Process and Thread

Akshay Teotia

15y2kVisual Basic .NET

hi friends

Describe the difference between a Thread and a Process?

5 Replies

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Sam Hobbs15y ago
Accepted answer
Manoj, most of what you say is good. I hope that helps Akshay.

You say "caution must be taken so that different threads don't step on each other" and "threads share data structures that should only be modified by one thread at a time", and that is accurate. When we say "can communicate with each other directly" it helps to make it clear that threads usually don't communicate with each other as easily as a thread can communicate with just itself. Yes, it is easier for threads to communicate within a process than across processes, but it is best to use some method to synchronize the communication even with a process.

Also, it might be a little confusing to say that "Threads are easier to create than processes", since in .Net a process can be created by using a single line of code and it usually requires more than one line of code to create a thread. Certainly it is easier for Windows to create a thread than a process, and the most important criteria is that a process requires more of the system's resources than a thread.

It is arguable whether an "application consists of one or more processes". Certainly this depends on what the definition of an application is. If we define an application as a single executable (".exe") file then there is one and only one process for each application, with the exception of domains as I specify above.
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Sam Hobbs15y ago
Accepted answer
That article says "A processor executes threads, not processes, so each application has at least one process", which is wrong. An application has one and only one process, except for something called domains, which are not relevant to most applications; usually domains are used only by ASP applications. Also, it is confusing to say that a processor executes threads but not processes; a thread cannot execut without a process.

Note that this question has been asked a few times recently so there are some previous answers that are good. I suggest reading my article An Introduction to Virtual Memory in Windows; it explains about processes also but it does not explain much about threads.
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Akshay Teotia15y ago
hi sam ur knowledge about technology is to good this discussion is really good and helpful for me. thanks
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Manoj Sevda15y ago
Both threads and processes are methods of parallelizing an application. Processes are independent execution units that contain their own state information, use their own address spaces, and only interact with each other via interprocess communication mechanisms.

Thread is a coding construct that doesn't affect the architecture of an application. A single process might contains multiple threads; all threads within a process share the same state and same memory space, and can communicate with each other directly, because they share the same variables.

An application consists of one or more processes. A process, in the simplest terms, is an executing program. One or more threads run in the context of the process. A thread is the basic unit to which the operating system allocates processor time. A thread can execute any part of the process code, including parts currently being executed by another thread.

In simple words a process is an executing instance of an application. For example, when you double-click the Microsoft Word icon, you start a process that runs Word. A thread is a path of execution within a process. Also, a process can contain multiple threads. When you start Word, the operating system creates a process and begins executing the primary thread of that process.

a) A process can consist of multiple threads.
b) 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.
c) Multithreading requires careful programming since threads share data structures that should only be modified by one thread
at a time. Unlike threads, processes don't share the same address space.
d) Threads are easier to create than processes since they don't require a separate address space.
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Hemant Kumar15y ago

The major difference between threads and processes is  1.Threads share the address space of the process that  created it; processes have their own address.  2.Threads have direct access to the data segment of its  process; processes have their own copy of the data segment  of the parent process.   3.Threads can directly communicate with other threads of  its process; processes must use interprocess communication  to communicate with sibling processes.   4.Threads have almost no overhead; processes have  considerable overhead.  5.New threads are easily created; new processes require  duplication of the parent process.  6.Threads can exercise considerable control over threads of  the same process; processes can only exercise control over  child processes.   7.Changes to the main thread (cancellation, priority  change, etc.) may affect the behavior of the other threads  of the process; changes to the parent process does not  affect child processes. http://forums.sureshkumar.net/vb-asp-net-interview-technical-questions/17262-describe-difference-between-thread-process.html