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Unit 4: Process Management

Figure 4.3: Process Hierarchies Notes

Root Node Level 0

Child#1 Child#2 Child#3 Level 1

Level 2

The processes are linked by a tree structure. If a parent is signaled or killed, usually all its children
receive the same signal or are destroyed with the parent. This doesn’t have to be the case – it is
possible to detach children from their parents – but in many cases it is useful for processes to be
linked in this way.
When a child is created it may do one of two things.
1. Duplicate the parent process.
2. Load a completely new program.

Similarly the parent may do one of two things.
1. Continue executing along side its children.

2. Wait for some or all of its children to finish before proceeding.
The specific attributes of the child process that differ from the parent process are:

1. The child process has its own unique process ID.
2. The parent process ID of the child process is the process ID of its parent process.
3. The child process gets its own copies of the parent process’s open fi le descriptors.

Subsequently changing attributes of the file descriptors in the parent process won’t affect

the file descriptors in the child, and vice versa. However, the file position associated with

each descriptor is shared by both processes.
4. The elapsed processor times for the child process are set to zero.
5. The child doesn’t inherit file locks set by the parent process.

6. The child doesn’t inherit alarms set by the parent process.
7. The set of pending signals for the child process is cleared. (The child process inherits its
mask of blocked signals and signal actions from the parent process.)

4.3.2 Process State Transitions

Blocking: It occurs when process discovers that it cannot continue. If running process initiates an
I/O operation before its allotted time expires, the running process voluntarily relinquishes the
CPU.

This state transition is:
Block: Running? Block.
Time-Run-Out: It occurs when the scheduler decides that the running process has run long
enough and it is time to let another process have CPU time.

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