Fix nsSharableString::SetLength to correctly handle having a shared buffer. Override GetWritableFragment on nsSharableString (perhaps temporarily) to allow use of writing iterators on nsSharableString. b=114438 r=jag sr=jst

string/public/nsBufferHandle.h

@@ -189,7 +189,7 @@ class nsSharedBufferHandle
     protected:
       enum
         {
-          kIsShared                       = 0x01000000, // one reason _not_ to set this is for a stack based handle that wants to express `NULL'-ness et al
+          kIsImmutable                    = 0x01000000, // if this is set, the buffer cannot be modified even if its refcount is 1
           kIsSingleAllocationWithBuffer   = 0x02000000, // handle and buffer are one piece, no separate deallocation is possible for the buffer
           kIsUserAllocator                = 0x04000000, // can't |delete|, call a hook instead
 
@@ -204,9 +204,9 @@ class nsSharedBufferHandle
     public:
       nsSharedBufferHandle( CharT* aDataStart, CharT* aDataEnd, size_type aStorageLength, PRBool isSingleAllocation )
           : nsBufferHandle<CharT>(aDataStart, aDataEnd),
+            mFlags(0),
             mStorageLength(aStorageLength)
         {
-          mFlags = kIsShared;
           if ( isSingleAllocation )
             mFlags |= kIsSingleAllocationWithBuffer;
         }
@@ -236,9 +236,10 @@ class nsSharedBufferHandle
         }
 
       PRBool
-      IsShared() const
+      IsMutable() const
         {
-          return get_refcount() > 1;
+          // (get_refcount() == 1) && !(GetImplementationFlags() & kIsImmutable)
+          return (mFlags & (kRefCountMask | kIsImmutable) == 1);
         }
 
       void StorageLength( size_type aNewStorageLength )

string/public/nsSharableString.h

@@ -94,6 +94,9 @@ class NS_COM nsSharableString
     protected:
       virtual void do_AssignFromReadable( const abstract_string_type& aReadable );
       virtual const shared_buffer_handle_type*  GetSharedBufferHandle() const;
+//  protected:  // can't hide these (yet), since I call them from forwarding routines in |nsPromiseFlatString|
+    public:
+      virtual char_type* GetWritableFragment( fragment_type&, nsFragmentRequest, PRUint32 );
 
     protected:
       static shared_buffer_handle_type* GetSharedEmptyBufferHandle();
@@ -153,6 +156,9 @@ class NS_COM nsSharableCString
     protected:
       virtual void do_AssignFromReadable( const abstract_string_type& aReadable );
       virtual const shared_buffer_handle_type*  GetSharedBufferHandle() const;
+//  protected:  // can't hide these (yet), since I call them from forwarding routines in |nsPromiseFlatString|
+    public:
+      virtual char_type* GetWritableFragment( fragment_type&, nsFragmentRequest, PRUint32 );
 
     protected:
       static shared_buffer_handle_type* GetSharedEmptyBufferHandle();

string/src/nsSharableString.cpp

@@ -56,11 +56,11 @@ nsSharableString::SetCapacity( size_type aNewCapacity )
         // therefore *unconditionally* truncate the current length of
         // the string to the requested capacity.
 
-        if ( mBuffer->IsShared() )
+        if ( !mBuffer->IsMutable() )
           {
-            if ( aNewCapacity > Length() )
+            if ( aNewCapacity > mBuffer->DataLength() )
               mBuffer = NS_AllocateContiguousHandleWithData(mBuffer.get(),
-                            *this, PRUint32(aNewCapacity - Length() + 1));
+                    *this, PRUint32(aNewCapacity - mBuffer->DataLength() + 1));
             else
               mBuffer = NS_AllocateContiguousHandleWithData(mBuffer.get(),
                             Substring(*this, 0, aNewCapacity), PRUint32(1));
@@ -78,10 +78,10 @@ nsSharableString::SetCapacity( size_type aNewCapacity )
                   aNewCapacity = doubledCapacity;
 
