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Modern Operating Systems by Herbert Bos and Andrew S. Tanenb...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf
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Modern Operating Systems by Herbert Bos and Andrew...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
Modern Operating Systems by Herbert...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
Page 122
SEC. 2.1
PROCESSES
91
Windows. Screen-oriented programs also support voluntary termination. Word
processors, Internet browsers, and similar programs always have an icon or menu
item that the user can click to tell the process to remove any temporary files it has
open and then terminate.
The second reason for termination is that the process discovers a fatal error.
For example, if a user types the command
cc foo.c
to compile the program
foo.c
and no such file exists, the compiler simply
announces this fact and exits. Screen-oriented interactive processes generally do
not exit when given bad parameters. Instead they pop up a dialog box and ask the
user to try again.
The third reason for termination is an error caused by the process, often due to
a program bug. Examples include executing an illegal instruction, referencing
nonexistent memory, or dividing by zero.
In some systems (e.g., UNIX), a process
can tell the operating system that it wishes to handle certain errors itself, in which
case the process is signaled (interrupted) instead of terminated when one of the er-
rors occurs.
The fourth reason a process might terminate is that the process executes a sys-
tem call telling the operating system to kill some other process.
In UNIX this call
is
kill
.
The corresponding Win32 function is
TerminateProcess
.
In both cases, the
killer must have the necessary authorization to do in the killee.
In some systems,
when a process terminates, either voluntarily or otherwise, all processes it created
are immediately killed as well. Neither UNIX nor Windows works this way, how-
ever.
2.1.4 Process Hierarchies
In some systems, when a process creates another process, the parent process
and child process continue to be associated in certain ways. The child process can
itself create more processes, forming a process hierarchy. Note that unlike plants
and animals that use sexual reproduction, a process has only one parent (but zero,
one, two, or more children).
So a process is more like a hydra than like, say, a cow.
In UNIX, a process and all of its children and further descendants together
form a process group. When a user sends a signal from the keyboard, the signal is
delivered to all members of the process group currently associated with the
keyboard (usually all active processes that were created in the current window).
Individually, each process can catch the signal, ignore the signal, or take the de-
fault action, which is to be killed by the signal.
As another example of where the process hierarchy plays a key role, let us look
at how UNIX initializes itself when it is started, just after the computer is booted.
A special process, called
init
, is present in the boot image. When it starts running,
it reads a file telling how many terminals there are.
Then it forks off a new process
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