[英]cleanup in SIGPIPE
我有一个共享多个线程的套接字连接池,应该从池中删除无效连接,问题是我不知道SIGPIPE sighandler中哪个无效,在这种情况下有什么建议吗?
解决此问题的一种方法是忽略SIGPIPE。 这意味着您的写入操作( write
, sendmsg
或其他)将返回错误,并且只要您注意错误返回,就可以知道哪个文件描述符失败-因为一切都是同步的。
以下程序与套接字无关,而是使用命名管道。 只需在此处放置程序以演示我如何处理上述问题。 他们是我编写的一对程序,目的是更好地理解命名管道。 处理所有错误情况。 有两个可执行文件,必须分别进行编译。 在同一台PC上的两个单独的终端中运行每个可执行文件。 运行它们的顺序并不重要。 不论哪个先运行,都将创建命名管道,而另一个启动时将注意到其已创建(mkfifo错误处理)。 编写器每秒写入一次管道,而read()返回时,读取器则从管道读取数据。 在编写器方面,SIGPIPE被忽略,而处理EPIPE。 在两个终端窗口(读取器或写入器)中的任何一个上按键盘上的“ q”,这两个窗口都将退出。
如果不忽略SIGPIPE,将会发生以下情况:当我在写入器之前退出读取器时(通过在读取器终端中按q),write()将失败并触发SIGPIPE信号被写入器应用程序接收。 此操作的默认行为是立即退出应用程序。 当然,这不是我将要使用此代码的多线程应用程序所需要的。 因此,我忽略了该信号并检查了errno并对其进行了适当的处理。
writer.c:
#include <stdio.h> //for printf()
#include <stdlib.h> //for malloc()
#include <stdint.h> //for definitions of uint8_t etc..
#include <unistd.h> //for sleep()
#include <sys/stat.h> //for S_IRUSR, S_IWUSR, mkfifo()
#include <fcntl.h> //for O_WRONLY
#include <errno.h> //for errno, perror()
#include "kbhit.h"
#include <sys/types.h>
#include <signal.h> //for signal()
/* Named pipe considerations (http://www.unixguide.net/unix/programming/2.10.3.shtml):
*
* To use the pipe, you open it like a normal file, and use read()
* and write() just as though it was a plain pipe.
* However, the open() of the pipe may block. The following rules apply:
*
* If you open for both reading and writing (O_RDWR), then the open will not block.
*
* If you open for reading (O_RDONLY), the open will block until
* another process opens the FIFO for writing, unless O_NONBLOCK is
* specified, in which case the open succeeds.
*
* If you open for writing O_WRONLY, the open will block until
* another process opens the FIFO for reading, unless O_NONBLOCK is
* specified, in which case the open fails.
*
* When reading and writing the FIFO, the same considerations apply as for
* regular pipes and sockets, i.e. read() will return EOF when all
* writers have closed, and write() will raise SIGPIPE when
* there are no readers. If SIGPIPE is blocked or ignored, the call
* fails with EPIPE.
*
*/
static const char file_path[] = "/tmp/anurag";
static const char message[] = "Hello from writer!";
int main(void) {
int ret;
int fd=0;
char keypress=0;
/*
* (http://stackoverflow.com/questions/4351989/cleanup-in-sigpipe)
* EPIPE is returned if fd is connected to a pipe or socket whose reading end is closed.
* When this happens the writing process will also receive a SIGPIPE signal.
* (Thus, the write return value is seen only if the program catches, blocks or ignores this signal.)
*/
signal(SIGPIPE, SIG_IGN);
//Create the FIFO (named pipe)
ret = mkfifo(file_path, S_IRUSR | S_IWUSR);
if(ret == 0) {
printf("mkfifo(): Named pipe created.\n");
} else {
if ((ret == -1) && (errno == EEXIST)) {
perror("mkfifo()");
} else {
perror("mkfifo()");
}
}
printf("Will now begin waiting on open()...\n");
fd = open(file_path, O_WRONLY);
if(fd == -1) {
perror("open()");
} else if (fd > 0) {
printf("open(): Named pipe file descriptor opened for writing.\n");
}
while(keypress != 'q') {
if (kbhit()) {
keypress = getchar();
printf("Exiting...\n");
} else {
ret = write(fd, message, sizeof(message));
if(ret > 0) {
printf("write(): %d bytes to pipe: %s\n",ret,message);
} else if (ret <=0) {
if(errno == EPIPE) {
printf("write(): got EPIPE, reader closed the pipe, exiting...\n");
break;
} else {
perror("write()");
break;
}
}
}
sleep(1);
};
ret = close(fd);
if(ret == 0) {
printf("close(): Named pipe file descriptor closed.\n");
} else {
perror("close()");
}
ret = remove(file_path);
if(ret == 0) {
printf("remove(): Named pipe deleted.\n");
} else {
perror("remove()");
}
fflush(stdout);
fflush(stderr);
return EXIT_SUCCESS;
}
reader.c:
#include <stdio.h> //for printf()
#include <stdlib.h> //for malloc()
#include <stdint.h> //for definitions of uint8_t etc..
