UNIX编程(15)-进程间通信

. 管道

 

#include <unistd.h>

int pipe(int filedes[2]);

 

Returns: 0 if OK, 1 on error

参数filedes返回两个文件描述符：filedes[0]为读而打开，filedes[1]为写而打开。

 

例：经由管道父进程向子进程传递数据

#include "apue.h"

int
main(void)
{
    int     n;
    int     fd[2];
    pid_t   pid;
    char    line[MAXLINE];

    if (pipe(fd) < 0)
        err_sys("pipe error");
    if ((pid = fork()) < 0) {
        err_sys("fork error");
    } else if (pid > 0) {       /* parent */
        close(fd[0]);
        write(fd[1], "hello world\n", 12);
    } else {                /* child */
        close(fd[1]);
        n = read(fd[0], line, MAXLINE);
        write(STDOUT_FILENO, line, n);
    }
    exit(0);
}

例：将文件复制到分页程序

 

#include "apue.h"
#include <sys/wait.h>

#define DEF_PAGER   "/bin/more"     /* default pager program */

int
main(int argc, char *argv[])
{
    int    n;
    int    fd[2];
    pid_t  pid;
    char   *pager, *argv0;
    char   line[MAXLINE];
    FILE   *fp;

    if (argc != 2)
        err_quit("usage: a.out <pathname>");

    if ((fp = fopen(argv[1], "r")) == NULL)
        err_sys("can't open %s", argv[1]);
    if (pipe(fd) < 0)
        err_sys("pipe error");

    if ((pid = fork()) < 0) {
        err_sys("fork error");
    } else if (pid > 0) {                              /* parent */
        close(fd[0]);       /* close read end */

        /* parent copies argv[1] to pipe */
        while (fgets(line, MAXLINE, fp) != NULL) {
            n = strlen(line);
            if (write(fd[1], line, n) != n)
                err_sys("write error to pipe");
        }
        if (ferror(fp))
            err_sys("fgets error");

        close(fd[1]);   /* close write end of pipe for reader */

        if (waitpid(pid, NULL, 0) < 0)
            err_sys("waitpid error");
        exit(0);
    } else {                                        /* child */
        close(fd[1]);   /* close write end */
        if (fd[0] != STDIN_FILENO) {
            if (dup2(fd[0], STDIN_FILENO) != STDIN_FILENO)
                err_sys("dup2 error to stdin");
            close(fd[0]);   /* don't need this after dup2 */
        }

        /* get arguments for execl() */
        if ((pager = getenv("PAGER")) == NULL)
            pager = DEF_PAGER;
        if ((argv0 = strrchr(pager, '/')) != NULL)
            argv0++;        /* step past rightmost slash */
        else
            argv0 = pager;  /* no slash in pager */

        if (execl(pager, argv0, (char *)0) < 0)
            err_sys("execl error for %s", pager);
    }
    exit(0);
}

使父子进程同步的例程

#include "apue.h"

static int  pfd1[2], pfd2[2];

void
TELL_WAIT(void)
{
    if (pipe(pfd1) < 0 || pipe(pfd2) < 0)
        err_sys("pipe error");
}

void
TELL_PARENT(pid_t pid)
{
    if (write(pfd2[1], "c", 1) != 1)
        err_sys("write error");
}

void
WAIT_PARENT(void)
{
    char    c;

    if (read(pfd1[0], &c, 1) != 1)
        err_sys("read error");

    if (c != 'p')
        err_quit("WAIT_PARENT: incorrect data");
}

void
TELL_CHILD(pid_t pid)
{
    if (write(pfd1[1], "p", 1) != 1)
        err_sys("write error");
}

void
WAIT_CHILD(void)
{
    char    c;

    if (read(pfd2[0], &c, 1) != 1)
        err_sys("read error");

    if (c != 'c')
        err_quit("WAIT_CHILD: incorrect data");
}

2.popen和pclose函数

 

#include <stdio.h>

FILE *popen(const char *cmdstring, const char *type);

 

Returns: file pointer if OK, NULL on error

 

int pclose(FILE *fp);

 

Returns: termination status of cmdstring, or 1 on error

例：用popen向分页程序传递文件

 

#include "apue.h"
#include <sys/wait.h>

#define PAGER   "${PAGER:-more}" /* environment variable, or default */

int
main(int argc, char *argv[])
{
    char    line[MAXLINE];
    FILE    *fpin, *fpout;

    if (argc != 2)
        err_quit("usage: a.out <pathname>");
    if ((fpin = fopen(argv[1], "r")) == NULL)
        err_sys("can't open %s", argv[1]);

    if ((fpout = popen(PAGER, "w")) == NULL)
        err_sys("popen error");

