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authorZack Weinberg <zackw@panix.com>2016-12-06 10:14:42 -0500
committerZack Weinberg <zackw@panix.com>2016-12-08 15:45:33 -0500
commitc03073774f915fe7841c2b551fe304544143470f (patch)
tree724d0dff62918aba70b4e4fc17c80f35f2e6eafa /NEWS
parent3d6bfcace17a479c2e006a33567af80e6070583f (diff)
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Make _REENTRANT and _THREAD_SAFE aliases for _POSIX_C_SOURCE=199506L.
For many years, the only effect of these macros has been to make
unistd.h declare getlogin_r.  _POSIX_C_SOURCE >= 199506L also causes
this function to be declared.  However, people who don't carefully
read all the headers might be confused into thinking they need to
define _REENTRANT for any threaded code (as was indeed the case a long
time ago).

Therefore, remove __USE_REENTRANT, and make _REENTRANT and _THREAD_SAFE
into synonyms for _POSIX_C_SOURCE=199506L.  This will only affect
programs that don't select a higher conformance level some other way.
For instance, -std=c89 -D_REENTRANT will see a change in visible
declarations, but -std=c99 -D_POSIX_C_SOURCE=200809L -D_REENTRANT won't,
and -D_REENTRANT all by itself also won't, because _DEFAULT_SOURCE
implies _POSIX_C_SOURCE > 199506.

	* include/features.h: Remove __USE_REENTRANT.  Treat _REENTRANT
	and _THREAD_SAFE the same as _POSIX_C_SOURCE=199506L, if a higher
	POSIX conformance level has not been selected by other macros.
	* NEWS, manual/creature.texi: Document this change.

	* posix/unistd.h, posix/bits/unistd.h: Don't check __USE_REENTRANT.
	* include/libc-symbols.h: Don't define _REENTRANT.
	* scripts/check-installed-headers.sh: Don't undefine _REENTRANT.
Diffstat (limited to 'NEWS')
-rw-r--r--NEWS13
1 files changed, 13 insertions, 0 deletions
diff --git a/NEWS b/NEWS
index 922a5004ff..4fe8886e83 100644
--- a/NEWS
+++ b/NEWS
@@ -22,6 +22,19 @@ Version 2.25
   from that TS.  Note that most features from that TS are not supported by
   the GNU C Library.
 
+* The nonstandard feature selection macros _REENTRANT and _THREAD_SAFE are
+  now treated as compatibility synonyms for _POSIX_C_SOURCE=199506L.
+  Since the GNU C Library defaults to a much newer revision of POSIX, this
+  will only affect programs that specifically request an old conformance
+  mode.  For instance, a program compiled with -std=c89 -D_REENTRANT will
+  see a change in the visible declarations, but a program compiled with
+  just -D_REENTRANT, or -std=c99 -D_POSIX_C_SOURCE=200809L -D_REENTRANT,
+  will not.
+
+  Some C libraries once required _REENTRANT and/or _THREAD_SAFE to be
+  defined by all multithreaded code, but glibc has not required this for
+  many years.
+
 * The inclusion of <sys/sysmacros.h> by <sys/types.h> is deprecated.  This
   means that in a future release, the macros “major”, “minor”, and “makedev”
   will only be available from <sys/sysmacros.h>.