Make support for thread-unsafe C functions optional.

One of the aspects of CloudABI is that it aims to help you write code
that is thread-safe out of the box. This is very important if you want
to write libraries that are easy to reuse. For CloudABI we decided to
not provide the thread-unsafe functions. So far this is working out
pretty well, as thread-unsafety issues are detected really early on.

The following patch adds a knob to libc++,
_LIBCPP_HAS_NO_THREAD_UNSAFE_C_FUNCTIONS, that can be set to disable
thread-unsafe functions that can easily be avoided in practice. The
following functions are not thread-safe:

- <clocale>: locale handles should be preferred over setlocale().
- <cstdlib>: mbrlen(), mbrtowc() and wcrtomb() should be preferred over
  their non-restartable counterparts.
- <ctime>: asctime(), ctime(), gmtime() and localtime() are not
  thread-safe. The first two are also deprecated by POSIX.

Differential Revision:	http://reviews.llvm.org/D8703
Reviewed by:	marshall

llvm-svn: 240527

5 files changed, 14 insertions, 0 deletions

diff --git a/libcxx/include/__config b/libcxx/include/__config
index adf11d3cc4a..62efbf80aa1 100644
--- a/libcxx/include/__config
+++ b/libcxx/include/__config
@@ -766,4 +766,10 @@ extern "C" void __sanitizer_annotate_contiguous_container(
 #define _LIBCPP_PROVIDES_DEFAULT_RUNE_TABLE
 #endif
 
+// Thread-unsafe functions such as strtok(), mbtowc() and localtime()
+// are not available.
+#ifdef __CloudABI__
+#define _LIBCPP_HAS_NO_THREAD_UNSAFE_C_FUNCTIONS
+#endif
+
 #endif  // _LIBCPP_CONFIG
diff --git a/libcxx/include/clocale b/libcxx/include/clocale
index f8b8f0dd34b..05fa9c6edda 100644
--- a/libcxx/include/clocale
+++ b/libcxx/include/clocale
@@ -45,7 +45,9 @@ lconv* localeconv();
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 using ::lconv;
+#ifndef _LIBCPP_HAS_NO_THREAD_UNSAFE_C_FUNCTIONS
 using ::setlocale;
+#endif
 using ::localeconv;
 
 _LIBCPP_END_NAMESPACE_STD
diff --git a/libcxx/include/cstdlib b/libcxx/include/cstdlib
index 298040e3f49..55e15c82192 100644
--- a/libcxx/include/cstdlib
+++ b/libcxx/include/cstdlib
@@ -147,9 +147,11 @@ using ::ldiv;
 #undef lldiv
 using ::lldiv;
 #endif // _LIBCPP_HAS_NO_LONG_LONG
+#ifndef _LIBCPP_HAS_NO_THREAD_UNSAFE_C_FUNCTIONS
 using ::mblen;
 using ::mbtowc;
 using ::wctomb;
+#endif
 using ::mbstowcs;
 using ::wcstombs;
 #ifdef _LIBCPP_HAS_QUICK_EXIT
diff --git a/libcxx/include/cstring b/libcxx/include/cstring
index 21c9155cd4d..d60b9923c6c 100644
--- a/libcxx/include/cstring
+++ b/libcxx/include/cstring
@@ -102,7 +102,9 @@ inline _LIBCPP_INLINE_VISIBILITY       void* memchr(      void* __s, int __c, si
 inline _LIBCPP_INLINE_VISIBILITY       char* strstr(      char* __s1, const char* __s2) {return ::strstr(__s1, __s2);}
 #endif
 
+#ifndef _LIBCPP_HAS_NO_THREAD_UNSAFE_C_FUNCTIONS
 using ::strtok;
+#endif
 using ::memset;
 using ::strerror;
 using ::strlen;
diff --git a/libcxx/include/ctime b/libcxx/include/ctime
index fc4eb26f543..da9e3290bbb 100644
--- a/libcxx/include/ctime
+++ b/libcxx/include/ctime
@@ -61,10 +61,12 @@ using ::clock;
 using ::difftime;
 using ::mktime;
 using ::time;
+#ifndef _LIBCPP_HAS_NO_THREAD_UNSAFE_C_FUNCTIONS
 using ::asctime;
 using ::ctime;
 using ::gmtime;
 using ::localtime;
+#endif
 using ::strftime;
 
 _LIBCPP_END_NAMESPACE_STD