buddy.cpp

来自「MySQL数据库开发源码 值得一看哦」· C++ 代码 · 共 326 行

/* Copyright (C) 2003 MySQL AB

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA */

#include "buddy.hpp"

void Chunk256::setFree(bool free){
  // Bit 0 of allocationTimeStamp represents if the segment is free or not
  Uint32 offMask = 0x0; // A mask to set the 0 bit to 0
  allocationTimeStamp = 0x0;
  if(free) 
    // Set this bit to 0, if segment should be free
    allocationTimeStamp = allocationTimeStamp & offMask;
}

bool Chunk256::getFree(){
  Uint32 offMask = 0x0; 
  return ((allocationTimeStamp | offMask) == offMask ? true : false);
}

void Chunk256::setAllocationTimeStamp(Uint32 cTime){
  // Bits 1-31 of allocationTimeStamp represent the allocation time for segment
  
  // printf("\nSet allocation time. Current time %d", cTime);
  Uint32 onMask = 0x80000000; // A mask to set the 0 bit to 1
  allocationTimeStamp = 0x0;
  allocationTimeStamp = onMask | cTime;
}

Uint32 Chunk256::getAllocationTimeStamp(){
  Uint32 onMask = 0x80000000;
  allocationTimeStamp = allocationTimeStamp ^ onMask;
  printf("\nGet allocation time. Time is %d", allocationTimeStamp);
  return allocationTimeStamp;
};

bool BuddyMemory::allocate(int nChunksToAllocate) {
  
  // Allocate the memory block needed. This memory is deallocated in the
  // destructor of TransporterRegistry.

  printf("\nAllocating %d chunks...", nChunksToAllocate);

  startOfMemoryBlock = (Uint32*) malloc(256 * nChunksToAllocate);

  if (startOfMemoryBlock == NULL)
    return false;
  
  // Allocate the array of 256-byte chunks
  chunk = new Chunk256[nChunksToAllocate];
  
  // Initialize the chunk-array. Every 8 kB segment consists of 32 chunks.
  // Set all chunks to free and set the prev and next pointer 
  for (int i=0; i < nChunksToAllocate; i++) {
    chunk[i].setFree(true);
    if (i%32 == 0) {  
      // The first chunk in every segment will point to the prev and next segment
      chunk[i].prevSegmentOfSameSize = i-32;
      chunk[i].nextSegmentOfSameSize = i + 32;
      chunk[0].prevSegmentOfSameSize = END_OF_CHUNK_LIST;
      chunk[totalNoOfChunks-32].nextSegmentOfSameSize = END_OF_CHUNK_LIST;
    } else {
      // The rest of the chunks in the segments have undefined prev and next pointers
      chunk[i].prevSegmentOfSameSize = UNDEFINED_CHUNK;
      chunk[i].nextSegmentOfSameSize = UNDEFINED_CHUNK;
    }
  }
  
  // Initialize the freeSegment-pointers
  for (int i=0; i<sz_MAX; i++)
    freeSegment[i] = UNDEFINED_CHUNK;
     
  // There are only 8 kB segments at startup
  freeSegment[sz_8192] = 0;

  for (int i=0; i<sz_MAX; i++)
    printf("\nPointers: %d", freeSegment[i]);

  return true;
}


bool BuddyMemory::getSegment(Uint32 size, Segment * dst) {
  
  // The no of chunks the user asked for
  Uint32 nChunksAskedFor = ceil((double(size)/double(256)));
  int segm;

  printf("\n%d chunks asked for", nChunksAskedFor);

  // It may be that the closest segment size above 
  // nChunksAskedFor*256 is not a size that is available in 
  // the freeSegment-list, i.e. it may not be of FreeSegmentSize.
  int nChunksToAllocate = nChunksAskedFor;

