How do threads related to processes

A single-threaded process is a process with a single thread. A multi-threaded process is a process with multiple threads. As the diagram clearly shows that the multiple threads in it have its own registers, stack, and counter but they share the code and data segment. We will learn more about multi-threading and its models in the next blog. Hope you enjoyed this blog. Do share this blog with your friends to spread the knowledge.

Visit our YouTube channel for more content. Admin AfterAcademy 1 May Share this blog and spread the knowledge. Share On Facebook. Threads in same process share a common id called as thread group id tgid , also they have a unique id called as the process id pid.

Is a program in execution. It also includes the process stack that contains temporary data such as function parameters, return addressed and local variables , and a data section, which contains global variables. A process may also include a heap, which is memory that is dynamically allocated during process run time. A thread is a basic unit of CPU utilisation; it comprises a thread ID, a program counter, register set, and a stack. Difference between Thread and Process?

A process is an executing instance of an application and A thread is a path of execution within a process. Also, a process can contain multiple threads. Thus, the essential difference between a thread and a process is the work that each one is used to accomplish.

Another difference between a thread and a process is that threads within the same process share the same address space, whereas different processes do not. This allows threads to read from and write to the same data structures and variables, and also facilitates communication between threads. Communication between processes — also known as IPC, or inter-process communication — is quite difficult and resource-intensive. Multithreading requires careful programming since threads share data strucures that should only be modified by one thread at a time.

Unlike threads, processes don't share the same address space. Processes are independent of each other. Threads, since they share the same address space are interdependent, so caution must be taken so that different threads don't step on each other. This is really another way of stating 2 above. Process is basically a program in execution.

It is an active entity. A process is always stored in the main memory also termed as the primary memory or random access memory. Therefore, a process is termed as an active entity. It disappears if the machine is rebooted. Several process may be associated with a same program. On a multiprocessor system, multiple processes can be executed in parallel. On a uni-processor system, though true parallelism is not achieved, a process scheduling algorithm is applied and the processor is scheduled to execute each process one at a time yielding an illusion of concurrency.

Each of the instances are termed as a process. A thread is a subset of the process. Usually, a process has only one thread of control — one set of machine instructions executing at a time. A process may also be made up of multiple threads of execution that execute instructions concurrently.

Multiple threads of control can exploit the true parallelism possible on multiprocessor systems. On a uni-processor system, a thread scheduling algorithm is applied and the processor is scheduled to run each thread one at a time. All the threads running within a process share the same address space, file descriptors, stack and other process related attributes.

Since the threads of a process share the same memory, synchronizing the access to the shared data withing the process gains unprecedented importance. From the point of view of an interviewer, there are basically just 3 main things that I want to hear, besides obvious things like a process can have multiple threads:.

If you want more, Scott Langham's response pretty much covers everything. All these are from the perspective of an operating system. Different languages can implement different concepts, like tasks, light-wigh threads and so on, but they are just ways of using threads of fibers on Windows. There are no hardware and software threads. There are hardware and software exceptions and interrupts , or user-mode and kernel threads.

The following is what I got from one of the articles on The Code Project. I guess it explains everything needed clearly. A thread is another mechanism for splitting the workload into separate execution streams.

A thread is lighter weight than a process. This means, it offers less flexibility than a full blown process, but can be initiated faster because there is less for the Operating System to set up. When a program consists of two or more threads, all the threads share a single memory space.

Processes are given separate address spaces. But each thread is given its own stack. Threads can access each others memory, and they are scheduled by OS in an interleaved manner so they appear to run in parallel or with multi-core they really run in parallel. Processes , on the other hand, live in their private sandbox of virtual memory, provided and guarded by MMU. This is handy because it enables:. Thread : Thread is a functionality which is executed with the other part of the program based on the concept of "one with other"so thread is a part of process..

I've perused almost all answers there, alas, as an undergraduate student taking OS course currently I can't comprehend thoroughly the two concepts. I mean most of guys read from some OS books the differences i. Let's glance at the following example by making use of the image excerpted from one of the prior answers ,.

We have 3 threads working at once on a word document e. Libre Office. The first does spellchecking by underlining if the word is misspelt. The second takes and prints letters from keyboard. And the last does save document in every short times not to lose the document worked at if something goes wrong. In this case, the 3 threads cannot be 3 processes since they share a common memory which is the address space of their process and thus all have access to the document being edited.

So, the road is the word document along with two bulldozers which are the threads though one of them is lack in the image.

While building an algorithm in Python interpreted language that incorporated multi-threading I was surprised to see that execution time was not any better when compared to the sequential algorithm I had previously built. In an effort to understand the reason for this result I did some reading, and believe what I learned offers an interesting context from which to better understand the differences between multi-threading and multi-processes.

