The process of programming Linux systems

The process of programming Linux systems

One, operating system responsibilities: management of resources, the different devices and different programs associated.

Second, the system call is the operating system provided to the user program of a special set of function interface, the user program through this set of interfaces to obtain the services provided by the system kernel, such as: Open files, close files, read and write files.

Third, POSIX (Portable Operation System Interface)

In Linux, the Application Programming Interface (API) adheres to the POSIX standard, which ensures that applications can be ported on multiple operating systems at the source level.

Four, the system call according to the function logic can be divided into: Process Control, interprocess communication, File system control, system control, memory management, network management, socket control, user management.

A negative return value is usually used to indicate an error, and a value of 0 indicates a successful perror print error message

V. Process

Program: Executable (Static), process: execution instance of the program (dynamic)

Status of the process: Create, schedule, perish

Process has its own environment and resources

Use the EXEC function to read the program from the kernel into memory so that it executes as a process.

Vi. the life cycle of the process

Create

Scheduling

Ready state: Execution conditions are in place, waiting for CPU time to be allocated

Execution state: Consuming CPU

Wait state: Some execution conditions are not available to continue execution

Die

Vii. PCB (Process control block)

The OS controls and manages the concurrent execution of the process based on the PCB, which opens up a memory space during the creation of a process to hold the PCB data structures associated with this process

The PCB records all the information needed to describe the progress of the process and to control the operation of the process.

PCB is the only sign of process existence, Linux PCB stored in the TASK_STRUCT structure, open/include/linux/sched.h can find the definition of task_struct

Viii. Process Control

Process number 0~32767 No. 0 dispatch process, number 1th init process

In addition to the scheduling process, all processes are created directly or indirectly by the INIT process.

PID process number Getpid () ppid Parent Process number Getppid () Pgid Process Group number Getpgid ()

IX. file Descriptor: Allocate 0-1023 minimum available descriptors in process units

X. Process state Transitions

CPU Scheduling algorithm: Priority, first-come first scheduling, short time first, time slice rotation

Umask Mask, masking file permissions

PS Command View current process

Xi. Creating a Process fork () vfork ()

1.fork () returns 0 in the subprocess, returns a value greater than 0 in the parent process, after calling fork (), the source program is copied a copy, two parts of the program only Fork () The return value is not the same, two copies of the program executed at the same time, the parent-child process physical address is different, the virtual address is the same.

Q: If a program executes three fork () at the same time, it creates several processes

Fork (); 1 (0)

Fork (); 2 (0) 3 (1)

Fork (); 4 (0) 5 (1) 6 (2) 7 (3)

First call, Process # No. 0 created process # 1th

Second call, process number NO. 0 creates process number 2nd, process 1th creates process number 3rd

Third call, process No. 0 created process 4th, process 1th created process 5th, process 2nd created process 6th, process 3rd has created process 7th

Altogether created 2 of the n-th minus one process

2.vfork () generally with exec, the child process uses the parent process address space to ensure that the child process runs first, calling the Exec or exit stepfather process to run again

The EXEC function family is a process substitution function that assigns the new address space to the original process, the process number is unchanged, and the new program runs from main

exec only fails to return, the code behind exec does not execute

But note that exec is a family of functions, with EXECLP,EXECVP,EXECLE,EXECVE, etc.

The child process can only be terminated with exit (), and return is the first address returned to the function execution

Atexit (void (*function) (void)) Register exit handler function

12. Input/Output buffers

System Call No buffering

Standard IO library function input and output as row buffer

Standard IO library operation file is fully buffered

13.

Zombie Process: The child process ends and the parent process does not call wait () or waitpid () to reclaim its resources

Orphan process: The parent process ends and the child process does not end

Daemon: Special orphan process, out-of-terminal running in the background

Wait ()/waitpid (): Waits for the child process to end and reclaim its resources

Use PS to view process, kill+pid or pkill+ process name end process

The process of programming Linux systems