Add reference counter in CompressibleString

* remove stack searching to check if CompressibleString is in use
* add ref counter instead

Signed-off-by: HyukWoo Park <hyukwoo.park@samsung.com>

src/runtime/CompressibleString.cpp

@@ -47,6 +47,7 @@ CompressibleString::CompressibleString(VMInstance* instance)
     : String()
     , m_isOwnerMayFreed(false)
     , m_isCompressed(false)
+    , m_refCount(0)
     , m_vmInstance(instance)
     , m_lastUsedTickcount(fastTickCount())
 {
@@ -56,6 +57,7 @@ CompressibleString::CompressibleString(VMInstance* instance)
     v.push_back(this);
     GC_REGISTER_FINALIZER_NO_ORDER(this, [](void* obj, void*) {
         CompressibleString* self = (CompressibleString*)obj;
+        ASSERT(self->refCount() == 0);
         if (self->isCompressed()) {
             self->clearCompressedData();
         } else {
@@ -158,7 +160,8 @@ void CompressibleString::clearCompressedData()
 bool CompressibleString::compress()
 {
     ASSERT(!m_isCompressed);
-    if (UNLIKELY(!m_bufferData.length)) {
+    if (UNLIKELY(!m_bufferData.length || !!m_refCount)) {
+        ESCARGOT_LOG_INFO("Compression Failed due to string usage in stack\n");
         return false;
     }
 
@@ -188,23 +191,10 @@ void CompressibleString::decompress()
 constexpr static const size_t g_compressChunkSize = 1044465;
 static_assert(LZ4_COMPRESSBOUND(g_compressChunkSize) == 1024 * 1024, "");
 
-static ATTRIBUTE_NO_SANITIZE_ADDRESS bool testPointerExistsOnStack(size_t* start, size_t* end, const void* ptr)
-{
-    while (start != end) {
-        if (UNLIKELY(*start == (size_t)ptr)) {
-            // if there is reference on stack, we cannot compress string.
-            return true;
-        }
-        start++;
-    }
-
-    return false;
-}
-
 template <typename StringType>
 bool CompressibleString::compressWorker(void* callerSP)
 {
-    ASSERT(!m_isCompressed);
+    ASSERT(!m_isCompressed && !m_refCount);
     ASSERT(m_bufferData.length > 0);
 
 #if defined(STACK_GROWS_DOWN)
@@ -215,11 +205,6 @@ bool CompressibleString::compressWorker(void* callerSP)
     size_t* end = (size_t*)((size_t)callerSP & ~(sizeof(size_t) - 1));
 #endif
 
-    if (testPointerExistsOnStack(start, end, m_bufferData.buffer)) {
-        ESCARGOT_LOG_INFO("Compression Failed due to string usage in stack\n");
-        return false;
-    }
-
     size_t originByteLength = m_bufferData.length * sizeof(StringType);
     int lastBoundLength = 0;
     char* tempBuffer = nullptr;

src/runtime/CompressibleString.h

@@ -78,7 +78,8 @@ public:
         if (isCompressed()) {
             decompress();
         }
-        return StringBufferAccessData(m_bufferData.has8BitContent, m_bufferData.length, const_cast<void*>(m_bufferData.buffer));
+
+        return StringBufferAccessData(m_bufferData.has8BitContent, m_bufferData.length, const_cast<void*>(m_bufferData.buffer), &m_refCount);
     }
 
     bool isCompressed()
@@ -86,6 +87,11 @@ public:
         return m_isCompressed;
     }
 
+    size_t refCount()
+    {
+        return m_refCount;
+    }
+
     void* operator new(size_t);
     void* operator new[](size_t) = delete;
     void operator delete[](void*) = delete;
@@ -118,6 +124,7 @@ private:
 
     bool m_isOwnerMayFreed;
     bool m_isCompressed;
+    size_t m_refCount; // reference count representing the usage of this CompressibleString
     VMInstance* m_vmInstance;
     uint64_t m_lastUsedTickcount;
     typedef Vector<CompressedElement, GCUtil::gc_malloc_allocator<CompressedElement>> CompressedDataVector;

src/runtime/String.h

@@ -100,12 +100,27 @@ struct StringBufferAccessData {
     };
     void* extraData;
 
-    StringBufferAccessData(bool has8Bit, size_t len, void* buffer, void* extraDataKeepInStack = nullptr)
+    StringBufferAccessData(bool has8Bit, size_t len, void* buffer, void* extraDataToKeep = nullptr)
         : has8BitContent(has8Bit)
         , length(len)
         , buffer(buffer)
-        , extraData(extraDataKeepInStack)
+        , extraData(extraDataToKeep)
     {
+        if (extraData) {
+            // increase refCount in CompressibleString
+            size_t& count = *reinterpret_cast<size_t*>(extraData);
+            count++;
+        }
+    }
+
+    ~StringBufferAccessData()
+    {
+        if (extraData) {
+            // decrease refCount in CompressibleString
+            size_t& count = *reinterpret_cast<size_t*>(extraData);
+            ASSERT(count > 0);
+            count--;
+        }
     }
 
     char16_t uncheckedCharAtFor8Bit(size_t idx) const

src/runtime/StringView.h

@@ -139,9 +139,6 @@ protected:
         ASSERT(m_bufferData.hasSpecialImpl);
 
         StringBufferAccessData r = m_bufferData.bufferAsString->bufferAccessData();
-        // keep original buffer pointer in stack
-        // without this, compressible string can free this pointer
-        r.extraData = const_cast<void*>(r.buffer);
         r.length = m_bufferData.length;
         if (r.has8BitContent) {
             r.bufferAs8Bit += m_start;