一、有名管道FIFO
（一）知识点
1.在有名管道（named pipe或FIFO）提出后，管道（pipe）限制得到了克服。
- 值得注意的是，FIFO严格遵循先进先出（first in first out），对管道及FIFO的读总是从开始处返回数据，对它们的写则把数据添加到末尾。
- 它们不支持诸如lseek()等文件定位操作。
其中，filename是要创建的管道，mode是管道类型
创建成功后，使用open()、read()和write()函数
- 为读而打开的管道：在open()中设置O_RDONLY；
- 为写而打开的管道：在open()中设置O_WDONLY；
- 非阻塞打开：在open()中设定为O_NONBLOCK
（二）代码
testmf.c
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
int main()
{
int res = mkfifo("/tmp/myfifo", 0777);
if (res == 0) {
printf("FIFO created \n");
}
exit(EXIT_SUCCESS);
}
consumer.c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <limits.h>
#include <sys/types.h>
#include <sys/stat.h>
#define FIFO_NAME "/tmp/myfifo"
#define BUFFER_SIZE PIPE_BUF
int main()
{
int pipe_fd;
int res;
int open_mode = O_RDONLY;
char buffer[BUFFER_SIZE + 1];
int bytes = 0;
memset(buffer, 0, sizeof(buffer));
printf("Process %d opeining FIFO O_RDONLY \n", getpid());
pipe_fd = open(FIFO_NAME, open_mode);
printf("Process %d result %d\n", getpid(), pipe_fd);
if (pipe_fd != -1) {
do {
res = read(pipe_fd, buffer, BUFFER_SIZE);
bytes += res;
} while (res > 0);
close(pipe_fd);
} else {
exit(EXIT_FAILURE);
}
printf("Process %d finished, %d bytes read\n", getpid(), bytes);
exit(EXIT_SUCCESS);
}
producer.c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <limits.h>
#include <sys/types.h>
#include <sys/stat.h>
#define FIFO_NAME "/tmp/myfifo"
#define BUFFER_SIZE PIPE_BUF
#define TEN_MEG (1024 * 1024 * 10)
int main()
{
int pipe_fd;
int res;
int open_mode = O_WRONLY;
int bytes = 0;
char buffer[BUFFER_SIZE + 1];
if (access(FIFO_NAME, F_OK) == -1) {
res = mkfifo(FIFO_NAME, 0777);
if (res != 0) {
fprintf(stderr, "Could not create fifo %s \n",
FIFO_NAME);
exit(EXIT_FAILURE);
}
}
printf("Process %d opening FIFO O_WRONLY\n", getpid());
pipe_fd = open(FIFO_NAME, open_mode);
printf("Process %d result %d\n", getpid(), pipe_fd);
if (pipe_fd != -1) {
while (bytes < TEN_MEG) {
res = write(pipe_fd, buffer, BUFFER_SIZE);
if (res == -1) {
fprintf(stderr, "Write error on pipe\n");
exit(EXIT_FAILURE);
}
bytes += res;
}
close(pipe_fd);
} else {
exit(EXIT_FAILURE);
}
printf("Process %d finish\n", getpid());
exit(EXIT_SUCCESS);
}
二、管道PIPE
（一）知识点
管道是Linux中进程间通信的一种方式。这里所说的管道主要指无名管道，它具有以下特点：
-
它只能用于具有亲缘关系的进程之间的通信（也就是父子进程或者兄弟进程之间）。
-
它是一个半双工的通信模式，具有固定的读端和写端。需要双方通信时，需要建立起两个管道。
-
管道也可以看成是一种特殊的文件，对于它的读写也可以使用普通的read()和write()等函数。但是它不是普通的文件，并不属于其他任何文件系统，并且只存在于内核的内存空间中。
-
数据的读出和写入：一个进程向管道中写的内容被管道另一端的进程读出。写入的内容每次都添加在管道缓冲区的末尾，并且每次都是从缓冲区的头部读出数据。
-
一般情况下使用管道时，先创建一个管道，再通过fork()函数创建一子进程，该子进程会继承父进程所创建的管道。为了实现父子进程之间的读写，只需把无关的读端或写端的文件描述符关闭即可。例如在下图中将父进程的写端fd[1]和子进程的读端fd[0]关闭。此时，父子进程之间就建立起了一条“子进程写入父进程读取”的通道。
-
同样，也可以关闭父进程的fd[0]和子进程的fd[1]，这样就可以建立一条“父进程写入子进程读取”的通道。另外，父进程还可以创建多个子进程，各个子进程都继承了相应的fd[0]和fd[1]，这时，只需要关闭相应端口就可以建立其各子进程之间的通道
（二）代码
listargs.c
#include<stdio.h>
main( int ac, char *av[] )
{
int i;
printf("Number of args: %d, Args are:\n", ac);
for(i=0;i<ac;i++)
printf("args[%d] %s\n", i, av[i]);
fprintf(stderr,"This message is sent to stderr.\n");
}
pipe.c
#include<stdio.h>
#include<stdlib.h>
#include<unistd.h>
#define oops(m,x) { perror(m); exit(x); }
