Store Class Reference

The Store is a file based memory manager. More...

#include <store.h>

Inheritance diagram for Store:

Classes
struct	Node

Public Member Functions
	Store ()
	~Store ()
int	open (const char *name)
portable_off_t	alloc ()
int	write (const char *buf, uint size)
void	end ()
void	release (portable_off_t handle)
void	close ()
void	seek (portable_off_t handle)
int	read (char *buf, uint size)
void	printStats ()
portable_off_t	pos () const
void	dumpBlock (portable_off_t start, portable_off_t end)
Public Member Functions inherited from StorageIntf
virtual	~StorageIntf ()

Private Types
enum	State { Init, Reading, Writing }

Private Member Functions
void	printFreeList ()

Private Attributes
FILE *	m_file
portable_off_t	m_front
portable_off_t	m_cur
Node *	m_head
State	m_state
int	m_reads
int	m_writes

Detailed Description

The Store is a file based memory manager.

You can open the store using open(). Then obtain a handle via alloc() followed by a sequence of write() commands to store information, and finalize it using end().

Later on you locate the information with seek() using the handle obtained with alloc(), and then use a sequence of read() calls to read the information back.

If no longer needed the storage space can be freed using release().

The store will dynamically grow the file on disk if needed.

Definition at line 52 of file store.h.

Member Enumeration Documentation

enum Store::State

private

Enumerator
Init
Reading
Writing

Definition at line 102 of file store.h.

    {
      Init,
      Reading,
      Writing
    };

Constructor & Destructor Documentation

Store::Store

(

)

Creates a store.

Definition at line 50 of file store.cpp.

{
  m_file       = 0;
  m_front      = 0;
  m_cur        = 0;
  m_head       = 0;
  m_state      = Init;
  m_reads      = 0;
  m_writes     = 0;
}

Store::~Store

(

)

Releases the store object. Will close the underlying file if opened.

Definition at line 61 of file store.cpp.

{
  if (m_file)   fclose(m_file);

  // clean up free list
  while (m_head)
  {
    Node *node = m_head;
    m_head = node->next;
    delete node;
  }
}

Member Function Documentation

portable_off_t Store::alloc

(

)

Allocates a handle to write to and read from.

Definition at line 108 of file store.cpp.

{
  STORE_ASSERT(m_state==Reading);
  m_state=Writing;
  portable_off_t pos;
  if (m_head==0) // allocate new block
  {
    //printf("alloc: new block, pos=%lld\n",(long long)m_front);
    if (portable_fseek(m_file,0,SEEK_END)==-1) // go to end of the file
    {
      fprintf(stderr,"Store::alloc: Error seeking to end of file: %s\n",strerror(errno));
      exit(1);
    }
#if USE_FTELL
    pos = portable_ftell(m_file);
    STORE_ASSERT( (pos & (BLOCK_SIZE-1))==0 );
    m_front = pos + BLOCK_SIZE; // move front to end of this block
#else
    m_cur = m_front;
    pos   = m_cur;
    STORE_ASSERT( (pos & (BLOCK_SIZE-1))==0 );
    m_front = pos + BLOCK_SIZE;
#endif
  }
  else // reuse freed block
  {
    //printf("alloc: reuse block: pos=%lld\n",(long long)m_head->pos);
    Node *node = m_head;
    pos = node->pos;
    // point head to next free item
    m_head = node->next;
    delete node;
    // move to start of the block
    if (portable_fseek(m_file,pos,SEEK_SET)==-1)
    {
      fprintf(stderr,"Store::alloc: Error seeking to position %d: %s\n",
          (int)pos,strerror(errno));
      exit(1);
    }
    m_cur = pos;
    STORE_ASSERT( (pos & (BLOCK_SIZE-1))==0 );
  }
  //printf("%x: Store::alloc\n",(int)pos);
  return pos;
}

void Store::close

(

)

Closes the store

Definition at line 101 of file store.cpp.

{
  if (m_file) fclose(m_file);
  m_file=0;
  m_state  = Init;
}

void Store::dumpBlock	(	portable_off_t	start,
		portable_off_t	end
	)

Definition at line 400 of file store.cpp.

