Multiprocessing vs Multithreading

Multi-threaded programs and multi-process systems are the best ways of splitting up workload into multiple actions and partitioning the task into different for most computing tasks, multiple tasks for these multiple actions. To understanding the best choice for your program and workload, requires to understanding what they are and what the differences between them. So, let's find it -

What is Multiprocessing?

Multiprocessing sometimes refers to executing multiple processes (programs) at the same time. It relates to the hardware (the CPU units) rather than the software (running processes). If the underlying hardware provides more than one processor then that is multiprocessing. Several variations on the basic scheme exist, for example, multiple cores on one die or multiple dies in one package or multiple packages in one system. A system can be both multi-programmed by having multiple programs running at the same time and multiprocessing by having more than one physical processor. Multiprocessing can change the memory access model from uniform memory access to non-uniform memory access.

Advantages of Multiprocessing

• The main advantage of the multiprocessor system is to get more work done in a shorter period of time.

• These types of systems are used when very high speed is required to process a large volume of data.

• Multiprocessing systems can save money in comparison to single processor systems because the processors can share peripherals and power supplies.

• It also provides increased reliability in the sense that if one processor fails, the work does not halt, it only slows down. For example, if we have 10 processors and 1 fails, then the work does not halt, rather the remaining 9 processors can share the work of the 10th processor. Thus the whole system runs only 10 percent slower, rather than failing altogether.

What is Multithreading?

Multithreading is an execution model that allows a single process to have multiple code segments (i.e., threads) run concurrently within the “context” of that process. You can think of threads as child processes that share the parent process resources but execute independently. Multiple threads of a single process can share the CPU in a single CPU system or (purely) run in parallel in a multiprocessing system.

Advantages of Multithreading

• Less overhead to establish and terminate vs. a process, because very little memory copying is required (just the thread stack).

• Threads are faster to start than processes. And also faster for task-switching.

• In many cases, it is faster for an operating system to switch between threads for the active CPU task than it is to switch between different processes. The CPU caches and program context can be maintained between threads in a process, rather than being reloaded as in the case of switching a CPU to a different process.

• Threads all share a process’s memory pool is very beneficial. Not having separate copies, means that different threads can read and modify a shared pool of memory easily. While data sharing is possible with separate processes through shared memory and inter-process communication, this sharing is of an arm's-length nature and is not inherently built into the process model.

Differences between Multiprocessing and Multithreading

• In multiprocessing, the system allows executing multiple programs and tasks at the same time, whereas, in multithreading, the system executes multiple threads of the same or different processes at the same time.

• Multiprocessing increases the computing speed of the system. In contrast, Multithreading increase the responsiveness of the system.

• In multiprocessing, CPU has to switch between multiple programs so that it appears that multiple programs are running simultaneously. On other hands, in multithreading CPU has to switch between multiple threads to make it appear that all threads are running simultaneously.

• Multiple processes are executed concurrently. And multiple threads of a single process are executed concurrently.

• Multiprocessing allocates separate memory and resources for each process/program whereas, in multithreading threads belonging to the same process shares the same memory and resources as that of the process.

• Multiprocessing is sharing of computer resources among the number of processes or execution of different processes at the same time like working on MS Office while VLC player is running whereas Multithreading is the execution of the number of different tasks within the same process like in MS Word while you are writing the auto-correction is performed simultaneously.

• Multiprocessing is forking a process to work in non-blocking mode, allocates separate code and data space for each child process. And multithreading is a multitasking within a process, where child threads share the same code and data space with parent thread.

• Multi Processes are heavyweight tasks that require their own address space. Interprocess communication is very expensive and context switching from one process to another process is costly since they are running in different address spaces. On the other hand, multithreading threads are a lightweight process and can share same address space and inter-thread communication is less expensive than interprocess.

• Multithreading avoids pickling. Multi-processing relies on pickling objects in memory to send to other processes.

• Multiprocessing can be symmetric or asymmetric. On the other hand, multithreading is not classified.

 

The performance between multithreading and multiprocessing are extremely similar and the exact performance details are likely to depend on your specific application. Thank you!