root/magick/distribute-cache.c

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DEFINITIONS

This source file includes following definitions.
  1. dpc_read
  2. ConnectPixelCacheServer
  3. GetHostname
  4. AcquireDistributeCacheInfo
  5. DestroyDistributeCacheInfo
  6. DestroyDistributeCache
  7. dpc_send
  8. OpenDistributeCache
  9. ReadDistributeCacheIndexes
  10. ReadDistributeCachePixels
  11. RelinquishImageRegistry
  12. WriteDistributeCacheIndexes
  13. WriteDistributeCachePixels
  14. DistributePixelCacheClient
  15. DistributePixelCacheServer
  16. GetDistributeCacheFile
  17. GetDistributeCacheHostname
  18. GetDistributeCachePort
  19. OpenDistributePixelCache
  20. ReadDistributePixelCacheIndexes
  21. ReadDistributePixelCachePixels
  22. RelinquishDistributePixelCache
  23. WriteDistributePixelCacheIndexes
  24. WriteDistributePixelCachePixels

/*
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%                                                                             %
%                                                                             %
%    DDDD    IIIII   SSSSS  TTTTT  RRRR   IIIII  BBBB   U   U  TTTTT  EEEEE   %
%    D   D     I     SS       T    R   R    I    B   B  U   U    T    E       %
%    D   D     I      SSS     T    RRRR     I    BBBB   U   U    T    EEE     %
%    D   D     I        SS    T    R R      I    B   B  U   U    T    E       %
%    DDDDA   IIIII   SSSSS    T    R  R   IIIII  BBBB    UUU     T    EEEEE   %
%                                                                             %
%                      CCCC   AAA    CCCC  H   H  EEEEE                       %
%                     C      A   A  C      H   H  E                           %
%                     C      AAAAA  C      HHHHH  EEE                         %
%                     C      A   A  C      H   H  E                           %
%                      CCCC  A   A   CCCC  H   H  EEEEE                       %
%                                                                             %
%                                                                             %
%                 MagickCore Distributed Pixel Cache Methods                  %
%                                                                             %
%                              Software Design                                %
%                                   Cristy                                    %
%                                January 2013                                 %
%                                                                             %
%                                                                             %
%  Copyright 1999-2015 ImageMagick Studio LLC, a non-profit organization      %
%  dedicated to making software imaging solutions freely available.           %
%                                                                             %
%  You may not use this file except in compliance with the License.  You may  %
%  obtain a copy of the License at                                            %
%                                                                             %
%    http://www.imagemagick.org/script/license.php                            %
%                                                                             %
%  Unless required by applicable law or agreed to in writing, software        %
%  distributed under the License is distributed on an "AS IS" BASIS,          %
%  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.   %
%  See the License for the specific language governing permissions and        %
%  limitations under the License.                                             %
%                                                                             %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
% A distributed pixel cache is an extension of the traditional pixel cache
% available on a single host.  The distributed pixel cache may span multiple
% servers so that it can grow in size and transactional capacity to support
% very large images.  Start up the pixel cache server on one or more machines.
% When you read or operate on an image and the local pixel cache resources are
% exhausted, ImageMagick contacts one or more of these remote pixel servers to
% store or retrieve pixels.
%
*/

/*
  Include declarations.
*/
#include "magick/studio.h"
#include "magick/cache.h"
#include "magick/cache-private.h"
#include "magick/distribute-cache.h"
#include "magick/distribute-cache-private.h"
#include "magick/exception.h"
#include "magick/exception-private.h"
#include "magick/geometry.h"
#include "magick/image.h"
#include "magick/image-private.h"
#include "magick/list.h"
#include "magick/locale_.h"
#include "magick/memory_.h"
#include "magick/nt-base-private.h"
#include "magick/policy.h"
#include "magick/random_.h"
#include "magick/registry.h"
#include "magick/splay-tree.h"
#include "magick/string_.h"
#include "magick/string-private.h"
#include "magick/version.h"
#include "magick/version-private.h"
#undef MAGICKCORE_HAVE_DISTRIBUTE_CACHE
#if defined(MAGICKCORE_HAVE_SOCKET) && defined(MAGICKCORE_THREAD_SUPPORT)
#include <netinet/in.h>
#include <netdb.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#define CHAR_TYPE_CAST
#define CLOSE_SOCKET(socket) (void) close(socket)
#define HANDLER_RETURN_TYPE void *
#define HANDLER_RETURN_VALUE (void *) NULL
#define SOCKET_TYPE int
#define MAGICKCORE_HAVE_DISTRIBUTE_CACHE
#elif defined(MAGICKCORE_WINDOWS_SUPPORT)
#define CHAR_TYPE_CAST (char *)
#define CLOSE_SOCKET(socket) (void) closesocket(socket)
#define HANDLER_RETURN_TYPE DWORD WINAPI
#define HANDLER_RETURN_VALUE 0
#define SOCKET_TYPE SOCKET
#define MAGICKCORE_HAVE_DISTRIBUTE_CACHE
#else
#define CLOSE_SOCKET(socket) 
#define HANDLER_RETURN_TYPE  void *
#define HANDLER_RETURN_VALUE  (void *) NULL
#define SOCKET_TYPE  int
#undef send
#undef recv
#define send(file,buffer,length,flags)  0
#define recv(file,buffer,length,flags)  0
#endif

/*
  Define declarations.
*/
#define DPCHostname  "127.0.0.1"
#define DPCPendingConnections  10
#define DPCPort  6668
#define DPCSessionKeyLength  8
#ifndef MSG_NOSIGNAL
#  define MSG_NOSIGNAL 0
#endif

