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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 121
90
PROCESSES AND THREADS
CHAP. 2
program. For example, when a user types a command, say,
sort
, to the shell, the
shell forks off a child process and the child executes
sort
.
The reason for this two-
step process is to allow the child to manipulate its file descriptors after the
fork
but
before the
execve
in order to accomplish redirection of standard input, standard
output, and standard error.
In Windows, in contrast, a single Win32 function call,
CreateProcess
, handles
both process creation and loading the correct program into the new process. This
call has 10 parameters, which include the program to be executed, the com-
mand-line parameters to feed that program, various security attributes, bits that
control whether open files are inherited, priority information, a specification of the
window to be created for the process (if any), and a pointer to a structure in which
information about the newly created process is returned to the caller.
In addition to
CreateProcess
, Win32 has about 100 other functions for managing and synchro-
nizing processes and related topics.
In both UNIX and Windows systems, after a process is created, the parent and
child have their own distinct address spaces.
If either process changes a word in its
address space, the change is not visible to the other process.
In UNIX, the child’s
initial address space is a
copy
of the parent’s, but there are definitely two distinct
address spaces involved; no writable memory is shared. Some UNIX imple-
mentations share the program text between the two since that cannot be modified.
Alternatively, the child may share all of the parent’s memory, but in that case the
memory is shared
copy-on-write
, which means that whenever either of the two
wants to modify part of the memory, that chunk of memory is explicitly copied
first to make sure the modification occurs in a private memory area. Again, no
writable memory is shared.
It is, however, possible for a newly created process to
share some of its creator’s other resources, such as open files. In Windows, the
parent’s and child’s address spaces are different from the start.
2.1.3 Process Termination
After a process has been created, it starts running and does whatever its job is.
However, nothing lasts forever, not even processes. Sooner or later the new proc-
ess will terminate, usually due to one of the following conditions:
1. Normal exit (voluntary).
2. Error exit (voluntary).
3. Fatal error (involuntary).
4.
Killed by another process (involuntary).
Most processes terminate because they have done their work. When a compiler
has compiled the program given to it, the compiler executes a system call to tell the
operating system that it is finished. This call is
exit
in UNIX and
ExitProcess
in
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