Mozilla/mozilla/xpcom/string/src/nsXPIDLString.cpp

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/*
 * The contents of this file are subject to the Mozilla Public
 * License Version 1.1 (the "License"); you may not use this file
 * except in compliance with the License. You may obtain a copy of
 * the License at http://www.mozilla.org/MPL/
 * 
 * Software distributed under the License is distributed on an "AS
 * IS" basis, WITHOUT WARRANTY OF ANY KIND, either express or
 * implied. See the License for the specific language governing
 * rights and limitations under the License.
 * 
 * The Original Code is Mozilla.
 * 
 * The Initial Developer of the Original Code is Netscape
 * Communications.  Portions created by Netscape Communications are
 * Copyright (C) 2001 by Netscape Communications.  All
 * Rights Reserved.
 * 
 * Contributor(s): 
 *   Scott Collins <scc@mozilla.org> (original author)
 */

// XXX TODO:
//
// nsSharableString will need to be careful to use GetSharedBufferHandle
// where necessary so that an nsXPIDLString can be passed as an
// nsSharableString&.  We must be careful to ensure that an
// nsXPIDLString can be used as an nsSharableString& and that an
// nsXPIDLString and an nsSharableString can share buffers created by
// the other (and buffers created by nsSharableString::Adopt rather than
// its other assignment methods).

#include "nsXPIDLString.h"

#if DEBUG_STRING_STATS
size_t nsXPIDLString::sCreatedCount     = 0;
size_t nsXPIDLString::sAliveCount       = 0;
size_t nsXPIDLString::sHighWaterCount   = 0;
size_t nsXPIDLString::sAssignCount      = 0;
size_t nsXPIDLString::sShareCount       = 0;

size_t nsXPIDLCString::sCreatedCount    = 0;
size_t nsXPIDLCString::sAliveCount      = 0;
size_t nsXPIDLCString::sHighWaterCount  = 0;
size_t nsXPIDLCString::sAssignCount     = 0;
size_t nsXPIDLCString::sShareCount      = 0;
#endif


template <class CharT>
class nsImportedStringHandle
    : public nsSharedBufferHandle<CharT>
  {
    public:
      nsImportedStringHandle() : nsSharedBufferHandle<CharT>(0, 0, 0, PR_FALSE) { }

      CharT** AddressOfStorageStart() { return &(this->mDataStart); }
      void RecalculateBoundaries() const;
  };


template <class CharT>
void
nsImportedStringHandle<CharT>::RecalculateBoundaries() const
  {
    size_t data_length = 0;

    CharT* storage_start = NS_CONST_CAST(CharT*, this->DataStart());
    if ( storage_start )
      {
        data_length = nsCharTraits<CharT>::length(storage_start);
      }

    nsImportedStringHandle<CharT>* mutable_this = NS_CONST_CAST(nsImportedStringHandle<CharT>*, this);
    mutable_this->DataStart(storage_start);
    mutable_this->DataEnd(storage_start + data_length);
    mutable_this->StorageLength(data_length + 1);
  }


#if DEBUG_STRING_STATS
const nsXPIDLString::buffer_handle_type*
nsXPIDLString::GetFlatBufferHandle() const
  {
    --sShareCount;
    return GetSharedBufferHandle();
  }


const nsXPIDLString::buffer_handle_type*
nsXPIDLString::GetBufferHandle() const
  {
    --sShareCount;
    return GetSharedBufferHandle();
  }


void
nsXPIDLString::DebugPrintStats( FILE* aOutFile )
  {
    fprintf(aOutFile, "nsXPIDLString stats: %ld alive now [%ld max] of %ld created; %ld getter_Copies, %ld attempts to share\n",
                       sAliveCount, sHighWaterCount, sCreatedCount, sAssignCount, sShareCount);
  }
#endif


const nsXPIDLString::shared_buffer_handle_type*
nsXPIDLString::GetSharedBufferHandle() const
  {
    self_type* mutable_this = NS_CONST_CAST(self_type*, this);
    if ( !mBuffer->DataStart() )
      // XXXldb This isn't any good.  What if we just called
      // PrepareForUseAsOutParam and it hasn't been filled in yet?
      mutable_this->mBuffer = GetSharedEmptyBufferHandle();
    else if ( !mBuffer->DataEnd() )
      {
        // Our handle may not be an nsImportedStringHandle.  However, if it
        // is not, this cast will still be safe since no other handle will
        // be in this state.
        const nsImportedStringHandle<char_type>* handle = NS_STATIC_CAST(const nsImportedStringHandle<char_type>*, mBuffer.get());
        handle->RecalculateBoundaries();
      }

