Multithreading is a process of executing multiple threads simultaneously. A program can be divided into a number of small processes. Each small process can be addressed as a single thread (a lightweight process). Multithreaded programs contain two or more threads that can run concurrently. This means that a single program can perform two or more tasks simultaneously. For example, one thread is writing content on a file at the same time another thread is performing spelling check.
Thread is basically a lightweight subprocess, a smallest unit of processing. Multiprocessing and multithreading, both are used to achieve multitasking. But we use multithreading than mulitprocessing because threads share a common memory area. They don’t allocate separate memory area so save memory, and context-switching between the threads takes less time than processes.
Multithreading is mostly used in games, animation etc.
Multitasking is a process of executing multiple tasks simultaneously. We use multitasking to utilize the CPU. Multitasking can be achieved by two ways:
- Process-based Multitasking(Multiprocessing)
- Thread-based Multitasking(Multithreading)
In Java, the Java Virtual Machine (JVM) allows an application to have multiple threads of execution running concurrently. It allows a program to be more responsible to the user. When a program contains multiple threads then the CPU can switch between the two threads to execute them at the same time.
In this diagram, two threads are being executed having more than one task. The task of each thread is switched to the task of another thread.
1)Process-based Multitasking (Multiprocessing)
- Each process have its own address in memory i.e. each process allocates separate memory area.
- Process is heavyweight.
- Cost of communication between the process is high.
- Switching from one process to another require some time for saving and loading registers, memory maps, updating lists etc.
2)Thread-based Multitasking (Multithreading)
- Threads share the same address space.
- Thread is lightweight.
- Cost of communication between the thread is low.
- Note:At least one process is required for each thread.
Advantages of multithreading over multiprocessing :
- Reduces the computation time.
- Improves performance of an application.
- Threads share the same address space so it saves the memory.
- Context switching between threads is usually less expensive than between processes.
- Cost of communication between threads is relatively low.