#include <stdio.h>

#include <sys/shm.h>

#include <sys/stat.h>

int main ()

{

    int segment_id;

    char* shared_memory;

    struct shmid_ds shmbuffer;

    int segment_size;

    const int shared_segment_size = 0x6400;

    /* Allocate a shared memory segment. */

    segment_id = shmget (IPC_PRIVATE, shared_segment_size, IPC_CREAT | IPC_EXCL | S_IRUSR | S_IWUSR);

    /* Attach the shared memory segment. */

    shared_memory = (char*) shmat (segment_id, 0, 0);

    printf (“shared memory attached at address %p\n”, shared_memory);

    /* Determine the segment’s size. */

    shmctl (segment_id, IPC_STAT, &shmbuffer);

    segment_size = shmbuffer.shm_segsz;

    printf (“segment size: %d\n”, segment_size);

    /* Write a string to the shared memory segment. */

    sprintf (shared_memory, “Hello, world.”);

    /* Detach the shared memory segment. */

    shmdt (shared_memory);

    /* Reattach the shared memory segment, at a different address. */

    shared_memory = (char*) shmat (segment_id, (void*) 0x5000000, 0);

    printf (“shared memory reattached at address %p\n”, shared_memory);

    /* Print out the string from shared memory. */

    printf (“%s\n”, shared_memory);

    /* Detach the shared memory segment. */

    shmdt (shared_memory);

    /* Deallocate the shared memory segment. */

    shmctl (segment_id, IPC_RMID, 0);

    return 0;

} 

ipcs命令可用查看进程间通信机制的信息

使用-m可查看共享内存的信息

% ipcs -m

------ Shared Memory Segments --------

key shmid owner perms bytes nattch status

0x00000000 1627649 user 640 25600 0

ipcrm命令可删除进程间通信对象.

% ipcrm shm 1627649

[liuchao@localhost ~]$ ipcs

------ Shared Memory Segments --------

key shmid owner perms bytes nattch status

0x00000000 196608 liuchao 600 393216 2 dest

0x764867bd 65537 liuchao 600 1 0

0x2c0056d5 98306 liuchao 600 1 0

0x500e7827 131075 liuchao 600 1 0

0x20e0f21d 163844 liuchao 600 1 0

0x00000000 229381 liuchao 600 393216 2 dest

0x00000000 262150 liuchao 600 393216 2 dest

0x00000000 294919 liuchao 600 393216 2 dest

0x00000000 327688 liuchao 600 393216 2 dest

0x00000000 360457 liuchao 600 393216 2 dest

0x00000000 393226 liuchao 600 393216 2 dest

0x00000000 425995 liuchao 600 393216 2 dest

0x00000000 458764 liuchao 600 393216 2 dest

0x00000000 491533 liuchao 600 393216 2 dest

0x00000000 557070 liuchao 600 393216 2 dest

0x00000000 589839 liuchao 600 393216 2 dest

------ Semaphore Arrays --------

key semid owner perms nsems

0x59d9bc4a 0 liuchao 600 1

0x3bd464f2 32769 liuchao 600 1

------ Message Queues --------

key msqid owner perms used-bytes messages

#include <sys/ipc.h>

#include <sys/sem.h>

#include <sys/types.h>

/* We must define union semun ourselves. */

union semun {

    int val;

    struct semid_ds *buf;

    unsigned short int *array;

    struct seminfo *__buf;

};

/* Obtain a binary semaphore’s ID, allocating if necessary. */

int binary_semaphore_allocation (key_t key, int sem_flags)

{

    return semget (key, 1, sem_flags);

}

/* Deallocate a binary semaphore. All users must have finished their

use. Returns -1 on failure. */

int binary_semaphore_deallocate (int semid)

{

    union semun ignored_argument;

    return semctl (semid, 1, IPC_RMID, ignored_argument);

}

#include <sys/types.h>

#include <sys/ipc.h>

#include <sys/sem.h>

/* We must define union semun ourselves. */

union semun {

    int val;

    struct semid_ds *buf;

    unsigned short int *array;

    struct seminfo *__buf;

};

/* Initialize a binary semaphore with a value of 1. */

int binary_semaphore_initialize (int semid)

