Please tell me the difference between heavy weight process and light weight process. All i know is that a heavy weight process has its own address space and light weight processes share the same address space. Is there any other difference?

Answer:

In computing, a process is a running instance of a program. The operating system uses processes to separate the different applications and execute them concurrently. This improves the system’s responsiveness and performance. Processes can be broadly classified into two categories: heavyweight processes and lightweight processes. The primary difference between the two lies in their memory management, which impacts their speed, overhead, and usage scenarios.

Heavyweight Process

A heavyweight process, often simply referred to as a process, is a program in execution that has its own address space and system resources, such as file descriptors and signal handlers. The operating system manages these processes separately and allocates dedicated resources to each one.

Every process has its own Program Control Block (PCB), which contains essential information like the process state, program counter, CPU registers, and memory tables.

When the CPU switches from executing one process to another, it involves a context switch, which includes saving the state of the current process and restoring the saved state of the new process.

This operation is relatively costly in terms of time and CPU resources.

The isolation provided by separate address spaces ensures that one process cannot directly access or modify the memory contents of another process. This separation is crucial for system stability and security.

Lightweight Process

A lightweight process, often referred to as a thread, is a sequence of instructions within a program that can be scheduled and executed by the operating system.

Multiple threads within a single process share the same address space and system resources. This sharing enables threads to communicate with each other more easily and efficiently compared to heavyweight processes.

Each thread has its own stack, program counter, and register values, but other resources like file descriptors, heap memory, and global variables are shared among all threads of a process.

Because threads share the same address space, a context switch between threads of the same process is much faster and less resource-intensive compared to a context switch between heavyweight processes.

Comparison

1. Memory Management: The most significant difference between heavyweight and lightweight processes is their memory management. Heavyweight processes have their own separate address space, while lightweight processes (threads) share the same address space.

2. Context Switching: Context switching between heavyweight processes is relatively slow and resource-intensive because it involves switching the entire address space. In contrast, context switching between lightweight processes is faster and more efficient because they share the same address space.

3. Communication: Inter-process communication (IPC) between heavyweight processes is more complex and slower because they have separate address spaces. Threads, on the other hand, can directly communicate through shared memory, which is much faster and simpler.

4. Overhead: Heavyweight processes have more overhead because they require more system resources and the operating system must manage them separately. Lightweight processes have less overhead because they share resources and the operating system can manage them more efficiently.

5. Use Cases: Heavyweight processes are suitable for tasks that require isolation, stability, and security, such as running different applications on an operating system. Lightweight processes are suitable for tasks that require fast communication and efficient resource usage, such as the different modules of a single application.

Summary

Heavyweight and lightweight processes have their own advantages and disadvantages.

Heavyweight processes provide better isolation and are suitable for separate applications, while lightweight processes provide faster communication and are suitable for different parts of a single application.

The choice between using heavyweight or lightweight processes depends on the requirements of the application and the operating system’s capabilities.