                 // XXX We should be able to use |realloc| under certain
-                // conditions (contiguous buffer handle, kIsShared
-                // (,etc.)?)
+                // conditions (contiguous buffer handle, not
+                // kIsImmutable (,etc.)?)
                 mBuffer = NS_AllocateContiguousHandleWithData(mBuffer.get(),
-                                 *this, PRUint32(aNewCapacity - Length() + 1));
+                    *this, PRUint32(aNewCapacity - mBuffer->DataLength() + 1));
               }
             else if ( aNewCapacity < mBuffer->DataLength() )
               {
@@ -100,7 +100,7 @@ nsSharableString::SetCapacity( size_type aNewCapacity )
 void
 nsSharableString::SetLength( size_type aNewLength )
   {
-    if ( aNewLength > mBuffer->DataLength() )
+    if ( !mBuffer->IsMutable() || aNewLength > mBuffer->DataLength() )
       {
         SetCapacity(aNewLength);
         mBuffer->DataEnd( mBuffer->DataStart() + aNewLength );
@@ -128,7 +128,7 @@ nsSharableString::do_AssignFromReadable( const abstract_string_type& aReadable )
       {
         // null-check |mBuffer.get()| here only for the constructor
         // taking |const abstract_string_type&|
-        if ( mBuffer.get() && !mBuffer->IsShared() &&
+        if ( mBuffer.get() && mBuffer->IsMutable() &&
              mBuffer->StorageLength() > aReadable.Length() &&
              !aReadable.IsDependentOn(*this) )
           {
@@ -175,6 +175,22 @@ nsSharableString::GetSharedEmptyBufferHandle()
     return sBufferHandle;
   }
 
+// The need to override GetWritableFragment may be temporary, depending
+// on the protocol we choose for callers who want to mutate strings
+// using iterators.  See
+// <URL: http://bugzilla.mozilla.org/show_bug.cgi?id=114140 >
+nsSharableString::char_type*
+nsSharableString::GetWritableFragment( fragment_type& aFragment, nsFragmentRequest aRequest, PRUint32 aOffset )
+  {
+    // This makes writing iterators safe to use, but it imposes a
+    // double-malloc performance penalty on users who intend to modify
+    // the length of the string but call |BeginWriting| before they call
+    // |SetLength|.
+    if ( mBuffer->IsMutable() )
+      SetCapacity( mBuffer->DataLength() );
+    return nsAFlatString::GetWritableFragment( aFragment, aRequest, aOffset );
+  }
+
 
 void
 nsSharableCString::SetCapacity( size_type aNewCapacity )
@@ -205,11 +221,11 @@ nsSharableCString::SetCapacity( size_type aNewCapacity )
         // therefore *unconditionally* truncate the current length of
         // the string to the requested capacity.
 
-        if ( mBuffer->IsShared() )
+        if ( !mBuffer->IsMutable() )
           {
-            if ( aNewCapacity > Length() )
+            if ( aNewCapacity > mBuffer->DataLength() )
               mBuffer = NS_AllocateContiguousHandleWithData(mBuffer.get(),
-                            *this, PRUint32(aNewCapacity - Length() + 1));
+                    *this, PRUint32(aNewCapacity - mBuffer->DataLength() + 1));
             else
               mBuffer = NS_AllocateContiguousHandleWithData(mBuffer.get(),
                             Substring(*this, 0, aNewCapacity), PRUint32(1));
@@ -227,10 +243,10 @@ nsSharableCString::SetCapacity( size_type aNewCapacity )
                   aNewCapacity = doubledCapacity;
 