{
  portable_fseek(m_file,s,SEEK_SET);
  int size = (int)(e-s);
  uchar *buf = new uchar[size];
  if (fread(buf,size,1,m_file)==(size_t)size)
  {
    int i,j;
    for (i=0;i<size;i+=16)
    {
      printf("%08x: ",(int)s+i);
      for (j=i;j<QMIN(size,i+16);j++)
      {
        printf("%02x ",buf[i+j]);
      }
      printf("  ");
      for (j=i;j<QMIN(size,i+16);j++)
      {
        printf("%c",(buf[i+j]>=32 && buf[i+j]<128)?buf[i+j]:'.');
      }
      printf("\n");
    }
  }
  delete[] buf;
  portable_fseek(m_file,m_cur,SEEK_SET);
}

void Store::end

(

)

Ends the sequence of writes.

Note

After this call, first alloc() has to be called before new writes can be done.

Definition at line 249 of file store.cpp.

{
  STORE_ASSERT(m_state==Writing);
#if USE_FTELL
  portable_off_t curPos = portable_ftell(m_file);
#else
  portable_off_t curPos = m_cur;
#endif
  int bytesInBlock = (int)(BLOCK_SIZE - (curPos & (BLOCK_SIZE-1)));
  //printf("%x: Store::end erasing %x bytes\n",(int)curPos&~(BLOCK_SIZE-1),bytesInBlock);
  //printf("end: bytesInBlock=%x\n",bytesInBlock);
  // zero out rest of the block
  int i;
  for (i=0;i<bytesInBlock;i++)
  {
    fputc(0,m_file);
  }
  m_state=Reading;
}

int Store::open

(

const char *

name

)

Opens the file underlying the store using name as the file name. Returns 0 upon success, or -1 otherwise.

Definition at line 74 of file store.cpp.

{
  int i;
  STORE_ASSERT(m_state==Init);
  if (m_file) return 0; // already open
  m_file = portable_fopen(name,"w+b");
  if (m_file==0) return -1;

  // first block serves as header, so offset=0 can be used as the end of the list.
  for (i=0;i<BLOCK_SIZE/8;i++)
  {
    fputc('D',m_file);
    fputc('O',m_file);
    fputc('X',m_file);
    fputc('Y',m_file);
    fputc('G',m_file);
    fputc('E',m_file);
    fputc('N',m_file);
    fputc(0,m_file);
  }
  m_front  = BLOCK_SIZE;
  m_cur    = BLOCK_SIZE;
  m_head   = 0;
  m_state  = Reading;
  return 0;
}

portable_off_t Store::pos ( ) const

inline

Definition at line 97 of file store.h.

{ return m_cur; }

void Store::printFreeList ( )

private

Definition at line 382 of file store.cpp.

{
  printf("FreeList: ");
  while (m_head)
  {
    portable_off_t pos = m_head->pos;
    printf("%x ",(int)pos);
    m_head = m_head->next;
  }
  printf("\n");
}

void Store::printStats

(

)

Definition at line 394 of file store.cpp.

{
  printf("ObjStore: block size %d bytes, total size %ld blocks, wrote %d blocks, read %d blocks\n",
      BLOCK_SIZE,(long)(m_front/BLOCK_SIZE),m_reads,m_writes);
}

int Store::read ( char *  buf, uint  size  )

virtual

Reads size bytes from the store into the array pointed to be buf.

Note

Before reading seek() has to be called to set the right start of the store.

Implements StorageIntf.

Definition at line 319 of file store.cpp.

{
  STORE_ASSERT(m_state==Reading);
  //printf("%x: Store::read total=%d\n",(int)portable_ftell(m_file),size);
  do
  {
#if USE_FTELL
    portable_off_t curPos = portable_ftell(m_file);
#else
    portable_off_t curPos = m_cur;
#endif
    int bytesInBlock = (int)(BLOCK_SIZE - BLOCK_POINTER_SIZE - (curPos & (BLOCK_SIZE-1)));
    int bytesLeft    = bytesInBlock<(int)size ? (int)size-bytesInBlock : 0;
    int numBytes     = size - bytesLeft;
    //printf("  Store::read: pos=%x num=%d left=%d\n",(int)curPos,numBytes,bytesLeft);