/*
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%                                                                             %
%                                                                             %
%                                                                             %
+   A c q u i r e D i s t r i b u t e C a c h e I n f o                       %
%                                                                             %
%                                                                             %
%                                                                             %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
%  AcquireDistributeCacheInfo() allocates the DistributeCacheInfo structure.
%
%  The format of the AcquireDistributeCacheInfo method is:
%
%      DistributeCacheInfo *AcquireDistributeCacheInfo(ExceptionInfo *exception)
%
%  A description of each parameter follows:
%
%    o exception: return any errors or warnings in this structure.
%
*/

static inline MagickOffsetType dpc_read(int file,const MagickSizeType length,
  unsigned char *restrict message)
{
  register MagickOffsetType
    i;

  ssize_t
    count;

#if !defined(MAGICKCORE_HAVE_DISTRIBUTE_CACHE)
  magick_unreferenced(file);
  magick_unreferenced(message);
#endif

  count=0;
  for (i=0; i < (MagickOffsetType) length; i+=count)
  {
    count=recv(file,CHAR_TYPE_CAST message+i,(size_t) MagickMin(length-i,
      (MagickSizeType) SSIZE_MAX),0);
    if (count <= 0)
      {
        count=0;
        if (errno != EINTR)
          break;
      }
  }
  return(i);
}

static int ConnectPixelCacheServer(const char *hostname,const int port,
  size_t *session_key,ExceptionInfo *exception)
{
#if defined(MAGICKCORE_HAVE_DISTRIBUTE_CACHE)
  char
    service[MaxTextExtent];

  const char
    *shared_secret;

  int
    status;

  SOCKET_TYPE
    client_socket;

  ssize_t
    count;

  struct addrinfo
    hint,
    *result;

  unsigned char
    secret[MaxTextExtent];

  /*
    Connect to distributed pixel cache and get session key.
  */
  *session_key=0;
  shared_secret=GetPolicyValue("shared-secret");
  if (shared_secret == (const char *) NULL)
    {
      (void) ThrowMagickException(exception,GetMagickModule(),CacheError,
        "DistributedPixelCache","'%s'","shared secret expected");
      return(-1);
    }
#if defined(MAGICKCORE_WINDOWS_SUPPORT)
  NTInitializeWinsock(MagickTrue);
#endif
  (void) ResetMagickMemory(&hint,0,sizeof(hint));
  hint.ai_family=AF_INET;
  hint.ai_socktype=SOCK_STREAM;
  hint.ai_flags=AI_PASSIVE;
  (void) FormatLocaleString(service,MaxTextExtent,"%d",port);
  status=getaddrinfo(hostname,service,&hint,&result);
  if (status != 0)
    {
      (void) ThrowMagickException(exception,GetMagickModule(),CacheError,
        "DistributedPixelCache","'%s'",hostname);
      return(-1);
    }
  client_socket=socket(result->ai_family,result->ai_socktype,
    result->ai_protocol);
  if (client_socket == -1)
    {
      freeaddrinfo(result);
      (void) ThrowMagickException(exception,GetMagickModule(),CacheError,
        "DistributedPixelCache","'%s'",hostname);
      return(-1);
    }
  status=connect(client_socket,result->ai_addr,result->ai_addrlen);
  if (status == -1)
    {
      CLOSE_SOCKET(client_socket);
      freeaddrinfo(result);
      (void) ThrowMagickException(exception,GetMagickModule(),CacheError,
        "DistributedPixelCache","'%s'",hostname);
      return(-1);
    }
  count=recv(client_socket,CHAR_TYPE_CAST secret,MaxTextExtent,0);
  if (count != -1)
    {
      StringInfo
        *nonce;

      nonce=AcquireStringInfo(count);
      (void) memcpy(GetStringInfoDatum(nonce),secret,(size_t) count);
      *session_key=GetMagickSignature(nonce);
      nonce=DestroyStringInfo(nonce);
    }
  if (*session_key == 0)
    {
      CLOSE_SOCKET(client_socket);
      client_socket=(SOCKET_TYPE) (-1);
    }
  freeaddrinfo(result);
  return(client_socket);
#else
  magick_unreferenced(hostname);
  magick_unreferenced(port);
  magick_unreferenced(session_key);
  magick_unreferenced(exception);
  (void) ThrowMagickException(exception,GetMagickModule(),MissingDelegateError,
    "DelegateLibrarySupportNotBuiltIn","distributed pixel cache");
  return(MagickFalse);
#endif
}

static char *GetHostname(int *port,ExceptionInfo *exception)
{
  char
    *host,
    *hosts,
    **hostlist;

  int
    argc;

  register ssize_t
    i;

  static size_t
    id = 0;

  /*
    Parse host list (e.g. 192.168.100.1:6668,192.168.100.2:6668).
  */
  hosts=(char *) GetImageRegistry(StringRegistryType,"cache:hosts",exception);
  if (hosts == (char *) NULL)
    {
      *port=DPCPort;
      return(AcquireString(DPCHostname));
    }
  (void) SubstituteString(&hosts,","," ");
  hostlist=StringToArgv(hosts,&argc);
  hosts=DestroyString(hosts);
  if (hostlist == (char **) NULL)
    {
      *port=DPCPort;
      return(AcquireString(DPCHostname));
    }
  hosts=AcquireString(hostlist[(id++ % (argc-1))+1]);
  for (i=0; i < (ssize_t) argc; i++)
    hostlist[i]=DestroyString(hostlist[i]);
  hostlist=(char **) RelinquishMagickMemory(hostlist);
  (void) SubstituteString(&hosts,":"," ");
  hostlist=StringToArgv(hosts,&argc);
  if (hostlist == (char **) NULL)
    {
      *port=DPCPort;
      return(AcquireString(DPCHostname));
    }
  host=AcquireString(hostlist[1]);
  if (hostlist[2] == (char *) NULL)
    *port=DPCPort;
  else
    *port=StringToLong(hostlist[2]);
  for (i=0; i < (ssize_t) argc; i++)
    hostlist[i]=DestroyString(hostlist[i]);
  hostlist=(char **) RelinquishMagickMemory(hostlist);
  return(host);
}

