In Java, a thread is a path or direction taken during the execution of any program. Any program has a minimum of one thread, better called the main thread. The Java Virtual Machine or JVM provides it at the beginning of any program's execution. After the main thread is offered, its main thread will involve the prime method.
Wondering what are threads in Java? Well, threads are the execution threads in programs. In short, multiple threads of execution might get run by the application that runs on the JVM. The prime focus of individual threads varies depending on certain parameters. The higher-priority threads will be executed before the lower ones.
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Multithreading in Java is the concept in the current operating systems. It refers to more than one task executing simultaneously within one program. Multithreading can be achieved in Java using the thread class as well as the runnable interface. Now, what are the runnable interface and thread class? Simply put, Java's runnable interface and thread class allow for creating and controlling a particular thread in Java. The thread class controls any thread in the following ways:
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As we now know the entire lifecycle of a java thread, let us know how threads are created in java. A process is the programs dispatched from a ready state and scheduled in the CPU for the execution process. A process may create other processes that are referred to as the child processes. The process might take time for termination and is isolated. That means it doesn't share the memory with another process. It has several states, such as the following:
On the contrary, a thread is a segment of the process. So, it is a process with different threads that are contained within the process. In simple terms, the thread has three different states:
A thread will take less time for termination when compared to the other type. However, unlike the process, they don't isolate.
These are the major differences between Differences Between Processes and Threads in Java:
Processes | Threads | |
---|---|---|
Definition | An instance of a program running independently | A lightweight unit of execution within a process |
Memory | Each process has its own separate memory space | Threads share the same memory space |
Communication | Inter-process communication is more complex | Inter-thread communication is relatively easier |
Creation | Creation of a new process requires more resources | Creating a new thread is less resource-intensive |
Overhead | Context switching between processes has higher overhead | Context switching between threads has lower overhead |
Independence | Processes are independent of each other | Threads are dependent on the parent process |
Scalability | Processes are more scalable due to independent memory | Threads may suffer from contention and scalability issues |
Fault Isolation | A process crash does not affect other processes | A thread crash may lead to the entire process crashing |
Parallelism | Processes can run in parallel on multi-core systems | Threads can take advantage of multi-threading and run in parallel |
Synchronization | Processes require explicit synchronization mechanisms | Threads can use synchronization constructs like locks and monitors |
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Threads allow programs to operate more effectively by performing a wide range of things concurrently. In short, they can be used for performing complex tasks in the background without the interruption of the main program.
Learn more about the Life cycle of threads in Java here. As of now, here's presenting the list of benefits of threads in Java:
Any thread in java programs enables a program to operate efficiently by performing multiple things concurrently. Threads are used for performing complex tasks in the background without interrupting a main program. Here are the best example of threads in java:
package com.journaldev.threads; public class HeavyWorkRunnable implements Runnable { @Override public void run() { System.out.println("Doing heavy processing - START "+Thread.currentThread().getName()); try { Thread.sleep(1000); //Get database connection, delete unused data from DB doDBProcessing(); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("Doing heavy processing - END "+Thread.currentThread().getName()); } private void doDBProcessing() throws InterruptedException { Thread.sleep(5000); } }
Another example is mentioned in the following (extending Thread class)
package com.journaldev.threads; public class MyThread extends thread { public MyThread(String name) { super(name); } @Override public void run() { System.out.println("MyThread - START "+Thread.currentThread().getName()); try { Thread.sleep(1000); //Get database connection, delete unused data from DB doDBProcessing(); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("MyThread - END "+Thread.currentThread().getName()); } private void doDBProcessing() throws InterruptedException { Thread.sleep(5000); } }
Here's presenting the list of limitations of using threads in Java:
Here's a step-by-step narrative presenting the best way to create and use threads in Java:
Method 1: Extending Java.lang.Thread class
When using the first method, one needs to follow the below-offered steps:
Step 1: First, the thread will be created by the new class extending the thread class
Step 2: It creates the instance of the class
Step 3: The run method includes its functionality that needs to be implemented by the thread
Method 2: Implementing Runnable Interface
So, this is a seamless method to create the thread. Here's presenting the steps to follow:
Step 1: First, it is imperative to create a class
Step 2: After creating the class, it is imperative to implement a runnable interface and then use the run() method.
Note that the code for executing this thread will be written inside run().
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To start a thread, you need to call the thread's start(). The JVM calls the run() method of the thread. When you wish to stop any thread from running, you can state by the calling stop() method. The method stops executing the running thread, thereby removing it from a waiting threads pool as well as garbage collection. The thread also moves to the dead state after reaching the end of the method automatically.
Thread safe is the method that can be used by a multitude of threads without the occurrence of problems. Synchronized, on the contrary, means the one thread that operates at a single time.
The number of services assigned to a given thread is referred to as its priority. Any thread generated in Java Virtual Machine will be offered priority. Considering the priority scale, it runs between 1 and 10, where:
The main priority of a thread is set to 5 by default. Note that every child thread consists of the same priority as the parent thread. The thread priority can be adjusted irrespective of whether it is the user-defined or main thread. One can adjust it using the class's constants as mentioned in the following:
Thread.MIN_PRIORITY; Thread.NORM_PRIORITY; Thread.MAX_PRIORITY;
The thread pool is the software design pattern that helps accomplish the concurrency of any execution in the computer program. Also referred to as the replicated workers (or even worker-crew model), it maintains multiple threads for tasks allocated for simultaneous execution by a supervising program.
Thread pools improve the overall performance of any application. What they do is reuse threads & avoid the overhead of creating newer ones every time a task gets executed. They also ensure the tasks are executed timely by queueing them and executing them right as the thread are available.
Want to know the mistakes to avoid while using threads? Discover them from the following points:
To write thread-safe codes, it is imperative to practice the following points:
Reducing the use of the shared data between threads
For multiple threads that need to synchronize, serializing is important, which you can do by using a message queue rather than using locks.
It is better to refrain from nested locks. Note that if they are not implemented, they may create live lock or deadlock issues. For nested locks, the locks may be released or taken in the same hierarchy.
For spin lock & mutex that will be used in a nested way, it is important to take mutex and then spin lock before releasing in the reverse order.
So, this post has elucidated everything about threads in Java. It has also narrated the benefits, limitations, examples, thread methods in java, and other details of multithreading.
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