From 6f786378658ecf367f3018a7a638d69957d6cdb9 Mon Sep 17 00:00:00 2001
From: khizmax <khizmax@gmail.com>
Date: Mon, 14 Aug 2017 13:31:59 +0300
Subject: [PATCH] issue #82: added doc about DCAS support

---
 cds/details/defs.h |  8 ++++++++
 cds/gc/dhp.h       |  9 +++++++++
 readme.md          | 10 ++++++++++
 3 files changed, 27 insertions(+)

diff --git a/cds/details/defs.h b/cds/details/defs.h
index 594c8229..6c737efa 100644
--- a/cds/details/defs.h
+++ b/cds/details/defs.h
@@ -169,6 +169,14 @@
    - \p boost.thread (thread-loal storage support), boost.system
    - \p google-test
 
+   Some parts of libcds may depend on DCAS (double-width compare-and-swap) atomic primitive if
+   the target architecture supports it. For x86, cmake build script enables -mcx16 compiler flag that
+   switches DCAS support on. You may manually disable DCAS support with the following  command line flags
+   in GCC/clang (for MS VC++ compiler DCAS is not supported):
+   - \p -DCDS_DISABLE_128BIT_ATOMIC - for 64bit build
+   - \p -DCDS_DISABLE_64BIT_ATOMIC - for 32bit build
+   @warning All your projects AND libcds MUST be compiled with the same flags - either with DCAS support or without it.
+
    \par Windows build
 
    Prerequisites: for building <b>cds</b> library and test suite you need:
diff --git a/cds/gc/dhp.h b/cds/gc/dhp.h
index 01ff54c6..3752a083 100644
--- a/cds/gc/dhp.h
+++ b/cds/gc/dhp.h
@@ -685,6 +685,15 @@ namespace cds { namespace gc {
 
         %DHP is an adaptive variant of classic \p cds::gc::HP, see @ref cds_garbage_collectors_comparison "Compare HP implementation"
 
+        @note: Internally, %DHP depends on free-list implementation. There are
+        DCAS-based free-list \p cds::intrusive::TaggedFreeList and more complicated CAS-based free-list
+        \p cds::intrusive::FreeList. For x86 architecture and GCC/clang, libcds selects appropriate free-list 
+        based on \p -mcx16 compiler flag. You may manually disable DCAS support specifying
+        \p -DCDS_DISABLE_128BIT_ATOMIC for 64bit build or \p -DCDS_DISABLE_64BIT_ATOMIC for 32bit build
+        in compiler command line. All your projects and libcds MUST be compiled with the same flags -
+        either with DCAS support or without it.
+        For MS VC++ compiler DCAS is not supported.
+
         See \ref cds_how_to_use "How to use" section for details how to apply SMR.
     */
     class DHP
diff --git a/readme.md b/readme.md
index 54c6f15b..539796d5 100644
--- a/readme.md
+++ b/readme.md
@@ -46,6 +46,16 @@ Evolution of libcds (Gource visualization by Landon Wilkins): https://www.youtub
    - *nix: [use CMake](build/cmake/readme.md)
    - Windows: use MS Visual C++ 2015 project
 
+Some parts of libcds may depend on DCAS (double-width compare-and-swap) atomic primitive if
+the target architecture supports it. For x86, cmake build script enables `-mcx16` compiler flag that
+switches DCAS support on. You may manually disable DCAS support with the following command line flags
+in GCC/clang (for MS VC++ compiler DCAS is not supported):
+  - `-DCDS_DISABLE_128BIT_ATOMIC` - for 64bit build
+  - `-DCDS_DISABLE_64BIT_ATOMIC` - for 32bit build
+
+**All your projects AND libcds MUST be compiled with the same flags - either with DCAS support or without it.**
+   
+   
 **Pull request requirements**
 - Pull-request to *master* branch will be unconditionally rejected
 - *integration* branch is intended for pull-request. Usually, *integration* branch is the same as *master*
-- 
2.34.1