#include <unistd.h> //for sleep()
#include <sys/stat.h> //for S_IRUSR, S_IWUSR, mkfifo()
#include <fcntl.h> //for O_WRONLY
#include <errno.h> //for errno, perror()
#include <string.h> //for memset()
#include "kbhit.h"
/* Named pipe considerations (http://www.unixguide.net/unix/programming/2.10.3.shtml):
*
* To use the pipe, you open it like a normal file, and use read()
* and write() just as though it was a plain pipe.
* However, the open() of the pipe may block. The following rules apply:
*
* If you open for both reading and writing (O_RDWR), then the open will not block.
*
* If you open for reading (O_RDONLY), the open will block until
* another process opens the FIFO for writing, unless O_NONBLOCK is
* specified, in which case the open succeeds.
*
* If you open for writing O_WRONLY, the open will block until
* another process opens the FIFO for reading, unless O_NONBLOCK is
* specified, in which case the open fails.
*
* When reading and writing the FIFO, the same considerations apply as for
* regular pipes and sockets, i.e. read() will return EOF when all
* writers have closed, and write() will raise SIGPIPE when
* there are no readers. If SIGPIPE is blocked or ignored, the call
* fails with EPIPE.
*
*/
static const char file_path[] = "/tmp/anurag";
static char message[100] = {0};
int main(void) {
int ret;
int fd=0;
char keypress=0;
//Create the FIFO (named pipe)
ret = mkfifo(file_path, S_IRUSR | S_IWUSR);
if(ret == 0) {
printf("mkfifo(): Named pipe created.\n");
} else {
if ((ret == -1) && (errno == EEXIST)) {
perror("mkfifo()");
} else {
perror("mkfifo()");
}
}
printf("Will now begin waiting on open()...\n");
fd = open(file_path, O_RDONLY);
if(fd == -1) {
perror("open()");
} else if (fd > 0) {
printf("open(): Named pipe file descriptor opened for reading.\n");
}
while(keypress != 'q') {
if (kbhit()) {
keypress = getchar();
printf("Exiting...\n");
} else {
memset(message,0,100);
ret = read(fd, message, 100);
if(ret > 0) {
printf("read(): %d bytes from pipe: %s\n",ret, message);
} else if (ret == 0){
printf("read(): got EOF, writer closed the pipe, exiting...\n");
break;
} else if (ret < 0){
perror("read()");
break;
}
}
sleep(1);
};
ret = close(fd);
if(ret == 0) {
printf("close(): Named pipe file descriptor closed.\n");
} else {
perror("close()");
}
ret = remove(file_path);
if(ret == 0) {
printf("remove(): Named pipe deleted.\n");
} else {
perror("remove()");
}
fflush(stdout);
fflush(stderr);
return EXIT_SUCCESS;
}
以上两个c文件都使用kbhit()来轮询从键盘接收的字符。 这是该代码:
kbhit.c:
//Taken from: http://cboard.cprogramming.com/c-programming/63166-kbhit-linux.html
#include <stdio.h>
#include <termios.h>
#include <unistd.h>
#include <fcntl.h>
#include "kbhit.h"
int kbhit(void) {
struct termios oldt, newt;
int ch;
int oldf;
tcgetattr(STDIN_FILENO, &oldt);
newt = oldt;
newt.c_lflag &= ~(ICANON | ECHO);
tcsetattr(STDIN_FILENO, TCSANOW, &newt);
oldf = fcntl(STDIN_FILENO, F_GETFL, 0);
fcntl(STDIN_FILENO, F_SETFL, oldf | O_NONBLOCK);
ch = getchar();
tcsetattr(STDIN_FILENO, TCSANOW, &oldt);
fcntl(STDIN_FILENO, F_SETFL, oldf);
if (ch != EOF) {
ungetc(ch, stdin);
return 1;
}
return 0;
}
kbhit.h:
#ifndef KBHIT_H_
#define KBHIT_H_
//Console related variables and functions
int kbhit(void);
#endif /* KBHIT_H_ */
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