What is the difference between runnable and waiting in Java thread?

Terry 22 Published: 12/03/2024

What is the difference between runnable and waiting in Java thread?

A fundamental question in Java threading!

In Java, a thread can be in one of two states: RUNNABLE or WAITING. Understanding the differences between these two states is crucial for effective multithreading programming.

Runnable State (RUNNABLE)

A thread in the RUNNABLE state is ready to run and execute its code. This is the normal, operational mode of a thread. In this state:

The thread's priority is taken into account when scheduling. The thread can be executed by the operating system or JVM (Java Virtual Machine) at any time. If no other threads are running or waiting for CPU resources, this thread will be scheduled to run.

When a thread enters the RUNNABLE state, it's said to have been "scheduled" or "re-scheduled." This means that the thread has been chosen by the JVM or operating system as the next one to execute.

Waiting State (WAITING)

A thread in the WAITING state is blocked and waiting for something to happen. It may be waiting:

For a specific amount of time (e.g., using Thread.sleep()). For a particular event or condition to occur (e.g., receiving a message from another thread or a network request completing). For I/O operations to complete (e.g., disk read/write, network I/O).

While in the WAITING state:

The thread's priority is not taken into account for scheduling. The thread will not be executed until it is awakened from its waiting state by some external event or condition.

There are a few key implications of a thread being in the WAITING state:

Other threads can still run while your waiting thread remains blocked. Your waiting thread won't consume CPU resources or system resources like memory and I/O. Your waiting thread can be interrupted, which means its waiting state is terminated, allowing it to return to the RUNNABLE state.

To illustrate these differences, consider a simple example:

Suppose you have two threads: Thread A, which is constantly calculating pi, and Thread B, which waits for a message from a socket server. Initially, both threads are in the RUNNABLE state, competing for CPU resources.

When Thread B receives the message from the socket server, it enters the WAITING state, allowing Thread A to focus on its calculations without interruption.

Once Thread B is awakened by some event (e.g., receiving another message), it will return to the RUNNABLE state and resume execution, possibly competing with Thread A for CPU resources again.

In summary, a RUNNABLE thread is ready to execute, while a WAITING thread is blocked and waiting for an external event or condition. Understanding these states is crucial for effective multithreading programming in Java, allowing you to design efficient and scalable applications.

What is the difference between runnable and thread in java

I'd be happy to explain the differences between Runnable and Thread in Java.

In Java, both Runnable and Thread are used for creating threads, but they serve slightly different purposes and offer distinct benefits. Let's dive into the details:

Runnable

A Runnable is an interface that defines a single method, run(), which contains the code to be executed by the thread. When you implement this interface and provide your own implementation of the run() method, you're essentially creating a task or a piece of work that can be performed by a separate thread.

The key benefits of using Runnable are:

Decoupling: By separating the execution logic from the thread itself, you gain flexibility in designing your program's architecture. Reusability: A single implementation of Runnable can be used to create multiple threads, making it a great option for tasks that need to be executed concurrently. Lightweight: Since Runnable is an interface, implementing it doesn't require creating a new thread class, which can lead to more efficient memory usage.

However, when you use Runnable, the thread's lifecycle management (e.g., starting, stopping) becomes more complex, as these operations need to be handled manually using APIs like Thread.start() or Thread.join().

Thread

On the other hand, a Thread is a class that represents an individual thread of execution. When you extend the Thread class and override its run() method (just like with Runnable), you're essentially creating a new thread that can run concurrently with other threads in your program.

The benefits of using Thread are:

Native control: As a concrete class, Thread provides direct access to thread-related methods and APIs, allowing for more fine-grained control over the thread's lifecycle. Simplified management: Creating a Thread instance automatically establishes its own execution context, making it easier to manage threads in your program. Native thread support: Java provides built-in support for threads through the Thread class, which includes features like synchronization primitives (e.g., locks) and thread-related exceptions.

However, using Thread can lead to a more complex design, as you need to handle thread creation, management, and termination manually, which can result in additional boilerplate code.

In summary

Use Runnable when: You want to decouple the execution logic from the thread itself. You need to create multiple threads from a single task implementation. You prioritize lightweight, reusable code. Use Thread when: You require native control over thread-related APIs and methods. You need to establish a new thread's lifecycle (e.g., starting, stopping) manually. You want to take advantage of Java's built-in thread support.

In conclusion, both Runnable and Thread are useful in different situations. By understanding the strengths and weaknesses of each, you can make informed decisions about how to structure your multithreaded applications in Java.