TCP/IP network programming (transcription note 3)--zombie process and multitasking concurrent server

<title>TCP/IP network programming (transcription note 3) – Zombie process and multitasking concurrent server</title> TCP/IP network programming (transcription note 3) – Zombie process and multitasking concurrent server table of Contents

• The production of zombie processes
• Avoid zombie processes
• Signal
• Multi-tasking Concurrent server

The production of zombie processes

1. Child process exits first, parent process does not exit ==> zombie process
   
2. The parent process exits first, the child process does not exit the ==> child process is reclaimed by the No. 0 process and does not produce a zombie process
   

pid_t pid = fork (); if (PID = = 0) {  child    printf (' Child:%d\n', Getpid ());    printf ("Child exited\n");    Else {    printf ("Parent:%d\n", Getpid ());    Sleep (30);}

Avoid zombie processes

Notifies the parent process when the child process exits:
Parent process Call

int status;wait (&status); wifexited (status); Wexitstatus (status);

This allows you to wait for the child process to exit and get his return value
If the parent process exits with a command called exit, then the child process is reclaimed by process # No. 0

When you call wait, the parent process blocks itself until the child process exits, and if you do not want to block, you can use

Waitpid ( -1, &status, Wnohang);

Signal

void keyboard(int Sig) {if(sig = = SIGINT) {printf ("Ctrl + C pressed\N"); }}void Timeout(int Sig) {if(sig = = SIGALRM) {printf (" Time Out ...\N");        Exit (0); }}int Main() {... signal (SIGINT, keyboard);    Signal (SIGALRM, timeout); Alarm (3);// when the time is over, a signal is generated and the Timeoutu function is called automatically...}

Use Sigaction, signal obsolete

struct sigaction Act; act.sa_flags = 0;sigemptyset (&act.sa_mask); act.sa_handler = timeout; sigaction (SIGALRM, &act, 0);

Using signals to eliminate zombie processes
Principle: As long as the child process exit to tell the parent process a sound, "I want to quit" can eliminate the zombie process, that wait/waitpid is, the call, the child process exit signal isSIGCHLD

Multi-tasking Concurrent server

void Read_childproc(int Sig) {int Status;if(sig = = SIGCHLD) {if(wifexited (status)) {printf ("Child quit ...%d\N", Wexitstatus (status)); }        }}int Main(int argc,Char*argv[]) {int Server_sock;int Client_sock;struct sockaddr_in server_addr;struct sockaddr_in client_addr;// SocketServer_sock = socket (af_inet, sock_stream, 0);// Bindmemset (&server_addr, 0,sizeof(SERVER_ADDR));        server_addr.sin_family = af_inet;        SERVER_ADDR.SIN_ADDR.S_ADDR = htonl (Inaddr_any);        Server_addr.sin_port = htons (Atoi (argv[1])); Bind (Server_sock, (struct sockaddr*) &server_addr,sizeof(SERVER_ADDR));// ListenListen (Server_sock, 5);// sigaction        struct sigaction Act; Act.sa_handler = Read_childproc;Char buf[Buf_size];int Str_len;pid_t PID; while(1) {socklen_t client_size=sizeof(CLIENT_ADDR); Client_sock = Accept (Server_sock, (struct sockaddr*) &client_addr, &client_size); PID = fork ();if(PID = = 0) {// Child process replication, this time opened 4 FD, requires a child process close one, the parent process close one, look at the image belowClose (Server_sock); while((Str_len = Read (Client_sock, buf, buf_size))! = 0)                        {Write (Client_sock, buf, Str_len);                        } close (Server_sock); printf"Client Disconnected ...\N"); }Else{// The parent process hands the client to the child process and continues to listen to the server FDClose (Client_sock);        }} close (Server_sock); Close (Client_sock);return0;}

TCP/IP network programming (transcription note 3)--zombie process and multitasking concurrent server