TMapFile.cxx

Go to the documentation of this file.

// @(#)root/io:$Id$
// Author: Fons Rademakers   08/07/97
 
/*************************************************************************
 * Copyright (C) 1995-2000, Rene Brun and Fons Rademakers.               *
 * All rights reserved.                                                  *
 *                                                                       *
 * For the licensing terms see $ROOTSYS/LICENSE.                         *
 * For the list of contributors see $ROOTSYS/README/CREDITS.             *
 *************************************************************************/
#ifdef WIN32
#pragma optimize("",off)
#endif
 
/**
\class TMapFile
\ingroup IO
 
This class implements a shared memory region mapped to a file.
Objects can be placed into this shared memory area using the Add()
member function. To actually place a copy of the object is shared
memory call Update() also whenever the mapped object(s) change(s)
call Update() to put a fresh copy in the shared memory. This extra
step is necessary since it is not possible to share objects with
virtual pointers between processes (the vtbl ptr points to the
originators unique address space and can not be used by the
consumer process(es)). Consumer processes can map the memory region
from this file and access the objects stored in it via the Get()
method (which returns a copy of the object stored in the shared
memory with correct vtbl ptr set). Only objects of classes with a
Streamer() member function defined can be shared.
 
I know the current implementation is not ideal (you need to copy to
and from the shared memory file) but the main problem is with the
class' virtual_table pointer. This pointer points to a table unique
for every process. Therefore, different options are:
  -# One could allocate an object directly in shared memory in the
     producer, but the consumer still has to copy the object from
     shared memory into a local object which has the correct vtbl
     pointer for that process (copy ctor's can be used for creating
     the local copy).
  -# Another possibility is to only allow objects without virtual
     functions in shared memory (like simple C structs), or to
     forbid (how?) the consumer from calling any virtual functions
     of the objects in shared memory.
  -# A last option is to copy the object internals to shared memory
     and copy them again from there. This is what is done in the
     TMapFile (using the object Streamer() to make a deep copy).
 
Option 1) saves one copy, but requires solid copy ctor's (along the
full inheritance chain) to rebuild the object in the consumer. Most
classes don't provide these copy ctor's, especially not when objects
contain collections, etc. 2) is too limiting or dangerous (calling
accidentally a virtual function will segv). So since we have a
robust Streamer mechanism I opted for 3).
**/
 
 
#ifdef WIN32
#  include <windows.h>
#  include <process.h>
#  ifdef GetObject
#    undef GetObject
#  endif
#  define HAVE_SEMOP
 
# ifdef CreateSemaphore
#   undef CreateSemaphore
# endif
 
# ifdef AcquireSemaphore
#   undef AcquireSemaphore;
# endif
 
# ifdef ReleaseSemaphore
#   undef ReleaseSemaphore
# endif
 
# ifdef DeleteSemaphore
#   undef DeleteSemaphore
# endif
 
#else
#  define INVALID_HANDLE_VALUE -1
#endif
 
#include <fcntl.h>
#include <errno.h>
 
#include "TMapFile.h"
#include "TKeyMapFile.h"
#include "TDirectoryFile.h"
#include "TBrowser.h"
#include "TStorage.h"
#include "TString.h"
#include "TSystem.h"
#include "TClass.h"
#include "TROOT.h"
#include "TBufferFile.h"
#include "TVirtualMutex.h"
#include "mmprivate.h"
 
#include <cmath>
 
#if defined(R__UNIX) && !defined(R__MACOSX) && !defined(R__WINGCC)
#define HAVE_SEMOP
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#if defined(R__HPUX) || \
    defined (R__SOLARIS) || defined(R__AIX) || defined(R__HIUX) || \
    __GLIBC_MINOR__ > 0
union semun {
   int val;                      // value for SETVAL
   struct semid_ds *buf;         // buffer for IPC_STAT & IPC_SET
   ushort *array;                // array for GETALL & SETALL
};
#endif
#if defined(R__LINUX) || defined(R__LYNXOS) || defined(R__HURD)
#  define       SEM_A   0200     // alter permission
#  define       SEM_R   0400     // read permission
#endif
#endif
 
 
Long_t TMapFile::fgMapAddress = 0;
void  *TMapFile::fgMmallocDesc = 0;
 
//void *ROOT::Internal::gMmallocDesc = 0; //is initialized in TStorage.cxx
 
 
namespace {
////////////////////////////////////////////////////////////////////////////////
/// Delete memory and return true if memory belongs to a TMapFile.
   static bool FreeIfTMapFile(void* ptr) {
      if (TMapFile *mf = TMapFile::WhichMapFile(ptr)) {
         if (mf->IsWritable())
            ::mfree(mf->GetMmallocDesc(), ptr);
         return true;
      }
      return false;
   }
}
 
 
////////////////////////////////////////////////////////////////////////////////
/// Set ROOT::Internal::gFreeIfTMapFile on library load.
 
struct SetFreeIfTMapFile_t {
   SetFreeIfTMapFile_t() {
      ROOT::Internal::gFreeIfTMapFile = FreeIfTMapFile;
   }
   ~SetFreeIfTMapFile_t() {
      ROOT::Internal::gFreeIfTMapFile = nullptr;
   }
} gSetFreeIfTMapFile;
 
 
////////////////////////////////////////////////////////////////////////////////
//// Constructor.
 
