Outline
- 1.
pipe使用框架
- 2.
fifo使用框架
- 3.
file lock使用框架
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4.semaphore使用框架
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5.shared memory使用框架
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6.memory mapped file使用框架
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7.unix socket使用框架
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1. pipe使用框架：
实现 "ls | wc -l"
int pipefd[2];
pipe(pipefd);
if(!fork()) {
close(pipefd[0]);
dup2(pipefd[1], 1);
execlp("ls", "ls", NULL);
exit(0);
} else {
wait(NULL);
close(pipefd[1]);
dup2(pipefd[0], 0);
execlp("wc", "wc", "-l", NULL);
exit(0);
}
注：一般pipe大小为10K
2. fifo使用框架
实现echo writer reader，即writer在fifo中写，reader在fifo中读并回显
writer:
mknod("fifoname", S_FIFO | 0666, 0);
fd = open("fifoname", O_WRONLY);
write(fd, input, sizeof(input));
//unlink("fifoname");
reader:
fd = open("fifoname", O_RDONLY);
read(fd, output, sizeof(output));
printf("%s", output);
注意：若reader先关闭，则writer在执行write时收到sigpipe信号；反之，reader执行reader时返回0.
open在没有读者/写者时候，都见先阻塞，直到第一个读者/写者到来.
3. file lock使用框架
所谓file lock，就是对文件加读/写锁，读写锁的原则是一个文件可以有多个读者（没有写者），但是只能有一个写者（没有读者）。具体到程序即，获取多个读锁不会阻塞，但是获取多个写锁会阻塞；有读者时，获取写锁会阻塞；有写者时，获取读锁会阻塞。
下面这个例子，有参数时，给文件加读锁；无参数时，给文件加写锁。按回车后，释放锁。
- /*
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* =====================================================================================
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*
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* Filename: rw_locks.c
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*
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* Description:
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*
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* Version: 1.0
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* Created: 08/10/11 13:14:57
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* Revision: none
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* Compiler: gcc
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*
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* Author: YOUR NAME (),
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* Company:
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*
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* =====================================================================================
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*/
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#include <stdio.h>
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#include <error.h>
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#include <fcntl.h>
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#include <unistd.h>
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int main(int argc, char *argv[])
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{
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int fd;
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struct flock flock;
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flock.l_type = F_WRLCK; //锁的模式必须与文件打开模式显适应
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flock.l_whence = SEEK_SET;
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flock.l_start = 0;
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flock.l_len = 0;
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flock.l_pid = getpid();
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fd = open("tt", O_RDWR);
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if (fd == -1) {
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perror("open file error");
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return -1;
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}
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if(argc > 1)
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flock.l_type = F_RDLCK;
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printf("Trying to obtain a %s lock!\n",
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flock.l_type == F_RDLCK ? "read_lock" : "write lock");
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if (fcntl(fd, F_SETLKW, &flock) == -1) {
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perror("fcntl error");
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return -1;
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}
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printf("Got a lock!\n");
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printf("Press to release the lock\n");
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getchar();
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flock.l_type = F_UNLCK; //UNLOCK
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if (fcntl(fd, F_SETLK, &flock)) { //F_SETLK 用于解锁，也可用于加锁，但与F_SETLKW的区别在于不会被阻塞，立即返回-1
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perror("fcntl error");
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return -1;
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}
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printf("Lock released!\n");
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close(fd);
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return 0;
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}
3. mseeage queue使用框架
ftok("filename", 'A') //存在的文件名加任意int产生key
msgget //IPC_CREAT
msgsnd / msgrcv
//msgctl(id, IPC_RMID, NULL)
注：可存在多个读写者
4. semaphore使用框架
semapore中要特别注意的一点是semaphore set创建以后需要进行初始化（semop），在初始化完成前（通过检查semid_ds中的sem_otime域），其他使用该set的进程需要等待
- #include <stdio.h>
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#include <error.h>
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#include <unistd.h>
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#include <sys/sem.h>
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#include <sys/ipc.h>
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#include <sys/types.h>
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#include <sys/ipc.h>
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#define SEMNUM 1
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int main(int argc, char *argv[])
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{
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key_t key;
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int semid;
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struct sembuf buf = {0, 1, 0};
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key = ftok("tt", 'A');
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if (key == -1) {
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perror("ftok error");
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return -1;
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}
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semid = semget(key, SEMNUM, IPC_CREAT | IPC_EXCL | 0666);
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if (semid == -1) {
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perror("semget error");
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return -1;
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}
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puts("initialize the semaphore set...");
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puts("press to continue");
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getchar();
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for (buf.sem_num = 0; buf.sem_num < SEMNUM; buf.sem_num++) {
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if (semop(semid, &buf, 1) == -1) {
