WIP: Introduce CompressibleString

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

+// Copyright 2015 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 "config.h"
+#include "platform/text/CompressibleString.h"
+
+// TODO: This seems illegal: Fix checkdeps?
+#include "components/compression/compression_utils.h"
+#include "wtf/Assertions.h"
+#include "wtf/Partitions.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;
+    }
+
+    CompressibleStringImpl* add(CompressibleStringImpl* string)
+    {
+        string->ref();
+        return *m_table.add(string).storedValue;
+    }
+
+    HashSet<CompressibleStringImpl*>& table()
+    {
+        return m_table;
+    }
+
+    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->compress();
+        }
+    }
+
+private:
+    CompressibleStringTable() { }
+
+    static void destroy(CompressibleStringTable* table)
+    {
+        HashSet<CompressibleStringImpl*>::iterator end = table->m_table.end();
+        for (HashSet<CompressibleStringImpl*>::iterator iter = table->m_table.begin(); iter != end; ++iter)
+            (*iter)->deref();
+        delete table;
+    }
+
+    HashSet<CompressibleStringImpl*> m_table;
+};
+
+static inline CompressibleStringTable& compressibleStringTable()
+{
+    // Once possible we should make this non-lazy (constructed in WTFThreadData's constructor).
+    WTFThreadData& data = wtfThreadData();
+    CompressibleStringTable* table = data.compressibleStringTable();
+    if (UNLIKELY(!table))
+        table = CompressibleStringTable::create(data);
+    return *table;
+}
+
+void CompressibleStringImpl::purgeMemory()
+{
+    compressibleStringTable().compressAll();

[haraken, 2015/11/26 11:50:03]

For now this is okay, but compressing the table of this thread is not enough. We
need to compress tables of all threads.

[hajimehoshi, 2015/11/27 11:03:58]

Commented.

+}
+
+CompressibleStringImpl::CompressibleStringImpl(PassRefPtr<StringImpl> impl)
+    : m_impl(impl)
+    , m_compressedData(nullptr)
+    , m_originalLength(m_impl->length())
+    , m_is8Bit(m_impl->is8Bit())

[haraken, 2015/11/26 11:50:03]

You need to check !m_impl. If it's guaranteed to be non-null, you can add
ASSERT(m_impl).

[hajimehoshi, 2015/11/27 11:03:58]

Done.

+{
+}
+
+unsigned CompressibleStringImpl::contentSizeInBytes() const
+{
+    if (is8Bit())
+        return m_originalLength;
+    return m_originalLength * 2;
+}
+
+String CompressibleStringImpl::toString()
+{
+    if (UNLIKELY(isCompressed()))
+        uncompress();
+    return m_impl.get();
+}
+
+const LChar* CompressibleStringImpl::characters8()
+{
+    return toString().characters8();
+}
+
+const UChar* CompressibleStringImpl::characters16()
+{
+    return toString().characters16();
+}
+
+void CompressibleStringImpl::compress()
+{
+    ASSERT(m_impl);
+    ASSERT(!isCompressed());
+
+    // TODO(hajimehoshi): Now components offers funcitons accepting only
+    // std::strings. This is not efficient. We should offer char* version.
+    std::string in, out;
+    if (m_is8Bit)
+        in = std::string(reinterpret_cast<const char*>(m_impl->characters8()), contentSizeInBytes());
+    else
+        in = std::string(reinterpret_cast<const char*>(m_impl->characters16()), contentSizeInBytes());
+    compression::GzipCompress(in, &out);
+
+    m_impl = nullptr;
+    m_compressedData = SharedBuffer::create(out.c_str(), out.size());
+}
+
+void CompressibleStringImpl::uncompress()
+{
+    ASSERT(m_compressedData);
+    ASSERT(!m_impl);
+
+    std::string in(m_compressedData->data(), m_compressedData->size());
+    std::string out;
+    compression::GzipUncompress(in, &out);
+
+    if (m_is8Bit) {
+        LChar* data = nullptr;
+        m_impl = StringImpl::createUninitialized(out.size() / sizeof(LChar), data);
+        memcpy(data, out.c_str(), out.size());
+    } else {
+        UChar* data = nullptr;
+        m_impl = StringImpl::createUninitialized(out.size() / sizeof(UChar), data);
+        memcpy(data, out.c_str(), out.size());
+    }
+
+    m_compressedData = nullptr;
+    ASSERT(m_is8Bit == m_impl->is8Bit());
+    ASSERT(m_originalLength == m_impl->length());
+}
+
+CompressibleString::CompressibleString()
+    : m_impl(nullptr)
+{
+}
+
+CompressibleString::CompressibleString(const CompressibleString& rhs)
+    : m_impl(rhs.m_impl)
+{
+}
+
+CompressibleString::CompressibleString(PassRefPtr<StringImpl> impl)
+    : m_impl(impl ? adoptRef(new CompressibleStringImpl(impl)) : nullptr)
+{
+    if (m_impl && contentSizeInBytes() > 100000)
+        compressibleStringTable().add(m_impl.get());

[haraken, 2015/11/26 11:50:03]

Who removes the compressible string from the table?

- You need to add the CompressibleStringImpl to the table when the
CompressibleStringImpl is constructed (not when the CompressibleString is
constructed).

- You need to remove the CompressibleStringImpl to the table when the
CompressibleStringImpl is destructed (not when the CompressibleString is
destructed).

- The table should not call ref/deref. If the table adds a reference to the
CompressibleStringImpl, the CompressibleStringImpl never gets destructed until
the table gets destructed (i.e., until the Blink shuts down). In the current
implementation, all CompressibleStringImpls will leak.

Please create a small test code and confirm that:

- compression/decomrepssion is working as expected; and
- the CompressibleStrings are not leaking.

[hajimehoshi, 2015/11/27 11:03:58]

Done. (Skipped checking leaking as we talked offline.)

+}
+
+void CompressibleString::compress() const
+{
+    m_impl->compress();
+}
+
+void CompressibleString::uncompress() const
+{
+    m_impl->uncompress();
+}
+
+} // namespace blink