MagickPrivate DistributeCacheInfo *AcquireDistributeCacheInfo(
  ExceptionInfo *exception)
{
  char
    *hostname;

  DistributeCacheInfo
    *server_info;

  size_t
    session_key;

  /*
    Connect to the distributed pixel cache server.
  */
  server_info=(DistributeCacheInfo *) AcquireMagickMemory(sizeof(*server_info));
  if (server_info == (DistributeCacheInfo *) NULL)
    ThrowFatalException(ResourceLimitFatalError,"MemoryAllocationFailed");
  (void) ResetMagickMemory(server_info,0,sizeof(*server_info));
  server_info->signature=MagickSignature;
  server_info->port=0;
  hostname=GetHostname(&server_info->port,exception);
  session_key=0;
  server_info->file=ConnectPixelCacheServer(hostname,server_info->port,
    &session_key,exception);
  if (server_info->file == -1)
    server_info=DestroyDistributeCacheInfo(server_info);
  else
    {
      server_info->session_key=session_key;
      (void) CopyMagickString(server_info->hostname,hostname,MaxTextExtent);
      server_info->debug=IsEventLogging();
    }
  hostname=DestroyString(hostname);
  return(server_info);
}

/*
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%                                                                             %
%                                                                             %
%                                                                             %
+   D e s t r o y D i s t r i b u t e C a c h e I n f o                       %
%                                                                             %
%                                                                             %
%                                                                             %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
%  DestroyDistributeCacheInfo() deallocates memory associated with an
%  DistributeCacheInfo structure.
%
%  The format of the DestroyDistributeCacheInfo method is:
%
%      DistributeCacheInfo *DestroyDistributeCacheInfo(
%        DistributeCacheInfo *server_info)
%
%  A description of each parameter follows:
%
%    o server_info: the distributed cache info.
%
*/
MagickPrivate DistributeCacheInfo *DestroyDistributeCacheInfo(
  DistributeCacheInfo *server_info)
{
  assert(server_info != (DistributeCacheInfo *) NULL);
  assert(server_info->signature == MagickSignature);
  if (server_info->file > 0)
    CLOSE_SOCKET(server_info->file);
  server_info->signature=(~MagickSignature);
  server_info=(DistributeCacheInfo *) RelinquishMagickMemory(server_info);
  return(server_info);
}

/*
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%                                                                             %
%                                                                             %
%                                                                             %
+   D i s t r i b u t e P i x e l C a c h e S e r v e r                       %
%                                                                             %
%                                                                             %
%                                                                             %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
%  DistributePixelCacheServer() waits on the specified port for commands to
%  create, read, update, or destroy a pixel cache.
%
%  The format of the DistributePixelCacheServer() method is:
%
%      void DistributePixelCacheServer(const int port)
%
%  A description of each parameter follows:
%
%    o port: connect the distributed pixel cache at this port.
%
%    o exception: return any errors or warnings in this structure.
%
*/

static MagickBooleanType DestroyDistributeCache(SplayTreeInfo *registry,
  const size_t session_key)
{
  /*
    Destroy distributed pixel cache.
  */
  return(DeleteNodeFromSplayTree(registry,(const void *) session_key));
}

static inline MagickOffsetType dpc_send(int file,const MagickSizeType length,
  const unsigned char *restrict message)
{
  MagickOffsetType
    count;

  register MagickOffsetType
    i;

#if !defined(MAGICKCORE_HAVE_DISTRIBUTE_CACHE)
  magick_unreferenced(file);
  magick_unreferenced(message);
#endif

  /*
    Ensure a complete message is sent.
  */
  count=0;
  for (i=0; i < (MagickOffsetType) length; i+=count)
  {
    count=(MagickOffsetType) send(file,CHAR_TYPE_CAST message+i,(size_t) MagickMin(length-i,
      (MagickSizeType) SSIZE_MAX),MSG_NOSIGNAL);
    if (count <= 0)
      {
        count=0;
        if (errno != EINTR)
          break;
      }
  }
  return(i);
}

static MagickBooleanType OpenDistributeCache(SplayTreeInfo *registry,int file,
  const size_t session_key,ExceptionInfo *exception)
{
  Image
    *image;

  MagickBooleanType
    status;

  MagickOffsetType
    count;

  MagickSizeType
    length;

  register unsigned char
    *p;

  unsigned char
    message[MaxTextExtent];

  /*
    Open distributed pixel cache.
  */
  image=AcquireImage((ImageInfo *) NULL);
  if (image == (Image *) NULL)
    return(MagickFalse);
  length=sizeof(image->storage_class)+sizeof(image->colorspace)+
    sizeof(image->channels)+sizeof(image->columns)+sizeof(image->rows);
  count=dpc_read(file,length,message);
  if (count != (MagickOffsetType) length)
    return(MagickFalse);
  /*
    Deserialize the image attributes.
  */
  p=message;
  (void) memcpy(&image->storage_class,p,sizeof(image->storage_class));
  p+=sizeof(image->storage_class);
  (void) memcpy(&image->colorspace,p,sizeof(image->colorspace));
  p+=sizeof(image->colorspace);
  (void) memcpy(&image->channels,p,sizeof(image->channels));
  p+=sizeof(image->channels);
  (void) memcpy(&image->columns,p,sizeof(image->columns));
  p+=sizeof(image->columns);
  (void) memcpy(&image->rows,p,sizeof(image->rows));
  p+=sizeof(image->rows);
  if (SyncImagePixelCache(image,exception) == MagickFalse)
    return(MagickFalse);
  status=AddValueToSplayTree(registry,(const void *) session_key,image);
  return(status);
}

static MagickBooleanType ReadDistributeCacheIndexes(SplayTreeInfo *registry,
  int file,const size_t session_key,ExceptionInfo *exception)
{
  const IndexPacket
    *indexes;

  Image
    *image;

  MagickOffsetType
    count;

  MagickSizeType
    length;