{

    union semun argument;

    unsigned short values[1];

    values[0] = 1;

    argument.array = values;

    return semctl (semid, 0, SETALL, argument);

}

#include <sys/types.h>

#include <sys/ipc.h>

#include <sys/sem.h>

/* Wait on a binary semaphore. Block until the semaphore value is positive, then

decrement it by 1. */

int binary_semaphore_wait (int semid)

{

    struct sembuf operations[1];

    /* Use the first (and only) semaphore. */

    operations[0].sem_num = 0;

    /* Decrement by 1. */

    operations[0].sem_op = -1;

    /* Permit undo’ing. */

    operations[0].sem_flg = SEM_UNDO;

    return semop (semid, operations, 1);

}

/* Post to a binary semaphore: increment its value by 1.

This returns immediately. */

int binary_semaphore_post (int semid)

{

    struct sembuf operations[1];

    /* Use the first (and only) semaphore. */

    operations[0].sem_num = 0;

    /* Increment by 1. */

    operations[0].sem_op = 1;

    /* Permit undo’ing. */

    operations[0].sem_flg = SEM_UNDO;

    return semop (semid, operations, 1);

}

(mmap-write.c) Write a Random Number to a Memory-Mapped File

#include <stdlib.h>

#include <stdio.h>

#include <fcntl.h>

#include <sys/mman.h>

#include <sys/stat.h>

#include <time.h>

#include <unistd.h>

#define FILE_LENGTH 0x100

/* Return a uniformly random number in the range [low,high]. */

int random_range (unsigned const low, unsigned const high)

{

    unsigned const range = high - low + 1;

    return low + (int) (((double) range) * rand () / (RAND_MAX + 1.0));

}

int main (int argc, char* const argv[])

{

    int fd;

    void* file_memory;

    /* Seed the random number generator. */

    srand (time (NULL));

    /* Prepare a file large enough to hold an unsigned integer. */

    fd = open (argv[1], O_RDWR | O_CREAT, S_IRUSR | S_IWUSR);

    lseek (fd, FILE_LENGTH+1, SEEK_SET);

    write (fd, “”, 1);

    lseek (fd, 0, SEEK_SET);

    /* Create the memory mapping. */

    file_memory = mmap (0, FILE_LENGTH, PROT_WRITE, MAP_SHARED, fd, 0);

    close (fd);

    /* Write a random integer to memory-mapped area. */

    sprintf((char*) file_memory, “%d\n”, random_range (-100, 100));

    /* Release the memory (unnecessary because the program exits). */

    munmap (file_memory, FILE_LENGTH);

    return 0;

}

(mmap-read.c) Read an Integer from a Memory-Mapped File, and Double It

#include <stdlib.h>

#include <stdio.h>

#include <fcntl.h>

#include <sys/mman.h>

#include <sys/stat.h>

#include <unistd.h>

#define FILE_LENGTH 0x100

int main (int argc, char* const argv[])

{

    int fd;

    void* file_memory;

    int integer;

    /* Open the file. */

    fd = open (argv[1], O_RDWR, S_IRUSR | S_IWUSR);

    /* Create the memory mapping. */

    file_memory = mmap (0, FILE_LENGTH, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);

    close (fd);

    /* Read the integer, print it out, and double it. */

    sscanf (file_memory, “%d”, &integer);

    printf (“value: %d\n”, integer);

    sprintf ((char*) file_memory, “%d\n”, 2 * integer);

    /* Release the memory (unnecessary because the program exits). */

    munmap (file_memory, FILE_LENGTH);

    return 0;

}

int pipe_fds[2];

int read_fd;

int write_fd;

pipe (pipe_fds);

read_fd = pipe_fds[0];

write_fd = pipe_fds[1];

#include <stdlib.h>

#include <stdio.h>

#include <unistd.h>

/* Write COUNT copies of MESSAGE to STREAM, pausing for a second between each. */

void writer (const char* message, int count, FILE* stream)

{

    for (; count > 0; --count) {

        /* Write the message to the stream, and send it off immediately. */

        fprintf (stream, “%s\n”, message);

        fflush (stream);