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perror("semop error");
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semctl(semid, 0, IPC_RMID);
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return -1;
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}
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}
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//-----------------------------------
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buf.sem_num = 0;
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buf.sem_op = -1;
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buf.sem_flg = 0;
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puts("Acquire a resource");
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if (semop(semid, &buf, 1) == -1) {
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perror("semop error");
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return -1;
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}
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puts("Resource locked");
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puts("Press to unlock");
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getchar();
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buf.sem_op = 1;
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if (semop(semid, &buf, 1) == -1) {
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perror("semop error");
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return -1;
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}
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puts("Resource unlocked");
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puts("Press to destroy");
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getchar();
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if (semctl(semid, 0, IPC_RMID) == -1) {
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perror("semctl error");
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return -1;
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}
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return 0;
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}
- #include <stdio.h>
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#include <error.h>
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#include <sys/sem.h>
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#include <sys/types.h>
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#include <sys/ipc.h>
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#include <unistd.h>
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#include <stdlib.h>
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#include <errno.h>
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int main()
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{
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key_t key;
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int semid;
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union semun{
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int val;
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struct semid_ds *buf;
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unsigned short *array;
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struct seminfo *__buf;
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}arg;
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struct sembuf buf;
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struct semid_ds ds;
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key = ftok("tt", 'A');
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if (key == -1) {
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perror("ftok error");
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return -1;
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}
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semid = semget(key, 1, IPC_CREAT | IPC_EXCL );
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puts("waiting for initialization");
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if (semid == -1) {
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if (errno == EEXIST) {
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while(1) {
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semid = semget(key, 1, 0666);
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if (semid < 0) {
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perror("semget error");
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return -1;
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}
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arg.buf = &ds;
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if (semctl(semid, 0, IPC_STAT, arg) == -1) {
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perror("semctl1 error");
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//return -1;
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}
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if (arg.buf->sem_otime != 0)
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break;
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}
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} else {
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perror("semget2 error");
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return -1;
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}
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}
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puts("initialization is done");
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puts("locking resource");
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buf.sem_num = 0;
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buf.sem_op = -1;
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buf.sem_flg = 0;
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if (semop(semid, &buf, 1) == -1) {
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perror("semop error");
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return -1;
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}
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puts("Resource locked");
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puts("press to unlock");
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getchar();
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buf.sem_op = 1;
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if (semop(semid, &buf, 1) == -1) {
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perror("semop error");
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return -1;
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}
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puts("Resource unlocked");
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return 0;
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}
5. shared memory使用框架
ftok
shmget //IPC_CREAT
data = shmat(id, (void *)0, 0)
//do sth with the return pointer
shmdt
//shmctl(id, IPC_RMID, NULL)
6. memory mapped file使用框架
open
data = mmap((void *)0, statbuf.st_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0)
read / write
munmap(data, statbuf.st_size)
注意，若使用MAP_PRIVATE则各进程分别获取file的一份拷贝，并且最终修改不会写入文件中
7. unix socket使用框架
sockaddr_un local;
local.sun_family = AF_UNIX;
strcpy(local.sun_path, "/a/b/c")
server端
fd = socket(...)
unlink("a/b/c")
bind
listen
newfd = accept
recv / send
close
client端
fd=socket(...)
unlink("/a/b/c")
connect
send / recv
close
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