    if (numBytes>0)
    {
      //printf("%x: Store::read: %d out of %d bytes\n",(int)portable_ftell(m_file),numBytes,size);
      if ((int)fread(buf,1,numBytes,m_file)!=numBytes)
      {
        fprintf(stderr,"Error reading from store: %s\n",strerror(errno));
        exit(1);
      }
      m_cur+=numBytes;
      m_reads++;
    }
    if (bytesLeft>0)
    {
      portable_off_t newPos;
      // read offset of the next block
#if USE_FTELL
      STORE_ASSERT(((portable_ftell(m_file)+BLOCK_POINTER_SIZE)&(BLOCK_SIZE-1))==0);
#else
      STORE_ASSERT(((m_cur+BLOCK_POINTER_SIZE)&(BLOCK_SIZE-1))==0);
#endif
      if (fread((char *)&newPos,BLOCK_POINTER_SIZE,1,m_file)!=1)
      {
        fprintf(stderr,"Error reading from store: %s\n",strerror(errno));
        exit(1);
      }
      //printf("%x: Store::read: continue in next block, %d bytes to go\n",(int)newPos,bytesLeft);
      //printf("  Store::read: next block=%x\n",(int)newPos);
      STORE_ASSERT(newPos!=0);
      STORE_ASSERT((newPos&(BLOCK_SIZE-1))==0);
      curPos = newPos;
      // move to next block
      if (portable_fseek(m_file,curPos,SEEK_SET)==-1)
      {
        fprintf(stderr,"Store::read: Error seeking to position %d: %s\n",
            (int)curPos,strerror(errno));
        exit(1);
      }
      m_cur = curPos;
    }

    size-=numBytes;
    buf+=numBytes;
  }
  while (size>0);
  return size;
}

void Store::release

(

portable_off_t

handle

)

Releases the memory corresponding to the handle returned with alloc()

Definition at line 269 of file store.cpp.

{
  STORE_ASSERT(m_state==Reading);
  //printf("release: block pos=%lld\n",(long long)pos);
  STORE_ASSERT(pos>0 && (pos & (BLOCK_SIZE-1))==0);
  // goto end of the block
  portable_off_t cur = pos, next;
  while (1)
  {
    // add new node to the free list
    Node *node = new Node;
    node->next = m_head;
    node->pos = cur;

    m_head = node;
    // goto the end of cur block
    if (portable_fseek(m_file,cur+BLOCK_SIZE-BLOCK_POINTER_SIZE,SEEK_SET)==-1)
    {
      fprintf(stderr,"Store::release: Error seeking to position %d: %s\n",
          (int)(cur+BLOCK_SIZE-BLOCK_POINTER_SIZE),strerror(errno));
      exit(1);
    }
    // read pointer to next block
    if (fread(&next,BLOCK_POINTER_SIZE,1,m_file)!=1)
    {
      fprintf(stderr,"Store::release: Error reading from store: %s\n",strerror(errno));
      exit(1);
    }
    m_cur = cur+BLOCK_SIZE;
    if (next==0) break; // found end of list -> cur is last element
    STORE_ASSERT((next & (BLOCK_SIZE-1))==0);
    cur = next;
    //printf("%x: Store::release\n",(int)cur);
  }
}

void Store::seek

(

portable_off_t

handle

)

Goes to the start of information corresponding to handle pos

Definition at line 305 of file store.cpp.

{
  STORE_ASSERT(m_state==Reading);
  //printf("%x: Store::seek\n",(int)pos);
  if (portable_fseek(m_file,pos,SEEK_SET)==-1)
  {
    fprintf(stderr,"Store::seek: Error seeking to position %d: %s\n",
        (int)pos,strerror(errno));
    exit(1);
  }
  m_cur = pos;
  STORE_ASSERT((pos&(BLOCK_SIZE-1))==0);
}

int Store::write ( const char *  buf, uint  size  )

virtual

Writes size bytes in array buf to the store. First alloc() has to be called.

Note

The information can only be read after end() has been called.

Implements StorageIntf.

Definition at line 154 of file store.cpp.

