Operating Systems Lecture 06 page
Process Control Blocks
PCBs
Where the OS can find all the information it needs to know
about a process.
• memory
• open streams/files
• devices, including abstract ones like windows
• links to condition handlers (signals)
• processor registers (single thread)
• process identification
• process state - including waiting information
• priority
• owner
• which processor
• links to other processes (parent, children)
• process group
• resource limits/usage
• access rights
• process result - may be waited for by another process
Doesn't have to be kept together !
Different information is required at different times
UNIX for example has two separate places in memory with
this information. One of them is in the kernel the other is
in user space. Windows does the same.
Operating Systems Lecture 06 page
Linux PCBs
In the same order as the previous slide.
/* memory management info */ !
struct mm_struct *mm;
/* open file information */ !
struct files_struct *files;
/* tss for this task */ !
struct thread_struct tss;
int pid;
volatile long state; /* -1 unrunnable, 0
runnable, >0 stopped */
long priority;
unsigned short uid,euid,suid,fsuid;
#ifdef __SMP__ !
int processor; !
#endif
struct task_struct *p_opptr, *p_pptr,
*p_cptr, *p_ysptr, *p_osptr;
/* limits */ !
struct rlimit rlim[RLIM_NLIMITS]; !
long utime, stime, cutime, cstime,
start_time;
2
Operating Systems Lecture 06 page
UNIX process parts
The PCB is the box labelled process structure
but the user structure maintains some of
the information as well (only required when
the process is resident).
3
Operating Systems Lecture 06 page
Windows NT PCBs
Information is scattered in a variety of objects.
Executive Process Block (EPROCESS)
includes
• KPROCESS and PEB
• pid and ppid (the ppid is not visible to Win32)
• file name of program
• window station - the screen or remote terminal
• exit status
• create and exit times
• links to next process
• memory quotas
• memory management info
• Ports for exceptions and debugging
• Security information
4
