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) 1996-2008, PostgreSQL Global Development Group
   9  *
  10  * $PostgreSQL$
  11  *
  12  *-------------------------------------------------------------------------
  13  */
  14
  15 #include "c.h"
  16
  17 #include <pwd.h>
  18 #if defined(FRONTEND) && defined(ENABLE_THREAD_SAFETY)
  19 #endif
  20
  21
  22 /*
  23  *      Threading sometimes requires specially-named versions of functions
  24  *      that return data in static buffers, like strerror_r() instead of
  25  *      strerror().  Other operating systems use pthread_setspecific()
  26  *      and pthread_getspecific() internally to allow standard library
  27  *      functions to return static data to threaded applications. And some
  28  *      operating systems have neither.
  29  *
  30  *      Additional confusion exists because many operating systems that
  31  *      use pthread_setspecific/pthread_getspecific() also have *_r versions
  32  *      of standard library functions for compatibility with operating systems
  33  *      that require them.      However, internally, these *_r functions merely
  34  *      call the thread-safe standard library functions.
  35  *
  36  *      For example, BSD/OS 4.3 uses Bind 8.2.3 for getpwuid().  Internally,
  37  *      getpwuid() calls pthread_setspecific/pthread_getspecific() to return
  38  *      static data to the caller in a thread-safe manner.      However, BSD/OS
  39  *      also has getpwuid_r(), which merely calls getpwuid() and shifts
  40  *      around the arguments to match the getpwuid_r() function declaration.
  41  *      Therefore, while BSD/OS has getpwuid_r(), it isn't required.  It also
  42  *      doesn't have strerror_r(), so we can't fall back to only using *_r
  43  *      functions for threaded programs.
  44  *
  45  *      The current setup is to try threading in this order:
  46  *
  47  *              use *_r function names if they exit
  48  *                      (*_THREADSAFE=yes)
  49  *              use non-*_r functions if they are thread-safe
  50  *
  51  *      One thread-safe solution for gethostbyname() might be to use getaddrinfo().
  52  *
  53  *      Run src/test/thread to test if your operating system has thread-safe
  54  *      non-*_r functions.
  55  */
  56
  57
  58 /*
  59  * Wrapper around strerror and strerror_r to use the former if it is
  60  * available and also return a more useful value (the error string).
  61  */
  62 char *
  63 pqStrerror(int errnum, char *strerrbuf, size_t buflen)
  64 {
  65 #if defined(FRONTEND) && defined(ENABLE_THREAD_SAFETY) && defined(HAVE_STRERROR_R)
  66         /* reentrant strerror_r is available */
  67 #ifdef STRERROR_R_INT
  68         /* SUSv3 version */
  69         if (strerror_r(errnum, strerrbuf, buflen) == 0)
  70                 return strerrbuf;
  71         else
  72                 return "Unknown error";
  73 #else
  74         /* GNU libc */
  75         return strerror_r(errnum, strerrbuf, buflen);
  76 #endif
  77 #else
  78         /* no strerror_r() available, just use strerror */
  79         strlcpy(strerrbuf, strerror(errnum), buflen);
  80
  81         return strerrbuf;
  82 #endif
  83 }
  84
  85 /*
  86  * Wrapper around getpwuid() or getpwuid_r() to mimic POSIX getpwuid_r()
  87  * behaviour, if it is not available or required.
  88  */
  89 #ifndef WIN32
  90 int
  91 pqGetpwuid(uid_t uid, struct passwd * resultbuf, char *buffer,
  92                    size_t buflen, struct passwd ** result)
  93 {
  94 #if defined(FRONTEND) && defined(ENABLE_THREAD_SAFETY) && defined(HAVE_GETPWUID_R)
  95
  96 #ifdef GETPWUID_R_5ARG
  97         /* POSIX version */
  98         getpwuid_r(uid, resultbuf, buffer, buflen, result);
  99 #else
 100
 101         /*
 102          * Early POSIX draft of getpwuid_r() returns 'struct passwd *'.
 103          * getpwuid_r(uid, resultbuf, buffer, buflen)
 104          */
 105         *result = getpwuid_r(uid, resultbuf, buffer, buflen);
 106 #endif
 107 #else
 108
 109         /* no getpwuid_r() available, just use getpwuid() */
 110         *result = getpwuid(uid);
 111 #endif
 112
 113         return (*result == NULL) ? -1 : 0;
 114 }
 115 #endif
 116
 117 /*
 118  * Wrapper around gethostbyname() or gethostbyname_r() to mimic
 119  * POSIX gethostbyname_r() behaviour, if it is not available or required.
 120  * This function is called _only_ by our getaddinfo() portability function.
 121  */
 122 #ifndef HAVE_GETADDRINFO
 123 int
 124 pqGethostbyname(const char *name,
 125                                 struct hostent * resultbuf,
 126                                 char *buffer, size_t buflen,
 127                                 struct hostent ** result,
 128                                 int *herrno)
 129 {
 130 #if defined(FRONTEND) && defined(ENABLE_THREAD_SAFETY) && defined(HAVE_GETHOSTBYNAME_R)
 131
 132         /*
 133          * broken (well early POSIX draft) gethostbyname_r() which returns 'struct
 134          * hostent *'
 135          */
 136         *result = gethostbyname_r(name, resultbuf, buffer, buflen, herrno);
 137         return (*result == NULL) ? -1 : 0;
 138 #else
 139
 140         /* no gethostbyname_r(), just use gethostbyname() */
 141         *result = gethostbyname(name);
 142
 143         if (*result != NULL)
 144                 *herrno = h_errno;
 145
 146         if (*result != NULL)
 147                 return 0;
 148         else
 149                 return -1;
 150 #endif
 151 }
 152
 153 #endif