Mailinglist Archive: opensuse (3166 mails)

["Quinlan, Grant" <Grant_Quinlan@xxxxxxx>]

From: Rohit [mailto:rohits@xxxxxxxxxxxxxx]
Subject: [SLE] OT : theory : process and a thread

Hi all,

What is the difference between a process and a thread - except for I know
that a process has a unique PID associated with it..
_________________________________________________________

The high level overview goes like this:

An OS contains many processes.
The OS gives each process it's own  unique PID, a private allotment of 
memory, it's own private set of slices of time to run on the CPU(s), and
allotments of other resources as needed.

A process contains one or more threads. Each thread has it's own thread id 
(TID) and shares with all other threads in the same process the memory, 
time, and other resources allocated to the process. All threads share the
rights and permissions of the process owner. 

A process is dedicated to a single atomic task (meaning the task is 
fully independent of any other tasks). The threads within that 
process work together "in parallel" to accomplish the task.

At least that's how the theory works, in practice the lines between a
process
and thread can get blurry. Processes can share memory and resources and work
together to get common task accomplished (this can allow the task to get
more 
than it's "fair share" of memory and time, and thus complete sooner). For 
example a small personal web server (such as TomCat) will often run entirely

within a single process, but a web server that needs to handle heavy loads 
(such as Apache) will use many processes working together so that it can 
better keep up. In Linux on IBM z-Series (mainframe hardware) there is no 
such thing as a process, everything is a thread. To allow Linux apps to
compile 
and run a thread is declared the parent, and it's thread id is returned as
the 
process id. Resources are allocated to the parent thread and the child
threads 
share all the resources of the parent thread.

                         Grant Q