#if DEBUG_STRING_STATS
    ++sShareCount;
#endif
    return mBuffer.get();
  }


nsXPIDLString::char_type**
nsXPIDLString::PrepareForUseAsOutParam()
  {
    nsImportedStringHandle<char_type>* handle = new nsImportedStringHandle<char_type>();
    NS_ASSERTION(handle, "Trouble!  We couldn't get a new handle during |getter_Copies|.");

    mBuffer = handle;
#if DEBUG_STRING_STATS
    ++sAssignCount;
#endif
    return handle->AddressOfStorageStart();
  }

/* static */
nsXPIDLString::shared_buffer_handle_type*
nsXPIDLString::GetSharedEmptyBufferHandle()
  {
    static shared_buffer_handle_type* sBufferHandle = nsnull;
    static char_type null_char = char_type(0);

    if (!sBufferHandle) {
      sBufferHandle = new nsNonDestructingSharedBufferHandle<char_type>(&null_char, &null_char, 1);
      sBufferHandle->AcquireReference(); // To avoid the |Destroy|
                                         // mechanism unless threads
                                         // race to set the refcount, in
                                         // which case we'll pull the
                                         // same trick in |Destroy|.
      sBufferHandle->SetImplementationFlags(sBufferHandle->GetImplementationFlags() | shared_buffer_handle_type::kIsNULL);
    }
    return sBufferHandle;
  }


#if DEBUG_STRING_STATS
const nsXPIDLCString::buffer_handle_type*
nsXPIDLCString::GetFlatBufferHandle() const
  {
    --sShareCount;
    return GetSharedBufferHandle();
  }


const nsXPIDLCString::buffer_handle_type*
nsXPIDLCString::GetBufferHandle() const
  {
    --sShareCount;
    return GetSharedBufferHandle();
  }


void
nsXPIDLCString::DebugPrintStats( FILE* aOutFile )
  {
    fprintf(aOutFile, "nsXPIDLCString stats: %ld alive now [%ld max] of %ld created; %ld getter_Copies, %ld attempts to share\n",
                       sAliveCount, sHighWaterCount, sCreatedCount, sAssignCount, sShareCount);
  }
#endif


const nsXPIDLCString::shared_buffer_handle_type*
nsXPIDLCString::GetSharedBufferHandle() const
  {
    self_type* mutable_this = NS_CONST_CAST(self_type*, this);
    if ( !mBuffer->DataStart() )
      // XXXldb This isn't any good.  What if we just called
      // PrepareForUseAsOutParam and it hasn't been filled in yet?
      mutable_this->mBuffer = GetSharedEmptyBufferHandle();
    else if ( !mBuffer->DataEnd() )
      {
        // Our handle may not be an nsImportedStringHandle.  However, if it
        // is not, this cast will still be safe since no other handle will
        // be in this state.
        const nsImportedStringHandle<char_type>* handle = NS_STATIC_CAST(const nsImportedStringHandle<char_type>*, mBuffer.get());
        handle->RecalculateBoundaries();
      }

#if DEBUG_STRING_STATS
    ++sShareCount;
#endif
    return mBuffer.get();
  }


nsXPIDLCString::char_type**
nsXPIDLCString::PrepareForUseAsOutParam()
  {
    nsImportedStringHandle<char_type>* handle = new nsImportedStringHandle<char_type>();
    NS_ASSERTION(handle, "Trouble!  We couldn't get a new handle during |getter_Copies|.");

    mBuffer = handle;
#if DEBUG_STRING_STATS
    ++sAssignCount;
#endif
    return handle->AddressOfStorageStart();
  }

/* static */
nsXPIDLCString::shared_buffer_handle_type*
nsXPIDLCString::GetSharedEmptyBufferHandle()
  {
    static shared_buffer_handle_type* sBufferHandle = nsnull;
    static char_type null_char = char_type(0);

    if (!sBufferHandle) {
      sBufferHandle = new nsNonDestructingSharedBufferHandle<char_type>(&null_char, &null_char, 1);
      sBufferHandle->AcquireReference(); // To avoid the |Destroy|
                                         // mechanism unless threads
                                         // race to set the refcount, in
                                         // which case we'll pull the
                                         // same trick in |Destroy|.
      sBufferHandle->SetImplementationFlags(sBufferHandle->GetImplementationFlags() | shared_buffer_handle_type::kIsNULL);
    }
    return sBufferHandle;
  }