        /* Snooze a while. */

        sleep (1);

    }

}

/* Read random strings from the stream as long as possible. */

void reader (FILE* stream)

{

    char buffer[1024];

    /* Read until we hit the end of the stream. fgets reads until either a newline or the end-of-file. */

    while (!feof (stream) && !ferror (stream) && fgets (buffer, sizeof (buffer), stream) != NULL)

        fputs (buffer, stdout);

}

int main ()

{

    int fds[2];

    pid_t pid;

    /* Create a pipe. File descriptors for the two ends of the pipe are placed in fds. */

    pipe (fds);

    /* Fork a child process. */

    pid = fork ();

    if (pid == (pid_t) 0) {

        FILE* stream;

        /* This is the child process. Close our copy of the write end of the file descriptor. */

        close (fds[1]);

        /* Convert the read file descriptor to a FILE object, and read from it. */

        stream = fdopen (fds[0], “r”);

        reader (stream);

        close (fds[0]);

    }

    else {

        /* This is the parent process. */

        FILE* stream;

        /* Close our copy of the read end of the file descriptor. */

        close (fds[0]);

        /* Convert the write file descriptor to a FILE object, and write to it. */

        stream = fdopen (fds[1], “w”);

        writer (“Hello, world.”, 5, stream);

        close (fds[1]);

    }

    return 0;

}

#include <stdio.h>

#include <sys/types.h>

#include <sys/wait.h>

#include <unistd.h>

int main ()

{

    int fds[2];

    pid_t pid;

    /* Create a pipe. File descriptors for the two ends of the pipe are placed in fds. */

    pipe (fds);

    /* Fork a child process. */

    pid = fork ();

    if (pid == (pid_t) 0) {

        /* This is the child process. Close our copy of the write end of the file descriptor. */

        close (fds[1]);

        /* Connect the read end of the pipe to standard input. */

        dup2 (fds[0], STDIN_FILENO);

        /* Replace the child process with the “sort” program. */

        execlp (“sort”, “sort”, 0);

    }

    else {

        /* This is the parent process. */

        FILE* stream;

        /* Close our copy of the read end of the file descriptor. */

        close (fds[0]);

        /* Convert the write file descriptor to a FILE object, and write to it. */

        stream = fdopen (fds[1], “w”);

        fprintf (stream, “This is a test.\n”);

        fprintf (stream, “Hello, world.\n”);

        fprintf (stream, “My dog has fleas.\n”);

        fprintf (stream, “This program is great.\n”);

        fprintf (stream, “One fish, two fish.\n”);

        fflush (stream);

        close (fds[1]);

        /* Wait for the child process to finish. */

        waitpid (pid, NULL, 0);

   }

   return 0;

}

#include <stdio.h>

#include <unistd.h>

int main ()

{

    FILE* stream = popen (“sort”, “w”);

    fprintf (stream, “This is a test.\n”);

    fprintf (stream, “Hello, world.\n”);

    fprintf (stream, “My dog has fleas.\n”);

    fprintf (stream, “This program is great.\n”);

    fprintf (stream, “One fish, two fish.\n”);

    return pclose (stream);

}

% mkfifo /tmp/fifo

% ls -l /tmp/fifo

prw-rw-rw- 1 samuel users 0 Jan 16 14:04 /tmp/fifo

(socket-server.c) Local Namespace Socket Server

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include <sys/socket.h>

#include <sys/un.h>

#include <unistd.h>

/* Read text from the socket and print it out. Continue until the

socket closes. Return nonzero if the client sent a “quit”

message, zero otherwise. */

int server (int client_socket)

{

    while (1) {

        int length;

        char* text;

        /* First, read the length of the text message from the socket. If read returns zero, the client closed the connection. */

        if (read (client_socket, &length, sizeof (length)) == 0)

            return 0;

        /* Allocate a buffer to hold the text. */

        text = (char*) malloc (length);

        /* Read the text itself, and print it. */

        read (client_socket, text, length);

        printf (“%s\n”, text);

        /* Free the buffer. */

        free (text);

        /* If the client sent the message “quit,” we’re all done. */

        if (!strcmp (text, “quit”))

            return 1;

