我有一个套接字连接池，它在多个线程中共享，应该从池中删除死连接，问题是我不知道哪个死了来自SIGPIPE sighandler，在这种情况下有什么建议吗？
答案 0 :(得分：5)
解决这个问题的一种方法是忽略SIGPIPE。这意味着你的写操作（write，sendmsg，等等）将返回错误，只要你注意错误返回，你就会知道哪个文件描述符失败了 - 因为一切是同步的。
答案 1 :(得分：0)
以下程序与套接字无关，而是使用命名管道。只是在这里提出程序来演示我如何处理上述问题。它们是我编写的一对程序，用于更好地理解命名管道。处理所有错误条件。有两个可执行文件必须单独编译。在同一台PC上的两个独立终端中运行每个可执行文件。运行它们的顺序并不重要。无论哪个先运行，都会创建命名管道，另一个在启动时会注意到它已经创建（mkfifo错误处理）。编写器每秒写一次管道，读取器返回时读取器从管道读取。在编者方面，SIGPIPE被忽略，而是处理EPIPE。
在两个终端窗口（阅读器或编写器）中的任意一个按键盘上的“q”键如果没有忽略SIGPIPE，那么当我在编写器之前退出阅读器时（通过在阅读器终端中按q），write（）将失败并触发写入器接收SIGPIPE信号应用。默认行为是立即退出应用程序。这当然不是我在将要使用此代码的多线程应用程序中所需要的。所以我忽略了信号并检查了errno并正确处理了它。
<强> 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;
}
<强> 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;
}
上述两个c文件都使用kbhit（）来轮询从键盘接收的字符。以下是代码：
<强> 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;
}
<强> kbhit.h：
#ifndef KBHIT_H_
#define KBHIT_H_
//Console related variables and functions
int kbhit(void);
#endif /* KBHIT_H_ */