    /* copy argv[1] to pager */
    while (fgets(line, MAXLINE, fpin) != NULL) {
        if (fputs(line, fpout) == EOF)
            err_sys("fputs error to pipe");
    }
    if (ferror(fpin))
        err_sys("fgets error");
    if (pclose(fpout) == -1)
        err_sys("pclose error");

    exit(0);
}

大小写过滤程序

#include "apue.h"
#include <ctype.h>

int
main(void)
{
    int     c;

    while ((c = getchar()) != EOF) {
        if (isupper(c))
            c = tolower(c);
        if (putchar(c) == EOF)
            err_sys("output error");
        if (c == '\n')
            fflush(stdout);
    }
    exit(0);
}

 

#include "apue.h"
#include <sys/wait.h>

int
main(void)
{
    char    line[MAXLINE];
    FILE    *fpin;

    if ((fpin = popen("myuclc", "r")) == NULL)
        err_sys("popen error");
    for ( ; ; ) {
        fputs("prompt> ", stdout);
        fflush(stdout);
        if (fgets(line, MAXLINE, fpin) == NULL) /* read from pipe */
            break;
        if (fputs(line, stdout) == EOF)
            err_sys("fputs error to pipe");
    }
    if (pclose(fpin) == -1)
        err_sys("pclose error");
    putchar('\n');
    exit(0);
}

3.协同进程

 

对两个数求和的简单过滤程序

#include "apue.h"

int
main(void)
{
    int     n,  int1,  int2;
    char    line[MAXLINE];

    while ((n = read(STDIN_FILENO, line, MAXLINE)) > 0) {
        line[n] = 0;        /* null terminate */
        if (sscanf(line, "%d%d", &int1, &int2) == 2) {
            sprintf(line, "%d\n", int1 + int2);
            n = strlen(line);
            if (write(STDOUT_FILENO, line, n) != n)
                err_sys("write error");
        } else {
            if (write(STDOUT_FILENO, "invalid args\n", 13) != 13)
                err_sys("write error");
        }
    }
    exit(0);
}

 

include "apue.h"

static void sig_pipe(int);      /* our signal handler */

int
main(void)
{
    int     n, fd1[2], fd2[2];
    pid_t   pid;
    char    line[MAXLINE];

    if (signal(SIGPIPE, sig_pipe) == SIG_ERR)
        err_sys("signal error");

    if (pipe(fd1) < 0 || pipe(fd2) < 0)
        err_sys("pipe error");

    if ((pid = fork()) < 0) {
        err_sys("fork error");
    } else if (pid > 0) {                         /* parent */
        close(fd1[0]);
        close(fd2[1]);
        while (fgets(line, MAXLINE, stdin) != NULL) {
            n = strlen(line);
            if (write(fd1[1], line, n) != n)
                err_sys("write error to pipe");
            if ((n = read(fd2[0], line, MAXLINE)) < 0)
                err_sys("read error from pipe");
            if (n == 0) {
                err_msg("child closed pipe");
                break;
            }
            line[n] = 0;    /* null terminate */
            if (fputs(line, stdout) == EOF)
                err_sys("fputs error");
        }
        if (ferror(stdin))
            err_sys("fgets error on stdin");
        exit(0);
    } else {                                  /* child */
        close(fd1[1]);
        close(fd2[0]);
        if (fd1[0] != STDIN_FILENO) {
            if (dup2(fd1[0], STDIN_FILENO) != STDIN_FILENO)
                err_sys("dup2 error to stdin");
            close(fd1[0]);
        }

        if (fd2[1] != STDOUT_FILENO) {
            if (dup2(fd2[1], STDOUT_FILENO) != STDOUT_FILENO)
                err_sys("dup2 error to stdout");
            close(fd2[1]);
        }
        if (execl("./add2", "add2", (char *)0) < 0)
            err_sys("execl error");
    }
    exit(0);
}

static void
sig_pipe(int signo)
{
    printf("SIGPIPE caught\n");
    exit(1);
}

4.FIFO

 

#include <sys/stat.h>

int mkfifo(const char *pathname, mode_t mode);

 

Returns: 0 if OK, 1 on error

5.XSI IPC

消息队列，信号量，共享存储称作XSI IPC

1)标识符和键

标识符是IPC对象的内部名

键是IPC对象的外部名

 

2）权限结构

XSI IPC 为每一个IPC结构设置了一个ipc_perm结构

struct ipc_perm {
     uid_t  uid;  /* owner's effective user id */
     gid_t  gid;  /* owner's effective group id */
     uid_t  cuid; /* creator's effective user id */
     gid_t  cgid; /* creator's effective group id */
     mode_t mode; /* access modes */
     .
     .
     .
   };

