Thread Scheduler in Java

Priority: Each thread is assigned a priority value ranging from 1 to 10. A thread with a higher priority has a greater chance of being selected by the thread scheduler for execution.

Time of Arrival: When multiple threads have the same priority and are in the runnable state, the thread scheduler takes their arrival time into account. The thread that arrived first is given priority over the others and gets selected for execution.

By considering these factors, the thread scheduler efficiently manages the execution of threads in a Java program, ensuring that the most important and timely threads are given priority.

Thread Scheduler Algorithms

• First Come First Serve Scheduling
• Time-slicing scheduling
• Preemptive-Priority Scheduling

First Come First Serve Scheduling

In the First Come First Serve scheduling algorithm for multithreading in Java, the scheduler chooses threads based on their arrival order in the runnable queue. The thread that arrives first will be selected first for execution.

Thread threads1 arrived first, followed by Thread threads3, Thread threads2, Thread threads4, and Thread threads5, and the order in which the threads will be processed is determined by the time of arrival of the threads.

Preemptive Priority Scheduling

Priority for Prevention CPU Scheduling Algorithm is a pre-emptive CPU scheduling algorithm that operates based on a process's priority. The scheduler in this algorithm schedules tasks based on priority, which means that a higher priority process should be executed first.

Priority for Prevention CPU Scheduling Algorithm defines a rank for each process using a rank-based system, where lower rank processes have higher priority and higher rank processes have lower priority. For example, if this Preemptive Algorithm is to be used to execute ten processes, the process with rank 1 will have the highest priority, the process with rank 2 will have a comparatively lower priority, and the process with rank 10 will have the lowest priority.

Time-slicing scheduling

A time slice is a period of time during which a process is assigned to run in a preemptive multitasking CPU. Every time-slice, the scheduler runs each process. The length of each time slice can be very important in balancing CPU performance and responsiveness.

If the time slice is very short, the scheduler will require more processing time. If the time slice is too long, the scheduler will require more processing time.

When a process is assigned to the CPU, the clock timer for that time slice is set. If the process completes its burst before the time slice, the CPU simply swaps it out as in a traditional FCFS(first Come first Serve) calculation. If the time slice is the first to expire, the CPU moves it to the end of the ongoing queue.

Advantages of Time-slicing scheduling

• Fair Allocation of CPU Resources: Time-slicing scheduling ensures that CPU resources are distributed equally among different processes or threads. This helps prevent any single process from dominating the CPU and allows for a balanced execution of tasks.
• Equal Weight to All Processes: Each process or thread is given an equal opportunity to execute, regardless of its priority or importance. This promotes fairness and prevents any particular process from being favored over others.
• Simple Integration: Time-slicing scheduling is straightforward to incorporate into a system. It doesn't require complex algorithms or extensive modifications, making it easier to implement and maintain.
• Optimal Average Processing Time: Context switching, which is the mechanism used to save and switch between preempted processes, is efficiently utilized in time-slicing scheduling. This results in a good average processing time performance for the overall system.

Disadvantages of Time-slicing scheduling

• Delayed Processor Output with Short Slicing Time: When the time quantum (slicing time) is set to a short duration, it can cause delays in the processor's output. This happens because frequent context switches add overhead and reduce the time available for actual processing.
• Time Wasted on Context Switching: Context switching, the process of saving and restoring the state of preempted processes, requires time and resources. With time-slicing scheduling, there can be a significant amount of time wasted on these context switches, affecting overall system efficiency.
• Impact of Time Quantum on Performance: The performance of time-slicing scheduling is heavily influenced by the chosen time quantum. Selecting an inappropriate time quantum can result in either poor responsiveness or excessive context switching, leading to reduced efficiency.
• b Inflexible Process Priorities: Time-slicing scheduling does not allow for fixed process priorities. As a result, more important or critical tasks cannot be given higher priority over less important ones. This can be a limitation in scenarios where certain processes require immediate attention.
• Difficulty in Determining Suitable Time Quantum: Finding the optimal time quantum for time-slicing scheduling can be challenging. It requires considering the characteristics of the system, workload, and desired performance, making it a complex task to determine the most suitable value.