int main(int ac, char **av)
{
int thepipe[2],
newfd,
pid;
if ( ac != 3 ){
fprintf(stderr, "usage: pipe cmd1 cmd2\n");
exit(1);
}
if ( pipe( thepipe ) == -1 )
oops("Cannot get a pipe", 1);
if ( (pid = fork()) == -1 )
oops("Cannot fork", 2);
if ( pid > 0 ){
close(thepipe[1]);
if ( dup2(thepipe[0], 0) == -1 )
oops("could not redirect stdin",3);
close(thepipe[0]);
execlp( av[2], av[2], NULL);
oops(av[2], 4);
}
close(thepipe[0]);
if ( dup2(thepipe[1], 1) == -1 )
oops("could not redirect stdout", 4);
close(thepipe[1]);
execlp( av[1], av[1], NULL);
oops(av[1], 5);
}
pipedemo.c
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<unistd.h>
int main()
{
int len, i, apipe[2];
char buf[BUFSIZ];
if ( pipe ( apipe ) == -1 ){
perror("could not make pipe");
exit(1);
}
printf("Got a pipe! It is file descriptors: { %d %d }\n",
apipe[0], apipe[1]);
while ( fgets(buf, BUFSIZ, stdin) ){
len = strlen( buf );
if ( write( apipe[1], buf, len) != len ){
perror("writing to pipe");
break;
}
for ( i = 0 ; i<len ; i++ )
buf[i] = 'X' ;
len = read( apipe[0], buf, BUFSIZ ) ;
if ( len == -1 ){
perror("reading from pipe");
break;
}
if ( write( 1 , buf, len ) != len ){
perror("writing to stdout");
break;
}
}
}
pipedemo2.c
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<unistd.h>
#define CHILD_MESS "I want a cookie\n"
#define PAR_MESS "testing..\n"
#define oops(m,x) { perror(m); exit(x); }
main()
{
int pipefd[2];
int len;
char buf[BUFSIZ];
int read_len;
if ( pipe( pipefd ) == -1 )
oops("cannot get a pipe", 1);
switch( fork() ){
case -1:
oops("cannot fork", 2);
case 0:
len = strlen(CHILD_MESS);
while ( 1 ){
if (write( pipefd[1], CHILD_MESS, len) != len )
oops("write", 3);
sleep(5);
}
default:
len = strlen( PAR_MESS );
while ( 1 ){
if ( write( pipefd[1], PAR_MESS, len)!=len )
oops("write", 4);
sleep(1);
read_len = read( pipefd[0], buf, BUFSIZ );
if ( read_len <= 0 )
break;
write( 1 , buf, read_len );
}
}
}
stdinredir1.c
#include<stdio.h>
#include<fcntl.h>
int main()
{
int fd ;
char line[100];
fgets( line, 100, stdin ); printf("%s", line );
fgets( line, 100, stdin ); printf("%s", line );
fgets( line, 100, stdin ); printf("%s", line );
close(0);
fd = open("/etc/passwd", O_RDONLY);
if ( fd != 0 ){
fprintf(stderr,"Could not open data as fd 0\n");
exit(1);
}
fgets( line, 100, stdin ); printf("%s", line );
fgets( line, 100, stdin ); printf("%s", line );
fgets( line, 100, stdin ); printf("%s", line );
}
stdinredir2.c
#include<stdio.h>
#include<stdlib.h>
#include<fcntl.h>
//#define CLOSE_DUP
//#define USE_DUP2
main()
{
int fd ;
int newfd;
char line[100];
fgets( line, 100, stdin ); printf("%s", line );
fgets( line, 100, stdin ); printf("%s", line );
fgets( line, 100, stdin ); printf("%s", line );
fd = open("data", O_RDONLY);
#ifdef CLOSE_DUP
close(0);
newfd = dup(fd);
#else
newfd = dup2(fd,0);
#endif
if ( newfd != 0 ){
fprintf(stderr,"Could not duplicate fd to 0\n");
exit(1);
}
close(fd);
fgets( line, 100, stdin ); printf("%s", line );
fgets( line, 100, stdin ); printf("%s", line );
fgets( line, 100, stdin ); printf("%s", line );
}
testtty.c
#include <unistd.h>
int main()
