TMapFile

class TMapFile : public TObject

    protected:

          TMapFile TMapFile()
          TMapFile TMapFile(const char* name, const char* title, Option_t* option, Int_t size, TMapFile*& newMapFile)
          TMapFile TMapFile(const TMapFile& f, Long_t offset = 0)
             Int_t AcquireSemaphore()
              void CreateSemaphore(Int_t pid = 0)
              void DeleteSemaphore()
         TMapFile* FindShadowMapFile()
             Int_t GetBestBuffer()
              void InitDirectory()
      static void* MapToAddress()
              void operator=(const TMapFile& rhs)
             Int_t ReleaseSemaphore()
          TObject* Remove(TObject* obj, Bool_t lock)
          TObject* Remove(const char* name, Bool_t lock)
              void SumBuffer(Int_t bufsize)

    public:

             virtual void ~TMapFile()
                     void Add(const TObject* obj, const char* name)
             virtual void Browse(TBrowser* b)
                   Bool_t cd(const char* path = 0)
           static TClass* Class()
                     void Close(Option_t* option)
         static TMapFile* Create(const char* name, Option_t* option = READ, Int_t size = kDefaultMapSize, const char* title)
                 TObject* Get(const char* name, TObject* retObj = 0)
                    void* GetBaseAddr() const
                    void* GetBreakval() const
              TDirectory* GetDirectory() const
                    Int_t GetFd() const
                 TMapRec* GetFirst() const
                 TMapRec* GetLast() const
                    void* GetMmallocDesc() const
      virtual const char* GetName() const
              const char* GetOption() const
                    Int_t GetSize() const
      virtual const char* GetTitle() const
          virtual TClass* IsA() const
           virtual Bool_t IsFolder() const
                   Bool_t IsWritable() const
             virtual void ls(Option_t* option) const
                     void operator delete(void* vp)
                    void* OrgAddress(void* addr) const
             virtual void Print(Option_t* option) const
                 TObject* Remove(TObject* obj)
                 TObject* Remove(const char* name)
                     void RemoveAll()
              static void SetMapAddress(Long_t addr)
             virtual void ShowMembers(TMemberInspector& insp, char* parent)
             virtual void Streamer(TBuffer& b)
                     void StreamerNVirtual(TBuffer& b)
                     void Update(TObject* obj = 0)
         static TMapFile* WhichMapFile(void* addr)

  Data Members
    private:

              Int_t fFd            Descriptor of mapped file
              Int_t fVersion       ROOT version (or -1 for shadow map file)
              char* fName          Name of mapped file
              char* fTitle         Title of mapped file
              char* fOption        Directory creation options
              void* fMmallocDesc   Pointer to mmalloc descriptor
            ULong_t fBaseAddr      Base address of mapped memory region
              Int_t fSize          Original start size of memory mapped region
           TMapRec* fFirst         List of streamed objects is shared memory
           TMapRec* fLast          Last object in list of shared objects
             Long_t fOffset        Offset in bytes for region mapped by reader
        TDirectory* fDirectory     Pointer to directory associated to this mapfile
             TList* fBrowseList    List of KeyMapFile objects
             Bool_t fWritable      TRUE if mapped file opened in RDWR mode
              Int_t fSemaphore     Modification semaphore (or getpid() for WIN32)
            ULong_t fhSemaphore    HANDLE of WIN32 Mutex object to implement semaphore
           TObject* fGetting       Don't deadlock in update mode, when from Get() Add() is called
              Int_t fWritten       Number of objects written sofar
           Double_t fSumBuffer     Sum of buffer sizes of objects written sofar
           Double_t fSum2Buffer    Sum of squares of buffer sizes of objects written so far
      static Long_t fgMapAddress   Map to this address, set address via SetMapAddress()
       static void* fgMmallocDesc  Used in Close() and operator delete()

    public:

      static const enum TObject:: kDefaultMapSize  

Class Description

                                                                      
 TMapFile                                                             
                                                                      
 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:                 
   1) 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).                                                
   2) 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.                                
   3) 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).                            
                                                                      

 Default ctor. Does not much except setting some basic values.

 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.

 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.

 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).

 Create the directory associated to this mapfile

 Add an object to the list of objects to be stored in shared memory.
 To place the object actually into shared memory call Update().

 Update an object (or all objects, if obj == 0) in shared memory.

 Remove object from shared memory. Returns pointer to removed
 object if successful, 0 otherwise.

 Remove object by name from shared memory. Returns pointer to removed
 object if successful, 0 otherwise.

 Remove all objects from shared memory.

 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.

 Create semaphore used for synchronizing access to shared memory.

 Delete the semaphore.

 Acquire semaphore. Returns 0 if OK, -1 on error.

 Release semaphore. Returns 0 if OK, -1 on error.

 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.

 Returns shadow map file.

 Print some info about the mapped file.

 Returns kTRUE in case object is a folder (i.e. contains browsable lists).

 Browse contents of TMapFile.

 Cd to associated directory,

 List contents of TMapFile.

 Increment statistics for buffer sizes of objects in this file.

 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.

 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).

 Set preferred map address. Find out preferred map address as follows:
 1) Run consumer program to find the preferred map address:
       $ 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
    Remember begin of mapped region, i.e. 0x40b4c000

 2) 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.

 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.

Inline Functions

               void operator=(const TMapFile& rhs)
               void operator delete(void* vp)
              void* GetBaseAddr() const
              void* GetBreakval() const
        TDirectory* GetDirectory() const
              Int_t GetFd() const
              void* GetMmallocDesc() const
        const char* GetName() const
              Int_t GetSize() const
        const char* GetOption() const
        const char* GetTitle() const
           TMapRec* GetFirst() const
           TMapRec* GetLast() const
             Bool_t IsWritable() const
              void* OrgAddress(void* addr) const
           TObject* Remove(TObject* obj)
           TObject* Remove(const char* name)
          TMapFile* WhichMapFile(void* addr)
            TClass* Class()
            TClass* IsA() const
               void ShowMembers(TMemberInspector& insp, char* parent)
               void Streamer(TBuffer& b)
               void StreamerNVirtual(TBuffer& b)