src/port/thread.c

   1 /*-------------------------------------------------------------------------
   2  *
   3  * thread.c
   4  *
   5  *                Prototypes and macros around system calls, used to help make
   6  *                threaded libraries reentrant and safe to use from threaded applications.
   7  *
   8  * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
   9  *
  10  * $PostgreSQL$
  11  *
  12  *-------------------------------------------------------------------------
  13  */
  14
  15 #include "c.h"
  16
  17 #include <pwd.h>
  18
  19
  20 /*
  21  *      Threading sometimes requires specially-named versions of functions
  22  *      that return data in static buffers, like strerror_r() instead of
  23  *      strerror().  Other operating systems use pthread_setspecific()
  24  *      and pthread_getspecific() internally to allow standard library
  25  *      functions to return static data to threaded applications. And some
  26  *      operating systems have neither.
  27  *
  28  *      Additional confusion exists because many operating systems that
  29  *      use pthread_setspecific/pthread_getspecific() also have *_r versions
  30  *      of standard library functions for compatibility with operating systems
  31  *      that require them.      However, internally, these *_r functions merely
  32  *      call the thread-safe standard library functions.
  33  *
  34  *      For example, BSD/OS 4.3 uses Bind 8.2.3 for getpwuid().  Internally,
  35  *      getpwuid() calls pthread_setspecific/pthread_getspecific() to return
  36  *      static data to the caller in a thread-safe manner.      However, BSD/OS
  37  *      also has getpwuid_r(), which merely calls getpwuid() and shifts
  38  *      around the arguments to match the getpwuid_r() function declaration.
  39  *      Therefore, while BSD/OS has getpwuid_r(), it isn't required.  It also
  40  *      doesn't have strerror_r(), so we can't fall back to only using *_r
  41  *      functions for threaded programs.
  42  *
  43  *      The current setup is to try threading in this order:
  44  *
  45  *              use *_r function names if they exit
  46  *                      (*_THREADSAFE=yes)
  47  *              use non-*_r functions if they are thread-safe
  48  *
  49  *      One thread-safe solution for gethostbyname() might be to use getaddrinfo().
  50  *
  51  *      Run src/test/thread to test if your operating system has thread-safe
  52  *      non-*_r functions.
  53  */
  54
  55
  56 /*
  57  * Wrapper around strerror and strerror_r to use the former if it is
  58  * available and also return a more useful value (the error string).
  59  */
  60 char *
  61 pqStrerror(int errnum, char *strerrbuf, size_t buflen)
  62 {
  63 #if defined(FRONTEND) && defined(ENABLE_THREAD_SAFETY) && defined(HAVE_STRERROR_R)
  64         /* reentrant strerror_r is available */
  65 #ifdef STRERROR_R_INT
  66         /* SUSv3 version */
  67         if (strerror_r(errnum, strerrbuf, buflen) == 0)
  68                 return strerrbuf;
  69         else
  70                 return "Unknown error";
  71 #else
  72         /* GNU libc */
  73         return strerror_r(errnum, strerrbuf, buflen);
  74 #endif
  75 #else
  76         /* no strerror_r() available, just use strerror */
  77         strlcpy(strerrbuf, strerror(errnum), buflen);
  78
  79         return strerrbuf;
  80 #endif
  81 }
  82
  83 /*
  84  * Wrapper around getpwuid() or getpwuid_r() to mimic POSIX getpwuid_r()
  85  * behaviour, if it is not available or required.
  86  */
  87 #ifndef WIN32
  88 int
  89 pqGetpwuid(uid_t uid, struct passwd * resultbuf, char *buffer,
  90                    size_t buflen, struct passwd ** result)
  91 {
  92 #if defined(FRONTEND) && defined(ENABLE_THREAD_SAFETY) && defined(HAVE_GETPWUID_R)
  93
  94 #ifdef GETPWUID_R_5ARG
  95         /* POSIX version */
  96         getpwuid_r(uid, resultbuf, buffer, buflen, result);
  97 #else
  98
  99         /*
 100          * Early POSIX draft of getpwuid_r() returns 'struct passwd *'.
 101          * getpwuid_r(uid, resultbuf, buffer, buflen)
 102          */
 103         *result = getpwuid_r(uid, resultbuf, buffer, buflen);
 104 #endif
 105 #else
 106
 107         /* no getpwuid_r() available, just use getpwuid() */
 108         *result = getpwuid(uid);
 109 #endif
 110
 111         return (*result == NULL) ? -1 : 0;
 112 }
 113 #endif
 114
 115 /*
 116  * Wrapper around gethostbyname() or gethostbyname_r() to mimic
 117  * POSIX gethostbyname_r() behaviour, if it is not available or required.
 118  * This function is called _only_ by our getaddinfo() portability function.
 119  */
 120 #ifndef HAVE_GETADDRINFO
 121 int
 122 pqGethostbyname(const char *name,
 123                                 struct hostent * resultbuf,
 124                                 char *buffer, size_t buflen,
 125                                 struct hostent ** result,
 126                                 int *herrno)
 127 {
 128 #if defined(FRONTEND) && defined(ENABLE_THREAD_SAFETY) && defined(HAVE_GETHOSTBYNAME_R)
 129
 130         /*
 131          * broken (well early POSIX draft) gethostbyname_r() which returns 'struct
 132          * hostent *'
 133          */
 134         *result = gethostbyname_r(name, resultbuf, buffer, buflen, herrno);
 135         return (*result == NULL) ? -1 : 0;
 136 #else
 137
 138         /* no gethostbyname_r(), just use gethostbyname() */
 139         *result = gethostbyname(name);
 140
 141         if (*result != NULL)
 142                 *herrno = h_errno;
 143
 144         if (*result != NULL)
 145                 return 0;
 146         else
 147                 return -1;
 148 #endif
 149 }
 150
 151 #endif