linux 如何分析 打印python 线程栈

errno是什么？

经常在调用linux 系统api 的时候会出现一些错误，比方说使用open() write() creat()之类的函数，有些时候会返回-1，也就是调用失败(返回值往往只有0成功，-1失败，使用errno记录失败的原因)，这个时候往往需要知道失败的原因。这个时候使用errno这个全局变量就相当有用了。

用法：
  在程序代码中包含 #include <errno.h>,然后每次程序调用失败的时候，系统会自动用用错误代码填充errno这个全局变量，这样你只需要读errno这个全局变量就可以获得失败原因了。从而根据错误的原因做相应的操作。

使用strerror(errno)：获取errno对应的错误信息，方便打印。如printf("error:%s\n", strerror(errno))

  根据man errno 描述，errno是线程安全的。

有下面几种方法可以方便的得到错误信息

(1)void perror(const char *s)
 函数说明
 perror ( )用来将上一个函数发生错误的原因输出到标准错误(stderr),参数s 所指的字符串会先打印出,后面再加上错误原因 字符串。此错误原因依照全局变量 errno 的值来决定要输出的字符串。
   (2) char *strerror(int errno)
 将错误代码转换为字符串错误信息,可以将该字符串和其它的信息组合输出到用户界面例如
 fprintf(stderr,"error in CreateProcess %s, Process ID %d ",strerror(errno),processID)
 注：假设processID是一个已经获取了的整形ID
   (3)printf("%m", errno);
 另外不是所有的地方发生错误的时候都可以通过error获取错误代码，例如下面的代码段
 /*注：下面的头文件使用""而没有直接使用尖括号是因为博客大巴中尖括号当作html符号，所以其内部的头文件名字会被直接忽略*/
 #include"stdio.h"
 #include "stdlib.h"
 #include "errno.h"
 #include "netdb.h"
 #include "sys/types.h"
 #include "netinet/in.h"
 int main (int argc, char *argv[])
 {
 struct hostent *h;
 if (argc != 2)
 {
 fprintf (stderr ,"usage: getip address\n");
 exit(1);
 }
 /* 取得主机信息 */
 if((h=gethostbyname(argv[1])) == NULL)
 {
 /* 如果gethostbyname 失败，则给出错误信息 */
 herror(“gethostbyname”);
 exit(1);
 }
 /* 列印程序取得的信息 */
 printf(“Host name : %s\n”, h->h_name);
 printf(“IP Address : %s\n”, inet_ntoa (*((struct in_addr *)h->h_addr))）;
 return 0;
 }

 /*************************************/

  通过上面的代码可以看到：使用gethostbyname()函数，你不能使用perror()来输出错误信息（因为错误代码存储在 h_errno 中而不是errno 中。所以，你需要调用herror()函数。
你简单的传给gethostbyname() 一个机器名（“bbs.tsinghua.edu.cn”），然后就从返回的结构struct hostent 中得到了IP 等其他信息．程序中输出IP 地址的程序需要解释一下：h->h_addr 是一个char*，但是inet_ntoa()函数需要传递的是一个struct in_addr 结构。所以上面将h->h_addr 强制转换为struct in_addr*，然后通过它得到了所有数据。

errno.h中定义的错误代码值如下：

查 看错误代码errno是调试程序的一个重要方法。当linuc C api函数发生异常时,一般会将errno变量(需include errno.h)赋一个整数值,不同的值表示不同的含义,可以通过查看该值推测出错的原因。在实际编程中用这一招解决了不少原本看来莫名其妙的问题。比较 麻烦的是每次都要去linux源代码里面查找错误代码的含义，现在把它贴出来，以后需要查时就来这里看了。
以下来自linux 2.4.20-18的内核代码中的/usr/include/asm/errno.h

