void BufferManager::unfixPage(BufferFrame& frame, bool isDirty) {
// Adjust the lru-list.
pthread_rwlock_wrlock(&lruBuffer_latch);
bool foundFrame = false;
//cout << "trying to unfix page with id " << frame.pageId << endl;
//printBufferStatus();
BufferFrame *frameInBuffer = NULL;
for(vector<BufferFrame*>::iterator i = lruBuffer.begin(); i != lruBuffer.end(); ++i) {
if((*i)->pageId == frame.pageId) {
frameInBuffer = *i;
lruBuffer.erase(i);
lruBuffer.push_back(frameInBuffer);
foundFrame = true;
if(isDirty) {
frameInBuffer->writeDataToFile();
}
int er = pthread_rwlock_unlock(&(frameInBuffer->latch));
// pthread_rwlock_unlock(&(frame.latch));
if(er!=0)
cerr << "result code of unlocking frame: " << er;
// cout << frame.pageId << " unlocked\n";
break;
}
}
pthread_rwlock_unlock(&lruBuffer_latch);
//Error handling.
if(!foundFrame) {
cerr << "Can not unfix a frame which is not cached!" << endl;
}
}
// gets the requested data from file and puts a new bufferFrame into the hashmap
// if required, this method replaces frames in the buffer
void BufferManager::cachePageFromFile(unsigned pageId) {
// lock hash table and lru queue
pthread_rwlock_wrlock(&buffer_latch);
pthread_rwlock_wrlock(&lruBuffer_latch);
// if buffer is full, replace a frame in buffer with page from file
if(lruBuffer.size() >= size) {
// Search for the first lockable buffer frame
BufferFrame *toBeFreed = NULL;
for(vector<BufferFrame*>::iterator i = lruBuffer.begin(); i != lruBuffer.end(); ++i) {
// try to lock this frame, if not possible continue with next frame in lruBuffer
int lockResult = pthread_rwlock_trywrlock(&((*i)->latch));
//cout << "lockResult: " << lockResult << " for pageId " << (*i)->pageId << endl;
if(lockResult == 0) {
pthread_rwlock_unlock(&((*i)->latch));
// cout << (*i)->pageId << " wr_locked and unlocked\n";
toBeFreed = *i;
// if we found our candidate frame, delete it from the buffers and deallocate the memory
int cnt = buffer.erase(toBeFreed->pageId); // delete from hash map
assert(cnt == 1);
toBeFreed->writeDataToFile(); // save changes
lruBuffer.erase(i);
//free mmapped memory
if (munmap(toBeFreed->getData(), FRAME_SIZE) == -1) {
cerr << "Error un-mmapping the file";
}
delete toBeFreed; // deallocate memory
break;
}
}
if(toBeFreed==NULL) {
cerr<<"no candidate was found => release locks and return!!!";
pthread_rwlock_unlock(&lruBuffer_latch);
pthread_rwlock_unlock(&buffer_latch);
return;
}
}
// add new frame to hash map and append to end of lruBuffer
BufferFrame *bf = new BufferFrame(file, pageId);
buffer[pageId] = bf;
lruBuffer.push_back(bf);
// release locks
pthread_rwlock_unlock(&lruBuffer_latch);
pthread_rwlock_unlock(&buffer_latch);
}