  RectangleInfo
    region;

  register const PixelPacket
    *p;

  register unsigned char
    *q;

  unsigned char
    message[MaxTextExtent];

  /*
    Read distributed pixel cache indexes.
  */
  image=(Image *) GetValueFromSplayTree(registry,(const void *) session_key);
  if (image == (Image *) NULL)
    return(MagickFalse);
  length=sizeof(region.width)+sizeof(region.height)+sizeof(region.x)+
    sizeof(region.y)+sizeof(length);
  count=dpc_read(file,length,message);
  if (count != (MagickOffsetType) length)
    return(MagickFalse);
  q=message;
  (void) memcpy(&region.width,q,sizeof(region.width));
  q+=sizeof(region.width);
  (void) memcpy(&region.height,q,sizeof(region.height));
  q+=sizeof(region.height);
  (void) memcpy(&region.x,q,sizeof(region.x));
  q+=sizeof(region.x);
  (void) memcpy(&region.y,q,sizeof(region.y));
  q+=sizeof(region.y);
  (void) memcpy(&length,q,sizeof(length));
  q+=sizeof(length);
  p=GetVirtualPixels(image,region.x,region.y,region.width,region.height,
    exception);
  if (p == (const PixelPacket *) NULL)
    return(MagickFalse);
  indexes=GetVirtualIndexQueue(image);
  count=dpc_send(file,length,(unsigned char *) indexes);
  if (count != (MagickOffsetType) length)
    return(MagickFalse);
  return(MagickTrue);
}

static MagickBooleanType ReadDistributeCachePixels(SplayTreeInfo *registry,
  int file,const size_t session_key,ExceptionInfo *exception)
{
  Image
    *image;

  MagickOffsetType
    count;

  MagickSizeType
    length;

  RectangleInfo
    region;

  register const PixelPacket
    *p;

  register unsigned char
    *q;

  unsigned char
    message[MaxTextExtent];

  /*
    Read distributed pixel cache pixels.
  */
  image=(Image *) GetValueFromSplayTree(registry,(const void *) session_key);
  if (image == (Image *) NULL)
    return(MagickFalse);
  length=sizeof(region.width)+sizeof(region.height)+sizeof(region.x)+
    sizeof(region.y)+sizeof(length);
  count=dpc_read(file,length,message);
  if (count != (MagickOffsetType) length)
    return(MagickFalse);
  q=message;
  (void) memcpy(&region.width,q,sizeof(region.width));
  q+=sizeof(region.width);
  (void) memcpy(&region.height,q,sizeof(region.height));
  q+=sizeof(region.height);
  (void) memcpy(&region.x,q,sizeof(region.x));
  q+=sizeof(region.x);
  (void) memcpy(&region.y,q,sizeof(region.y));
  q+=sizeof(region.y);
  (void) memcpy(&length,q,sizeof(length));
  q+=sizeof(length);
  p=GetVirtualPixels(image,region.x,region.y,region.width,region.height,
    exception);
  if (p == (const PixelPacket *) NULL)
    return(MagickFalse);
  count=dpc_send(file,length,(unsigned char *) p);
  if (count != (MagickOffsetType) length)
    return(MagickFalse);
  return(MagickTrue);
}

static void *RelinquishImageRegistry(void *image)
{
  return((void *) DestroyImageList((Image *) image));
}

static MagickBooleanType WriteDistributeCacheIndexes(SplayTreeInfo *registry,
  int file,const size_t session_key,ExceptionInfo *exception)
{
  Image
    *image;

  IndexPacket
    *indexes;

  MagickOffsetType
    count;

  MagickSizeType
    length;

  RectangleInfo
    region;

  register unsigned char
    *p;

  register PixelPacket
    *q;

  unsigned char
    message[MaxTextExtent];

  /*
    Write distributed pixel cache indexes.
  */
  image=(Image *) GetValueFromSplayTree(registry,(const void *) session_key);
  if (image == (Image *) NULL)
    return(MagickFalse);
  length=sizeof(region.width)+sizeof(region.height)+sizeof(region.x)+
    sizeof(region.y)+sizeof(length);
  count=dpc_read(file,length,message);
  if (count != (MagickOffsetType) length)
    return(MagickFalse);
  p=message;
  (void) memcpy(&region.width,p,sizeof(region.width));
  p+=sizeof(region.width);
  (void) memcpy(&region.height,p,sizeof(region.height));
  p+=sizeof(region.height);
  (void) memcpy(&region.x,p,sizeof(region.x));
  p+=sizeof(region.x);
  (void) memcpy(&region.y,p,sizeof(region.y));
  p+=sizeof(region.y);
  (void) memcpy(&length,p,sizeof(length));
  p+=sizeof(length);
  q=GetAuthenticPixels(image,region.x,region.y,region.width,region.height,
    exception);
  if (q == (PixelPacket *) NULL)
    return(MagickFalse);
  indexes=GetAuthenticIndexQueue(image);
  count=dpc_read(file,length,(unsigned char *) indexes);
  if (count != (MagickOffsetType) length)
    return(MagickFalse);
  return(SyncAuthenticPixels(image,exception));
}

static MagickBooleanType WriteDistributeCachePixels(SplayTreeInfo *registry,
  int file,const size_t session_key,ExceptionInfo *exception)
{
  Image
    *image;

  MagickOffsetType
    count;

  MagickSizeType
    length;

  RectangleInfo
    region;

  register PixelPacket
    *q;

  register unsigned char
    *p;

  unsigned char
    message[MaxTextExtent];