{
  STORE_ASSERT(m_state==Writing);
  //printf("%x: Store::write\n",(int)portable_ftell(m_file));
  do
  {
#if USE_FTELL
    portable_off_t curPos = portable_ftell(m_file);
#else
    portable_off_t curPos = m_cur;
#endif
    int bytesInBlock = (int)(BLOCK_SIZE - BLOCK_POINTER_SIZE - (curPos & (BLOCK_SIZE-1)));
    int bytesLeft    = bytesInBlock<(int)size ? (int)size-bytesInBlock : 0;
    int numBytes     = size - bytesLeft;
    STORE_ASSERT(bytesInBlock>=0);
    STORE_ASSERT(numBytes<=(int)(BLOCK_SIZE-BLOCK_POINTER_SIZE));
    if (numBytes>0)
    {
      if ((int)fwrite(buf,1,numBytes,m_file)!=numBytes)
      {
        fprintf(stderr,"Error writing: %s\n",strerror(errno));
        exit(1);
      }
      m_cur+=numBytes;
      m_writes++;
    }
    if (bytesLeft>0) // still more bytes to write
    {
#if USE_FTELL
      STORE_ASSERT(((portable_ftell(m_file)+BLOCK_POINTER_SIZE)&(BLOCK_SIZE-1))==0);
#else
      STORE_ASSERT(((m_cur+BLOCK_POINTER_SIZE)&(BLOCK_SIZE-1))==0);
#endif
      // allocate new block
      if (m_head==0) // no free blocks to reuse
      {
        //printf("%x: Store::write: new: pos=%x\n",(int)m_front,(int)portable_ftell(m_file));
        // write pointer to next block
        if (fwrite(&m_front,BLOCK_POINTER_SIZE,1,m_file)!=1)
        {
          fprintf(stderr,"Error writing to store: %s\n",strerror(errno));
          exit(1);
        }
        m_cur+=BLOCK_POINTER_SIZE;
#if USE_FTELL
        STORE_ASSERT(portable_ftell(m_file)==(curPos&~(BLOCK_SIZE-1))+BLOCK_SIZE);
#else
        STORE_ASSERT(m_cur==(curPos&~(BLOCK_SIZE-1))+BLOCK_SIZE);
#endif
        // move to next block
        if (portable_fseek(m_file,0,SEEK_END)==-1) // go to end of the file
        {
          fprintf(stderr,"Store::alloc: Error seeking to end of file: %s\n",strerror(errno));
          exit(1);
        }
        m_cur=m_front;
#if USE_FTELL
        STORE_ASSERT(portable_ftell(m_file)==m_front);
#else
        STORE_ASSERT(m_cur==m_front);
#endif
        // move front to the next of the block
        m_front+=BLOCK_SIZE;
      }
      else // reuse block from the free list
      {
        // write pointer to next block
        if (fwrite(&m_head->pos,BLOCK_POINTER_SIZE,1,m_file)!=1)
        {
          fprintf(stderr,"Error writing to store: %s\n",strerror(errno));
          exit(1);
        }
        Node *node = m_head;
        portable_off_t pos = node->pos;
        // point head to next free item
        m_head = node->next;
        delete node;
        // move to start of the block
        if (portable_fseek(m_file,pos,SEEK_SET)==-1)
        {
          fprintf(stderr,"Store::write: Error seeking to position %d: %s\n",
              (int)pos,strerror(errno));
          exit(1);
        }
        m_cur = pos;
        //printf("%x: Store::write: reuse\n",(int)pos);
      }
    }
    size-=numBytes;
    buf+=numBytes;
  }
  while (size>0);
  return size;
}

Member Data Documentation

portable_off_t Store::m_cur

private

Definition at line 116 of file store.h.

FILE* Store::m_file

private

Definition at line 114 of file store.h.

portable_off_t Store::m_front

private

Definition at line 115 of file store.h.

Node* Store::m_head

private

Definition at line 117 of file store.h.

int Store::m_reads

private

Definition at line 119 of file store.h.

State Store::m_state

private

Definition at line 118 of file store.h.

int Store::m_writes

private

Definition at line 120 of file store.h.

---

The documentation for this class was generated from the following files:

• doxygen-1.8.11/src/store.h
• doxygen-1.8.11/src/store.cpp