TMapRec::TMapRec(const char *name, const TObject *obj, Int_t size, void *buf)
{
   fName      = StrDup(name);
   fClassName = 0;
   fObject    = (TObject*)obj;
   fBuffer    = buf;
   fBufSize   = size;
   fNext      = 0;
}
 
////////////////////////////////////////////////////////////////////////////////
/// Destructor.
 
TMapRec::~TMapRec()
{
   delete [] fName;
   delete [] fClassName;
}
 
////////////////////////////////////////////////////////////////////////////////
/// This method returns a pointer to the original object.
 
/// NOTE: this pointer is only valid in the process that produces the shared
/// memory file. In a consumer process this pointer is illegal! Be careful.
 
TObject *TMapRec::GetObject() const
{
   return fObject;
}
 
 
 
 
ClassImp(TMapFile);
 
////////////////////////////////////////////////////////////////////////////////
/// Default ctor. Does not much except setting some basic values.
 
TMapFile::TMapFile()
{
   fFd          = -1;
   fVersion     = 0;
   fName        = nullptr;
   fTitle       = nullptr;
   fOption      = nullptr;
   fMmallocDesc = nullptr;
   fBaseAddr    = 0;
   fSize        = 0;
   fFirst       = nullptr;
   fLast        = nullptr;
   fOffset      = 0;
   fDirectory   = nullptr;
   fBrowseList  = nullptr;
   fWritable    = kFALSE;
   fSemaphore   = -1;
   fhSemaphore  = 0;
   fGetting     = nullptr;
   fWritten     = 0;
   fSumBuffer   = 0;
   fSum2Buffer  = 0;
}
 
////////////////////////////////////////////////////////////////////////////////
/// Create a memory mapped file.
///
/// This opens a file (to which the
/// memory will be mapped) and attaches a memory region to it.
/// Option can be either: "NEW", "CREATE", "RECREATE", "UPDATE" or
/// "READ" (see TFile). The default open mode is "READ". The size
/// argument specifies the maximum size of shared memory file in bytes.
/// This protected ctor is called via the static Create() method.
 
TMapFile::TMapFile(const char *name, const char *title, Option_t *option,
                   Int_t size, TMapFile *&newMapFile)
{
#ifndef WIN32
   fFd          = -1;
   fSemaphore   = -1;
   fhSemaphore  = 0;
#else
   fFd          = (Int_t) INVALID_HANDLE_VALUE;
   fSemaphore   = (Int_t) INVALID_HANDLE_VALUE;
#endif
   fMmallocDesc = nullptr;
   fSize        = size;
   fFirst       = 0;
   fOffset      = 0;
   fVersion     = gROOT->GetVersionInt();
   fTitle       = StrDup(title);
   fOption      = StrDup(option);
   fDirectory   = nullptr;
   fBrowseList  = nullptr;
   fGetting     = nullptr;
   fWritten     = 0;
   fSumBuffer   = 0;
   fSum2Buffer  = 0;
 
   char  *cleanup = nullptr;
   Bool_t create  = kFALSE;
   Bool_t recreate, update, read;
 
   {
      TString opt = option;
 
      if (!opt.CompareTo("NEW", TString::kIgnoreCase) ||
          !opt.CompareTo("CREATE", TString::kIgnoreCase))
         create = kTRUE;
      recreate = opt.CompareTo("RECREATE", TString::kIgnoreCase)
                 ? kFALSE : kTRUE;
      update   = opt.CompareTo("UPDATE", TString::kIgnoreCase)
                 ? kFALSE : kTRUE;
      read     = opt.CompareTo("READ", TString::kIgnoreCase)
                 ? kFALSE : kTRUE;
      if (!create && !recreate && !update && !read) {
         read    = kTRUE;
         delete [] fOption;
         fOption = StrDup("READ");
      }
   }
 
   const char *fname;
   if ((fName = gSystem->ExpandPathName(name))) {
      fname = fName;
   } else {
      Error("TMapFile", "error expanding path %s", name);
      goto zombie;
   }
 
   if (recreate) {
      if (!gSystem->AccessPathName(fname, kFileExists))
         gSystem->Unlink(fname);
      recreate = kFALSE;
      create   = kTRUE;
      delete [] fOption;
      fOption  = StrDup("CREATE");
   }
   if (create && !gSystem->AccessPathName(fname, kFileExists)) {
      Error("TMapFile", "file %s already exists", fname);
      goto zombie;
   }
   if (update) {
      if (gSystem->AccessPathName(fname, kFileExists)) {
         update = kFALSE;
         create = kTRUE;
      }
      if (update && gSystem->AccessPathName(fname, kWritePermission)) {
         Error("TMapFile", "no write permission, could not open file %s", fname);
         goto zombie;
      }
   }
   if (read) {
      if (gSystem->AccessPathName(fname, kFileExists)) {
         Error("TMapFile", "file %s does not exist", fname);
         goto zombie;
      }
      if (gSystem->AccessPathName(fname, kReadPermission)) {
         Error("TMapFile", "no read permission, could not open file %s", fname);
         goto zombie;
      }
   }
 