#ifndef _I386_ERRNO_H
 #define _I386_ERRNO_H
 #define EPERM   1 /* Operation not permitted */
 #define ENOENT   2 /* No such file or directory */
 #define ESRCH   3 /* No such process */
 #define EINTR   4 /* Interrupted system call */
 #define EIO       5 /* I/O error */
 #define ENXIO   6 /* No such device or address */
 #define E2BIG   7 /* Arg list too long */
 #define ENOEXEC   8 /* Exec format error */
 #define EBADF   9 /* Bad file number */
 #define ECHILD 10 /* No child processes */
 #define EAGAIN 11 /* Try again */
 #define ENOMEM 12 /* Out of memory */
 #define EACCES 13 /* Permission denied */
 #define EFAULT 14 /* Bad address */
 #define ENOTBLK 15 /* Block device required */
 #define EBUSY 16 /* Device or resource busy */
 #define EEXIST 17 /* File exists */
 #define EXDEV 18 /* Cross-device link */
 #define ENODEV 19 /* No such device */
 #define ENOTDIR 20 /* Not a directory */
 #define EISDIR 21 /* Is a directory */
 #define EINVAL 22 /* Invalid argument */
 #define ENFILE 23 /* File table overflow */
 #define EMFILE 24 /* Too many open files */
 #define ENOTTY 25 /* Not a typewriter */
 #define ETXTBSY 26 /* Text file busy */
 #define EFBIG 27 /* File too large */
 #define ENOSPC 28 /* No space left on device */
 #define ESPIPE 29 /* Illegal seek */
 #define EROFS 30 /* Read-only file system */
 #define EMLINK 31 /* Too many links */
 #define EPIPE 32 /* Broken pipe */
 #define EDOM 33 /* Math argument out of domain of func */
 #define ERANGE 34 /* Math result not representable */
 #define EDEADLK 35 /* Resource deadlock would occur */
 #define ENAMETOOLONG 36 /* File name too long */
 #define ENOLCK 37 /* No record locks available */
 #define ENOSYS 38 /* Function not implemented */
 #define ENOTEMPTY 39 /* Directory not empty */
 #define ELOOP 40 /* Too many symbolic links encountered */
 #define EWOULDBLOCK EAGAIN /* Operation would block */
 #define ENOMSG 42 /* No message of desired type */
 #define EIDRM 43 /* Identifier removed */
 #define ECHRNG 44 /* Channel number out of range */
 #define EL2NSYNC 45 /* Level 2 not synchronized */
 #define EL3HLT 46 /* Level 3 halted */
 #define EL3RST 47 /* Level 3 reset */
 #define ELNRNG 48 /* Link number out of range */
 #define EUNATCH 49 /* Protocol driver not attached */
 #define ENOCSI 50 /* No CSI structure available */
 #define EL2HLT 51 /* Level 2 halted */
 #define EBADE 52 /* Invalid exchange */
 #define EBADR 53 /* Invalid request descriptor */
 #define EXFULL 54 /* Exchange full */
 #define ENOANO 55 /* No anode */
 #define EBADRQC 56 /* Invalid request code */
 #define EBADSLT 57 /* Invalid slot */
 #define EDEADLOCK EDEADLK
 #define EBFONT 59 /* Bad font file format */
 #define ENOSTR 60 /* Device not a stream */
 #define ENODATA 61 /* No data available */
 #define ETIME 62 /* Timer expired */
 #define ENOSR 63 /* Out of streams resources */
 #define ENONET 64 /* Machine is not on the network */
 #define ENOPKG 65 /* Package not installed */
 #define EREMOTE 66 /* Object is remote */
 #define ENOLINK 67 /* Link has been severed */
 #define EADV 68 /* Advertise error */
 #define ESRMNT 69 /* Srmount error */
 #define ECOMM 70 /* Communication error on send */
 #define EPROTO 71 /* Protocol error */
 #define EMULTIHOP 72 /* Multihop attempted */
