Summary of Previous Class

1
Summary of Previous Class

• Stack grows and shrinks implicitly
• The heap grows and shrinks in response to
  malloc() and free() calls
• Space taken by global variables remains constant
  throughout

2
Todays topics

• Process Creation
• File System Interface
• System Calls for processes/files

3
The Address Space of an Unix Process
4
Process

• Address Space
• Contents of registers
• Other stuff open files, etc
• How is a new process created?

5
Creating a Process Before fork()
fork( )
parent process
6
Creating a Process After fork()
fork( ) // returns p
fork( ) // returns 0
parent process
child process (process id p)
7
More fork()

• How many processes does this piece of code
  create?
• int main()
• fork()
• fork()

8
What is the output of this?

• int main()
• int i
• for (i0 ilt3 i)
• fork()
• printf(d\n,i)
• return (0)

9
Process Hierarchies

• UNIX Parent creates a child process, child can
  create more processes
• Forms a hierarchy
• UNIX calls this a "process group
• All processes within a group are logically
  related
• Windows has no concept of process hierarchy
• all processes are created equal