   // Open file to which memory will be mapped
   if (create || update) {
#ifndef WIN32
      fFd = open(fname, O_RDWR | O_CREAT, 0644);
#else
      fFd = (Int_t) CreateFile(fname,                    // pointer to name of the file
                     GENERIC_WRITE | GENERIC_READ,       // access (read-write) mode
                     FILE_SHARE_WRITE | FILE_SHARE_READ, // share mode
                     NULL,                               // pointer to security attributes
                     OPEN_ALWAYS,                        // how to create
                     FILE_ATTRIBUTE_TEMPORARY,           // file attributes
                     (HANDLE) NULL);                     // handle to file with attributes to copy
#endif
      if (fFd == (Int_t)INVALID_HANDLE_VALUE) {
         SysError("TMapFile", "file %s can not be opened", fname);
         goto zombie;
      }
      fWritable = kTRUE;
   } else {
#ifndef WIN32
      fFd = open(fname, O_RDONLY);
#else
      fFd = (Int_t) CreateFile(fname,                    // pointer to name of the file
                     GENERIC_READ,                       // access (read-write) mode
                     FILE_SHARE_WRITE | FILE_SHARE_READ, // share mode
                     NULL,                               // pointer to security attributes
                     OPEN_EXISTING,                      // how to create
                     FILE_ATTRIBUTE_TEMPORARY,           // file attributes
                     (HANDLE) NULL);                     // handle to file with attributes to copy
#endif
      if (fFd == (Int_t)INVALID_HANDLE_VALUE) {
         SysError("TMapFile", "file %s can not be opened for reading", fname);
         goto zombie;
      }
      fWritable = kFALSE;
   }
 
   // Attach memory region to file.
   void *mapto;
   TMapFile *mapfil;
 
   if (((mapto = MapToAddress()) == (void *)-1) ||
#ifndef WIN32
       ((fMmallocDesc = mmalloc_attach(fFd, mapto, fSize)) == 0)) {
#else
       ((fMmallocDesc = mmalloc_attach((HANDLE) fFd, mapto, fSize)) == 0)) {
#endif
 
      if (mapto == (void *)-1) {
         Error("TMapFile", "no memory mapped file capability available\n"
                           "Use rootn.exe or link application against \"-lNew\"");
      } else {
         if (fMmallocDesc == 0 && fWritable)
            Error("TMapFile", "mapped file not in mmalloc format or\n"
                              "already open in RW mode by another process");
         if (fMmallocDesc == 0 && !fWritable)
            Error("TMapFile", "mapped file not in mmalloc format");
      }
#ifndef WIN32
      close(fFd);
#else
      CloseHandle((HANDLE) fFd);
#endif
      fFd = -1;
      if (create)
         gSystem->Unlink(fname);
      goto zombie;
 
   } else if ((mapfil = (TMapFile *) mmalloc_getkey(fMmallocDesc, 0)) != 0) {
 
      // File contains mmalloc heap. If we are in write mode and mapped
      // file already connected in write mode switch to read-only mode.
      // Check if ROOT versions are compatible.
      // If so update mapped version of TMapFile to reflect current
      // situation (only if not opened in READ mode).
      if (mapfil->fVersion != fVersion) {
         Error("TMapFile", "map file %s (%d) incompatible with current ROOT version (%d)",
               fname, mapfil->fVersion, fVersion);
         mmalloc_detach(fMmallocDesc);
#ifndef WIN32
         close(fFd);
#else
         CloseHandle((HANDLE) fFd);
#endif
         fFd = -1;
         fMmallocDesc = 0;
         goto zombie;
      }
 
      if (mapfil->fWritable && fWritable) {
         Warning("TMapFile", "map file already open in write mode, opening in read-only mode");
         fWritable = kFALSE;
      }
 
      fBaseAddr = mapfil->fBaseAddr;
      fSize     = mapfil->fSize;
 
      if (fWritable) {
         // create new TMapFile object in mapped heap to get correct vtbl ptr
         CreateSemaphore();
         ROOT::Internal::gMmallocDesc = fMmallocDesc;
         TMapFile *mf = new TMapFile(*mapfil);
         mf->fFd        = fFd;
         mf->fWritable  = kTRUE;
         cleanup        = mf->fOption;
         mf->fOption    = StrDup(fOption);
         mf->fSemaphore = fSemaphore;
#ifdef WIN32
         mf->CreateSemaphore(fSemaphore);
#endif
         mmalloc_setkey(fMmallocDesc, 0, mf);
         ROOT::Internal::gMmallocDesc = 0;
         mapfil = mf;
      } else {
         ROOT::Internal::gMmallocDesc = 0;    // make sure we are in sbrk heap
         fOffset      = ((struct mdesc *) fMmallocDesc)->offset;
         TMapFile *mf = new TMapFile(*mapfil, fOffset);
         delete [] mf->fOption;
         mf->fFd          = fFd;
         mf->fOption      = StrDup("READ");
         mf->fMmallocDesc = fMmallocDesc;
         mf->fWritable    = kFALSE;
         mapfil = mf;
      }
 
