The Tor Browser: layout/style/nsCSSDataBlock.h@97036ab72558 (annotated)

layout/style/nsCSSDataBlock.h@97036ab72558 (annotated)

layout/style/nsCSSDataBlock.h

Tue, 06 Jan 2015 21:39:09 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Tue, 06 Jan 2015 21:39:09 +0100
branch: TOR_BUG_9701
changeset 8: 97036ab72558
permissions: -rw-r--r--

Conditionally force memory storage according to privacy.thirdparty.isolate;
This solves Tor bug #9701, complying with disk avoidance documented in
https://www.torproject.org/projects/torbrowser/design/#disk-avoidance.

 /* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 /*
  * compact representation of the property-value pairs within a CSS
  * declaration, and the code for expanding and compacting it
  */
 #ifndef nsCSSDataBlock_h__
 #define nsCSSDataBlock_h__
 #include "mozilla/MemoryReporting.h"
 #include "nsCSSProps.h"
 #include "nsCSSPropertySet.h"
 #include "nsCSSValue.h"
 #include "imgRequestProxy.h"
 struct nsRuleData;
 class nsCSSExpandedDataBlock;
 namespace mozilla {
 namespace css {
 class Declaration;
 }
 }
 /**
  * An |nsCSSCompressedDataBlock| holds a usually-immutable chunk of
  * property-value data for a CSS declaration block (which we misname a
  * |css::Declaration|).  Mutation is accomplished through
  * |nsCSSExpandedDataBlock| or in some cases via direct slot access.
  */
 class nsCSSCompressedDataBlock {
 private:
     friend class nsCSSExpandedDataBlock;
     // Only this class (via |CreateEmptyBlock|) or nsCSSExpandedDataBlock
     // (in |Compress|) can create compressed data blocks.
     nsCSSCompressedDataBlock(uint32_t aNumProps)
       : mStyleBits(0), mNumProps(aNumProps)
     {}
 public:
     ~nsCSSCompressedDataBlock();
     /**
      * Do what |nsIStyleRule::MapRuleInfoInto| needs to do for a style
      * rule using this block for storage.
      */
     void MapRuleInfoInto(nsRuleData *aRuleData) const;
     /**
      * Return the location at which the *value* for the property is
      * stored, or null if the block does not contain a value for the
      * property.
      *
      * Inefficient (by design).
      *
      * Must not be called for shorthands.
      */
     const nsCSSValue* ValueFor(nsCSSProperty aProperty) const;
     /**
      * Attempt to replace the value for |aProperty| stored in this block
      * with the matching value stored in |aFromBlock|.
      * This method will fail (returning false) if |aProperty| is not
      * already in this block.  It will set |aChanged| to true if it
      * actually made a change to the block, but regardless, if it
      * returns true, the value in |aFromBlock| was erased.
      */
     bool TryReplaceValue(nsCSSProperty aProperty,
                            nsCSSExpandedDataBlock& aFromBlock,
                            bool* aChanged);
     /**
      * Clone this block, or return null on out-of-memory.
      */
     nsCSSCompressedDataBlock* Clone() const;
     /**
      * Create a new nsCSSCompressedDataBlock holding no declarations.
      */
     static nsCSSCompressedDataBlock* CreateEmptyBlock();
     size_t SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf) const;
     bool HasDefaultBorderImageSlice() const;
     bool HasDefaultBorderImageWidth() const;
     bool HasDefaultBorderImageOutset() const;
     bool HasDefaultBorderImageRepeat() const;
 private:
     void* operator new(size_t aBaseSize, uint32_t aNumProps) {
         NS_ABORT_IF_FALSE(aBaseSize == sizeof(nsCSSCompressedDataBlock),
                           "unexpected size for nsCSSCompressedDataBlock");
         return ::operator new(aBaseSize + DataSize(aNumProps));
     }
 public:
     // Ideally, |nsCSSProperty| would be |enum nsCSSProperty : int16_t|.  But
     // not all of the compilers we use are modern enough to support small
     // enums.  So we manually squeeze nsCSSProperty into 16 bits ourselves.
     // The static assertion below ensures it fits.
     typedef int16_t CompressedCSSProperty;
     static const size_t MaxCompressedCSSProperty = INT16_MAX;
 private:
     static size_t DataSize(uint32_t aNumProps) {
         return size_t(aNumProps) *
                (sizeof(nsCSSValue) + sizeof(CompressedCSSProperty));
     }
     int32_t mStyleBits; // the structs for which we have data, according to
                         // |nsCachedStyleData::GetBitForSID|.
