11. Process Control Theory

11. Process Control Theory

Process: A process is a run of an application with a certain independent function. A program that is not running is not called a process, only a program that is running will produce a process.

Characteristics of the process:

1. Dynamic nature
2. Concurrency of
3. Independence
4. of Asynchrony

Status of the process:

When we run a program, the program is in the ready state. Because the program requires resources, such as memory, hard disk space, and so on. So the CPU issues an I/O request. If a program is running at this point, these resources are being used. Will not be satisfied, it will cause the process to go into a blocking state. When the resource request is satisfied, it enters the ready state again. Waiting for the CPU to dispatch, in the process of execution, if a process in the system specified within a time slice is not able to execute, he will again into the ready state, again waiting for CPU scheduling. So loop, know that the program runs out.

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Process ID:

Process ID (PID): The system gives each process a unique identifier, which is a number.

The ID of the parent process (PPID).

The user ID (UID) of the startup process.

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Mutex for process:

A process mutex is when a resource is used by a number of processes, but the resource allows at most one process at a time to make

, the other process must wait until the resource is freed by the resource being consumed.

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Critical resources:

In the operating system, at some point, only a single process is allowed access to a resource called a critical resource.

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Critical section:

The program code that accesses critical resources in a process is called a critical section. In order to achieve mutually exclusive access to critical resources, the processes should be guaranteed to enter the respective critical areas.

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Synchronization of Processes:

A process in which a group of processes executes in a certain order is called inter-process synchronization. This set of processes with a synchronous relationship is called a collaborative process, most notably producer and consumer processes.

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Scheduling of processes:

According to a certain algorithm, from a set of processes to run to choose one to occupy the CPU operation.

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Common scheduling algorithms:

1. First come first serve
2. Short process First
3. High priority priority
4. Time Slice Rotation method

Timing of scheduling:

1. Preemptive scheduling
2. Non-preemptive scheduling

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Deadlock:

Multiple processes are deadlocked as a result of competing resources, resulting in the inability of these processes to proceed forward.

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Let's look at the function that gets the process:

The function that gets the process ID is: getpid.

View the information for this function: Man 2 getpid:

NAME

Getpid, Getppid-get process identification

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Synopsis

#include <sys/types.h>

#include <unistd.h>

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pid_t getpid (void);

pid_t getppid (void);

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DESCRIPTION

Getpid () returns the process ID of the calling process. (This is often

Used by routines that generate unique temporary filenames.)

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Getppid () returns the process ID of the the parent of the calling process.

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ERRORS

These functions is always successful.

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Conforming to

posix.1-2001, 4.3BSD, SVr4.

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NOTES

Since glibc version 2.3.4, the glibc wrapper function for Getpid ()

Caches PIDs, so as-avoid additional system calls when a process

Calls Getpid () repeatedly. Normally this caching is invisible

Correct operation relies on support in the wrapper functions for

Fork (2), Vfork (2), and Clone (2): If an application bypasses the GLIBC

Wrappers for these system calls by using Syscall (2)

Getpid () in the child would return the wrong value (to be precise:it

Would return the PID of the parent process). See also clones (2) for dis-

Cussion of a case where getpid () could return the wrong value even when

Invoking Clone (2) via the glibc wrapper function.

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See ALSO

Clone (2), fork (2), Kill (2), EXEC (3), Mkstemp (3), Tempnam (3), tmp-

File (3), Tmpnam (3), credentials (7)

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Colophon

This page was part of release 3.22 of the Linux man-pages project. A

Description of the project, and information about reporting bugs, can

be found at http://www.kernel.org/doc/man-pages/.

Gets the process ID of the function getpid. The return value of the function is the ID of the process that called the function. Required Header files:

<sys/types.h> <unistd.h>

The function has no arguments. The return value is the ID of the process that called the function.

Example GETPID.C:

#include <sys/types.h>

#include <unistd.h>

#include <stdio.h>

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void Main () {

???? int id = 0;

???? id = getpid ();

???? printf ("process ' s ID%d\n", id);

}

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Results of the operation:

Above, the generated getpid is a program, and when we do not go to run, he is a program. When we run, he becomes a process. The ID of the process is changing all the times.

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11. Process Control Theory