      // store shadow mapfile (it contains the real fFd in case map
      // is not writable)
      fVersion  = -1;   // make this the shadow map file
      R__LOCKGUARD(gROOTMutex);
      gROOT->GetListOfMappedFiles()->AddLast(this);
 
   } else {
 
      // New file. If the file is writable create a new copy of the
      // TMapFile which will now be allocated on the memory mapped heap.
      if (!fWritable) {
         Error("TMapFile", "map file is not writable");
         mmalloc_detach(fMmallocDesc);
#ifndef WIN32
         close(fFd);
#else
         CloseHandle((HANDLE) fFd);
#endif
         fFd = -1;
         fMmallocDesc = 0;
         goto zombie;
      }
 
      fBaseAddr = (ULong_t)((struct mdesc *) fMmallocDesc)->base;
 
      CreateSemaphore();
 
      ROOT::Internal::gMmallocDesc = fMmallocDesc;
 
      mapfil = new TMapFile(*this);
      mmalloc_setkey(fMmallocDesc, 0, mapfil);
 
      ROOT::Internal::gMmallocDesc = 0;
 
      // store shadow mapfile
      fVersion  = -1;   // make this the shadow map file
      R__LOCKGUARD(gROOTMutex);
      gROOT->GetListOfMappedFiles()->AddLast(this);
 
   }
 
   mapfil->InitDirectory();
   {
      R__LOCKGUARD(gROOTMutex);
      gROOT->GetListOfMappedFiles()->AddFirst(mapfil);
   }
 
   if (cleanup) delete [] cleanup;
 
   newMapFile = mapfil;
 
   return;
 
zombie:
   // error in file opening occured, make this object a zombie
   MakeZombie();
   newMapFile   = this;
   ROOT::Internal::gMmallocDesc = 0;
}
 
////////////////////////////////////////////////////////////////////////////////
/// Private copy ctor.
///
/// Used by the the ctor to create a new version
/// of TMapFile in the memory mapped heap. It's main purpose is to
/// correctly create the string data members.
 
TMapFile::TMapFile(const TMapFile &f, Long_t offset) : TObject(f)
{
   fFd          = f.fFd;
   fVersion     = f.fVersion;
   fName        = StrDup((char *)((Long_t)f.fName + offset));
   fTitle       = StrDup((char *)((Long_t)f.fTitle + offset));
   fOption      = StrDup((char *)((Long_t)f.fOption + offset));
   fMmallocDesc = f.fMmallocDesc;
   fBaseAddr    = f.fBaseAddr;
   fSize        = f.fSize;
   fFirst       = f.fFirst;
   fLast        = f.fLast;
   fWritable    = f.fWritable;
   fSemaphore   = f.fSemaphore;
   fOffset      = offset;
   fDirectory   = nullptr;
   fBrowseList  = nullptr;
   fGetting     = nullptr;
   fWritten     = f.fWritten;
   fSumBuffer   = f.fSumBuffer;
   fSum2Buffer  = f.fSum2Buffer;
#ifdef WIN32
   CreateSemaphore(fSemaphore);
#else
   fhSemaphore = f.fhSemaphore;
#endif
}
 
////////////////////////////////////////////////////////////////////////////////
/// TMapFiles may not be deleted, since we want to keep the complete
/// TMapFile object in the mapped file for later re-use. To enforce this
/// the delete operator has been made private. Use Close() to properly
/// terminate a TMapFile (also done via the TROOT dtor).
 
TMapFile::~TMapFile()
{
   if (fDirectory == gDirectory) gDirectory = gROOT;
   delete fDirectory; fDirectory = nullptr;
   if (fBrowseList) {
      fBrowseList->Delete();
      delete fBrowseList;
      fBrowseList = nullptr;
   }
 
 
   // if shadow map file we are done here
   if (fVersion == -1)
      return;
 
   // Writable mapfile is allocated in mapped memory. This object should
   // not be deleted by ::operator delete(), because it is needed if we
   // want to connect later to the file again.
   if (fWritable)
      TObject::SetDtorOnly(this);
 
   Close("dtor");
 
   fgMmallocDesc = fMmallocDesc;
 
   delete [] fName; fName = nullptr;
   delete [] fOption; fOption = nullptr;
   delete [] fTitle; fTitle = nullptr;
}
 
////////////////////////////////////////////////////////////////////////////////
/// Create the directory associated to this mapfile
 
void TMapFile::InitDirectory()
{
   gDirectory = nullptr;
   fDirectory = new TDirectoryFile();
   fDirectory->SetName(GetName());
   fDirectory->SetTitle(GetTitle());
   fDirectory->Build();
   fDirectory->SetMother(this);
   gDirectory = fDirectory;
}
 
////////////////////////////////////////////////////////////////////////////////
/// Add an object to the list of objects to be stored in shared memory.
/// To place the object actually into shared memory call Update().
 
void TMapFile::Add(const TObject *obj, const char *name)
{
   if (!fWritable || !fMmallocDesc) return;
 
   Bool_t lock = fGetting != obj ? kTRUE : kFALSE;
 
   if (lock)
      AcquireSemaphore();
 