     uint32_t mNumProps;
     // nsCSSValue elements are stored after these fields, and
     // nsCSSProperty elements are stored -- each one compressed as a
     // CompressedCSSProperty -- after the nsCSSValue elements.  Space for them
     // is allocated in |operator new| above.  The static assertions following
     // this class make sure that the value and property elements are aligned
     // appropriately.
     nsCSSValue* Values() const {
         return (nsCSSValue*)(this + 1);
     }
     CompressedCSSProperty* CompressedProperties() const {
         return (CompressedCSSProperty*)(Values() + mNumProps);
     }
     nsCSSValue* ValueAtIndex(uint32_t i) const {
         NS_ABORT_IF_FALSE(i < mNumProps, "value index out of range");
         return Values() + i;
     }
     nsCSSProperty PropertyAtIndex(uint32_t i) const {
         NS_ABORT_IF_FALSE(i < mNumProps, "property index out of range");
         nsCSSProperty prop = (nsCSSProperty)CompressedProperties()[i];
         NS_ABORT_IF_FALSE(!nsCSSProps::IsShorthand(prop), "out of range");
         return prop;
     }
     void CopyValueToIndex(uint32_t i, nsCSSValue* aValue) {
         new (ValueAtIndex(i)) nsCSSValue(*aValue);
     }
     void RawCopyValueToIndex(uint32_t i, nsCSSValue* aValue) {
         memcpy(ValueAtIndex(i), aValue, sizeof(nsCSSValue));
     }
     void SetPropertyAtIndex(uint32_t i, nsCSSProperty aProperty) {
         NS_ABORT_IF_FALSE(i < mNumProps, "set property index out of range");
         CompressedProperties()[i] = (CompressedCSSProperty)aProperty;
     }
     void SetNumPropsToZero() {
         mNumProps = 0;
     }
 };
 // Make sure the values and properties are aligned appropriately.  (These
 // assertions are stronger than necessary to keep them simple.)
 static_assert(sizeof(nsCSSCompressedDataBlock) == 8,
               "nsCSSCompressedDataBlock's size has changed");
 static_assert(NS_ALIGNMENT_OF(nsCSSValue) == 4 || NS_ALIGNMENT_OF(nsCSSValue) == 8,
               "nsCSSValue doesn't align with nsCSSCompressedDataBlock");
 static_assert(NS_ALIGNMENT_OF(nsCSSCompressedDataBlock::CompressedCSSProperty) == 2,
               "CompressedCSSProperty doesn't align with nsCSSValue");
 // Make sure that sizeof(CompressedCSSProperty) is big enough.
 static_assert(eCSSProperty_COUNT_no_shorthands <=
               nsCSSCompressedDataBlock::MaxCompressedCSSProperty,
               "nsCSSProperty doesn't fit in StoredSizeOfCSSProperty");
 class nsCSSExpandedDataBlock {
     friend class nsCSSCompressedDataBlock;
 public:
     nsCSSExpandedDataBlock();
     ~nsCSSExpandedDataBlock();
 private:
     /* Property storage may not be accessed directly; use AddLonghandProperty
      * and friends.
      */
     nsCSSValue mValues[eCSSProperty_COUNT_no_shorthands];
 public:
     /**
      * Transfer all of the state from a pair of compressed data blocks
      * to this expanded block.  This expanded block must be clear
      * beforehand.
      *
      * This method DELETES both of the compressed data blocks it is
      * passed.  (This is necessary because ownership of sub-objects
      * is transferred to the expanded block.)
      */
     void Expand(nsCSSCompressedDataBlock *aNormalBlock,
                 nsCSSCompressedDataBlock *aImportantBlock);
     /**
      * Allocate new compressed blocks and transfer all of the state
      * from this expanded block to the new blocks, clearing this
      * expanded block.  A normal block will always be allocated, but
      * an important block will only be allocated if there are
      * !important properties in the expanded block; otherwise
      * |*aImportantBlock| will be set to null.
      */
     void Compress(nsCSSCompressedDataBlock **aNormalBlock,
                   nsCSSCompressedDataBlock **aImportantBlock);
     /**
      * Copy a value into this expanded block.  This does NOT destroy
      * the source value object.  |aProperty| cannot be a shorthand.
      */
     void AddLonghandProperty(nsCSSProperty aProperty, const nsCSSValue& aValue);
     /**
      * Clear the state of this expanded block.
      */
     void Clear();
     /**
      * Clear the data for the given property (including the set and
      * important bits).  Can be used with shorthand properties.
      */
     void ClearProperty(nsCSSProperty aPropID);
     /**
