UNIX Environment Advanced programming 8.9 competitive conditions

In this section, the Tell_wait and Tell_parent,tell_child in the book do not figure out exactly how the synchronization mechanism is implemented.

proc/tellwait1.c 8-6#include "apue.h" static void Charatatime (const 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");    }    return 0;} static void Charatatime (const char* str) {    const char* ptr;    int C;    Setbuf (stdout, NULL); /* Set unbuffered *    /for (ptr = str; (c = *ptr++)! = 0;    {        PUTC (c, stdout);    }}

Lib/tellwait.c#include "apue.h" static volatile sig_atomic_t Sigflag; /* Set nonzero by sig Handler */static sigset_t Newmask, Oldmask, zeromask;static void sig_usr (int signo)/* One signal Han Dler for SIGUSR1 and SIGUSR2 */{sigflag = 1;}    void tell_wait (void) {if (Signal (SIGUSR1, sig_usr) = = Sig_err) {Err_sys ("Signal (SIGUSR1) error");    } if (Signal (SIGUSR2, sig_usr) = = Sig_err) {Err_sys ("Signal (SIGUSR2) error");    } sigemptyset (&zeromask);    Sigemptyset (&newmask);    Sigaddset (&newmask, SIGUSR1);    Sigaddset (&newmask, SIGUSR2);     /* * Block SIGUSR1 and SIGUSR2, and save current signal mask.    */if (Sigprocmask (Sig_block, &newmask, &oldmask) < 0) {Err_sys ("Sig_block error");    }}voidtell_parent (pid_t pid) {Kill (PID, SIGUSR2);/* Tell PARENT we ' re do */}void wait_parent (void) {while (Sigflag = = 0) {sigsuspend (&zeromask);/* and wait for parent */}sigflag = 0;/* * Reset signal mask to orIginal value.    */if (Sigprocmask (Sig_setmask, &oldmask, NULL) < 0) {Err_sys ("Sig_setmask error"); }}void tell_child (pid_t pid) {Kill (PID, SIGUSR1);/* Tell child we ' re do */}void wait_child (void) {while (Sigflag = = 0) sigs Uspend (&zeromask);/* and wait for child */sigflag = 0;/* * Reset signal mask to original value. */if (Sigprocmask (Sig_setmask, &oldmask, NULL) < 0) Err_sys ("Sig_setmask error");}

proc/tellwait2.c 8-7#include "apue.h" static void Charatatime (const char*); int main () {    pid_t pid;    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);    }    return 0;} static void Charatatime (const char* str) {    const char* ptr;    int C;    Setbuf (stdout, NULL); /* Set unbuffered *    /for (ptr = str; (c = *ptr++)! = 0;    {        PUTC (c, stdout);    }}

Proc/tellwait3.c#include "apue.h" static void Charatatime (const char*); int main () {    pid_t pid;    Tell_wait ();    if (PID = fork ()) < 0)    {        Err_sys ("fork Error");    }    else if (PID = = 0)    {        charatatime ("Output from child\n");        Tell_parent (Getppid ()); /* Parent goes First    *    /} else    {        wait_child ();        Charatatime ("Output from parent\n");    }    return 0;} static void Charatatime (const char* str) {    const char* ptr;    int C;    Setbuf (stdout, NULL); /* Set unbuffered *    /for (ptr = str; (c = *ptr++)! = 0;    {        PUTC (c, stdout);    }}

UNIX Environment Advanced programming 8.9 competitive conditions