   ROOT::Internal::gMmallocDesc = fMmallocDesc;
 
   const char *n;
   if (name && *name)
      n = name;
   else
      n = obj->GetName();
 
   if (Remove(n, kFALSE)) {
      //Warning("Add", "replaced object with same name %s", n);
   }
 
   TMapRec *mr = new TMapRec(n, obj, 0, 0);
   if (!fFirst) {
      fFirst = mr;
      fLast  = mr;
   } else {
      fLast->fNext = mr;
      fLast        = mr;
   }
 
   ROOT::Internal::gMmallocDesc = nullptr;
 
   if (lock)
      ReleaseSemaphore();
}
 
////////////////////////////////////////////////////////////////////////////////
/// Update an object (or all objects, if obj == 0) in shared memory.
 
void TMapFile::Update(TObject *obj)
{
   if (!fWritable || !fMmallocDesc) return;
 
   AcquireSemaphore();
 
   ROOT::Internal::gMmallocDesc = fMmallocDesc;
 
   Bool_t all = (obj == 0) ? kTRUE : kFALSE;
 
   TMapRec *mr = fFirst;
   while (mr) {
      if (all || mr->fObject == obj) {
         TBufferFile *b;
         if (!mr->fBufSize) {
            b = new TBufferFile(TBuffer::kWrite, GetBestBuffer());
            mr->fClassName = StrDup(mr->fObject->ClassName());
         } else
            b = new TBufferFile(TBuffer::kWrite, mr->fBufSize, mr->fBuffer);
         b->MapObject(mr->fObject);  //register obj in map to handle self reference
         mr->fObject->Streamer(*b);
         mr->fBufSize = b->BufferSize();
         mr->fBuffer  = b->Buffer();
         SumBuffer(b->Length());
         b->DetachBuffer();
         delete b;
      }
      mr = mr->fNext;
   }
 
   ROOT::Internal::gMmallocDesc = nullptr;
 
   ReleaseSemaphore();
}
 
////////////////////////////////////////////////////////////////////////////////
/// Remove object from shared memory.
///
/// Returns pointer to removed object if successful, 0 otherwise.
 
TObject *TMapFile::Remove(TObject *obj, Bool_t lock)
{
   if (!fWritable || !fMmallocDesc) return 0;
 
   if (lock)
      AcquireSemaphore();
 
   TObject *retObj = 0;
   TMapRec *prev = 0, *mr = fFirst;
   while (mr) {
      if (mr->fObject == obj) {
         if (mr == fFirst) {
            fFirst = mr->fNext;
            if (mr == fLast)
               fLast = 0;
         } else {
            prev->fNext = mr->fNext;
            if (mr == fLast)
               fLast = prev;
         }
         retObj = obj;
         delete mr;
         break;
      }
      prev = mr;
      mr   = mr->fNext;
   }
 
   if (lock)
      ReleaseSemaphore();
 
   return retObj;
}
 
////////////////////////////////////////////////////////////////////////////////
/// Remove object by name from shared memory.
///
/// Returns pointer to removed object if successful, 0 otherwise.
 
TObject *TMapFile::Remove(const char *name, Bool_t lock)
{
   if (!fWritable || !fMmallocDesc) return 0;
 
   if (lock)
      AcquireSemaphore();
 
   TObject *retObj = 0;
   TMapRec *prev = 0, *mr = fFirst;
   while (mr) {
      if (!strcmp(mr->fName, name)) {
         if (mr == fFirst) {
            fFirst = mr->fNext;
            if (mr == fLast)
               fLast = 0;
         } else {
            prev->fNext = mr->fNext;
            if (mr == fLast)
               fLast = prev;
         }
         retObj = mr->fObject;
         delete mr;
         break;
      }
      prev = mr;
      mr   = mr->fNext;
   }
 
   if (lock)
      ReleaseSemaphore();
 
   return retObj;
}
 
////////////////////////////////////////////////////////////////////////////////
/// Remove all objects from shared memory.
 
void TMapFile::RemoveAll()
{
   if (!fWritable || !fMmallocDesc) return;
 
   AcquireSemaphore();
 
   TMapRec *mr = fFirst;
   while (mr) {
      TMapRec *t = mr;
      mr = mr->fNext;
      delete t;
   }
   fFirst = fLast = 0;
 
   ReleaseSemaphore();
}
 
////////////////////////////////////////////////////////////////////////////////
/// Return pointer to object retrieved from shared memory.
///
/// The object must
/// be deleted after use. If delObj is a pointer to a previously allocated
/// object it will be deleted. Returns 0 in case object with the given
/// name does not exist.
 
TObject *TMapFile::Get(const char *name, TObject *delObj)
{
   if (!fMmallocDesc) return 0;
 
   AcquireSemaphore();
 
   delete delObj;
 
   TObject *obj = 0;
   TMapRec *mr = GetFirst();
   while (OrgAddress(mr)) {
      if (!strcmp(mr->GetName(fOffset), name)) {
         if (!mr->fBufSize) goto release;
         TClass *cl = TClass::GetClass(mr->GetClassName(fOffset));
         if (!cl) {
            Error("Get", "unknown class %s", mr->GetClassName(fOffset));
            goto release;
         }
 
         obj = (TObject *)cl->New();
         if (!obj) {
            Error("Get", "cannot create new object of class %s", mr->GetClassName(fOffset));
            goto release;
         }
 
         fGetting = obj;
         TBufferFile *b = new TBufferFile(TBuffer::kRead, mr->fBufSize, mr->GetBuffer(fOffset));
         b->MapObject(obj);  //register obj in map to handle self reference
         obj->Streamer(*b);
         b->DetachBuffer();
         delete b;
         fGetting = 0;
         goto release;
      }
      mr = mr->GetNext(fOffset);
   }
 
release:
   ReleaseSemaphore();
 
   return obj;
}
 
////////////////////////////////////////////////////////////////////////////////
/// Create semaphore used for synchronizing access to shared memory.
 