  // Find the FreeSegmentSize closest above nChunksAskedFor
  if ((nChunksToAllocate != 1) && (nChunksToAllocate % 2 != 0))
    nChunksToAllocate++;

  printf("\n%d chunks to allocate", nChunksToAllocate);
  int segmSize = logTwoPlus(nChunksToAllocate) - 1;
  if (size-pow(2,segmSize) > 256) 
    segmSize ++;
  printf("\nSegment size: %f", pow(2,int(8+segmSize)));

  while ((segmSize <= sz_GET_MAX) && (freeSegment[segmSize] == UNDEFINED_CHUNK))
    segmSize++;

  segm = freeSegment[segmSize];
  if (segm != UNDEFINED_CHUNK){
    // Free segment of asked size or larger is found
    
    // Remove the found segment from the freeSegment-list
    removeFromFreeSegmentList(segmSize, segm);

    // Set all chunks to allocated (not free) and set the allocation time
    // for the segment we are about to allocate
    for (int i = segm; i <= segm+nChunksToAllocate; i++) {
      chunk[i].setFree(false);
      chunk[i].setAllocationTimeStamp(currentTime);
    }

    // Before returning the segment, check if it is larger than the segment asked for
    if (nChunksAskedFor < nChunksToAllocate) 
      release(nChunksAskedFor, nChunksToAllocate - nChunksAskedFor - 1);
    
    Segment segment;
    segment.segmentAddress = startOfMemoryBlock+(segm * 256);
    segment.segmentSize = 256 * nChunksAskedFor;
    segment.releaseId = segm;

    printf("\nSegment: segment address = %d, segment size = %d, release Id = %d", 
	   segment.segmentAddress, segment.segmentSize, segment.releaseId);  

    return true;
  }
  printf("\nNo segments of asked size or larger are found");
  return false;
}

void BuddyMemory::removeFromFreeSegmentList(int sz, int index) {
  // Remove the segment from the freeSegment list

  printf("\nRemoving segment from list...");
  if (index != UNDEFINED_CHUNK) {
    Chunk256 prevChunk;
    Chunk256 nextChunk;
    int prevChunkIndex = chunk[index].prevSegmentOfSameSize;
    int nextChunkIndex = chunk[index].nextSegmentOfSameSize;
  
    if (prevChunkIndex == END_OF_CHUNK_LIST) {
      if (nextChunkIndex == END_OF_CHUNK_LIST)
	// We are about to remove the only element in the list
	freeSegment[sz] = UNDEFINED_CHUNK;
      else {
	// We are about to remove the first element in the list
	nextChunk = chunk[nextChunkIndex];
	nextChunk.prevSegmentOfSameSize = END_OF_CHUNK_LIST;
	freeSegment[sz] = nextChunkIndex;
      }
    } else {
      if (nextChunkIndex == END_OF_CHUNK_LIST) {
	// We are about to remove the last element in the list
	prevChunk = chunk[prevChunkIndex];
	prevChunk.nextSegmentOfSameSize = END_OF_CHUNK_LIST;
      } else {
	// We are about to remove an element in the middle of the list
	prevChunk = chunk[prevChunkIndex];
	nextChunk = chunk[nextChunkIndex];
	prevChunk.nextSegmentOfSameSize = nextChunkIndex;
	nextChunk.prevSegmentOfSameSize = prevChunkIndex;
      }
    }
  }
  for (int i=0; i<sz_MAX; i++)
    printf("\nPointers: %d", freeSegment[i]);
}

void BuddyMemory::release(int releaseId, int size) {

  int nChunksToRelease = (size == 0 ? 1 : ceil(double(size)/double(256)));
  //nChunksToRelease = ceil(double(size)/double(256));
  int startChunk = releaseId;
  int endChunk = releaseId + nChunksToRelease - 1;

  printf("\n%d chunks to release (initially)", nChunksToRelease);
 
  // Set the chunks we are about to release to free
  for (int i = startChunk; i <= endChunk; i++){
    chunk[i].setFree(true);
  }

  // Look at the chunks before the segment we are about to release
  for (int i = releaseId-1; i >= 0; i--) {
    if (!chunk[i].getFree())
      break;
    else {
      startChunk = i;
      nChunksToRelease++;
      // Look at the next-pointer. If it is valid, we have a 
      // chunk that is the start of a free segment. Remove it 
      // from the freeSegment-list.
      if (chunk[i].nextSegmentOfSameSize != UNDEFINED_CHUNK)
	removeFromFreeSegmentList(size, i);
    }
  }
  