Multi-core systems may exercise multiple threads of execution, and so Python should support multi-threading. But Python is not a compiled language and instead is an interpreted language 1. This means that the program must be interpreted in order to run, and the interpreter is not aware of the program before it begins execution.

What it does know, however, are the rules of Python and it then dynamically applies those rules. Optimizations in Python must then be principally optimizations of the interpreter itself, and not the code that is to be run. Specifically, Python uses the Global Interpreter Lock to manage multi-threading. On the other hand a compiled language is, well, compiled. The program is processed "entirely", where first it is interpreted according to its syntactical definitions, then mapped to a language agnostic intermediate representation, and finally linked into an executable code.

This process allows the code to be highly optimized because it is all available at the time of compilation. The various program interactions and relationships are defined at the time the executable is created and robust decisions about optimization can be made.

In modern environments Python's interpreter must permit multi-threading, and this must both be safe and efficient. This is where the difference between being an interpreted language versus a compiled language enters the picture.

The interpreter must not to disturb internally shared data from different threads, while at the same time optimizing the use of processors for computations. As has been noted in the previous posts both a process and a thread are independent sequential executions with the primary difference being that memory is shared across multiple threads of a process, while processes isolate their memory spaces.

In Python data is protected from simultaneous access by different threads by the Global Interpreter Lock. It requires that in any Python program only one thread can be executed at any time. On the other hand it is possible to run multiple processes since the memory for each process is isolated from any other process, and processes can run on multiple cores. In modern UNIX implementations, each process can have multiple threads of execution.

One way of envisaging threads is as a set of processes that share the same virtual memory, as well as a range of other attributes. Each thread is executing the same program code and shares the same data area and heap.

However, each thread has it own stack containing local variables and function call linkage information. This book is a source of great clarity; Julia Evans mentioned its help in clearing up how Linux groups really work in this article. Threads within the same process share the Memory, but each thread has its own stack and registers, and threads store thread-specific data in the heap. Threads never execute independently, so the inter-thread communication is much faster when compared to inter-process communication.

Processes never share the same memory. When a child process creates it duplicates the memory location of the parent process. Process communication is done by using pipe, shared memory, and message parsing.

Context switching between threads is very slow. Consider process like a unit of ownership or what resources are needed by a task. A thread is a dispatchable unit of execution or in simple words the progress through a sequence of instructions. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. What is the difference between a process and a thread?

Ask Question. Asked 13 years, 1 month ago. Active 7 months ago. Viewed 1. What is the technical difference between a process and a thread? NAND 7 7 silver badges 22 22 bronze badges. James Fassett James Fassett Related: stackoverflow. It probably warrants saying that each OS has a different idea of what is a 'thread' or 'process'.

Some mainstream OS' don't have a concept of 'thread', there are also some embedded OS' that only have 'threads'. Add a comment. Active Oldest Votes. Greg Hewgill Greg Hewgill k gold badges silver badges bronze badges. Hardware threads are probably referring to multiple thread contexts within a core e.

If the process A creates a thread, the thread also need some space to execute. So will it increase size of the space which is created for process A, or space for thread created somewhere else? Please correct me if my question is wrong. Thanks — duslabo. JeshwanthKumarNK: Creating a new thread allocates at least enough memory for a new stack. This memory is allocated by the OS in process A.

This answer seems wrong. If both processes and threads were independent sequences of execution, then a process that contained two threads would have to have three sequences of execution, and that can't be right. Only a thread is a sequence of execution -- a process is a container that can hold one or more sequences of execution. Show 6 more comments. This information was found on Microsoft Docs here: About Processes and Threads Microsoft Windows supports preemptive multitasking, which creates the effect of simultaneous execution of multiple threads from multiple processes.

Scott Langham Scott Langham For people who want to know why cant you format a floppy at the same time : stackoverflow. LuisVasconcellos - If there were no threads, then the process wouldn't do anything. Like context switches, interprocess communications require processor time. All that time adds up when many programs are running at once or when many users each require several processes running at the same time.

The more processes running, the greater the percentage of time the CPU and operating system will spend doing expensive context switches. With enough processes to run, a server might eventually spend almost all of its time switching among processes and never do any real work. To avoid that problem, programmers can use threads. A thread is like a child process, except all the threads associated with a given process share the same address space.

For example, when there are many users for the same program, a programmer can write the application so that a new thread is created for each user. Each thread has its own flow of control, but it shares the same address space and most data with all other threads running in the same process. As far as each user can tell, the program appears to be running just for him. The advantage? It takes much less CPU time to switch among threads than between processes, because there's no need to switch address spaces.

In addition, because they share address space, threads in a process can communicate more easily with one another. If the program is running on a computer with multiple processors, a single-process program can be run by only one CPU, while a threaded program can divide the threads up among all available processors. So moving a threaded program to a multiprocessor server should make it run faster.

The downside? Programs using threads are harder to write and debug. Not all programming libraries are designed for use with threads.