    }

}

int main (int argc, char* const argv[])

{

    const char* const socket_name = argv[1];

    int socket_fd;

    struct sockaddr_un name;

    int client_sent_quit_message;

    /* Create the socket. */

    socket_fd = socket (PF_LOCAL, SOCK_STREAM, 0);

    /* Indicate that this is a server. */

    name.sun_family = AF_LOCAL;

    strcpy (name.sun_path, socket_name);

    bind (socket_fd, &name, SUN_LEN (&name));

    /* Listen for connections. */

    listen (socket_fd, 5);

    /* Repeatedly accept connections, spinning off one server() to deal with each client. Continue until a client sends a “quit” message. */

    do {

        struct sockaddr_un client_name;

        socklen_t client_name_len;

        int client_socket_fd;

        /* Accept a connection. */

        client_socket_fd = accept (socket_fd, &client_name, &client_name_len);

        /* Handle the connection. */

        client_sent_quit_message = server (client_socket_fd);

        /* Close our end of the connection. */

        close (client_socket_fd);

    } while (!client_sent_quit_message);

    /* Remove the socket file. */

    close (socket_fd);

    unlink (socket_name);

    return 0;

}

(socket-client.c) Local Namespace Socket Client

#include <stdio.h>

#include <string.h>

#include <sys/socket.h>

#include <sys/un.h>

#include <unistd.h>

/* Write TEXT to the socket given by file descriptor SOCKET_FD. */

void write_text (int socket_fd, const char* text)

{

    /* Write the number of bytes in the string, including NUL-termination. */

    int length = strlen (text) + 1;

    write (socket_fd, &length, sizeof (length));

    /* Write the string. */

    write (socket_fd, text, length);

}

int main (int argc, char* const argv[])

{

    const char* const socket_name = argv[1];

    const char* const message = argv[2];

    int socket_fd;

    struct sockaddr_un name;

    /* Create the socket. */

    socket_fd = socket (PF_LOCAL, SOCK_STREAM, 0);

    /* Store the server’s name in the socket address. */

    name.sun_family = AF_LOCAL;

    strcpy (name.sun_path, socket_name);

    /* Connect the socket. */

    connect (socket_fd, &name, SUN_LEN (&name));

    /* Write the text on the command line to the socket. */

    write_text (socket_fd, message);

    close (socket_fd);

    return 0;

}

(socket-inet.c) Read from a WWW Server

#include <stdlib.h>

#include <stdio.h>

#include <netinet/in.h>

#include <netdb.h>

#include <sys/socket.h>

#include <unistd.h>

#include <string.h>

/* Print the contents of the home page for the server’s socket. Return an indication of success. */

void get_home_page (int socket_fd)

{

    char buffer[10000];

    ssize_t number_characters_read;

    /* Send the HTTP GET command for the home page. */

    sprintf (buffer, “GET /\n”);

    write (socket_fd, buffer, strlen (buffer));

    /* Read from the socket. The call to read may not

    return all the data at one time, so keep trying until we run out. */

    while (1) {

        number_characters_read = read (socket_fd, buffer, 10000);

        if (number_characters_read == 0)

            return;

        /* Write the data to standard output. */

        fwrite (buffer, sizeof (char), number_characters_read, stdout);

    }

}

int main (int argc, char* const argv[])

{

    int socket_fd;

    struct sockaddr_in name;

    struct hostent* hostinfo;

    /* Create the socket. */

    socket_fd = socket (PF_INET, SOCK_STREAM, 0);

    /* Store the server’s name in the socket address. */

    name.sin_family = AF_INET;

    /* Convert from strings to numbers. */

    hostinfo = gethostbyname (argv[1]);

    if (hostinfo == NULL)

        return 1;

    else

        name.sin_addr = *((struct in_addr *) hostinfo->h_addr);

    /* Web servers use port 80. */

    name.sin_port = htons (80);

    /* Connect to the Web server */

    if (connect (socket_fd, &name, sizeof (struct sockaddr_in)) == -1) {

        perror (“connect”);

        return 1;

    }

    /* Retrieve the server’s home page. */

    get_home_page (socket_fd);

    return 0;

}