  /*
    Write distributed pixel cache pixels.
  */
  image=(Image *) GetValueFromSplayTree(registry,(const void *) session_key);
  if (image == (Image *) NULL)
    return(MagickFalse);
  length=sizeof(region.width)+sizeof(region.height)+sizeof(region.x)+
    sizeof(region.y)+sizeof(length);
  count=dpc_read(file,length,message);
  if (count != (MagickOffsetType) length)
    return(MagickFalse);
  p=message;
  (void) memcpy(&region.width,p,sizeof(region.width));
  p+=sizeof(region.width);
  (void) memcpy(&region.height,p,sizeof(region.height));
  p+=sizeof(region.height);
  (void) memcpy(&region.x,p,sizeof(region.x));
  p+=sizeof(region.x);
  (void) memcpy(&region.y,p,sizeof(region.y));
  p+=sizeof(region.y);
  (void) memcpy(&length,p,sizeof(length));
  p+=sizeof(length);
  q=GetAuthenticPixels(image,region.x,region.y,region.width,region.height,
    exception);
  if (q == (PixelPacket *) NULL)
    return(MagickFalse);
  count=dpc_read(file,length,(unsigned char *) q);
  if (count != (MagickOffsetType) length)
    return(MagickFalse);
  return(SyncAuthenticPixels(image,exception));
}

static HANDLER_RETURN_TYPE DistributePixelCacheClient(void *socket)
{
  const char
    *shared_secret;

  ExceptionInfo
    *exception;

  MagickBooleanType
    status;

  MagickOffsetType
    count;

  RandomInfo
    *random_info;

  register unsigned char
    *p;

  size_t
    key,
    session_key;

  SOCKET_TYPE
    client_socket;

  SplayTreeInfo
    *registry;

  StringInfo
    *secret;

  unsigned char
    command,
    session[2*MaxTextExtent];

  /*
    Distributed pixel cache client.
  */
  shared_secret=GetPolicyValue("shared-secret");
  if (shared_secret == (const char *) NULL)
    ThrowFatalException(CacheFatalError,"shared secret expected");
  p=session;
  (void) CopyMagickString((char *) p,shared_secret,MaxTextExtent);
  p+=strlen(shared_secret);
  random_info=AcquireRandomInfo();
  secret=GetRandomKey(random_info,DPCSessionKeyLength);
  (void) memcpy(p,GetStringInfoDatum(secret),DPCSessionKeyLength);
  session_key=GetMagickSignature(secret);
  random_info=DestroyRandomInfo(random_info);
  exception=AcquireExceptionInfo();
  registry=NewSplayTree((int (*)(const void *,const void *)) NULL,
    (void *(*)(void *)) NULL,RelinquishImageRegistry);
  client_socket=(*(int *) socket);
  count=dpc_send(client_socket,DPCSessionKeyLength,GetStringInfoDatum(secret));
  secret=DestroyStringInfo(secret);
  for ( ; ; )
  {
    count=dpc_read(client_socket,1,(unsigned char *) &command);
    if (count <= 0)
      break;
    count=dpc_read(client_socket,sizeof(key),(unsigned char *) &key);
    if ((count != (MagickOffsetType) sizeof(key)) || (key != session_key))
      break;
    status=MagickFalse;
    switch (command)
    {
      case 'o':
      {
        status=OpenDistributeCache(registry,client_socket,session_key,
          exception);
        count=dpc_send(client_socket,sizeof(status),(unsigned char *) &status);
        break;
      }
      case 'r':
      {
        status=ReadDistributeCachePixels(registry,client_socket,session_key,
          exception);
        break;
      }
      case 'R':
      {
        status=ReadDistributeCacheIndexes(registry,client_socket,session_key,
          exception);
        break;
      }
      case 'w':
      {
        status=WriteDistributeCachePixels(registry,client_socket,session_key,
          exception);
        break;
      }
      case 'W':
      {
        status=WriteDistributeCacheIndexes(registry,client_socket,session_key,
          exception);
        break;
      }
      case 'd':
      {
        status=DestroyDistributeCache(registry,session_key);
        break;
      }
      default:
        break;
    }
    if (status == MagickFalse)
      break;
    if (command == 'd')
      break;
  }
  count=dpc_send(client_socket,sizeof(status),(unsigned char *) &status);
  CLOSE_SOCKET(client_socket);
  exception=DestroyExceptionInfo(exception);
  registry=DestroySplayTree(registry);
  return(HANDLER_RETURN_VALUE);
}

MagickExport void DistributePixelCacheServer(const int port,
  ExceptionInfo *exception)
{
#if defined(MAGICKCORE_HAVE_DISTRIBUTE_CACHE)
  char
    service[MaxTextExtent];

  int
    status;

#if defined(MAGICKCORE_THREAD_SUPPORT)
  pthread_attr_t
    attributes;

  pthread_t
    threads;
#elif defined(MAGICKCORE_WINDOWS_SUPPORT)
  DWORD
    threadID;
#else
  Not implemented!
#endif

  register struct addrinfo
    *p;

  SOCKET_TYPE
    server_socket;

  struct addrinfo
    hint,
    *result;

  struct sockaddr_in
    address;

  /*
    Launch distributed pixel cache server.
  */
  magick_unreferenced(exception);
#if defined(MAGICKCORE_WINDOWS_SUPPORT)
  NTInitializeWinsock(MagickFalse);
#endif
  (void) ResetMagickMemory(&hint,0,sizeof(hint));
  hint.ai_family=AF_INET;
  hint.ai_socktype=SOCK_STREAM;
  hint.ai_flags=AI_PASSIVE;
  (void) FormatLocaleString(service,MaxTextExtent,"%d",port);
  status=getaddrinfo((const char *) NULL,service,&hint,&result);
  if (status != 0)
    ThrowFatalException(CacheFatalError,"UnableToListen");
  server_socket=(SOCKET_TYPE) 0;
  for (p=result; p != (struct addrinfo *) NULL; p=p->ai_next)
  {
    int
      one;

