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thread.c
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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) 1996-2017, 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  * 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 that function is not available or required.
86  *
87  * Per POSIX, the possible cases are:
88  * success: returns zero, *result is non-NULL
89  * uid not found: returns zero, *result is NULL
90  * error during lookup: returns an errno code, *result is NULL
91  * (caller should *not* assume that the errno variable is set)
92  */
93 #ifndef WIN32
94 int
95 pqGetpwuid(uid_t uid, struct passwd *resultbuf, char *buffer,
96  size_t buflen, struct passwd **result)
97 {
98 #if defined(FRONTEND) && defined(ENABLE_THREAD_SAFETY) && defined(HAVE_GETPWUID_R)
99  return getpwuid_r(uid, resultbuf, buffer, buflen, result);
100 #else
101  /* no getpwuid_r() available, just use getpwuid() */
102  errno = 0;
103  *result = getpwuid(uid);
104  /* paranoia: ensure we return zero on success */
105  return (*result == NULL) ? errno : 0;
106 #endif
107 }
108 #endif
109 
110 /*
111  * Wrapper around gethostbyname() or gethostbyname_r() to mimic
112  * POSIX gethostbyname_r() behaviour, if it is not available or required.
113  * This function is called _only_ by our getaddinfo() portability function.
114  */
115 #ifndef HAVE_GETADDRINFO
116 int
117 pqGethostbyname(const char *name,
118  struct hostent *resultbuf,
119  char *buffer, size_t buflen,
120  struct hostent **result,
121  int *herrno)
122 {
123 #if defined(FRONTEND) && defined(ENABLE_THREAD_SAFETY) && defined(HAVE_GETHOSTBYNAME_R)
124 
125  /*
126  * broken (well early POSIX draft) gethostbyname_r() which returns 'struct
127  * hostent *'
128  */
129  *result = gethostbyname_r(name, resultbuf, buffer, buflen, herrno);
130  return (*result == NULL) ? -1 : 0;
131 #else
132 
133  /* no gethostbyname_r(), just use gethostbyname() */
134  *result = gethostbyname(name);
135 
136  if (*result != NULL)
137  *herrno = h_errno;
138 
139  if (*result != NULL)
140  return 0;
141  else
142  return -1;
143 #endif
144 }
145 
146 #endif
int pqGethostbyname(const char *name, struct hostent *resultbuf, char *buffer, size_t buflen, struct hostent **result, int *herrno)
Definition: thread.c:117
int pqGetpwuid(uid_t uid, struct passwd *resultbuf, char *buffer, size_t buflen, struct passwd **result)
Definition: thread.c:95
char * pqStrerror(int errnum, char *strerrbuf, size_t buflen)
Definition: thread.c:61
size_t strlcpy(char *dst, const char *src, size_t siz)
Definition: strlcpy.c:45
WalTimeSample buffer[LAG_TRACKER_BUFFER_SIZE]
Definition: walsender.c:214
int uid_t
Definition: win32_port.h:241
const char * name
Definition: encode.c:521
const char * strerror(int errnum)
Definition: strerror.c:19