation on System Services
  • Binder IPC documentation

Day 2: Linux Drivers & Device Abstraction

Goals: Review kernel modules, drivers, interrupts, DMA, and device memory.

Study:

  • Character vs block devices
    • Character devices: sequential access (sensors, GPIO)
    • Block devices: random access (storage)
    • Device file representation (/dev/)
  • File operations: read/write/ioctl
    • File operation structures (file_operations)
    • IOCTL for device-specific commands
    • Error handling and return codes
  • Interrupt handling
    • Top-half vs bottom-half handlers
    • Interrupt context vs process context
    • IRQ handlers and work queues
  • DMA basics
    • Direct Memory Access concepts
    • DMA buffers and mappings
    • Scatter-gather DMA
  • Device memory management
    • Memory-mapped I/O (MMIO)
    • I/O memory access patterns
    • Cache coherency

Exercises:

  1. Draw the flow: App → Framework API → Driver → Device
    • Show each layer’s responsibilities
    • Include interrupt handling path
    • Show DMA data flow
  2. Discuss how drivers handle concurrent access
    • Mutexes in kernel space
    • Spinlocks for interrupt handlers
    • Read-write locks for read-heavy operations
    • Per-device locking strategies
  3. Design a driver interface
    • Define file operations
    • Handle concurrent reads/writes
    • Implement error handling

Mock Question:

“Design a driver interface for a temperature sensor that allows multiple apps to read concurrently. How would you avoid race conditions?”

Key Points to Cover:

  • Device file operations (open, read, release)
  • Synchronization mechanisms (mutexes, read-write locks)
  • Buffer management for sensor data
  • Interrupt handling for sensor updates
  • Thread-safe data access patterns

Resources:

  • “Linux Device Drivers” by Corbet, Rubini, and Kroah-Hartman
  • Linux kernel documentation: Documentation/driver-api/
  • Kernel source: drivers/ directory

Day 3: NDK & JNI Integration

Goals: Focus on native-Android integration and thread safety.

Study:

  • JNI basics: bridging Java ↔ C/C++
    • JNI function naming conventions
    • Type mappings (jint, jstring, jobject)
    • Calling conventions
  • Memory management
    • Local vs global references
    • malloc/free in native code
    • Java object lifecycle in JNI
    • Preventing memory leaks
  • Native threads and Java threads
    • pthread vs Java threads
    • Attaching native threads to JVM
    • Thread-local storage
    • Synchronization between Java and native threads
  • Exception handling in JNI
    • Throwing exceptions from native code
    • Checking for pending exceptions
    • Exception propagation

Exercises:

  1. Write pseudocode: Safe JNI function handling multiple threads
    • Thread-safe native function
    • Proper reference management
    • Exception handling
    • Synchronization mechanisms
  2. Discuss memory leak prevention in native code
    • Reference management (local vs global)
    • Resource cleanup in JNI
    • Best practices for native memory
  3. Design a JNI wrapper
    • Safe Java ↔ Native interface
    • Thread-safe operations
    • Error handling and reporting

Mock Question:

“Design a JNI bridge for real-time sensor processing, supporting multiple concurrent calls. How do you ensure thread safety?”

Key Points to Cover:

  • JNI function design for concurrent access
  • Native thread management and JVM attachment
  • Synchronization mechanisms (mutexes, atomic operations)
  • Memory management (local/global references)
  • Exception handling and error propagation
  • Performance considerations (minimize JNI overhead)

Resources:

  • JNI Specification (Oracle)
  • Android NDK documentation
  • “The Java Native Interface” by Sheng Liang

Day 4: Concurrency Fundamentals

Goals: Threading, locks, atomic operations, thread-safe data structures.