6.消息队列

每个队列都有一个msq_ds与其相关联

struct msqid_ds {
     struct ipc_perm  msg_perm;     /* see Section 15.6.2 */
     msgqnum_t        msg_qnum;     /* # of messages on queue */
     msglen_t         msg_qbytes;   /* max # of bytes on queue */
     pid_t            msg_lspid;    /* pid of last msgsnd() */
     pid_t            msg_lrpid;    /* pid of last msgrcv() */
     time_t           msg_stime;    /* last-msgsnd() time */
     time_t           msg_rtime;    /* last-msgrcv() time */
     time_t           msg_ctime;    /* last-change time */
     .
     .
     .
   };

#include <sys/msg.h>

int msgget(key_t key, int flag);

 

Returns: message queue ID if OK, 1 on error

 

 

#include <sys/msg.h>

int msgctl(int msqid, int cmd, struct msqid_ds *buf );

 

Returns: 0 if OK, 1 on error

 

[View full width]

#include <sys/msg.h>

int msgsnd(int msqid, const void *ptr, size_t
nbytes, int flag);

 

Returns: 0 if OK, 1 on error

[View full width]

#include <sys/msg.h>

ssize_t msgrcv(int msqid, void *ptr, size_t nbytes
, long type, int flag);

 

Returns: size of data portion of message if OK, 1 on error

7.信号量

 

struct semid_ds {
     struct ipc_perm  sem_perm;  /* see Section 15.6.2 */
     unsigned short   sem_nsems; /* # of semaphores in set */
     time_t           sem_otime; /* last-semop() time */
     time_t           sem_ctime; /* last-change time */
     .
     .
     .
   };

 

#include <sys/sem.h>

int semget(key_t key, int nsems, int flag);

 

Returns: semaphore ID if OK, 1 on error

 

 

#include <sys/sem.h>

int semctl(int semid, int semnum, int  cmd,
           ... /* union semun arg */);

 

Returns: (see following)

 

[View full width]

#include <sys/sem.h>

int semop(int semid, struct sembuf semoparray[],
 size_t nops);

 

Returns: 0 if OK, 1 on error

8.共享存储

struct shmid_ds {
     struct ipc_perm  shm_perm;    /* see Section 15.6.2 */
     size_t           shm_segsz;   /* size of segment in bytes */
     pid_t            shm_lpid;    /* pid of last shmop() */
     pid_t            shm_cpid;    /* pid of creator */
     shmatt_t         shm_nattch;  /* number of current attaches */
     time_t           shm_atime;   /* last-attach time */
     time_t           shm_dtime;   /* last-detach time */
     time_t           shm_ctime;   /* last-change time */
     .
     .
     .
   };

 

#include <sys/shm.h>

int shmget(key_t key, size_t size, int flag);

 

Returns: shared memory ID if OK, 1 on error

 

 

#include <sys/shm.h>

int shmctl(int shmid, int cmd, struct shmid_ds *buf);

 

Returns: 0 if OK, 1 on error

#include <sys/shm.h>

void *shmat(int shmid, const void *addr, int flag);

 

Returns: pointer to shared memory segment if OK, 1 on error

 

 

#include <sys/shm.h>

int shmdt(void *addr);

 

Returns: 0 if OK, 1 on error

打印不同数据所存放的区域

#include "apue.h"
#include <sys/shm.h>

#define ARRAY_SIZE  40000
#define MALLOC_SIZE 100000
#define SHM_SIZE    100000
#define SHM_MODE    0600    /* user read/write */

char    array[ARRAY_SIZE];  /* uninitialized data = bss */

int
main(void)
{
    int     shmid;
    char    *ptr, *shmptr;

    printf("array[] from %lx to %lx\n", (unsigned long)&array[0],
      (unsigned long)&array[ARRAY_SIZE]);
    printf("stack around %lx\n", (unsigned long)&shmid);

    if ((ptr = malloc(MALLOC_SIZE)) == NULL)
        err_sys("malloc error");
    printf("malloced from %lx to %lx\n", (unsigned long)ptr,
      (unsigned long)ptr+MALLOC_SIZE);

    if ((shmid = shmget(IPC_PRIVATE, SHM_SIZE, SHM_MODE)) < 0)
        err_sys("shmget error");
    if ((shmptr = shmat(shmid, 0, 0)) == (void *)-1)
        err_sys("shmat error");
    printf("shared memory attached from %lx to %lx\n",
      (unsigned long)shmptr, (unsigned long)shmptr+SHM_SIZE);

    if (shmctl(shmid, IPC_RMID, 0) < 0)
        err_sys("shmctl error");

    exit(0);
}