AK: Add FlyString, a simple flyweight string class

FlyString is a flyweight string class that wraps a RefPtr<StringImpl> known to be unique among the set of FlyStrings. The class is very unoptimized at the moment. When to use FlyString: - When you want O(1) string comparison - When you want to deduplicate a lot of identical strings When not to use FlyString: - For strings that don't need either of the above features - For strings that are likely to be unique
lanmonster · Mar 22, 2020 · 4f72f6b · 4f72f6b
1 parent 0395b25
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Showing 15 changed files with 232 additions and 28 deletions.
diff --git a/AK/FlyString.cpp b/AK/FlyString.cpp
@@ -0,0 +1,91 @@
+/*
+ * Copyright (c) 2020, Andreas Kling <[email protected]>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ * list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ * this list of conditions and the following disclaimer in the documentation
+ * and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <AK/FlyString.h>
+#include <AK/HashTable.h>
+#include <AK/String.h>
+#include <AK/StringUtils.h>
+
+namespace AK {
+
+struct FlyStringImplTraits : public AK::Traits<StringImpl*> {
+ static unsigned hash(const StringImpl* s) { return s ? s->hash() : 0; }
+ static bool equals(const StringImpl* a, const StringImpl* b)
+ {
+ ASSERT(a);
+ ASSERT(b);
+ if (a == b)
+ return true;
+ if (a->length() != b->length())
+ return false;
+ return !__builtin_memcmp(a->characters(), b->characters(), a->length());
+ }
+};
+
+static HashTable<StringImpl*, FlyStringImplTraits>& fly_impls()
+{
+ static HashTable<StringImpl*, FlyStringImplTraits>* table;
+ if (!table)
+ table = new HashTable<StringImpl*, FlyStringImplTraits>;
+ return *table;
+}
+
+void FlyString::did_destroy_impl(Badge<StringImpl>, StringImpl& impl)
+{
+ fly_impls().remove(&impl);
+}
+
+FlyString::FlyString(const String& string)
+{
+ if (string.is_null())
+ return;
+ auto it = fly_impls().find(const_cast<StringImpl*>(string.impl()));
+ if (it == fly_impls().end()) {
+ fly_impls().set(const_cast<StringImpl*>(string.impl()));
+ string.impl()->set_fly({}, true);
+ m_impl = string.impl();
+ } else {
+ ASSERT((*it)->is_fly());
+ m_impl = *it;
+ }
+}
+
+FlyString::FlyString(const StringView& string)
+ : FlyString(static_cast<String>(string))
+{
+}
+
+FlyString::FlyString(const char* string)
+ : FlyString(static_cast<String>(string))
+{
+}
+
+int FlyString::to_int(bool& ok) const
+{
+ return StringUtils::convert_to_int(view(), ok);
+}
+
+}
diff --git a/AK/FlyString.h b/AK/FlyString.h
@@ -0,0 +1,64 @@
+/*
+ * Copyright (c) 2020, Andreas Kling <[email protected]>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ * list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ * this list of conditions and the following disclaimer in the documentation
+ * and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/String.h>
+
+namespace AK {
+
+class FlyString {
+public:
+ FlyString() {}
+ FlyString(const String&);
+ FlyString(const StringView&);
+ FlyString(const char*);
+
+ bool operator==(const FlyString& other) const { return m_impl == other.m_impl; }
+ bool operator!=(const FlyString& other) const { return m_impl != other.m_impl; }
+
+ const StringImpl* impl() const { return m_impl; }
+ const char* characters() const { return m_impl ? m_impl->characters() : nullptr; }
+ size_t length() const { return m_impl ? m_impl->length() : 0; }
+
+ StringView view() const { return { characters(), length() }; }
+
+ int to_int(bool& ok) const;
+
+ static void did_destroy_impl(Badge<StringImpl>, StringImpl&);
+
+private:
+ RefPtr<StringImpl> m_impl;
+};
+
+template<>
+struct Traits<FlyString> : public GenericTraits<FlyString> {
+ static unsigned hash(const FlyString& s) { return s.impl() ? s.impl()->hash() : 0; }
+};
+
+}
+
+using AK::FlyString;
diff --git a/AK/Forward.h b/AK/Forward.h
@@ -45,6 +45,7 @@ class StringBuilder;
 class StringImpl;
 class StringView;
 class URL;
+class FlyString;
 class Utf8View;
 
 template<typename T>
@@ -137,5 +138,6 @@ using AK::StringImpl;
 using AK::StringView;
 using AK::Traits;
 using AK::URL;
+using AK::FlyString;
 using AK::Utf8View;
 using AK::Vector;
diff --git a/AK/StringImpl.cpp b/AK/StringImpl.cpp
@@ -24,6 +24,7 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
+#include <AK/FlyString.h>
 #include <AK/HashTable.h>
 #include <AK/Memory.h>
 #include <AK/StdLibExtras.h>
@@ -72,6 +73,8 @@ StringImpl::StringImpl(ConstructWithInlineBufferTag, size_t length)
 