{
char *buf = "abcde\n";
write(0, buf, 6);
}
whotofile.c
#include<stdio.h>
#include<stdlib.h>
#include<unistd.h>
int main()
{
int pid ;
int fd;
printf("About to run who into a file\n");
if( (pid = fork() ) == -1 ){
perror("fork"); exit(1);
}
if ( pid == 0 ){
close(1); /* close, */
fd = creat( "userlist", 0644 ); /* then open */
execlp( "who", "who", NULL ); /* and run */
perror("execlp");
exit(1);
}
if ( pid != 0 ){
wait(NULL);
printf("Done running who. results in userlist\n");
}
return 0;
}
三、SIGNAL
（一）知识点
多任务操作系统环境﹣多进程：
- 同步关系：多进程为了完成同一个任务相互协作
- 互斥关系：不同进程为了争夺有限的系统资源，进入竞争状态
进程之间的互斥与同步关系存在的根源在于临界资源
-
临界资源是在同一个时刻只允许有限个（通常只有一个）进程可
以访问（读）或修改（写）的资源； -
访问临界资源的代码叫做临界区，临界区本身也会成为临界资源。
-
信号量﹣解决进程之间的同步与互斥问题
-
称为信号量的变量
-
在该信号量下等待资源的进程等待队列
-
对信号量进行的两个原子操作（ PV 操作）
（二）代码
sigactdemo.c
#include<stdio.h>
#include<unistd.h>
#include<signal.h>
#define INPUTLEN 100
void inthandler();
int main()
{
struct sigaction newhandler;
sigset_t blocked;
char x[INPUTLEN];
newhandler.sa_handler = inthandler;
newhandler.sa_flags = SA_RESTART|SA_NODEFER
|SA_RESETHAND;
sigemptyset(&blocked);
sigaddset(&blocked, SIGQUIT);
newhandler.sa_mask = blocked;
if (sigaction(SIGINT, &newhandler, NULL) == -1)
perror("sigaction");
else
while (1) {
fgets(x, INPUTLEN, stdin);
printf("input: %s", x);
}
return 0;
}
void inthandler(int s)
{
printf("Called with signal %d\n", s);
sleep(s * 4);
printf("done handling signal %d\n", s);
}
sigactdemo2.c
#include <unistd.h>
#include <signal.h>
#include <stdio.h>
void sig_alrm( int signo )
{
/*do nothing*/
}
unsigned int mysleep(unsigned int nsecs)
{
struct sigaction newact, oldact;
unsigned int unslept;
newact.sa_handler = sig_alrm;
sigemptyset( &newact.sa_mask );
newact.sa_flags = 0;
sigaction( SIGALRM, &newact, &oldact );
alarm( nsecs );
pause();
unslept = alarm ( 0 );
sigaction( SIGALRM, &oldact, NULL );
return unslept;
}
int main( void )
{
while( 1 )
{
mysleep( 2 );
printf( "Two seconds passed\n" );
}
return 0;
}
sigdemo1.c
#include<stdio.h>
#include<signal.h>
void f(int);
int main()
{
int i;
signal( SIGINT, f );
for(i=0; i<5; i++ ){
printf("hello\n");
sleep(2);
}
return 0;
}
void f(int signum)
{
printf("OUCH!\n");
}
sigdemo2.c
#include<stdio.h>
#include<signal.h>
main()
{
signal( SIGINT, SIG_IGN );
printf("you can't stop me!\n");
while( 1 )
{
sleep(1);
printf("haha\n");
}
}
sigdemo3.c
#include<stdio.h>
#include<string.h>
#include<signal.h>
#include<unistd.h>
#define INPUTLEN 100
int main(int argc, char *argv[])
{
void inthandler(int);
void quithandler(int);
char input[INPUTLEN];
int nchars;
signal(SIGINT, inthandler);//^C
signal(SIGQUIT, quithandler);//^\
do {
printf("\nType a message\n");
nchars = read(0, input, (INPUTLEN - 1));
if (nchars == -1)
perror("read returned an error");
else {
input[nchars] = '\0';
printf("You typed: %s", input);
}
}
while (strncmp(input, "quit", 4) != 0);
return 0;
}
void inthandler(int s)
{
printf(" Received signal %d .. waiting\n", s);
sleep(2);
printf(" Leaving inthandler \n");
}
void quithandler(int s)
{
printf(" Received signal %d .. waiting\n", s);
sleep(3);
printf(" Leaving quithandler \n");
}
