From d6ec7f0e92d39ae461b84283be922d28b819c62c Mon Sep 17 00:00:00 2001
From: "adam.b" <adam.b@samsung.com>
Date: Fri, 27 Nov 2020 11:58:52 +0000
Subject: [PATCH] Reference counting made atomic

The ARM assembled code and GCC builtin call have been removed and replace
with std::atomic<>.

Change-Id: I86299c36b82fbc7263e5a463da1475179cb20a04
---
 dali/public-api/object/ref-object.cpp | 104 +---------------------------------
 dali/public-api/object/ref-object.h   |   3 +-
 2 files changed, 4 insertions(+), 103 deletions(-)

diff --git a/dali/public-api/object/ref-object.cpp b/dali/public-api/object/ref-object.cpp
index f27065d..c3fd11f 100644
--- a/dali/public-api/object/ref-object.cpp
+++ b/dali/public-api/object/ref-object.cpp
@@ -55,115 +55,15 @@ RefObject& RefObject::operator=(const RefObject&)
 
 void RefObject::Reference()
 {
-  // clang-format off
-  // The inline assembly below was tested on an ARMv8 64 bit platform on
-  // 2015-02-06 and found to run in 11.8 nanoseconds, whereas
-  // __sync_add_and_fetch( address, 1 ) required 18.8 nanoseconds.
-  // Including the assembly here produced one fewer assembly instruction than if
-  // it was wrapped in a function and inlined here by the compiler.
-#if defined __aarch64__
-
-  asm volatile(
-  "1:\tldxr  w1, %[address] \n\t"
-      "add   w1, w1, %[one] \n\t"
-      "stxr  w2,  w1, %[address] \n\t"
-      "cbnz  w2,  1b \n\t"
-      // Outputs:
-    : // Q = A memory address with no offset
-      // ( https://gcc.gnu.org/onlinedocs/gcc/Machine-Constraints.html#Machine-Constraints )
-      [address] "+Q" (mCount)
-      // Inputs:
-    : [one] "Ir" (1)
-      // Clobbers: (explicitly clobber w1 register to hold the loaded value and
-      // register w2 to hold success/fail):
-    : "w1", "w2"
-  );
-
-  // 32 bit ARMv7 version of above:
-  // Better than the code emitted by GCC for __sync_add_and_fetch(), as that
-  // includes two dmb memory barrier instructions: one before and one after the
-  // loop.
-#elif defined __arm__
-
-  asm volatile(
-    "1:\tldrex r1, %[address] \n\t"
-        "add   r1, r1, %[one] \n\t"
-        "strex r2,  r1, %[address] \n\t"
-        "teq   r2,  %[zero] \n\t"
-        "bne   1b \n\t"
-        // Outputs:
-      : [address] "+Q" (mCount)
-        // Inputs:
-      : [zero] "Ir" (0),
-        [one]  "Ir" (1)
-        // Clobbers: (modified registers):
-      : "r1", "r2"
-    );
-
-#else
-
-  // gcc > 4.1 builtin atomic add and fetch:
-  __sync_add_and_fetch( &mCount, 1 );
-
-#endif
-  // clang-format on
+  ++mCount;
 }
 
 void RefObject::Unreference()
 {
-  // clang-format off
-
-  // The output register:
-  int32_t newValue;
-
-#if defined __aarch64__
-
-  asm volatile(
-  "1:\tldxr   %w[newValue], %[address] \n\t"
-      "sub   %w[newValue], %w[newValue], %[one] \n\t"
-      "stxr  w2,  %w[newValue], %[address] \n\t"
-      "cbnz  w2,  1b \n\t"
-    // Outputs:
-  : [newValue] "=&r" (newValue),
-    // Q = A memory address with no offset
-    // ( https://gcc.gnu.org/onlinedocs/gcc/Machine-Constraints.html#Machine-Constraints )
-    [address] "+Q" (mCount)
-    // Inputs:
-  : [one]  "Ir" (1)
-    // Clobbered: I.e., stuff that is modified.
-  : "w2"
-  );
-
-#elif defined __arm__
-
-  asm volatile(
-  "1:\tldrex %[newValue], %[address] \n\t"
-      "sub   %[newValue], %[newValue], %[one] \n\t"
-      "strex r2,  %[newValue], %[address] \n\t"
-      "teq   r2, %[zero] \n\t"
-      "bne   1b \n\t"
-    // Outputs:
-  : [newValue] "=&r" (newValue),
-    [address] "+Q" (mCount)
-    // Inputs:
-    : [zero] "Ir" (0),
-      [one]  "Ir" (1)
-    // Clobbered:
-  : "r2"
-  );
-
-#else
-
-  // gcc > 4.1 builtin atomic subtract and fetch (--mCount; return mCount)
-  newValue = __sync_sub_and_fetch( &mCount, 1 );
-
-#endif
-
-  if( newValue == 0 )
+  if( (--mCount) == 0 )
   {
     delete this;
   }
-  // clang-format on
 }
 
 uint32_t RefObject::ReferenceCount()
diff --git a/dali/public-api/object/ref-object.h b/dali/public-api/object/ref-object.h
index 56e0018..30c26b7 100644
--- a/dali/public-api/object/ref-object.h
+++ b/dali/public-api/object/ref-object.h
@@ -20,6 +20,7 @@
 
 // EXTERNAL INCLUDES
 #include <cstdint> // uint32_t
+#include <atomic>
 
 // INTERNAL INCLUDES
 #include <dali/public-api/common/dali-common.h>
@@ -101,7 +102,7 @@ protected:
   RefObject& operator=(const RefObject& rhs);
 
 private:
-  volatile uint32_t mCount; ///< Reference count
+  std::atomic_uint32_t mCount {0u}; ///< Reference count
 };
 
 /**
-- 
2.7.4