 StringImpl::~StringImpl()
 {
+ if (m_fly)
+ FlyString::did_destroy_impl({}, *this);
 #ifdef DEBUG_STRINGIMPL
  --g_stringimpl_count;
  g_all_live_stringimpls->remove(this);

diff --git a/AK/StringImpl.h b/AK/StringImpl.h
@@ -26,6 +26,7 @@
 
 #pragma once
 
+#include <AK/Badge.h>
 #include <AK/RefCounted.h>
 #include <AK/RefPtr.h>
 #include <AK/Types.h>
@@ -70,11 +71,15 @@ class StringImpl : public RefCounted<StringImpl> {
  return m_hash;
  }
 
+ bool is_fly() const { return m_fly; }
+ void set_fly(Badge<FlyString>, bool fly) const { m_fly = fly; }
+
 private:
  enum ConstructTheEmptyStringImplTag {
  ConstructTheEmptyStringImpl
  };
  explicit StringImpl(ConstructTheEmptyStringImplTag)
+ : m_fly(true)
  {
  m_inline_buffer[0] = '\0';
  }
@@ -89,6 +94,7 @@ class StringImpl : public RefCounted<StringImpl> {
  size_t m_length { 0 };
  mutable unsigned m_hash { 0 };
  mutable bool m_has_hash { false };
+ mutable bool m_fly { false };
  char m_inline_buffer[0];
 };
 

diff --git a/AK/StringView.cpp b/AK/StringView.cpp
@@ -28,6 +28,7 @@
 #include <AK/Memory.h>
 #include <AK/String.h>
 #include <AK/StringView.h>
+#include <AK/FlyString.h>
 #include <AK/Vector.h>
 
 namespace AK {
@@ -39,6 +40,13 @@ StringView::StringView(const String& string)
 {
 }
 
+StringView::StringView(const FlyString& string)
+ : m_impl(string.impl())
+ , m_characters(string.characters())
+ , m_length(string.length())
+{
+}
+
 StringView::StringView(const ByteBuffer& buffer)
  : m_characters((const char*)buffer.data())
  , m_length(buffer.size())

diff --git a/AK/StringView.h b/AK/StringView.h
@@ -55,6 +55,7 @@ class StringView {
 
  StringView(const ByteBuffer&);
  StringView(const String&);
+ StringView(const FlyString&);
 
  bool is_null() const { return !m_characters; }
  bool is_empty() const { return m_length == 0; }

diff --git a/AK/Tests/Makefile b/AK/Tests/Makefile
@@ -7,6 +7,7 @@ SHARED_TEST_SOURCES = \
  ../LogStream.cpp \
  ../JsonValue.cpp \
  ../JsonParser.cpp \
+ ../FlyString.cpp \
  ../FileSystemPath.cpp \
  ../URL.cpp \
  ../Utf8View.cpp

diff --git a/AK/Tests/TestString.cpp b/AK/Tests/TestString.cpp
@@ -26,7 +26,9 @@
 
 #include <AK/TestSuite.h>
 
+#include <AK/FlyString.h>
 #include <AK/String.h>
+#include <AK/StringBuilder.h>
 
 TEST_CASE(construct_empty)
 {
@@ -137,4 +139,24 @@ TEST_CASE(to_uppercase)
  EXPECT(String("AbC").to_uppercase() == "ABC");
 }
 
+TEST_CASE(flystring)
+{
+ {
+ FlyString a("foo");
+ FlyString b("foo");
+ EXPECT_EQ(a.impl(), b.impl());
+ }
+
+ {
+ String a = "foo";
+ FlyString b = a;
+ StringBuilder builder;
+ builder.append('f');
+ builder.append("oo");
+ FlyString c = builder.to_string();
+ EXPECT_EQ(a.impl(), b.impl());
+ EXPECT_EQ(a.impl(), c.impl());
+ }
+}
+
 TEST_MAIN(String)
diff --git a/DevTools/FormCompiler/Makefile b/DevTools/FormCompiler/Makefile
@@ -4,14 +4,15 @@ PROGRAM = FormCompiler
 
