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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 /manual
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 'manual')
-rw-r--r--manual/creature.texi14
1 files changed, 5 insertions, 9 deletions
diff --git a/manual/creature.texi b/manual/creature.texi
index 257f8718b1..5048886292 100644
--- a/manual/creature.texi
+++ b/manual/creature.texi
@@ -219,15 +219,11 @@ cause them to be disabled.
 @comment GNU
 @defvr Macro _REENTRANT
 @defvrx Macro _THREAD_SAFE
-If you define one of these macros, reentrant versions of several functions get
-declared.  Some of the functions are specified in POSIX.1c but many others
-are only available on a few other systems or are unique to @theglibc{}.
-The problem is the delay in the standardization of the thread safe C library
-interface.
-
-Unlike on some other systems, no special version of the C library must be
-used for linking.  There is only one version but while compiling this
-it must have been specified to compile as thread safe.
+These macros are obsolete.  They have the same effect as defining
+@code{_POSIX_C_SOURCE} with the value @code{199506L}.
+
+Some very old C libraries required one of these macros to be defined
+for basic functionality (e.g.@: @code{getchar}) to be thread-safe.
 @end defvr
 
 We recommend you use @code{_GNU_SOURCE} in new programs.  If you don't