#ifndef WIN32
void TMapFile::CreateSemaphore(int)
#else
void TMapFile::CreateSemaphore(int pid)
#endif
{
#ifdef HAVE_SEMOP
#ifndef WIN32
   // create semaphore to synchronize access (should use read/write lock)
   fSemaphore = semget(IPC_PRIVATE, 1, SEM_R|SEM_A|(SEM_R>>3)|(SEM_A>>3)|
                                       (SEM_R>>6)|(SEM_A>>6));
 
   // set semaphore to 1
   if (fSemaphore != -1) {
      union semun set;
      set.val = 1;
      semctl(fSemaphore, 0, SETVAL, set);
   }
#else
   char buffer[] ="ROOT_Semaphore_xxxxxxxx";
   int lbuf = strlen(buffer);
   if (!pid) fSemaphore = getpid();
   fhSemaphore = (ULong_t)CreateMutex(NULL,FALSE,itoa(fSemaphore,&buffer[lbuf-8],16));
   if (fhSemaphore == 0) fSemaphore = (Int_t)INVALID_HANDLE_VALUE;
#endif
#endif
}
 
////////////////////////////////////////////////////////////////////////////////
/// Delete the semaphore.
 
void TMapFile::DeleteSemaphore()
{
#ifdef HAVE_SEMOP
   // remove semaphore
#ifndef WIN32
   if (fSemaphore != -1) {
      int semid  = fSemaphore;
      fSemaphore = -1;
      union semun set;
      set.val = 0;
      semctl(semid, 0, IPC_RMID, set);
   }
#else
   if (fSemaphore != (Int_t)INVALID_HANDLE_VALUE) {
      CloseHandle((HANDLE)fhSemaphore);
      fhSemaphore = 0;
      fSemaphore  = (Int_t)INVALID_HANDLE_VALUE;
   }
#endif
#endif
}
 
////////////////////////////////////////////////////////////////////////////////
/// Acquire semaphore. Returns 0 if OK, -1 on error.
 
Int_t TMapFile::AcquireSemaphore()
{
#ifdef HAVE_SEMOP
#ifndef WIN32
   if (fSemaphore != -1) {
      struct sembuf buf = { 0, -1, SEM_UNDO };
      int intr = 0;
again:
      if (semop(fSemaphore, &buf, 1) == -1) {
#if defined(R__FBSD) || defined(R__OBSD)
         if (TSystem::GetErrno() == EINVAL)
#else
         if (TSystem::GetErrno() == EIDRM)
#endif
            fSemaphore = -1;
#if !defined(R__FBSD)
         if (TSystem::GetErrno() == EINTR) {
            if (intr > 2)
               return -1;
            TSystem::ResetErrno();
            intr++;
            goto again;
         }
#endif
      }
   }
#else
   // Enter Critical section to "write" lock
   if (fSemaphore != (Int_t)INVALID_HANDLE_VALUE)
      WaitForSingleObject((HANDLE)fhSemaphore,INFINITE);
#endif
#endif
 
   // file might have grown, update mapping on reader to new size
   if (!fWritable && fMmallocDesc) {
      if (mmalloc_update_mapping(fMmallocDesc) == -1)
         Error("AcquireSemaphore", "cannot update mapping");
   }
 
   return 0;
}
 
////////////////////////////////////////////////////////////////////////////////
/// Release semaphore. Returns 0 if OK, -1 on error.
 
Int_t TMapFile::ReleaseSemaphore()
{
#ifdef HAVE_SEMOP
#ifndef WIN32
   if (fSemaphore != -1) {
      struct sembuf buf = { 0, 1, SEM_UNDO };
      if (semop(fSemaphore, &buf, 1) == -1) {
#if defined(R__FBSD) || defined(R__OBSD)
         if (TSystem::GetErrno() == EINVAL)
#else
         if (TSystem::GetErrno() == EIDRM)
#endif
            fSemaphore = -1;
      }
   }
#else
   if (fSemaphore != (Int_t)INVALID_HANDLE_VALUE)
      ReleaseMutex((HANDLE)fhSemaphore);
#endif
#endif
   return 0;
}
 
////////////////////////////////////////////////////////////////////////////////
/// Close a mapped file.
///
/// First detach mapped memory then close file.
/// No member functions of a TMapFile that was opened in write mode
/// may be called after Close() (this includes, of course, "delete" which
/// would call the dtors). The option="dtor" is only used when called
/// via the ~TMapFile.
 
void TMapFile::Close(Option_t *option)
{
   if (!fMmallocDesc) return;
 
