Difference Between OS Thread and Java Threads

A thread in computer programming is a brief sequence of instructions that are intended to be scheduled and carried out by the CPU apart from the parent process. Multiple threads may be active at once in a program, which closes or suspends them when the task is finished, or the application is closed. A multithreading CPU has the capacity to run many threads simultaneously. The following are the differences between OS threads and java threads.

Threads in Java

In Java, a thread is the course or path followed while a program is being run. All programs typically have at least one main thread, which is provided by the JVM or Java Virtual Machine at the beginning of the program's execution. The main () method is now called by the main thread when it is given control of the main thread.

A program's execution thread is known as a thread. A program running on the Java Virtual Machine can execute several threads at once. Every thread has a different priority. Priority order determines which threads are run first.

Because it allows for the execution of several actions within a single function, thread is essential to the program. The program counter, stack, and local variables are frequently unique to each thread.

Java offers two different techniques to construct a thread −

• Extending java.lang.class of threads.

• Runnable interface implementation.

Extending Java.lang.class

This a new class extends the Thread class, an instance of that class is generated, and this results in the creation of a thread. The functionality that should be carried out by the Thread is included in the run () method. A thread is made runnable by using start () once it has been created. In the void run () procedure, a new thread is started.

Implementing Runnable Interface

This is the simplest way to create a thread. In this instance, a class is developed to implement the runnable interface and the run () method. Always the thread-running code is written inside the run () method.

The void run () method is invoked by the start () method. A new stack is provided to the thread when start () is called and run () is then called to introduce the thread into the program.

What are OS Threads?

A thread is a unique execution path. As it is a small process, the operating system can schedule it to operate alongside other threads. Threads are produced and managed by the operating system, sharing memory and resources with the programs that created them. This makes it possible for numerous threads to cooperate and operate effectively within a single application.

Within a process, a thread is a single sequence stream. Because they share some characteristics with processes, threads are often known as lightweight processes. Each thread is a part of only one process. The process may have numerous threads under an operating system that supports multithreading.

Thread Types

A distinct program counter, a stack of activation records, and a set of control blocks are used by each thread of the same process. The performance of the programs is improved using threads.

Two different thread types exist in an operating system− kernel-level thread and user-level thread.

Kernel-level Threads

• The OS implements and controls threads at the kernel level.

• Kernel level threads are implemented using system calls, and the OS is aware of them.

• User-level threads can be created and managed faster than kernel-level threads.

• A kernel-level thread has slower context switching.

• It has no impact on other threads whether one kernel-level thread performs a blocking action or not. Think of Window Solaris.

• The kernel is unaware of user-level threads because they are implemented and controlled by the user.

User-level Threads

• User-level threads are created by using user-level libraries, and the OS is unaware of them.

• Compared to kernel-level threads, user-level threads are easier to establish and maintain.

• It is quicker to switch contexts in user-level threads.

• The entire process becomes stalled if only one user-level thread does a blocking task. Consider Java threads, POSIX threads, etc.

Difference Between Java Thread and OS Thread

The following table highlights how Java threads are different from OS threads −

Java Thread	OS Thread
In the context of Java, a thread is the path taken during program execution	The smallest processing unit that an OS is capable of handling is a thread
At least one thread, referred to as the main thread, is present in Java programs	A process may have several threads
In Java, user threads and daemon threads are two distinct types of threads	There are two different kinds of OS threads− user-level threads and kernel-level threads
When the main () method is called with the main thread at the beginning of the program, it is controlled by the Java Virtual Machine (JVM)	Operating System oversees managing it
Thread communication is facilitated by the methods wait (), notify (), and notifyAll ()	Threads can communicate more easily and exchange common info
Monitors are used to implement thread synchronization, and synchronized blocks are used for blocking	Utilizing mutexes is the most common method for achieving thread synchronization
Which thread should run is decided by the thread scheduler in the Java Virtual Machine (JVM). Pre-emptive scheduling and time slicing are the two types	The application developer scheduling user-level threads (ULT) to kernel-level threads (KLT) via Light-Weight Process (LWP). The system scheduler scheduling kernel-level threads to carry out various distinct OS functions.

Conclusion

Any thread running within a JVM process is referred to as a "Java thread." Despite having various thread IDs, OS threads are all threads that are part of a process and share the same process ID and parent process ID.