Multithreading in Java

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is a recommended method to indicate that a thread has stopped?

Let the thread finish its execution

Terminate using exit()

Use the stop() method

Assign null to the Thread variable (correct)

Which priority constants are available for threads?

Thread.MAX_PRIORITY (correct)

Thread.HIGH_PRIORITY

Thread.NORM_PRIORITY (correct)

Thread.ABOVE_NORMAL_PRIORITY

Why might using a thread pool be advantageous?

It limits the number of tasks running concurrently.

It improves throughput and performance. (correct)

It simplifies creating threads for each task.

It eliminates the need for synchronization.

Which interface is used for managing and controlling tasks in a thread pool?

ExecutorService Signup and view all the answers

What potential issue arises from multiple threads accessing a shared resource simultaneously?

Race condition Signup and view all the answers

What can be a consequence of using the stop() method on threads?

It may lead to resource leaks. Signup and view all the answers

How can you create an Executor object in Java?

By using methods from the Executors class Signup and view all the answers

What issue might arise when one hundred threads attempt to add to a single bank account concurrently?

Race condition Signup and view all the answers

What is multithreading in Java primarily used for?

To enable concurrent execution of multiple program parts Signup and view all the answers

Which of the following is NOT a state of a thread?

Suspended Signup and view all the answers

What does the yield() method do in Java threading?

It temporarily releases time for other threads Signup and view all the answers

What is the purpose of the join() method in Java threads?

To pause a thread until another completes Signup and view all the answers

What does the isAlive() method indicate about a thread?

It checks if the thread is in a runnable or blocked state. Signup and view all the answers

What happens when a thread is interrupted while in a blocked state?

The thread is awakened and enters the ready state. Signup and view all the answers

Which method is considered outdated and inherently unsafe in Java threads?

stop() Signup and view all the answers

What is the implication of using the interrupt() method on a thread?

It sets the thread's interrupted flag and may change its state. Signup and view all the answers

What is the main issue presented in the scenario regarding Task 1 and Task 2?

Task 1's result is overridden by Task 2. Signup and view all the answers

What is a race condition in multithreaded programs?

A situation where threads access a common resource simultaneously causing conflict. Signup and view all the answers

How can the Account class be made thread-safe?

By applying the synchronized keyword in the deposit method only. Signup and view all the answers

What does the synchronized keyword achieve when used on a method?

It ensures that only one thread can execute the method at a time. Signup and view all the answers

In the context of synchronization, what is a critical region?

A portion of code that must be accessed by only one thread at a time. Signup and view all the answers

What happens if a thread attempts to enter a synchronized method while another thread is already executing it?

The second thread will be blocked until the first thread completes the method execution. Signup and view all the answers

When a synchronized instance method is invoked, what happens to the lock?

The lock is on the object that invokes the method. Signup and view all the answers

What type of lock does a static synchronized method acquire?

Lock on the class itself. Signup and view all the answers

Study Notes

Multithreading and Parallel Programming

Multithreading is a Java feature allowing concurrent execution of two or more program parts.
Threads are lightweight processes within a process, utilized for maximum CPU utilization.
Threads can exist in five states: New, Ready, Running, Blocked, and Finished.

Threads Concept

Multiple threads can run on multiple CPUs.
Multiple threads can share a single CPU.

Multithreading Definition

Multithreading is a Java feature that enables concurrent execution of different parts of a program, aiming for optimal CPU utilization.
Each program section is regarded as a thread, which is a lightweight process within a larger process.

Thread States

A thread's lifecycle involves states like New, Ready, Running, Blocked, and Finished.
The transitions between these states depend on various factors like thread creation, execution, and waiting.

Creating a Thread

Threads in Java can be created by extending the Thread class or implementing the Runnable interface.
Extending Thread involves creating a class that inherits from the Thread class and implementing the run() method.
Implementing Runnable involves creating a class that implements the Runnable interface and implementing the run() method.
Creating an object of the class, then invoking the start() method triggers the thread execution.

Creating Tasks and Threads

Method for creating and implementing an external Thread using Custom Tasks, in Java.

Example: Create and Run Three Threads

The first thread prints 'a' 100 times.
The second thread prints 'b' 100 times.
The third thread prints integers from 1 to 100.

The Thread Class

A thread object has methods for creating, managing, starting, and controlling threads.
It has states, priorities, methods, and states defined by their functions.
The class provides essential functions like start, sleep, interrupt, and isAlive methods.

The Static yield() Method

The yield() method of Thread class releases current thread's time slice to other threads, allowing other threads to run.
Implemented by placing Thread.yield() in the code to achieve this behavior.

The Static sleep(milliseconds) Method

The sleep(long mills) method suspends execution of the thread for the specified duration (milliseconds).

The join() Method

The join() method forces a thread to wait until another thread has finished executing.
Useful for maintaining a precise order of thread execution.
The method is used to wait until a specific thread finishes its execution sequence.

isAlive(), interrupt(), and isInterrupted()

isAlive() checks whether the thread is still running.
interrupt() can interrupt a waiting thread. A thread checks whether it has been interrupted.

The Deprecated stop(), suspend(), and resume() Methods

Java versions introduced deprecated methods, such as these within the Thread class, due to the unsafe nature.

Thread Priority

Each thread has a default priority (Thread.NORM_PRIORITY). This can be adjusted using setPriority(int priority).
Priorities relate to the relative execution speeds of multiple threads.

Thread Pools

Thread pools allow efficient utilization of threads by maintaining a pool of pre-created threads, used by tasks submitted to it repeatedly and minimizing the overhead associated with creating and destroying threads repeatedly.
Handling tasks asynchronously.

Why we Need Thread Pools

Managing the number of threads in concurrent execution.
Dealing with a large number of tasks in an application, rather than creating a new thread for each.
Running multiple tasks concurrently.

CPU-Intensive Task

Designed for operations requiring intensive CPU computation, where multiple threads are suitable concurrently.

IO-Intensive Operation

Optimized for operations that involve input/output (I/O), like network access or disk operations, where the thread may wait, therefore a larger thread pool size is preferable, not just the number of CPU cores.

What is the Ideal Pool Size?

The ideal pool size depends on the type of tasks (CPU-intensive or IO-intensive) and the number of CPU cores.

Thread Synchronization

A shared resource might be corrupted if accessed concurrently by multiple threads.
Critical region (a block of code) is the area in the program where multiple threads may interact with shared resources and is synchronized.
Using explicit synchronization mechanisms like the synchronized keyword is crucial to prevent race conditions in multithreaded applications, allowing only one thread to execute a code block at a time.

Race Condition

A race condition happens when the outcome of a program depends on the unpredictable order in which threads execute.
The common problem that arises from this is a program that may return an inaccurate result.

Synchronizing Statements

A synchronized statement ensures mutual exclusion in multithreaded programming by gaining access to a shared resource (object or static lock) and releasing it afterward.

Famous Thread Synchronization Problems

Producer/Consumer problem: A classical synchronisation problem involving the need to coordinate tasks that produce data with tasks that consume that data to prevent race conditions and deadlock.
Semaphores: Used for synchronization (signalling) between threads and offer a way to control access to shared resources in parallel programming.
Deadlock: A situation where two or more threads are blocked indefinitely, waiting for each other to release resources that they hold.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Explore the concept of multithreading in Java, including thread states and lifecycle. This quiz covers how threads operate to optimize CPU utilization, and different ways to create and manage threads. Test your knowledge on the fundamentals of concurrent execution in programming!