Java Concurrency: Part 3

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Questions and Answers

What distinguishes a process from a thread in terms of memory?

A process has its own memory space, while threads share the same memory space within a process.

List and briefly describe the five states of a thread lifecycle.

The five states are: NEW (created), RUNNABLE (executing/ready), BLOCKED (waiting for lock), WAITING (waiting indefinitely), TIMED_WAITING (waiting for a specific time), TERMINATED (completed execution).

What methods can be used to ensure thread safety?

Thread safety can be achieved through synchronization, using atomic classes, immutable objects, thread-local storage, and concurrent collections.

Differentiate between sleep() and wait() regarding their effect on thread locks.

sleep() retains the thread lock while pausing the thread, whereas wait() releases the lock and waits for a notification. Signup and view all the answers

Define deadlock and name two strategies to prevent it.

Deadlock occurs when threads are blocked indefinitely waiting for each other. Two prevention strategies are lock ordering and lock timeouts. Signup and view all the answers

Explain the producer-consumer problem and one way to solve it.

The producer-consumer problem involves producers adding data to a shared buffer and consumers removing it. One solution is using a BlockingQueue. Signup and view all the answers

What is the difference between notify() and notifyAll() methods?

notify() wakes a single waiting thread arbitrarily, while notifyAll() wakes all threads waiting on the object's monitor. Signup and view all the answers

Why is thread pooling advantageous in a multi-threaded application?

Thread pooling reuses a fixed number of threads, which decreases the overhead of creating and destroying threads and enhances resource management. Signup and view all the answers

What are race conditions and how can they be prevented?

Race conditions occur when multiple threads access shared data simultaneously, leading to unpredictable results. They can be prevented using synchronization and atomic operations. Signup and view all the answers

What does the volatile keyword do in Java?

The volatile keyword ensures that a variable is read directly from main memory, providing visibility but not atomicity. Signup and view all the answers

What advantages do Callable's call() method have over Runnable's run() method?

Callable's call() can return a value and throw checked exceptions, while Runnable's run() only returns void and cannot throw checked exceptions. Signup and view all the answers

In what way does the synchronized keyword contribute to thread safety?

The synchronized keyword ensures that only one thread can access a shared resource at a time, preventing race conditions. Signup and view all the answers

How does ConcurrentHashMap enhance performance in a multithreaded environment?

ConcurrentHashMap uses fine-grained locking mechanisms, allowing multiple threads to read and write concurrently without significant contention. Signup and view all the answers

Explain the difference in behavior between start() and run() methods when dealing with threads.

start() launches a new thread and invokes run() in that thread, while run() is executed in the current thread when called directly. Signup and view all the answers

What is thread interruption, and how does it affect thread execution?

Thread interruption is a signal to a thread to stop its current operation, requiring the thread to periodically check its interrupted status. Signup and view all the answers

Differentiate between CountDownLatch and CyclicBarrier in terms of usage.

CountDownLatch is one-time use that waits until a counter reaches zero, while CyclicBarrier can be reused after threads are released. Signup and view all the answers

How does ThreadLocal benefit multithreading?

ThreadLocal provides each thread with its own independent copy of a variable, preventing interference between threads. Signup and view all the answers

What is the purpose of the yield() method in thread management?

The yield() method suggests to the scheduler that the current thread is willing to pause and allow other threads to execute. Signup and view all the answers

Describe how CompletableFuture improves upon the basic Future implementation.

CompletableFuture supports asynchronous programming features such as chaining operations, combining multiple futures, and handling exceptions directly. Signup and view all the answers

What distinguishes parallel execution from concurrent execution in a multithreading context?

Parallel execution involves multiple tasks running simultaneously on different processors, while concurrent execution involves multiple tasks making progress without necessarily running at the same time. Signup and view all the answers

Study Notes

Processes vs. Threads

Processes are independent programs with their own memory space.
Threads are lightweight execution units within a process.
Threads share the process's heap memory, but each thread has its own stack.

Thread Lifecycle States

NEW: Created but not started.
RUNNABLE: Executing or ready to execute.
BLOCKED: Waiting for a monitor lock.
WAITING: Waiting indefinitely.
TIMED_WAITING: Waiting for a specified time.
TERMINATED: Completed execution.

