1 files changed, 62 insertions, 0 deletions
diff --git a/sysdeps/unix/sysv/linux/single-thread.h b/sysdeps/unix/sysv/linux/single-thread.h
new file mode 100644
index 0000000000..2c972f37b3
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/single-thread.h
@@ -0,0 +1,62 @@
+/* Single thread optimization, Linux version.
+   Copyright (C) 2019 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#ifndef _SINGLE_THREAD_H
+#define _SINGLE_THREAD_H
+
+/* The default way to check if the process is single thread is by using the
+   pthread_t 'multiple_threads' field.  However, for some architectures it is
+   faster to either use an extra field on TCB or global variables (the TCB
+   field is also used on x86 for some single-thread atomic optimizations).
+
+   The ABI might define SINGLE_THREAD_BY_GLOBAL to enable the single thread
+   check to use global variables instead of the pthread_t field.  */
+
+#ifdef SINGLE_THREAD_BY_GLOBAL
+# if IS_IN (libc)
+extern int __libc_multiple_threads;
+#  define SINGLE_THREAD_P \
+  __glibc_likely (__libc_multiple_threads == 0)
+# elif IS_IN (libpthread)
+extern int __pthread_multiple_threads;
+#  define SINGLE_THREAD_P \
+  __glibc_likely (__pthread_multiple_threads == 0)
+# elif IS_IN (librt)
+#   define SINGLE_THREAD_P					\
+  __glibc_likely (THREAD_GETMEM (THREAD_SELF,			\
+				 header.multiple_threads) == 0)
+# else
+/* For rtld, et cetera.  */
+#  define SINGLE_THREAD_P (1)
+# endif
+#else /* SINGLE_THREAD_BY_GLOBAL  */
+# if IS_IN (libc) || IS_IN (libpthread) || IS_IN (librt)
+#   define SINGLE_THREAD_P					\
+  __glibc_likely (THREAD_GETMEM (THREAD_SELF,			\
+				 header.multiple_threads) == 0)
+# else
+/* For rtld, et cetera.  */
+#  define SINGLE_THREAD_P (1)
+# endif
+#endif /* SINGLE_THREAD_BY_GLOBAL  */
+
+#define RTLD_SINGLE_THREAD_P \
+  __glibc_likely (THREAD_GETMEM (THREAD_SELF, \
+				 header.multiple_threads) == 0)
+
+#endif /* _SINGLE_THREAD_H  */