Study:

  • Mutex, semaphore, spinlock
    • When to use each primitive
    • Performance characteristics
    • Deadlock prevention
  • Atomic operations, CAS
    • Compare-and-swap (CAS) operations
    • Atomic read-modify-write
    • Memory ordering semantics
  • Thread pools and executors
    • Thread pool design patterns
    • Work-stealing schedulers
    • Task queuing strategies
  • Lock-free data structures
    • Lock-free queues and stacks
    • ABA problem and solutions
    • Memory reclamation (hazard pointers)
  • Thread synchronization patterns
    • Producer-consumer pattern
    • Readers-writers pattern
    • Barrier synchronization

Exercises:

  1. Implement a thread-safe queue (pseudo-code)
    • Using mutexes
    • Using lock-free approach
    • Compare performance trade-offs
  2. Identify potential deadlocks in a multi-threaded system
    • Lock ordering violations
    • Circular dependencies
    • Timeout-based solutions
  3. Design a thread pool
    • Task queue design
    • Worker thread management
    • Shutdown handling

Mock Question:

“Multiple threads produce events and push them to a logging queue. How would you design this queue to be thread-safe without bottlenecks?”

Key Points to Cover:

  • Lock-free vs lock-based design
  • Multiple producer, multiple consumer queue
  • Memory reclamation strategies
  • Performance optimization (avoiding contention)
  • Failure handling and backpressure

Resources:

Day 5: IPC & Cross-Process Communication

Goals: Design and reasoning about IPC frameworks.

Study:

  • Binder vs shared memory vs Unix sockets
    • Performance characteristics
    • Use cases for each mechanism
    • Trade-offs and limitations
  • Message ordering and delivery guarantees
    • At-least-once vs at-most-once vs exactly-once
    • Ordering guarantees
    • Reliability mechanisms
  • Serialization/deserialization (Protobuf)
    • Efficient binary formats
    • Schema evolution
    • Versioning strategies
  • IPC design patterns
    • Request-reply pattern
    • Publish-subscribe pattern
    • Streaming pattern
  • Security in IPC
    • Authentication and authorization
    • Secure channel establishment
    • Access control

Exercises:

  1. Diagram: Client processes → IPC → System service
    • Show message flow
    • Include serialization/deserialization
    • Show error handling paths
  2. Discuss trade-offs between shared memory and sockets
    • Performance comparison
    • Complexity trade-offs
    • Use case selection
  3. Design an IPC protocol
    • Message format
    • Request/response handling
    • Error handling
    • Timeout mechanisms

Mock Question:

“Design a cross-process messaging system for multiple apps communicating with a system service. How do you handle ordering and concurrency?”

Key Points to Cover:

  • IPC mechanism selection (Binder, shared memory, sockets)
  • Message ordering guarantees
  • Serialization format (Protobuf, custom binary)
  • Concurrency handling (thread pools, queuing)
  • Reliability (retries, acknowledgments)
  • Security (authentication, encryption)

Resources:

  • Android Binder documentation
  • “Unix Network Programming” by Stevens
  • Protocol Buffers documentation

Day 6: Logging & Telemetry Framework Design

Goals: Embedded logging systems, batching, persistence, reliability.

Study:

  • Event queues, batching strategies
    • In-memory queues (ring buffers)
    • Batching for efficiency
    • Priority queues for critical logs
  • Offline persistence, crash recovery
    • SQLite for structured logs
    • File-based logging
    • Atomic writes and journaling
  • Thread-safe buffers
    • Lock-free ring buffers
    • Multi-producer, single-consumer patterns
    • Memory barriers and ordering
  • Log compression and upload
    • Compression algorithms (gzip, Snappy)
    • Batch upload strategies
    • Retry mechanisms
  • Resource constraints
    • Memory limits
    • Storage limits
    • Network bandwidth

Exercises:

  1. Draw event flow: Producer → Buffer → Storage → Uploader
    • Show each component’s responsibilities
    • Include thread boundaries
    • Show data structures
  2. Pseudocode: Thread-safe ring buffer
    • Multiple producers, single consumer
    • Handle buffer overflow
    • Lock-free implementation
  3. Design log rotation and cleanup
    • Storage management
    • Old log deletion
    • Size-based rotation

Mock Question:

“Design a logging framework for device events that persists logs locally and uploads them periodically. How do you prevent log loss and ensure thread safety?”

Key Points to Cover:

  • Event collection from multiple sources
  • Thread-safe in-memory buffering (lock-free queue)
  • Persistent storage (SQLite or files)
  • Batching and compression
  • Upload mechanism with retries
  • Crash recovery (atomic writes, journaling)
  • Resource management (memory, storage limits)

Resources:

Day 7: Resource Management & Scheduling

Goals: CPU/memory allocation, prioritization, and contention handling.