                 // XXX We should be able to use |realloc| under certain
-                // conditions (contiguous buffer handle, kIsShared
-                // (,etc.)?)
+                // conditions (contiguous buffer handle, not
+                // kIsImmutable (,etc.)?)
                 mBuffer = NS_AllocateContiguousHandleWithData(mBuffer.get(),
-                                 *this, PRUint32(aNewCapacity - Length() + 1));
+                    *this, PRUint32(aNewCapacity - mBuffer->DataLength() + 1));
               }
             else if ( aNewCapacity < mBuffer->DataLength() )
               {
@@ -249,7 +265,7 @@ nsSharableCString::SetCapacity( size_type aNewCapacity )
 void
 nsSharableCString::SetLength( size_type aNewLength )
   {
-    if ( aNewLength > mBuffer->DataLength() )
+    if ( !mBuffer->IsMutable() || aNewLength > mBuffer->DataLength() )
       {
         SetCapacity(aNewLength);
         mBuffer->DataEnd( mBuffer->DataStart() + aNewLength );
@@ -261,7 +277,7 @@ nsSharableCString::SetLength( size_type aNewLength )
     // This is needed for |Truncate| callers and also for some callers
     // (such as nsACString::do_AppendFromReadable) that are manipulating
     // the internals of the string.  It also makes sense to do this
-    // since this class implements |nsAFlatString|, so the buffer must
+    // since this class implements |nsAFlatCString|, so the buffer must
     // always be null-terminated at its length.  Callers using writing
     // iterators can't be expected to null-terminate themselves since
     // they don't know if they're dealing with a string that has a
@@ -277,7 +293,7 @@ nsSharableCString::do_AssignFromReadable( const abstract_string_type& aReadable
       {
         // null-check |mBuffer.get()| here only for the constructor
         // taking |const abstract_string_type&|
-        if ( mBuffer.get() && !mBuffer->IsShared() &&
+        if ( mBuffer.get() && mBuffer->IsMutable() &&
              mBuffer->StorageLength() > aReadable.Length() &&
              !aReadable.IsDependentOn(*this) )
           {
@@ -324,3 +340,19 @@ nsSharableCString::GetSharedEmptyBufferHandle()
     return sBufferHandle;
   }
 
+// The need to override GetWritableFragment may be temporary, depending
+// on the protocol we choose for callers who want to mutate strings
+// using iterators.  See
+// <URL: http://bugzilla.mozilla.org/show_bug.cgi?id=114140 >
+nsSharableCString::char_type*
+nsSharableCString::GetWritableFragment( fragment_type& aFragment, nsFragmentRequest aRequest, PRUint32 aOffset )
+  {
+    // This makes writing iterators safe to use, but it imposes a
+    // double-malloc performance penalty on users who intend to modify
+    // the length of the string but call |BeginWriting| before they call
+    // |SetLength|.
+    if ( mBuffer->IsMutable() )
+      SetCapacity( mBuffer->DataLength() );
+    return nsAFlatCString::GetWritableFragment( aFragment, aRequest, aOffset );
+  }
+

xpcom/string/public/nsBufferHandle.h

@@ -189,7 +189,7 @@ class nsSharedBufferHandle
     protected:
       enum
         {
-          kIsShared                       = 0x01000000, // one reason _not_ to set this is for a stack based handle that wants to express `NULL'-ness et al
+          kIsImmutable                    = 0x01000000, // if this is set, the buffer cannot be modified even if its refcount is 1
           kIsSingleAllocationWithBuffer   = 0x02000000, // handle and buffer are one piece, no separate deallocation is possible for the buffer
           kIsUserAllocator                = 0x04000000, // can't |delete|, call a hook instead
 
@@ -204,9 +204,9 @@ class nsSharedBufferHandle
     public:
       nsSharedBufferHandle( CharT* aDataStart, CharT* aDataEnd, size_type aStorageLength, PRBool isSingleAllocation )
           : nsBufferHandle<CharT>(aDataStart, aDataEnd),
+            mFlags(0),
             mStorageLength(aStorageLength)
         {
-          mFlags = kIsShared;
           if ( isSingleAllocation )
             mFlags |= kIsSingleAllocationWithBuffer;
         }
@@ -236,9 +236,10 @@ class nsSharedBufferHandle
         }
 
       PRBool
-      IsShared() const
+      IsMutable() const
         {
-          return get_refcount() > 1;
+          // (get_refcount() == 1) && !(GetImplementationFlags() & kIsImmutable)
+          return (mFlags & (kRefCountMask | kIsImmutable) == 1);
         }
 
       void StorageLength( size_type aNewStorageLength )

xpcom/string/public/nsSharableString.h

@@ -94,6 +94,9 @@ class NS_COM nsSharableString
     protected:
       virtual void do_AssignFromReadable( const abstract_string_type& aReadable );
       virtual const shared_buffer_handle_type*  GetSharedBufferHandle() const;
+//  protected:  // can't hide these (yet), since I call them from forwarding routines in |nsPromiseFlatString|
+    public:
+      virtual char_type* GetWritableFragment( fragment_type&, nsFragmentRequest, PRUint32 );
 