   TMapFile *shadow = FindShadowMapFile();
   if (!shadow) {
      Error("Close", "shadow map == 0, should never happen!");
      return;
   }
 
   {
      R__LOCKGUARD(gROOTMutex);
      gROOT->GetListOfMappedFiles()->Remove(shadow);
      gROOT->GetListOfMappedFiles()->Remove(this);
   }
 
   if (shadow->fWritable) {
      fWritable = kFALSE;
      DeleteSemaphore();
   }
 
   if (fMmallocDesc) {
      if (strcmp(option, "dtor"))
         mmalloc_detach(fMmallocDesc);
 
      // If writable cannot access fMmallocDesc anymore since
      // it points to the just unmapped memory region. Any further
      // access to this TMapFile will cause a crash.
      if (!shadow->fWritable)
         fMmallocDesc = 0;
   }
 
   if (shadow->fFd != -1)
#ifndef WIN32
      close(shadow->fFd);
#else
      CloseHandle((HANDLE)shadow->fFd);
#endif
 
   delete shadow;
}
 
////////////////////////////////////////////////////////////////////////////////
/// Returns shadow map file.
 
TMapFile *TMapFile::FindShadowMapFile()
{
   R__LOCKGUARD(gROOTMutex);
   TObjLink *lnk = ((TList *)gROOT->GetListOfMappedFiles())->LastLink();
   while (lnk) {
      TMapFile *mf = (TMapFile*)lnk->GetObject();
      if (mf->fVersion == -1 && fBaseAddr == mf->fBaseAddr && fSize == mf->fSize)
         return mf;
      lnk = lnk->Prev();
   }
   return 0;
}
 
////////////////////////////////////////////////////////////////////////////////
/// Print some info about the mapped file.
 
void TMapFile::Print(Option_t *) const
{
   Printf("Memory mapped file:   %s", fName);
   Printf("Title:                %s", fTitle);
   if (fMmallocDesc) {
      Printf("Option:               %s", fOption);
      ULong_t size = (ULong_t)((struct mdesc *)fMmallocDesc)->top - fBaseAddr;
      Printf("Mapped Memory region: 0x%lx - 0x%lx (%.2f MB)", fBaseAddr, fBaseAddr + size,
             (float)size/1048576);
      Printf("Current breakval:     0x%lx", (ULong_t)GetBreakval());
   } else
      Printf("Option:               file closed");
}
 
////////////////////////////////////////////////////////////////////////////////
/// Returns kTRUE in case object is a folder (i.e. contains browsable lists).
 
Bool_t TMapFile::IsFolder() const
{
   if (fMmallocDesc && fVersion > 0) return kTRUE;
   return kFALSE;
}
 
////////////////////////////////////////////////////////////////////////////////
/// Browse contents of TMapFile.
 
void TMapFile::Browse(TBrowser *b)
{
   if (b && fMmallocDesc) {
 
      AcquireSemaphore();
 
      TMapRec *mr = GetFirst();
      TKeyMapFile *keymap;
      if (!fBrowseList) fBrowseList = new TList();
      while (OrgAddress(mr)) {
         keymap = (TKeyMapFile*)fBrowseList->FindObject(mr->GetName(fOffset));
         if (!keymap) {
            keymap = new TKeyMapFile(mr->GetName(fOffset),mr->GetClassName(fOffset),this);
            fBrowseList->Add(keymap);
         }
         b->Add(keymap, keymap->GetName());
         mr = mr->GetNext(fOffset);
      }
 
      ReleaseSemaphore();
 
   }
}
 
////////////////////////////////////////////////////////////////////////////////
/// Cd to associated directory.
 
Bool_t TMapFile::cd(const char *path)
{
   if (fDirectory)
      return fDirectory->cd(path);
   return kFALSE;
}
 
////////////////////////////////////////////////////////////////////////////////
/// List contents of TMapFile.
 
void TMapFile::ls(Option_t *) const
{
   if (fMmallocDesc) {
 
      ((TMapFile*)this)->AcquireSemaphore();
 
      Printf("%-20s %-20s %-10s", "Object", "Class", "Size");
      if (!fFirst)
         Printf("*** no objects stored in memory mapped file ***");
 
      TMapRec *mr = GetFirst();
      while (OrgAddress(mr)) {
         Printf("%-20s %-20s %-10d", mr->GetName(fOffset),
                mr->GetClassName(fOffset), mr->fBufSize);
         mr = mr->GetNext(fOffset);
      }
 
      ((TMapFile*)this)->ReleaseSemaphore();
 
   }
}
 
////////////////////////////////////////////////////////////////////////////////
/// Increment statistics for buffer sizes of objects in this file.
 
void TMapFile::SumBuffer(Int_t bufsize)
{
   fWritten++;
   fSumBuffer  += bufsize;
   fSum2Buffer += bufsize*bufsize;
}
 
////////////////////////////////////////////////////////////////////////////////
/// Return the best buffer size for objects in this file.
///
/// The best buffer size is estimated based on the current mean value
/// and standard deviation of all objects written so far to this file.
/// Returns mean value + one standard deviation.
 