      * Same as ClearProperty, but faster and cannot be used with shorthands.
      */
     void ClearLonghandProperty(nsCSSProperty aPropID);
     /**
      * Transfer the state for |aPropID| (which may be a shorthand)
      * from |aFromBlock| to this block.  The property being transferred
      * is !important if |aIsImportant| is true, and should replace an
      * existing !important property regardless of its own importance
      * if |aOverrideImportant| is true.
      *
      * Returns true if something changed, false otherwise.  Calls
      * |ValueAppended| on |aDeclaration| if the property was not
      * previously set, or in any case if |aMustCallValueAppended| is true.
      */
     bool TransferFromBlock(nsCSSExpandedDataBlock& aFromBlock,
                              nsCSSProperty aPropID,
                              bool aIsImportant,
                              bool aOverrideImportant,
                              bool aMustCallValueAppended,
                              mozilla::css::Declaration* aDeclaration);
     /**
      * Copies the values for aPropID into the specified aRuleData object.
      *
      * This is used for copying parsed-at-computed-value-time properties
      * that had variable references.  aPropID must be a longhand property.
      */
     void MapRuleInfoInto(nsCSSProperty aPropID, nsRuleData* aRuleData) const;
     void AssertInitialState() {
 #ifdef DEBUG
         DoAssertInitialState();
 #endif
     }
 private:
     /**
      * Compute the number of properties that will be present in the
      * result of |Compress|.
      */
     void ComputeNumProps(uint32_t* aNumPropsNormal,
                          uint32_t* aNumPropsImportant);
     void DoExpand(nsCSSCompressedDataBlock *aBlock, bool aImportant);
     /**
      * Worker for TransferFromBlock; cannot be used with shorthands.
      */
     bool DoTransferFromBlock(nsCSSExpandedDataBlock& aFromBlock,
                                nsCSSProperty aPropID,
                                bool aIsImportant,
                                bool aOverrideImportant,
                                bool aMustCallValueAppended,
                                mozilla::css::Declaration* aDeclaration);
 #ifdef DEBUG
     void DoAssertInitialState();
 #endif
     /*
      * mPropertiesSet stores a bit for every property that is present,
      * to optimize compression of blocks with small numbers of
      * properties (the norm) and to allow quickly checking whether a
      * property is set in this block.
      */
     nsCSSPropertySet mPropertiesSet;
     /*
      * mPropertiesImportant indicates which properties are '!important'.
      */
     nsCSSPropertySet mPropertiesImportant;
     /*
      * Return the storage location within |this| of the value of the
      * property |aProperty|.
      */
     nsCSSValue* PropertyAt(nsCSSProperty aProperty) {
         NS_ABORT_IF_FALSE(0 <= aProperty &&
                           aProperty < eCSSProperty_COUNT_no_shorthands,
                           "property out of range");
         return &mValues[aProperty];
     }
     const nsCSSValue* PropertyAt(nsCSSProperty aProperty) const {
         NS_ABORT_IF_FALSE(0 <= aProperty &&
                           aProperty < eCSSProperty_COUNT_no_shorthands,
                           "property out of range");
         return &mValues[aProperty];
     }
     void SetPropertyBit(nsCSSProperty aProperty) {
         mPropertiesSet.AddProperty(aProperty);
     }
     void ClearPropertyBit(nsCSSProperty aProperty) {
         mPropertiesSet.RemoveProperty(aProperty);
     }
     bool HasPropertyBit(nsCSSProperty aProperty) {
         return mPropertiesSet.HasProperty(aProperty);
     }
     void SetImportantBit(nsCSSProperty aProperty) {
         mPropertiesImportant.AddProperty(aProperty);
     }
     void ClearImportantBit(nsCSSProperty aProperty) {
         mPropertiesImportant.RemoveProperty(aProperty);
     }
     bool HasImportantBit(nsCSSProperty aProperty) {
         return mPropertiesImportant.HasProperty(aProperty);
     }
     void ClearSets() {
         mPropertiesSet.Empty();
         mPropertiesImportant.Empty();
     }
 };
 #endif /* !defined(nsCSSDataBlock_h__) */

The Tor Browser / annotate

layout/style/nsCSSDataBlock.h@97036ab72558 (annotated)

layout/style/nsCSSDataBlock.h