Study:

  • Process scheduling concepts (Linux CFS)
    • Completely Fair Scheduler (CFS)
    • Priority levels and nice values
    • CPU affinity
  • Memory allocation and reclamation
    • Memory allocation algorithms
    • Low Memory Killer (LMK) in Android
    • OOM killer mechanisms
  • Priority-based scheduling
    • Real-time priorities
    • Fairness vs throughput
    • Starvation prevention
  • Resource contention handling
    • CPU contention resolution
    • Memory contention (OOM handling)
    • I/O scheduling
  • Battery-aware scheduling
    • Power-aware CPU scheduling
    • Background task throttling
    • Wake lock management

Exercises:

  1. Design CPU/memory allocation for system services and apps
    • Priority assignment strategy
    • Resource quotas
    • Contention resolution
  2. Discuss trade-offs: Strict fairness vs throughput
    • When to prioritize fairness
    • When to optimize for throughput
    • Hybrid approaches
  3. Design a resource manager
    • Monitor resource usage
    • Allocate resources based on priority
    • Handle resource exhaustion

Mock Question:

“Design a resource manager for multiple system services and apps. How would you handle CPU/memory contention?”

Key Points to Cover:

  • Resource monitoring (CPU, memory, I/O)
  • Priority-based allocation
  • Contention detection and resolution
  • OOM handling strategies
  • Fairness guarantees
  • Battery-aware scheduling
  • APIs for resource requests

Resources:

  • Linux kernel documentation on CFS
  • Android Low Memory Killer documentation
  • “Operating System Concepts” - Scheduling chapters

Day 8: Event Loops & Async Systems

Goals: Event-driven architectures, non-blocking processing.

Study:

  • Looper, Handler, callback patterns
    • Android Looper implementation
    • Message queue processing
    • Handler for cross-thread communication
  • Non-blocking IO
    • epoll (Linux) for event notification
    • kqueue (BSD/macOS)
    • Async I/O patterns
  • Worker threads for CPU-intensive tasks
    • Thread pool design
    • Task queuing
    • Load balancing
  • Event-driven architecture
    • Event sources and sinks
    • Event filtering and routing
    • Backpressure handling
  • Performance optimization
    • Minimizing latency
    • Maximizing throughput
    • Avoiding thread contention

Exercises:

  1. Diagram: Event sources → Main loop → Worker threads
    • Show event flow
    • Include thread boundaries
    • Show task distribution
  2. Identify potential bottlenecks or deadlocks
    • Synchronization points
    • Resource contention
    • Lock ordering issues
  3. Design an event processing system
    • Event sources
    • Event loop implementation
    • Worker thread management
    • Error handling

Mock Question:

“Design a high-performance event loop handling multiple asynchronous hardware events. How do you maintain low latency?”

Key Points to Cover:

  • Event loop architecture (epoll/kqueue)
  • Event queue design (priority queues)
  • Worker thread pool for processing
  • Lock-free event queuing
  • Minimizing context switches
  • Latency optimization techniques
  • Backpressure handling

Resources:

  • Android Looper source code
  • “The Linux Programming Interface” - epoll chapter
  • Event-driven architecture patterns

Day 9: Trade-offs & System Reliability

Goals: Practice articulating design trade-offs and failure handling.

Study:

  • Latency vs throughput
    • When to optimize for latency
    • When to optimize for throughput
    • Hybrid approaches
  • Modularity vs overhead
    • Abstraction layers and their cost
    • When abstraction is worth it
    • Performance impact of modularity
  • Failure recovery strategies
    • Retry mechanisms
    • Circuit breakers
    • Graceful degradation
  • Consistency vs availability
    • CAP theorem implications
    • Eventual consistency
    • Strong consistency requirements
  • Memory vs CPU trade-offs
    • Caching strategies
    • Precomputation
    • Space-time trade-offs

Exercises:

  1. For any previous mock design, write 3 trade-offs and justify choices
    • Latency vs throughput
    • Memory vs CPU
    • Complexity vs performance
  2. Add failure handling: Network failure, device crash, buffer overflow
    • Retry strategies
    • Error recovery
    • Data loss prevention
  3. Design a fault-tolerant system
    • Failure detection
    • Recovery mechanisms
    • Data consistency

Mock Question:

“For your logging framework, discuss trade-offs between batching logs for efficiency vs real-time reporting.”