     protected:
       static shared_buffer_handle_type* GetSharedEmptyBufferHandle();
@@ -153,6 +156,9 @@ class NS_COM nsSharableCString
     protected:
       virtual void do_AssignFromReadable( const abstract_string_type& aReadable );
       virtual const shared_buffer_handle_type*  GetSharedBufferHandle() const;
+//  protected:  // can't hide these (yet), since I call them from forwarding routines in |nsPromiseFlatString|
+    public:
+      virtual char_type* GetWritableFragment( fragment_type&, nsFragmentRequest, PRUint32 );
 
     protected:
       static shared_buffer_handle_type* GetSharedEmptyBufferHandle();

xpcom/string/src/nsSharableString.cpp

@@ -56,11 +56,11 @@ nsSharableString::SetCapacity( size_type aNewCapacity )
         // therefore *unconditionally* truncate the current length of
         // the string to the requested capacity.
 
-        if ( mBuffer->IsShared() )
+        if ( !mBuffer->IsMutable() )
           {
-            if ( aNewCapacity > Length() )
+            if ( aNewCapacity > mBuffer->DataLength() )
               mBuffer = NS_AllocateContiguousHandleWithData(mBuffer.get(),
-                            *this, PRUint32(aNewCapacity - Length() + 1));
+                    *this, PRUint32(aNewCapacity - mBuffer->DataLength() + 1));
             else
               mBuffer = NS_AllocateContiguousHandleWithData(mBuffer.get(),
                             Substring(*this, 0, aNewCapacity), PRUint32(1));
@@ -78,10 +78,10 @@ nsSharableString::SetCapacity( size_type aNewCapacity )
                   aNewCapacity = doubledCapacity;
 
                 // XXX We should be able to use |realloc| under certain
-                // conditions (contiguous buffer handle, kIsShared
-                // (,etc.)?)
+                // conditions (contiguous buffer handle, not
+                // kIsImmutable (,etc.)?)
                 mBuffer = NS_AllocateContiguousHandleWithData(mBuffer.get(),
-                                 *this, PRUint32(aNewCapacity - Length() + 1));
+                    *this, PRUint32(aNewCapacity - mBuffer->DataLength() + 1));
               }
             else if ( aNewCapacity < mBuffer->DataLength() )
               {
@@ -100,7 +100,7 @@ nsSharableString::SetCapacity( size_type aNewCapacity )
 void
 nsSharableString::SetLength( size_type aNewLength )
   {
-    if ( aNewLength > mBuffer->DataLength() )
+    if ( !mBuffer->IsMutable() || aNewLength > mBuffer->DataLength() )
       {
         SetCapacity(aNewLength);
         mBuffer->DataEnd( mBuffer->DataStart() + aNewLength );
@@ -128,7 +128,7 @@ nsSharableString::do_AssignFromReadable( const abstract_string_type& aReadable )
       {
         // null-check |mBuffer.get()| here only for the constructor
         // taking |const abstract_string_type&|
-        if ( mBuffer.get() && !mBuffer->IsShared() &&
+        if ( mBuffer.get() && mBuffer->IsMutable() &&
              mBuffer->StorageLength() > aReadable.Length() &&
              !aReadable.IsDependentOn(*this) )
           {
@@ -175,6 +175,22 @@ nsSharableString::GetSharedEmptyBufferHandle()
     return sBufferHandle;
   }
 
+// The need to override GetWritableFragment may be temporary, depending
+// on the protocol we choose for callers who want to mutate strings
+// using iterators.  See
+// <URL: http://bugzilla.mozilla.org/show_bug.cgi?id=114140 >
+nsSharableString::char_type*
+nsSharableString::GetWritableFragment( fragment_type& aFragment, nsFragmentRequest aRequest, PRUint32 aOffset )
+  {
+    // This makes writing iterators safe to use, but it imposes a
+    // double-malloc performance penalty on users who intend to modify
+    // the length of the string but call |BeginWriting| before they call
+    // |SetLength|.
+    if ( mBuffer->IsMutable() )
+      SetCapacity( mBuffer->DataLength() );
+    return nsAFlatString::GetWritableFragment( aFragment, aRequest, aOffset );
+  }
+
 
 void
 nsSharableCString::SetCapacity( size_type aNewCapacity )
@@ -205,11 +221,11 @@ nsSharableCString::SetCapacity( size_type aNewCapacity )
         // therefore *unconditionally* truncate the current length of
         // the string to the requested capacity.
 