    server_socket=socket(p->ai_family,p->ai_socktype,p->ai_protocol);
    if (server_socket == -1)
      continue;
    one=1;
    status=setsockopt(server_socket,SOL_SOCKET,SO_REUSEADDR,
      CHAR_TYPE_CAST &one,(socklen_t) sizeof(one));
    if (status == -1)
      {
        CLOSE_SOCKET(server_socket);
        continue;
      }
    status=bind(server_socket,p->ai_addr,p->ai_addrlen);
    if (status == -1)
      {
        CLOSE_SOCKET(server_socket);
        continue;
      }
    break;
  }
  if (p == (struct addrinfo *) NULL)
    ThrowFatalException(CacheFatalError,"UnableToBind");
  freeaddrinfo(result);
  status=listen(server_socket,DPCPendingConnections);
  if (status != 0)
    ThrowFatalException(CacheFatalError,"UnableToListen");
#if defined(MAGICKCORE_THREAD_SUPPORT)
  pthread_attr_init(&attributes);
#endif
  for ( ; ; )
  {
    SOCKET_TYPE
      client_socket;

    socklen_t
      length;

    length=(socklen_t) sizeof(address);
    client_socket=accept(server_socket,(struct sockaddr *) &address,&length);
    if (client_socket == -1)
      ThrowFatalException(CacheFatalError,"UnableToEstablishConnection");
#if defined(MAGICKCORE_THREAD_SUPPORT)
    status=pthread_create(&threads,&attributes,DistributePixelCacheClient,
      (void *) &client_socket);
    if (status == -1)
      ThrowFatalException(CacheFatalError,"UnableToCreateClientThread");
#elif defined(MAGICKCORE_WINDOWS_SUPPORT)
    if (CreateThread(0,0,DistributePixelCacheClient,(void*) &client_socket,0,
        &threadID) == (HANDLE) NULL)
      ThrowFatalException(CacheFatalError,"UnableToCreateClientThread");
#else
    Not implemented!
#endif
  }
#else
  magick_unreferenced(port);
  magick_unreferenced(exception);
  ThrowFatalException(MissingDelegateError,"DelegateLibrarySupportNotBuiltIn");
#endif
}

/*
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%                                                                             %
%                                                                             %
%                                                                             %
+   G e t D i s t r i b u t e C a c h e F i l e                               %
%                                                                             %
%                                                                             %
%                                                                             %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
%  GetDistributeCacheFile() returns the file associated with this
%  DistributeCacheInfo structure.
%
%  The format of the GetDistributeCacheFile method is:
%
%      int GetDistributeCacheFile(const DistributeCacheInfo *server_info)
%
%  A description of each parameter follows:
%
%    o server_info: the distributed cache info.
%
*/
MagickPrivate int GetDistributeCacheFile(const DistributeCacheInfo *server_info)
{
  assert(server_info != (DistributeCacheInfo *) NULL);
  assert(server_info->signature == MagickSignature);
  return(server_info->file);
}

/*
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%                                                                             %
%                                                                             %
%                                                                             %
+   G e t D i s t r i b u t e C a c h e H o s t n a m e                       %
%                                                                             %
%                                                                             %
%                                                                             %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
%  GetDistributeCacheHostname() returns the hostname associated with this
%  DistributeCacheInfo structure.
%
%  The format of the GetDistributeCacheHostname method is:
%
%      const char *GetDistributeCacheHostname(
%        const DistributeCacheInfo *server_info)
%
%  A description of each parameter follows:
%
%    o server_info: the distributed cache info.
%
*/
MagickPrivate const char *GetDistributeCacheHostname(
  const DistributeCacheInfo *server_info)
{
  assert(server_info != (DistributeCacheInfo *) NULL);
  assert(server_info->signature == MagickSignature);
  return(server_info->hostname);
}

/*
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%                                                                             %
%                                                                             %
%                                                                             %
+   G e t D i s t r i b u t e C a c h e P o r t                               %
%                                                                             %
%                                                                             %
%                                                                             %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
%  GetDistributeCachePort() returns the port associated with this
%  DistributeCacheInfo structure.
%
%  The format of the GetDistributeCachePort method is:
%
%      int GetDistributeCachePort(const DistributeCacheInfo *server_info)
%
%  A description of each parameter follows:
%
%    o server_info: the distributed cache info.
%
*/
MagickPrivate int GetDistributeCachePort(const DistributeCacheInfo *server_info)
{
  assert(server_info != (DistributeCacheInfo *) NULL);
  assert(server_info->signature == MagickSignature);
  return(server_info->port);
}

/*
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%                                                                             %
%                                                                             %
%                                                                             %
+   O p e n D i s t r i b u t e P i x e l C a c h e                           %
%                                                                             %
%                                                                             %
%                                                                             %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
%  OpenDistributePixelCache() opens a pixel cache on a remote server.
%
%  The format of the OpenDistributePixelCache method is:
%
%      MagickBooleanType *OpenDistributePixelCache(
%        DistributeCacheInfo *server_info,Image *image)
%
%  A description of each parameter follows:
%
%    o server_info: the distributed cache info.
%
%    o image: the image.
%
*/
MagickPrivate MagickBooleanType OpenDistributePixelCache(
  DistributeCacheInfo *server_info,Image *image)
{
  MagickBooleanType
    status;

  MagickOffsetType
    count;

  register unsigned char
    *p;

  unsigned char
    message[MaxTextExtent];

  /*
    Open distributed pixel cache.
  */
  assert(server_info != (DistributeCacheInfo *) NULL);
  assert(server_info->signature == MagickSignature);
  assert(image != (Image *) NULL);
  assert(image->signature == MagickSignature);
  p=message;
  *p++='o';  /* open */
  /*
    Serialize image attributes (see ValidatePixelCacheMorphology()).
  */
  (void) memcpy(p,&server_info->session_key,sizeof(server_info->session_key));
  p+=sizeof(server_info->session_key);
  (void) memcpy(p,&image->storage_class,sizeof(image->storage_class));
  p+=sizeof(image->storage_class);
  (void) memcpy(p,&image->colorspace,sizeof(image->colorspace));
  p+=sizeof(image->colorspace);
  (void) memcpy(p,&image->channels,sizeof(image->channels));
  p+=sizeof(image->channels);
  (void) memcpy(p,&image->columns,sizeof(image->columns));
  p+=sizeof(image->columns);
  (void) memcpy(p,&image->rows,sizeof(image->rows));
  p+=sizeof(image->rows);
  count=dpc_send(server_info->file,p-message,message);
  if (count != (MagickOffsetType) (p-message))
    return(MagickFalse);
  status=MagickFalse;
  count=dpc_read(server_info->file,sizeof(status),(unsigned char *) &status);
  if (count != (MagickOffsetType) sizeof(status))
    return(MagickFalse);
  return(status);
}