 OBJS = \
  main.o \
+ ../../AK/FlyString.o \
+ ../../AK/JsonParser.o \
+ ../../AK/JsonValue.o \
+ ../../AK/LogStream.o \
  ../../AK/String.o \
- ../../AK/StringImpl.o \
  ../../AK/StringBuilder.o \
- ../../AK/StringView.o \
+ ../../AK/StringImpl.o \
  ../../AK/StringUtils.o \
- ../../AK/JsonValue.o \
- ../../AK/JsonParser.o \
- ../../AK/LogStream.o \
+ ../../AK/StringView.o \
  ../../Libraries/LibCore/IODevice.o \
  ../../Libraries/LibCore/File.o \
  ../../Libraries/LibCore/Object.o \

diff --git a/DevTools/IPCCompiler/Makefile b/DevTools/IPCCompiler/Makefile
@@ -4,14 +4,15 @@ PROGRAM = IPCCompiler
 
 OBJS = \
  main.o \
+ ../../AK/FlyString.o \
+ ../../AK/JsonParser.o \
+ ../../AK/JsonValue.o \
+ ../../AK/LogStream.o \
  ../../AK/String.o \
- ../../AK/StringImpl.o \
  ../../AK/StringBuilder.o \
- ../../AK/StringView.o \
+ ../../AK/StringImpl.o \
  ../../AK/StringUtils.o \
- ../../AK/JsonValue.o \
- ../../AK/JsonParser.o \
- ../../AK/LogStream.o \
+ ../../AK/StringView.o \
  ../../Libraries/LibCore/IODevice.o \
  ../../Libraries/LibCore/File.o \
  ../../Libraries/LibCore/Object.o \

diff --git a/Kernel/Makefile b/Kernel/Makefile
@@ -1,13 +1,14 @@
 OBJS = \
  ../AK/FileSystemPath.o \
+ ../AK/FlyString.o \
  ../AK/JsonParser.o \
  ../AK/JsonValue.o \
  ../AK/LogStream.o \
  ../AK/String.o \
  ../AK/StringBuilder.o \
  ../AK/StringImpl.o \
- ../AK/StringView.o \
  ../AK/StringUtils.o \
+ ../AK/StringView.o \
  ../Libraries/LibELF/ELFImage.o \
  ../Libraries/LibELF/ELFLoader.o \
  ../Libraries/LibBareMetal/Output/Console.o \

diff --git a/Libraries/LibC/Makefile b/Libraries/LibC/Makefile
@@ -1,16 +1,17 @@
 AK_OBJS = \
- ../../AK/StringImpl.o \
- ../../AK/String.o \
- ../../AK/StringView.o \
- ../../AK/StringBuilder.o \
- ../../AK/StringUtils.o \
  ../../AK/FileSystemPath.o \
- ../../AK/URL.o \
- ../../AK/JsonValue.o \
+ ../../AK/FlyString.o \
  ../../AK/JsonParser.o \
+ ../../AK/JsonValue.o \
  ../../AK/LogStream.o \
  ../../AK/MappedFile.o \
  ../../AK/SharedBuffer.o \
+ ../../AK/String.o \
+ ../../AK/StringBuilder.o \
+ ../../AK/StringImpl.o \
+ ../../AK/StringUtils.o \
+ ../../AK/StringView.o \
+ ../../AK/URL.o \
  ../../AK/Utf8View.o
 
 LIBC_OBJS = \

diff --git a/Libraries/LibWeb/CodeGenerators/Generate_CSS_PropertyID_cpp/Makefile b/Libraries/LibWeb/CodeGenerators/Generate_CSS_PropertyID_cpp/Makefile
@@ -4,14 +4,15 @@ PROGRAM = Generate_CSS_PropertyID_cpp
 
 OBJS = \
  Generate_CSS_PropertyID_cpp.o \
+ ../../../../AK/FlyString.o \
+ ../../../../AK/JsonParser.o \
+ ../../../../AK/JsonValue.o \
+ ../../../../AK/LogStream.o \
  ../../../../AK/String.o \
- ../../../../AK/StringImpl.o \
  ../../../../AK/StringBuilder.o \
- ../../../../AK/StringView.o \
+ ../../../../AK/StringImpl.o \
  ../../../../AK/StringUtils.o \
- ../../../../AK/JsonValue.o \
- ../../../../AK/JsonParser.o \
- ../../../../AK/LogStream.o \
+ ../../../../AK/StringView.o \
  ../../../../Libraries/LibCore/IODevice.o \
  ../../../../Libraries/LibCore/File.o \
  ../../../../Libraries/LibCore/Object.o \