-        if ( mBuffer->IsShared() )
+        if ( !mBuffer->IsMutable() )
           {
-            if ( aNewCapacity > Length() )
+            if ( aNewCapacity > mBuffer->DataLength() )
               mBuffer = NS_AllocateContiguousHandleWithData(mBuffer.get(),
-                            *this, PRUint32(aNewCapacity - Length() + 1));
+                    *this, PRUint32(aNewCapacity - mBuffer->DataLength() + 1));
             else
               mBuffer = NS_AllocateContiguousHandleWithData(mBuffer.get(),
                             Substring(*this, 0, aNewCapacity), PRUint32(1));
@@ -227,10 +243,10 @@ nsSharableCString::SetCapacity( size_type aNewCapacity )
                   aNewCapacity = doubledCapacity;
 
                 // XXX We should be able to use |realloc| under certain
-                // conditions (contiguous buffer handle, kIsShared
-                // (,etc.)?)
+                // conditions (contiguous buffer handle, not
+                // kIsImmutable (,etc.)?)
                 mBuffer = NS_AllocateContiguousHandleWithData(mBuffer.get(),
-                                 *this, PRUint32(aNewCapacity - Length() + 1));
+                    *this, PRUint32(aNewCapacity - mBuffer->DataLength() + 1));
               }
             else if ( aNewCapacity < mBuffer->DataLength() )
               {
@@ -249,7 +265,7 @@ nsSharableCString::SetCapacity( size_type aNewCapacity )
 void
 nsSharableCString::SetLength( size_type aNewLength )
   {
-    if ( aNewLength > mBuffer->DataLength() )
+    if ( !mBuffer->IsMutable() || aNewLength > mBuffer->DataLength() )
       {
         SetCapacity(aNewLength);
         mBuffer->DataEnd( mBuffer->DataStart() + aNewLength );
@@ -261,7 +277,7 @@ nsSharableCString::SetLength( size_type aNewLength )
     // This is needed for |Truncate| callers and also for some callers
     // (such as nsACString::do_AppendFromReadable) that are manipulating
     // the internals of the string.  It also makes sense to do this
-    // since this class implements |nsAFlatString|, so the buffer must
+    // since this class implements |nsAFlatCString|, so the buffer must
     // always be null-terminated at its length.  Callers using writing
     // iterators can't be expected to null-terminate themselves since
     // they don't know if they're dealing with a string that has a
@@ -277,7 +293,7 @@ nsSharableCString::do_AssignFromReadable( const abstract_string_type& aReadable
       {
         // null-check |mBuffer.get()| here only for the constructor
         // taking |const abstract_string_type&|
-        if ( mBuffer.get() && !mBuffer->IsShared() &&
+        if ( mBuffer.get() && mBuffer->IsMutable() &&
              mBuffer->StorageLength() > aReadable.Length() &&
              !aReadable.IsDependentOn(*this) )
           {
@@ -324,3 +340,19 @@ nsSharableCString::GetSharedEmptyBufferHandle()
     return sBufferHandle;
   }
 
+// The need to override GetWritableFragment may be temporary, depending
+// on the protocol we choose for callers who want to mutate strings
+// using iterators.  See
+// <URL: http://bugzilla.mozilla.org/show_bug.cgi?id=114140 >
+nsSharableCString::char_type*
+nsSharableCString::GetWritableFragment( fragment_type& aFragment, nsFragmentRequest aRequest, PRUint32 aOffset )
+  {
+    // This makes writing iterators safe to use, but it imposes a
+    // double-malloc performance penalty on users who intend to modify
+    // the length of the string but call |BeginWriting| before they call
+    // |SetLength|.
+    if ( mBuffer->IsMutable() )
+      SetCapacity( mBuffer->DataLength() );
+    return nsAFlatCString::GetWritableFragment( aFragment, aRequest, aOffset );
+  }
+