/*
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%                                                                             %
%                                                                             %
%                                                                             %
+   R e a d D i s t r i b u t e P i x e l C a c h e I n d e x e s             %
%                                                                             %
%                                                                             %
%                                                                             %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
%  ReadDistributePixelCacheIndexes() reads indexes from the specified region
%  of the distributed pixel cache.
%
%  The format of the ReadDistributePixelCacheIndexes method is:
%
%      MagickOffsetType ReadDistributePixelCacheIndexes(
%        DistributeCacheInfo *server_info,const RectangleInfo *region,
%        const MagickSizeType length,unsigned char *indexes)
%
%  A description of each parameter follows:
%
%    o server_info: the distributed cache info.
%
%    o image: the image.
%
%    o region: read the indexes from this region of the image.
%
%    o length: the length in bytes of the indexes.
%
%    o indexes: read these indexes from the pixel cache.
%
*/
MagickPrivate MagickOffsetType ReadDistributePixelCacheIndexes(
  DistributeCacheInfo *server_info,const RectangleInfo *region,
  const MagickSizeType length,unsigned char *indexes)
{
  MagickOffsetType
    count;

  register unsigned char
    *p;

  unsigned char
    message[MaxTextExtent];

  /*
    Read distributed pixel cache indexes.
  */
  assert(server_info != (DistributeCacheInfo *) NULL);
  assert(server_info->signature == MagickSignature);
  assert(region != (RectangleInfo *) NULL);
  assert(indexes != (unsigned char *) NULL);
  if (length > (MagickSizeType) SSIZE_MAX)
    return(-1);
  p=message;
  *p++='R';
  (void) memcpy(p,&server_info->session_key,sizeof(server_info->session_key));
  p+=sizeof(server_info->session_key);
  (void) memcpy(p,&region->width,sizeof(region->width));
  p+=sizeof(region->width);
  (void) memcpy(p,&region->height,sizeof(region->height));
  p+=sizeof(region->height);
  (void) memcpy(p,&region->x,sizeof(region->x));
  p+=sizeof(region->x);
  (void) memcpy(p,&region->y,sizeof(region->y));
  p+=sizeof(region->y);
  (void) memcpy(p,&length,sizeof(length));
  p+=sizeof(length);
  count=dpc_send(server_info->file,p-message,message);
  if (count != (MagickOffsetType) (p-message))
    return(-1);
  return(dpc_read(server_info->file,length,indexes));
}

/*
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%                                                                             %
%                                                                             %
%                                                                             %
+   R e a d D i s t r i b u t e P i x e l C a c h e P i x e l s               %
%                                                                             %
%                                                                             %
%                                                                             %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
%  ReadDistributePixelCachePixels() reads pixels from the specified region of
%  the distributed pixel cache.
%
%  The format of the ReadDistributePixelCachePixels method is:
%
%      MagickOffsetType ReadDistributePixelCachePixels(
%        DistributeCacheInfo *server_info,const RectangleInfo *region,
%        const MagickSizeType length,unsigned char *restrict pixels)
%
%  A description of each parameter follows:
%
%    o server_info: the distributed cache info.
%
%    o image: the image.
%
%    o region: read the pixels from this region of the image.
%
%    o length: the length in bytes of the pixels.
%
%    o pixels: read these pixels from the pixel cache.
%
*/
MagickPrivate MagickOffsetType ReadDistributePixelCachePixels(
  DistributeCacheInfo *server_info,const RectangleInfo *region,
  const MagickSizeType length,unsigned char *restrict pixels)
{
  MagickOffsetType
    count;

  register unsigned char
    *p;

  unsigned char
    message[MaxTextExtent];

  /*
    Read distributed pixel cache pixels.
  */
  assert(server_info != (DistributeCacheInfo *) NULL);
  assert(server_info->signature == MagickSignature);
  assert(region != (RectangleInfo *) NULL);
  assert(pixels != (unsigned char *) NULL);
  if (length > (MagickSizeType) SSIZE_MAX)
    return(-1);
  p=message;
  *p++='r';
  (void) memcpy(p,&server_info->session_key,sizeof(server_info->session_key));
  p+=sizeof(server_info->session_key);
  (void) memcpy(p,&region->width,sizeof(region->width));
  p+=sizeof(region->width);
  (void) memcpy(p,&region->height,sizeof(region->height));
  p+=sizeof(region->height);
  (void) memcpy(p,&region->x,sizeof(region->x));
  p+=sizeof(region->x);
  (void) memcpy(p,&region->y,sizeof(region->y));
  p+=sizeof(region->y);
  (void) memcpy(p,&length,sizeof(length));
  p+=sizeof(length);
  count=dpc_send(server_info->file,p-message,message);
  if (count != (MagickOffsetType) (p-message))
    return(-1);
  return(dpc_read(server_info->file,length,pixels));
}

/*
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%                                                                             %
%                                                                             %
%                                                                             %
+   R e l i n q u i s h D i s t r i b u t e P i x e l C a c h e               %
%                                                                             %
%                                                                             %
%                                                                             %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
%  RelinquishDistributePixelCache() frees resources acquired with
%  OpenDistributePixelCache().
%
%  The format of the RelinquishDistributePixelCache method is:
%
%      MagickBooleanType RelinquishDistributePixelCache(
%        DistributeCacheInfo *server_info)
%
%  A description of each parameter follows:
%
%    o server_info: the distributed cache info.
%
*/
MagickPrivate MagickBooleanType RelinquishDistributePixelCache(
  DistributeCacheInfo *server_info)
{
  MagickBooleanType
    status;

