Experimental CompressibleString UMA

third_party/WebKit/Source/platform/text/CompressibleString.cpp

Index: third_party/WebKit/Source/platform/text/CompressibleString.cpp
diff --git a/third_party/WebKit/Source/platform/text/CompressibleString.cpp b/third_party/WebKit/Source/platform/text/CompressibleString.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..23866efcebfc8fda58b72fcb1e0546dd710ebc79
--- /dev/null
+++ b/third_party/WebKit/Source/platform/text/CompressibleString.cpp
@@ -0,0 +1,140 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "platform/text/CompressibleString.h"
+
+#include "public/platform/Platform.h"
+#include "wtf/Assertions.h"
+#include "wtf/WTFThreadData.h"
+#include "wtf/text/WTFString.h"
+
+namespace blink {
+
+class CompressibleStringTable {
+    WTF_MAKE_NONCOPYABLE(CompressibleStringTable);
+public:
+    static CompressibleStringTable* create(WTFThreadData& data)
+    {
+        data.m_compressibleStringTable = new CompressibleStringTable;
+        data.m_compressibleStringTableDestructor = CompressibleStringTable::destroy;
+        return data.m_compressibleStringTable;
+    }
+
+    void add(CompressibleStringImpl* string)
+    {
+        ASSERT(!m_table.contains(string));
+        m_table.add(string);
+    }
+
+    bool contains(CompressibleStringImpl* string) const
+    {
+        return m_table.contains(string);
+    }
+
+    void remove(CompressibleStringImpl* string)
+    {
+        ASSERT(m_table.contains(string));
+        m_table.remove(string);
+    }
+
+    void compressAll()
+    {
+        HashSet<CompressibleStringImpl*>::iterator end = m_table.end();
+        for (HashSet<CompressibleStringImpl*>::iterator iter = m_table.begin(); iter != end; ++iter) {
+            CompressibleStringImpl* string = *iter;
+            if (!string->isCompressed())
+                string->compressString();
+        }
+    }
+
+private:
+    CompressibleStringTable() { }
+
+    static void destroy(CompressibleStringTable* table)
+    {
+        delete table;
+    }
+
+    HashSet<CompressibleStringImpl*> m_table;
+};
+
+void initializeCompressibleStringTable()
+{
+    WTFThreadData& data = wtfThreadData();
+    ASSERT(!data.compressibleStringTable());
+    CompressibleStringTable::create(data);
+}
+
+static inline CompressibleStringTable& compressibleStringTable()
+{
+    WTFThreadData& data = wtfThreadData();
+    ASSERT(data.compressibleStringTable());
+    return *data.compressibleStringTable();
+}
+
+static const unsigned CompressibleStringImplSizeThrehold = 100000;
+
+bool CompressibleStringImpl::s_isPageBackground = false;
+
+void CompressibleStringImpl::compressAll()
+{
+    compressibleStringTable().compressAll();
+}
+
+void CompressibleStringImpl::setPageBackground(bool isPageBackground)
+{
+    s_isPageBackground = isPageBackground;
+}
+
+CompressibleStringImpl::CompressibleStringImpl(PassRefPtr<StringImpl> impl)
+    : m_string(impl)
+    , m_isCompressed(false)
+{
+    ASSERT(impl);
+    if (originalContentSizeInBytes() > CompressibleStringImplSizeThrehold)
+        compressibleStringTable().add(this);
+}
+
+CompressibleStringImpl::~CompressibleStringImpl()
+{
+    if (originalContentSizeInBytes() > CompressibleStringImplSizeThrehold) {
+        compressibleStringTable().remove(this);
+    }
+}
+
+enum {
+    StringWasCompressedInBackgroundTab,
+    StringWasDecompressedInBackgroundTab,
+    StringWasDecompressedInForegroundTab,
+};
+
+static const char* histogramName()
+{
+    return "Memory.CompressibleStringCount";
+}
+
+// compressString does nothing but collect UMA so far.
+// TODO(hajimehoshi): Implement this.
+void CompressibleStringImpl::compressString()
+{
+    ASSERT(s_isPageBackground);
+    Platform::current()->histogramCustomCounts(histogramName(), StringWasCompressedInBackgroundTab, 0, 10000, 50);

[Ilya Sherman, 2016/01/20 01:42:38]

nit: I'd recommend have a wrapper method for emitting to this histogram, rather
than needing to repeat the constant arguments at each call site.

[Ilya Sherman, 2016/01/20 01:42:38]

Hmm, why did you choose this histogram representation?  You are currently
allocating 50 buckets, logarithmically sized, to record values up to 10,000 in
magnitude.  You're logging three distinct values to this histogram.  Please use
an enumerated histogram for this purpose.  Also, please take a moment to think
about what led you to implement this as you did, and possibly update some
documentation somewhere to be clearer.

[hajimehoshi, 2016/01/20 10:17:17]

This is because I misunderstood the usage of the API... Done.
Updated the description of this CL.

+    ASSERT(!isCompressed());
+    m_isCompressed = true;
+}
+
+// decompressString does nothing but collect UMA so far.
+// TODO(hajimehoshi): Implement this.
+void CompressibleStringImpl::decompressString()
+{
+    if (s_isPageBackground)
+        Platform::current()->histogramCustomCounts(histogramName(), StringWasDecompressedInBackgroundTab, 0, 10000, 50);
+    else
+        Platform::current()->histogramCustomCounts(histogramName(), StringWasDecompressedInForegroundTab, 0, 10000, 50);
+
+    ASSERT(isCompressed());
+    m_isCompressed = false;
+}
+
+} // namespace blink