 #define EDOTDOT 73 /* RFS specific error */
 #define EBADMSG 74 /* Not a data message */
 #define EOVERFLOW 75 /* Value too large for defined data type */
 #define ENOTUNIQ 76 /* Name not unique on network */
 #define EBADFD 77 /* File descriptor in bad state */
 #define EREMCHG 78 /* Remote address changed */
 #define ELIBACC 79 /* Can not access a needed shared library */
 #define ELIBBAD 80 /* Accessing a corrupted shared library */
 #define ELIBSCN 81 /* .lib section in a.out corrupted */
 #define ELIBMAX 82 /* Attempting to link in too many shared libraries */
 #define ELIBEXEC 83 /* Cannot exec a shared library directly */
 #define EILSEQ 84 /* Illegal byte sequence */
 #define ERESTART 85 /* Interrupted system call should be restarted */
 #define ESTRPIPE 86 /* Streams pipe error */
 #define EUSERS 87 /* Too many users */
 #define ENOTSOCK 88 /* Socket operation on non-socket */
 #define EDESTADDRREQ 89 /* Destination address required */
 #define EMSGSIZE 90 /* Message too long */
 #define EPROTOTYPE 91 /* Protocol wrong type for socket */
 #define ENOPROTOOPT 92 /* Protocol not available */
 #define EPROTONOSUPPORT 93 /* Protocol not supported */
 #define ESOCKTNOSUPPORT 94 /* Socket type not supported */
 #define EOPNOTSUPP 95 /* Operation not supported on transport endpoint */
 #define EPFNOSUPPORT 96 /* Protocol family not supported */
 #define EAFNOSUPPORT 97 /* Address family not supported by protocol */
 #define EADDRINUSE 98 /* Address already in use */
 #define EADDRNOTAVAIL 99 /* Cannot assign requested address */
 #define ENETDOWN 100 /* Network is down */
 #define ENETUNREACH 101 /* Network is unreachable */
 #define ENETRESET 102 /* Network dropped connection because of reset */
 #define ECONNABORTED 103 /* Software caused connection abort */
 #define ECONNRESET 104 /* Connection reset by peer */
 #define ENOBUFS 105 /* No buffer space available */
 #define EISCONN 106 /* Transport endpoint is already connected */
 #define ENOTCONN 107 /* Transport endpoint is not connected */
 #define ESHUTDOWN 108 /* Cannot send after transport endpoint shutdown */
 #define ETOOMANYREFS 109 /* Too many references: cannot splice */
 #define ETIMEDOUT 110 /* Connection timed out */
 #define ECONNREFUSED 111 /* Connection refused */
 #define EHOSTDOWN 112 /* Host is down */
 #define EHOSTUNREACH 113 /* No route to host */
 #define EALREADY 114 /* Operation already in progress */
 #define EINPROGRESS 115 /* Operation now in progress */
 #define ESTALE 116 /* Stale NFS file handle */
 #define EUCLEAN 117 /* Structure needs cleaning */
 #define ENOTNAM 118 /* Not a XENIX named type file */
 #define ENAVAIL 119 /* No XENIX semaphores available */
 #define EISNAM 120 /* Is a named type file */
 #define EREMOTEIO 121 /* Remote I/O error */
 #define EDQUOT 122 /* Quota exceeded */
 #define ENOMEDIUM 123 /* No medium found */
 #define EMEDIUMTYPE 124 /* Wrong medium type */
 #endif同时也可以使用strerror（）来自己翻译
 如：
 #include <stdio.h>
 #include <string.h>
 #include <errno.h> 
 int main(void)
 {
 int   fd;
 extern int errno;if((fd = open("/dev/dsp",O_WRONLY)) < 0)
 {
 printf("errno=%d\n",errno); 
 char * mesg = strerror(errno);
 printf("Mesg:%s\n",mesg); 
 }

 exit(0);
 }
 dsp设备忙的话将输出如下：
 errno=16
 Mesg:Device or resource busy