Process and Classroom Summary

2015.1.29

When the parent process waits for a child process to terminate, it must call the wait function. If a process waits for the parent process to terminate, you can do the following: The disadvantage is that CPU time is wasted
while (Getppid ()! = 1)
Sleep (1);

IPC: Inter-process communication

int main ()
{
pid_t pid;
if ((PID = fork ()) < 0)
{
Err_sys ("fork Error");
}
else if (PID = = 0)
{
if ((PID = fork ()) < 0)
{
Err_sys ("fork Error");
}
else if (PID > 0)
{
Exit (0);
}

Sleep (2);
printf ("second chile,parent pid =%d\n", Getppid ());
Exit (0);
}

if (Waitpid (pid,null,0)! = pid)
{
Err_sys ("Waitpid error");
}
Exit (0);
}

The results of the above program operation: Second chile,parent pid = 1;

Each process notifies the other after performing his set of initialization operations, and waits for the other party to complete its initialization before continuing:

#include "apue.h"
Tell_wait (); Tell ****wait***
if ((PID = fork ()) < 0)
{
Err_sys ("fork Error");
}
else if (pif = = 0)
{
Tell_parent (Getppid ()); /*tell Parent we ' re done*/
Wait_parent (); /*and Wait for parent*/
Exit (0);
}
Tell_child (PID);
Wait_chile ();
Exit (0);

Programs with competitive conditions:
#include <stdio.h>
static void Charartatime (char *);
int main (void)
{
pid_t pid;
if ((PID = fork ()) < 0)
{
Err_sys ("fork Error");
}
else if (PID = = 0)
{
Charatatime ("Output from child\n");
}
Else
{
Charatatime ("Output from parent\n");
}
Exit (0);
}

static void Charatatime (char *str)
{
Char *ptr;
int C;
Setbuf (Stdout,null);
for (ptr = str; (c = *ptr++)! = 0;)
{
PUTC (c,stdout);
}
}

Modify the program to avoid competition: The parent process runs first
#include <stdio.h>
static void Charartatime (char *);
int main (void)
{
pid_t pid;
Tell_wait (); Tell ****wait***

if ((PID = fork ()) < 0)
{
Err_sys ("fork Error");
}
else if (PID = = 0)
{
Wait_parent (); /*parent goes first*/
Charatatime ("Output from child\n");
}
Else
{
Charatatime ("Output from parent\n");
Tell_child (PID);
}
Exit (0);
}

static void Charatatime (char *str)
{
Char *ptr;
int C;
Setbuf (Stdout,null);
for (ptr = str; (c = *ptr++)! = 0;)
{
PUTC (c,stdout);
}
}

Change the program above to let the child process run first:

else if (PID = = 0)
{
Charatatime ("Output from child\n");
Tell_parent (Getppid ());
}
Else
{
Wait_chile (); /*child goes first*/
Charatatime ("Output from parent\n")
}

Recall the lesson today: the morning review of the knowledge points of yesterday's pointers, including: the basis of pointers, pointer operations, multi-level pointers, pointers array, const,
Void, character pointers, and strings, chuanjiang the connections and usages between pointers and arrays. The main point today is that the function of this piece of knowledge, including: function definition and declaration
function invocation, parameter passing, and return value, function and array, main function parameter, pointer function, recursive function. Finally, a little bit of knowledge about structure. Tell me about today.
The lesson of the harvest, recursive function I understand, the function of the method of the transfer of parameters I understand that today, from the stack and memory point of view to further understand the nature of function parameters, pointer array
The array pointers are further understood, with a further understanding of the subsequent assignment, int *p[2], int a[2][3], p[0] = a[0]. This period of time C, from
The point of view of knowledge, very few I do not know, but still need to practice more good points. This time of the class let me very relaxed, this gave me a good buffer time, before the holiday I want to read
UNIX Environment Advanced Programming This book, so I can play arm development Board after home, this is what I want to play!

Process and Classroom Summary