Int_t TMapFile::GetBestBuffer()
{
   if (!fWritten) return TBuffer::kMinimalSize;
   Double_t mean = fSumBuffer/fWritten;
   Double_t rms2 = TMath::Abs(fSum2Buffer/fSumBuffer - mean*mean);
   return (Int_t)(mean + std::sqrt(rms2));
}
 
////////////////////////////////////////////////////////////////////////////////
/// Return the current location in the memory region for this malloc heap which
/// represents the end of memory in use. Returns 0 if map file was closed.
 
void *TMapFile::GetBreakval() const
{
   if (!fMmallocDesc) return 0;
   return (void *)((struct mdesc *)fMmallocDesc)->breakval;
}
 
////////////////////////////////////////////////////////////////////////////////
/// Create a memory mapped file.
///
/// This opens a file (to which the
/// memory will be mapped) and attaches a memory region to it.
/// Option can be either: "NEW", "CREATE", "RECREATE", "UPDATE"
/// or "READ" (see TFile). The default open mode is "READ". The size
/// argument specifies the maximum size of shared memory file in bytes.
/// TMapFile's can only be created via this method. Create() enforces that
/// a TMapFile is always on the memory mapped heap (when "NEW", "CREATE"
/// or "RECREATE" are used).
 
TMapFile *TMapFile::Create(const char *name, Option_t *option, Int_t size,
                           const char *title)
{
   TMapFile *newMapFile;
   new TMapFile(name, title, option, size, newMapFile);
 
   return newMapFile;
}
 
////////////////////////////////////////////////////////////////////////////////
/// Set preferred map address.
///
/// Find out preferred map address as follows:
///   -# Run consumer program to find the preferred map address. Remember begin of mapped region, i.e. 0x40b4c000
/// ~~~{.cpp}
/// $ root
/// root [0] m = TMapFile::Create("dummy.map", "recreate", 10000000);
/// root [1] m.Print()
/// Memory mapped file:   dummy.map
/// Title:
/// Option:               CREATE
/// Mapped Memory region: 0x40b4c000 - 0x40d95f00 (2.29 MB)
/// Current breakval:     0x40b53000
/// root [2] .q
/// $ rm dummy.map
/// ~~~
///   -# Add to producer program, just before creating the TMapFile:
///    TMapFile::SetMapAddress(0x40b4c000);
///
/// Repeat this if more than one map file is being used.
/// The above procedure allow programs using, e.g., different number of
/// shared libraries (that cause the default mapping address to be
/// different) to create shared memory regions in the same location
/// without overwriting a shared library. The above assumes the consumer
/// program is larger (i.e. has more shared memory occupied) than the
/// producer. If this is not true inverse the procedure.
 
void TMapFile::SetMapAddress(Long_t addr)
{
   fgMapAddress = addr;
}
 
////////////////////////////////////////////////////////////////////////////////
/// Return the base address at which we would like the next TMapFile's
/// mapped data to start.
///
/// For now, we let the system decide (start address 0). There are
/// a lot of issues to deal with here to make this work reasonably,
/// including:
///   - Avoid memory collisions with existing mapped address spaces
///   - Reclaim address spaces when their mmalloc heaps are unmapped
///   - When mmalloc heaps are shared between processes they have to be
///   mapped at the same addresses in each
///
/// Once created, a mmalloc heap that is to be mapped back in must be
/// mapped at the original address.  I.e. each TMapFile will expect
/// to be remapped at it's original address. This becomes a problem if
/// the desired address is already in use.
 
void *TMapFile::MapToAddress()
{
#ifdef R__HAVE_MMAP
   if (TStorage::HasCustomNewDelete())
      return (void *)fgMapAddress;
   else
      return (void *)-1;
#else
   return (void *)-1;
#endif
}
 
////////////////////////////////////////////////////////////////////////////////
/// Need special "operator delete" in which we close the shared memory.
/// This has to be done after the dtor chain has been finished.
 
void TMapFile::operator delete(void *ptr)
{
   mmalloc_detach(fgMmallocDesc);
   fgMmallocDesc = 0;
 
   TObject::operator delete(ptr);
}
 
////////////////////////////////////////////////////////////////////////////////
 
TMapFile *TMapFile::WhichMapFile(void *addr)
{
   // Don't use gROOT so that this routine does not trigger TROOT's initialization
   // This is essential since this routine is called via operator delete
   // which is used during RegisterModule (i.e. during library loading, including the initial
   // start up).  Using gROOT leads to recursive call to RegisterModule and initialization of
   // the interpreter in the middle of the execution of RegisterModule (i.e. undefined behavior).
   if (!ROOT::Internal::gROOTLocal || !ROOT::Internal::gROOTLocal->GetListOfMappedFiles())
      return 0;
 
   TObjLink *lnk = ((TList *)ROOT::Internal::gROOTLocal->GetListOfMappedFiles())->LastLink();
   while (lnk) {
      TMapFile *mf = (TMapFile*)lnk->GetObject();
      if (!mf) return 0;
      if ((ULong_t)addr >= mf->fBaseAddr + mf->fOffset &&
          (ULong_t)addr <  (ULong_t)mf->GetBreakval() + mf->fOffset)
         return mf;
      lnk = lnk->Prev();
   }
   return 0;
}