Key Points to Cover:

  • Batching benefits (throughput, efficiency)
  • Real-time benefits (latency, responsiveness)
  • Hybrid approaches (priority-based)
  • Trade-off analysis
  • Use case considerations
  • Configuration options

Resources:

  • System design principles
  • Failure mode analysis
  • Trade-off documentation in existing systems

Day 10: Mock System Design Interview

Goals: Simulate a full interview session.

Activities:

  1. Pick one design scenario (logging, IPC, driver API, resource manager)
  2. Clarify requirements (5-10 minutes)
    • Ask about constraints (memory, CPU, battery)
    • Understand scale and requirements
    • Clarify non-functional requirements
  3. Draw architecture, concurrency model, data flow (15-20 minutes)
    • High-level architecture diagram
    • Component interactions
    • Data flow paths
    • Thread boundaries
  4. Discuss threading, memory, reliability, trade-offs (15-20 minutes)
    • Concurrency model
    • Synchronization mechanisms
    • Memory management
    • Failure handling
    • Trade-offs
  5. Explain interfaces/APIs (5-10 minutes)
    • API design
    • Method signatures
    • Error handling
    • Usage examples

Sample Mock Questions:

  1. “Design a cross-process Camera service with multiple clients, including event logging and telemetry.”

    Key Areas to Cover:

    • Camera service architecture
    • IPC mechanism (Binder)
    • Concurrency handling (multiple clients)
    • Resource management (camera hardware)
    • Logging and telemetry integration
    • Error handling and recovery

  2. “Design a JNI bridge for real-time sensor data that ensures thread safety and minimal latency.”

    Key Areas to Cover:

    • JNI interface design
    • Thread-safe native code
    • Real-time data processing
    • Latency optimization
    • Memory management
    • Error handling

  3. “Design a power management framework that coordinates between multiple system components.”

    Key Areas to Cover:

    • Power state management
    • Component coordination
    • Wake lock policies
    • Battery monitoring
    • Trade-offs (performance vs battery)

Tips:

  • Time yourself: 40-50 minutes per mock interview
  • Review: After each mock, evaluate:
    • Diagram clarity and completeness
    • Trade-off discussions
    • Concurrency reasoning
    • API design quality
    • Communication effectiveness
  • Practice explaining: Record yourself or practice with a peer
  • Focus on thinking process: Explain your reasoning, not just the solution

Self-Evaluation Checklist:

After each mock interview, check:

  • Clarified requirements and constraints
  • Drew clear architecture diagrams
  • Discussed concurrency model
  • Addressed memory management
  • Discussed failure handling
  • Explained trade-offs clearly
  • Designed clean APIs
  • Stayed within time limit
  • Communicated clearly

General Tips for the 10-Day Drill

Daily Routine

  1. Morning (2-3 hours): Study new concepts
  2. Afternoon (2-3 hours): Complete exercises and practice
  3. Evening (1 hour): Review and mock questions

Key Success Factors

  1. Don’t skip exercises: Hands-on practice is crucial
  2. Draw diagrams: Practice visualizing system designs
  3. Explain out loud: Practice articulating your thoughts
  4. Time yourself: Get comfortable with time pressure
  5. Review mistakes: Learn from each mock interview

Common Pitfalls to Avoid

  1. Over-engineering: Keep designs simple and practical
  2. Ignoring constraints: Always consider resource limits
  3. Missing thread safety: Always consider concurrent access
  4. Poor error handling: Design for failures
  5. Weak trade-off discussions: Be able to justify decisions

Conclusion

This 10-day drill provides intensive, focused preparation for Meta OS/Frameworks interviews. Each day builds on previous knowledge and adds new critical skills.

Remember:

  • Quality over quantity: Master each day’s topics before moving on
  • Practice explaining: Clear communication is as important as technical depth
  • Stay calm: Interviews test problem-solving, not perfect recall
  • Think systematically: Structure your approach to design problems

After the 10 days:

  • Continue practicing mock interviews
  • Review areas where you felt weak
  • Stay confident in your preparation
  • Get good rest before the interview

Good luck with your Meta OS/Frameworks interview! You’ve got this! 🚀