Multi-process programming

Create a process

Function Name: Fork

Function prototype: pid_t fork (void);

function function: Create a child process

Header file;<unistd.h>

Return value: Success: The PID of the child process returned in the parent process, 0 failed in the child process: 1

#include <unistd.h>void main () {fork ();p rintf ("program is end\n"); exit (0);} Run Result: Program is end          The result analysis: Once the fork function is called, a new process is generated in memory, and the new process is the same as the parent process code, which starts from the statement after the fork.

#include <unistd.h>void main () {pid_t pid;pid = fork ();p rintf ("pid is%d\n", PID); exit (0);} Operating result: PID is 3003          pid is 0

#include <unistd.h>void main () {pid_t pid;pid = fork (), if (PID > 0) {printf ("This is Father process\n"); exit (0);} Else{printf ("This is a child process\n"); exit (0);}} Run Result: This is Father process          

Create a process

Function Name: vfork

Function prototype: pid_t vfork (void);

function function: Create a child process and block the parent process

Header file:<sys/types.h> <unistd.h>

Return value: Success: The PID of the child process returned in the parent process, 0 failed in the child process: 1

#include <sys/types.h> #include <unistd.h>void main () {pid_t pid;pid = vfork (); if (pid > 0) {printf ("This is Father Process\n "); exit (0);} Else{printf ("This is a child process\n"); exit (0);}} Run Result: This is the child process, this is          father process

Consider the results of the following programs:

#include <stdio.h> #include <unistd.h>void main () {pid_t Pid;int count = 0;pid = Fork () count++;p rintf ("Count =%d\n ", count); exit (0);} Run Result: Count = 1          count = 1

#include <stdio.h> #include <unistd.h>void main () {pid_t Pid;int count = 0;pid = Vfork () count++;p rintf (" Count =%d\n ", count); exit (0);} Run Result: Count = 1          count = 2

Fork Contrast Vfork

1. Fork: Child processes have separate data segments and stacks

Vfork: Child processes share data segments and stacks with parent processes

2. Fork: The order of execution of the parent-child process is indeterminate

Vfork: Child processes run first, run after parent process

Process exit

When you exit normally, the parent process can use return 0, and exit (0), and the child process can only use exit (0);

When exiting abnormally, exit (1) is used;

Process wait

Function Name: Wait

Function prototype: pid_t wait (int *status);

function function: Suspends the process that invokes it until its child process ends

Header file:<sys/types.h> <sys/wait.h>

Return value: Success: Returns the ID of the terminated child process failed: 1

Parameter description: Status record the exit status of the child process

#include <unistd.h> #include <sys/types.h> #include <sys/wait.h>void main () {    pid_t pid;    PID = fork ();    if (PID > 0)    {        wait (NULL);p rintf ("This is Father process\n"); exit (0);    }    else    {printf ("This is a child process\n"); exit (0);}    } Run Result: This is the child process, this is          father process

Execute the program

Function name: Execl and System

function prototypes: int execl (const char *pathname,const char *arg ...);

function function: Run executable file

Header file:<unistd.h>

Return value: Success does not return, failure returns

Parameter description: Pathname: The path to the executable file to run ARG: The executable file runs the required parameters, the first one is the file name and ends with NULL

#include <unistd.h> #include <sys/types.h> #include <sys/wait.h>void main () {pid_t pid;pid = fork (); if (PID > 0) {Wait (NULL);p rintf ("This is Father process\n"); exit (0);}        Else{execl ("/bin/ls", "ls", "/home/", NULL);p rintf ("This is a child process\n"); exit (0);}} Operating result: Wind The is          father process

Attention:

Fork creates a new process that produces a new PID

exec retains the original process, but the code is replaced with new code to execute the new code

Multi-process programming