Thread Safety

Thread safety ensures code execution by multiple threads without issues.
Achieved through methods like: synchronization, atomic classes, immutable objects, thread-local storage, concurrent collections.

sleep() vs. wait()

sleep() keeps the lock and suspends the thread for a given time.
wait() releases the lock and suspends the thread until notified.

Deadlocks

Deadlock occurs when two or more threads are blocked forever, waiting for each other.
Prevention methods include lock ordering, timeouts, deadlock detection, tryLock(), and avoiding nested locks.

Producer-Consumer Problem

Producers add data to a shared buffer.
Consumers remove data from the shared buffer.
Solutions include BlockingQueue, wait()/notify(), semaphores, and lock conditions.

notify() vs. notifyAll()

notify() wakes one waiting thread.
notifyAll() wakes all waiting threads.

Thread Pooling

Thread pooling reuses a fixed number of threads to execute tasks.
Reduces overhead of thread creation and destruction, improving resource management.

Race Conditions

Race conditions occur when multiple threads access shared data simultaneously.
Prevention includes synchronization, atomic operations, and immutable objects.

Volatile Keyword

The volatile keyword ensures a variable is read directly from main memory.
Provides visibility to multiple threads, but not atomicity.

Runnable vs. Callable

Runnable's run() method returns void and cannot throw exceptions.
Callable's call() method can return values and throw exceptions.

synchronized Keyword

synchronized provides exclusive access to a shared resource or code block, preventing concurrent access by threads.

ConcurrentHashMap

ConcurrentHashMap uses segment-level locking (older versions) or node-level locking (Java 8+) to allow concurrent read and write operations.

start() vs. run()

start() creates a new thread and executes run().
Calling run() executes in the current thread.

Thread Interruption

Thread interruption signals a thread to stop its execution.
It's cooperative; the thread must check its interrupted status.

join() Method

join() makes the calling thread wait for the target thread to finish execution.

Thread Starvation and Livelock

Starvation occurs when a thread never gets CPU access or resources.
Livelock occurs when threads actively work but don't make progress.

Thread-Safe Singleton

Implementations include double-checked locking, static initialization, enum singletons, and volatile field with synchronized getInstance().

CountDownLatch vs. CyclicBarrier

CountDownLatch is a one-time use; threads wait until a counter reaches zero.
CyclicBarrier resets after threads are released and can be reused.

Future Interface

Future represents the result of an asynchronous computation.
Allows checking completion, waiting for completion, and retrieving results.

ThreadLocal

ThreadLocal provides thread-confined variables where each thread has its own copy of the variable.

Queue Methods (peek() and poll())

peek() returns the head element without removing it (null if empty).
poll() returns and removes the head element.

yield() Method

yield() suggests a thread to relinquish the processor but is just a hint to the scheduler.

Exception Handling

Exceptions in threads can be handles by try-catch blocks, UncaughtExceptionHandler, Future.get() for Callable tasks, and CompletableFuture exceptions.

ExecutorService Methods (execute() and submit())

execute() takes a Runnable and returns void, while submit() can take a Runnable or Callable and returns a Future.

Methods include synchronized collections, concurrent collections, volatile variables, AtomicReference, ThreadLocal, and immutable objects.

Executor Framework

The Executor framework decouples task submission from execution.
Manages thread life cycle, offering thread pool implementations.

CompletableFuture

CompletableFuture improves upon Future through chaining operations, merging multiple futures, exception handling, callbacks, and asynchronous operations.

Parallel vs. Concurrent Execution

Parallel execution means tasks run simultaneously on different cores.
Concurrent execution means tasks make progress even if not simultaneous.

Custom Synchronization

Implementations include ReentrantLock, AbstractQueuedSynchronizer, Condition objects, volatile and synchronized, and atomic variables.

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Description

This quiz covers the fundamental concepts of processes and threads, including their differences, lifecycle states, and thread safety measures. Additionally, it explores key functions like sleep() and wait(), as well as the issues related to deadlocks. Test your knowledge on multithreading in programming!