  // Look at the chunks after the segment we are about to release
  for (int i = endChunk+1; i <= totalNoOfChunks; i++) {
    if (!chunk[i].getFree())
      break;
    else {
      endChunk = i;
      nChunksToRelease++;
      // Look at the next-pointer. If it is valid, we have a 
      // chunk that is the start of a free segment. Remove it
      // from the free segment list
      if (chunk[i].nextSegmentOfSameSize != UNDEFINED_CHUNK)
	removeFromFreeSegmentList(size, i);
    }
  }
 
  // We have the start and end indexes and total no of free chunks. 
  // Separate the chunks into segments that can be added to the
  // freeSegments-list.
  int restChunk = 0;
  int segmSize; 
  
   printf("\n%d chunks to release (finally)", nChunksToRelease);
  
  segmSize = logTwoPlus(nChunksToRelease) - 1;
  if (segmSize > sz_MAX) {
    segmSize = sz_MAX;
  }
   
  nChunksToRelease = pow(2,segmSize);
  addToFreeSegmentList(nChunksToRelease*256, startChunk);
}

void BuddyMemory::addToFreeSegmentList(int sz, int index) {
  // Add a segment to the freeSegment list
 
  printf("\nAsked to add segment of size %d", sz);

  // Get an index in freeSegment list corresponding to sz size
  int segmSize = logTwoPlus(sz) - 1;
  if (sz - pow(2,segmSize) >= 256) 
    segmSize ++;
  sz = segmSize - 8; 
 
  int nextSegm = freeSegment[sz];

  printf("\nAdding a segment of size %f", pow(2,(8 + sz)));

  freeSegment[sz] = index;
  if (nextSegm == UNDEFINED_CHUNK) {
    // We are about to add a segment to an empty list
    chunk[index].prevSegmentOfSameSize = END_OF_CHUNK_LIST;
    chunk[index].nextSegmentOfSameSize = END_OF_CHUNK_LIST;
  }
  else {
    // Add the segment first in the list
    chunk[index].prevSegmentOfSameSize = END_OF_CHUNK_LIST;
    chunk[index].nextSegmentOfSameSize = nextSegm;
    chunk[nextSegm].prevSegmentOfSameSize = index;
  }

 for (int i=0; i<sz_MAX; i++)
    printf("\nPointers: %d", freeSegment[i]);

}

Uint32 BuddyMemory::logTwoPlus(Uint32 arg) {
  // Calculate log2(arg) + 1
            
  Uint32 resValue;

  arg = arg | (arg >> 8);
  arg = arg | (arg >> 4);
  arg = arg | (arg >> 2);
  arg = arg | (arg >> 1);
  resValue = (arg & 0x5555) + ((arg >> 1) & 0x5555);
  resValue = (resValue & 0x3333) + ((resValue >> 2) & 0x3333);
  resValue = resValue + (resValue >> 4);
  resValue = (resValue & 0xf) + ((resValue >> 8) & 0xf);

  return resValue;
}

bool BuddyMemory::memoryAvailable() {
  // Return true if there is at least 8 kB memory available
  for (int i = sz_8192; i < sz_MAX; i++)
    if (freeSegment[i] != UNDEFINED_CHUNK)
      return true;
  return false;	  
}


void BuddyMemory::refreshTime(Uint32 time) {
  if (time - currentTime > 1000) { 
    // Update current time
    currentTime = time;
    // Go through the chunk-list every second and release 
    // any chunks that have been allocated for too long
    for (int i=0; i<totalNoOfChunks; i++) {
      if ((!chunk[i].getFree()) && 
	  (currentTime-chunk[i].getAllocationTimeStamp() > ALLOCATION_TIMEOUT)) {
	release(i, 256);
	printf("\nChunks hve been allocated for too long");
      }
    } 
  }
}