  MagickOffsetType
    count;

  register unsigned char
    *p;

  unsigned char
    message[MaxTextExtent];

  /*
    Delete distributed pixel cache.
  */
  assert(server_info != (DistributeCacheInfo *) NULL);
  assert(server_info->signature == MagickSignature);
  p=message;
  *p++='d';
  (void) memcpy(p,&server_info->session_key,sizeof(server_info->session_key));
  p+=sizeof(server_info->session_key);
  count=dpc_send(server_info->file,p-message,message);
  if (count != (MagickOffsetType) (p-message))
    return(MagickFalse);
  count=dpc_read(server_info->file,sizeof(status),(unsigned char *) &status);
  if (count != (MagickOffsetType) sizeof(status))
    return(MagickFalse);
  return(status);
}

/*
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%                                                                             %
%                                                                             %
%                                                                             %
+   W r i t e D i s t r i b u t e P i x e l C a c h e I n d e x e s           %
%                                                                             %
%                                                                             %
%                                                                             %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
%  WriteDistributePixelCacheIndexes() writes image indexes to the specified
%  region of the distributed pixel cache.
%
%  The format of the WriteDistributePixelCacheIndexes method is:
%
%      MagickOffsetType WriteDistributePixelCacheIndexes(
%        DistributeCacheInfo *server_info,const RectangleInfo *region,
%        const MagickSizeType length,const unsigned char *indexes)
%
%  A description of each parameter follows:
%
%    o server_info: the distributed cache info.
%
%    o image: the image.
%
%    o region: write the indexes to this region of the image.
%
%    o length: the length in bytes of the indexes.
%
%    o indexes: write these indexes to the pixel cache.
%
*/
MagickPrivate MagickOffsetType WriteDistributePixelCacheIndexes(
  DistributeCacheInfo *server_info,const RectangleInfo *region,
  const MagickSizeType length,const unsigned char *indexes)
{
  MagickOffsetType
    count;

  register unsigned char
    *p;

  unsigned char
    message[MaxTextExtent];

  /*
    Write distributed pixel cache indexes.
  */
  assert(server_info != (DistributeCacheInfo *) NULL);
  assert(server_info->signature == MagickSignature);
  assert(region != (RectangleInfo *) NULL);
  assert(indexes != (unsigned char *) NULL);
  if (length > (MagickSizeType) SSIZE_MAX)
    return(-1);
  p=message;
  *p++='W';
  (void) memcpy(p,&server_info->session_key,sizeof(server_info->session_key));
  p+=sizeof(server_info->session_key);
  (void) memcpy(p,&region->width,sizeof(region->width));
  p+=sizeof(region->width);
  (void) memcpy(p,&region->height,sizeof(region->height));
  p+=sizeof(region->height);
  (void) memcpy(p,&region->x,sizeof(region->x));
  p+=sizeof(region->x);
  (void) memcpy(p,&region->y,sizeof(region->y));
  p+=sizeof(region->y);
  (void) memcpy(p,&length,sizeof(length));
  p+=sizeof(length);
  count=dpc_send(server_info->file,p-message,message);
  if (count != (MagickOffsetType) (p-message))
    return(-1);
  return(dpc_send(server_info->file,length,indexes));
}

/*
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%                                                                             %
%                                                                             %
%                                                                             %
+   W r i t e D i s t r i b u t e P i x e l C a c h e P i x e l s             %
%                                                                             %
%                                                                             %
%                                                                             %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
%  WriteDistributePixelCachePixels() writes image pixels to the specified
%  region of the distributed pixel cache.
%
%  The format of the WriteDistributePixelCachePixels method is:
%
%      MagickBooleanType WriteDistributePixelCachePixels(
%        DistributeCacheInfo *server_info,const RectangleInfo *region,
%        const MagickSizeType length,const unsigned char *restrict pixels)
%
%  A description of each parameter follows:
%
%    o server_info: the distributed cache info.
%
%    o image: the image.
%
%    o region: write the pixels to this region of the image.
%
%    o length: the length in bytes of the pixels.
%
%    o pixels: write these pixels to the pixel cache.
%
*/
MagickPrivate MagickOffsetType WriteDistributePixelCachePixels(
  DistributeCacheInfo *server_info,const RectangleInfo *region,
  const MagickSizeType length,const unsigned char *restrict pixels)
{
  MagickOffsetType
    count;

  register unsigned char
    *p;

  unsigned char
    message[MaxTextExtent];

  /*
    Write distributed pixel cache pixels.
  */
  assert(server_info != (DistributeCacheInfo *) NULL);
  assert(server_info->signature == MagickSignature);
  assert(region != (RectangleInfo *) NULL);
  assert(pixels != (const unsigned char *) NULL);
  if (length > (MagickSizeType) SSIZE_MAX)
    return(-1);
  p=message;
  *p++='w';
  (void) memcpy(p,&server_info->session_key,sizeof(server_info->session_key));
  p+=sizeof(server_info->session_key);
  (void) memcpy(p,&region->width,sizeof(region->width));
  p+=sizeof(region->width);
  (void) memcpy(p,&region->height,sizeof(region->height));
  p+=sizeof(region->height);
  (void) memcpy(p,&region->x,sizeof(region->x));
  p+=sizeof(region->x);
  (void) memcpy(p,&region->y,sizeof(region->y));
  p+=sizeof(region->y);
  (void) memcpy(p,&length,sizeof(length));
  p+=sizeof(length);
  count=dpc_send(server_info->file,p-message,message);
  if (count != (MagickOffsetType) (p-message))
    return(-1);
  return(dpc_send(server_info->file,length,pixels));
}

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