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) 1996-2021, PostgreSQL Global Development Group
   9  *
  10  * src/port/thread.c
  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
  52
  53 /*
  54  * Wrapper around getpwuid() or getpwuid_r() to mimic POSIX getpwuid_r()
  55  * behaviour, if that function is not available or required.
  56  *
  57  * Per POSIX, the possible cases are:
  58  * success: returns zero, *result is non-NULL
  59  * uid not found: returns zero, *result is NULL
  60  * error during lookup: returns an errno code, *result is NULL
  61  * (caller should *not* assume that the errno variable is set)
  62  */
  63 #ifndef WIN32
  64 int
  65 pqGetpwuid(uid_t uid, struct passwd *resultbuf, char *buffer,
  66                    size_t buflen, struct passwd **result)
  67 {
  68 #if defined(FRONTEND) && defined(ENABLE_THREAD_SAFETY) && defined(HAVE_GETPWUID_R)
  69         return getpwuid_r(uid, resultbuf, buffer, buflen, result);
  70 #else
  71         /* no getpwuid_r() available, just use getpwuid() */
  72         errno = 0;
  73         *result = getpwuid(uid);
  74         /* paranoia: ensure we return zero on success */
  75         return (*result == NULL) ? errno : 0;
  76 #endif
  77 }
  78 #endif
  79
  80 /*
  81  * Wrapper around gethostbyname() or gethostbyname_r() to mimic
  82  * POSIX gethostbyname_r() behaviour, if it is not available or required.
  83  * This function is called _only_ by our getaddrinfo() portability function.
  84  */
  85 #ifndef HAVE_GETADDRINFO
  86 int
  87 pqGethostbyname(const char *name,
  88                                 struct hostent *resultbuf,
  89                                 char *buffer, size_t buflen,
  90                                 struct hostent **result,
  91                                 int *herrno)
  92 {
  93 #if defined(FRONTEND) && defined(ENABLE_THREAD_SAFETY) && defined(HAVE_GETHOSTBYNAME_R)
  94
  95         /*
  96          * broken (well early POSIX draft) gethostbyname_r() which returns 'struct
  97          * hostent *'
  98          */
  99         *result = gethostbyname_r(name, resultbuf, buffer, buflen, herrno);
 100         return (*result == NULL) ? -1 : 0;
 101 #else
 102
 103         /* no gethostbyname_r(), just use gethostbyname() */
 104         *result = gethostbyname(name);
 105
 106         if (*result != NULL)
 107                 *herrno = h_errno;
 108
 109         if (*result != NULL)
 110                 return 0;
 111         else
 112                 return -1;
 113 #endif
 114 }
 115
 116 #endif