stack limit of Process and stack limit of thread

Hi All,
Please answer this question.

1. Assuming a linux-86/32 bit systems, the stack size of a process is 8 Mega Bytes .

if a pthread is being formed within that process, the pthread_attr_getstacksize function throws the stack size as 8MB? how come it is possible, that means all the PROCESS STACK == PTHREAD STACK?

what happens if a second thread is spawn?

Thanks
vlsireddy

I believe you have an answer, or the start of an answer, at the pthread_create man page.

Hi Sir,
Thanks for your answer. Excellent source. [on an other note, i searched it a lot, could not find the exact answer, but your link helped me understand it].

1. to wrap it up, in this case of 3 threads [the ulimit -s is set to 8MB]


./a.out hola salut servus

each of 3 threads [hola, salut, servus] come up with 8 MB of stack and as a whole can i conclude that PROCESS has 8*3=24MB of
stack with it.

In other words, Linux has dynamically extended the stack of process by 3 times [24MB]

Thanks

Originally Posted by particlereddy Hi Sir, Thanks for your answer. Excellent source. [on an other note, i searched it a lot, could not find the exact answer, but your link helped me understand it]. 1. to wrap it up, in this case of 3 threads [the ulimit -s is set to 8MB] ./a.out hola salut servus each of 3 threads [hola, salut, servus] come up with 8 MB of stack and as a whole can i conclude that PROCESS has 8*3=24MB of stack with it. In other words, Linux has dynamically extended the stack of process by 3 times [24MB] Thanks

That's how I understand it as well.

Hi,
i ran a quick simulation of finding the local variable address in PROCESS at main() and then find the address of local variable inside FIRST created pthread, seriously i dont see any relationship


[root@localhost threads]# ./threadex 1
threadinfo structure size 24
Thread 1: top of stack near 0x7f436d9deee8; argv_string=1
Joined with thread 1; returned value was 1
address of a 0x7fff66a5ffd8

main() function first local variable address: 0x7fff66a5ffd8
FIRST PTHREAD address: 0x7f436d9deee8

there is huge difference between above 2 hex numbers. looks like process has the luxury of all the system memory available as its stack

please let me know if you can reason why is it so?

this is x86-64 bit system.

Thanks

Originally Posted by particlereddy there is huge difference between above 2 hex numbers. looks like process has the luxury of all the system memory available as its stack please let me know if you can reason why is it so?

It's virtual memory, in other words the process thinks it has a full 64-bit address space for itself, actually orders of magnitude more than system memory. In reality, only those pages that are in used are mapped to physical memory by the MMU (at least that was state of the art 25 years ago), the others only exist in the process' fantasy.

You are not the first one with questions about process memory layout. An internet search of "linux process memory layout" results in some ten million hits. This is a good example: http://stackoverflow.com/questions/1...eaded-process; I'll leave it up to you to read the 9999999 others

Hi Sir,
Thanks. No more questions to you. I will reply back with all answers and understanding.

Thanks

Hi,
i got the answer. I was always thinking from the diagram perspective of stack, heap, bss, data,text. But this post tells that it is obsolete and now all the experiments which i did fall in place w.r.t to thsi post.

http://stackoverflow.com/questions/2...or-each-thread