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Old 12-11-2009, 06:21 AM   #1
shariefbe
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diff between "system calls" and "kernel threads"


Hello,
May i know what is the difference between systems calls and kernel threads. I googled for the answer but as a newbie i didnt get understand what the difference?
 
Old 12-11-2009, 06:33 AM   #2
JohnGraham
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Quote:
Originally Posted by shariefbe View Post
Hello,
May i know what is the difference between systems calls and kernel threads. I googled for the answer but as a newbie i didnt get understand what the difference?
They are two fundamentally different things:

1) A system call is a function call made from a program to a "system function" - these are functions like open() and sched_yield() that are specific to *nix (i.e. Windows would have different system calls).

2) A kernel thread is like a normal thread (i.e. independent thread of execution) except that it was spawned by a process in kernel-space.
 
Old 12-11-2009, 07:01 AM   #3
shariefbe
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i understand what is system call is. But still i am confused about threads.
 
Old 12-11-2009, 12:05 PM   #4
smeezekitty
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Quote:
Originally Posted by shariefbe View Post
i understand what is system call is. But still i am confused about threads.
Threads allow two diferent functions to execute at the same time.
Threads should be avoided when not necceray but used when you have to.
 
Old 12-13-2009, 08:44 AM   #5
resetreset
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the question is not what is different between the two, but what, if any, the SIMILARITY is - what made you think there is any?
 
Old 12-13-2009, 10:23 AM   #6
Recursion
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A system call is a request of some application in user space, requesting the services of the kernel to carry out a given task it doesn't have the right or privilege to do. The system call comes from user space, signals a trap into kernel space and then if approved carries out the service for the user mode app. So as an example, lets say we have a non modern Linux kernel and want to read out memory. Newer kernels disable this by default, but it can be re-enabled. We can read from /dev/mem, and doing so takes many read system calls, as the user space doesn't have access to /dev/mem. To see the system calls you can do something like this

Quote:
sudo strace cat /dev/mem > /dev/null
A thread is the line of execution of a process. So lets say we create an application in C which is just a for loop that continually increments a variable by 1 to 1 million. The assembled version of that C app, will be numerous add instructions allowing the system to count to 1 million. All of those instructions are held in the processes thread of execution, and are executed one at a time. In older systems there was one thread per process, though in modern systems, each process can have as many threads as resources available. A process is just a program in execution by the way.

Last edited by Recursion; 12-13-2009 at 10:25 AM.
 
  


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