Cache.cpp

Go to the documentation of this file.

/* SPDX-FileCopyrightText: 2009 Benoit Bolsee
 *
 * SPDX-License-Identifier: LGPL-2.1-or-later */
 
#include <string.h>
#include <assert.h>
#include <math.h>
#include <stdlib.h>
#include "Cache.hpp"
 
namespace iTaSC {
 
CacheEntry::~CacheEntry()
{
   for (unsigned int id=0; id < m_count; id++)
        m_channelArray[id].clear();
   if (m_channelArray)
       free(m_channelArray);
}
 
CacheItem *CacheChannel::_findBlock(CacheBuffer *buffer, unsigned short timeOffset, unsigned int *retBlock)
{
    // the timestamp is necessarily in this buffer
    unsigned int lowBlock, highBlock, midBlock;
    if (timeOffset <= buffer->lookup[0].m_timeOffset) {
        // special case: the item is in the first block, search from start
        *retBlock = 0;
        return &buffer->m_firstItem;
    }
    // general case, the item is in the middle of the buffer
    // before doing a dycotomic search, we will assume that timestamp
    // are regularly spaced so that we can try to locate the block directly
    highBlock = buffer->m_lastItemPositionW>>m_positionToBlockShiftW;
    lowBlock = midBlock = (timeOffset*highBlock)/(buffer->m_lastTimestamp-buffer->m_firstTimestamp);
    // give some space for security
    if (lowBlock > 0)
        lowBlock--;
    if (timeOffset <= buffer->lookup[lowBlock].m_timeOffset) {
        // bad guess, but we know this block is a good high block, just use it
        highBlock = lowBlock;
        lowBlock = 0;
    } else {
        // ok, good guess, now check the high block, give some space
        if (midBlock < highBlock)
            midBlock++;
        if (timeOffset <= buffer->lookup[midBlock].m_timeOffset) {
            // good guess, keep that block as the high block
            highBlock = midBlock;
        }
    }
    // the item is in a different block, do a dycotomic search
    // the timestamp is alway > lowBlock and <= highBlock
    while (1) {
        midBlock = (lowBlock+highBlock)/2;
        if (midBlock == lowBlock) {
            // low block and high block are contigous, we can start search from the low block
            break;
        } else if (timeOffset <= buffer->lookup[midBlock].m_timeOffset) {
            highBlock = midBlock;
        } else {
            lowBlock = midBlock;
        }
    }
    assert (lowBlock != highBlock);
    *retBlock = highBlock;
    return CACHE_BLOCK_ITEM_ADDR(this,buffer,lowBlock);
}
 
void CacheChannel::clear()
{
    CacheBuffer *buffer, *next;
    for (buffer=m_firstBuffer; buffer != 0; buffer = next) {
        next = buffer->m_next;
        free(buffer);
    }
    m_firstBuffer = NULL;
    m_lastBuffer = NULL;
    if (initItem) {
        free(initItem);
        initItem = NULL;
    }
}
 
CacheBuffer* CacheChannel::allocBuffer()
{
    CacheBuffer* buffer;
    if (!m_busy)
        return NULL;
    buffer = (CacheBuffer*)malloc(CACHE_BUFFER_HEADER_SIZE+(m_bufferSizeW<<2));
    if (buffer) {
        memset(buffer, 0, CACHE_BUFFER_HEADER_SIZE);
    }
    return buffer;
}
 
CacheItem* CacheChannel::findItemOrLater(unsigned int timestamp, CacheBuffer **rBuffer)
{
    CacheBuffer* buffer;
    CacheItem *item, *limit;
    if (!m_busy)
        return NULL;
    if (timestamp == 0 && initItem) {
        *rBuffer = NULL;
        return initItem;
    }
    for (buffer=m_firstBuffer; buffer; buffer = buffer->m_next) {
        if (buffer->m_firstFreePositionW == 0)
            // buffer is empty, this must be the last and we didn't find the timestamp
            return NULL;
        if (timestamp < buffer->m_firstTimestamp) {
            *rBuffer = buffer;
            return &buffer->m_firstItem;
        }
        if (timestamp <= buffer->m_lastTimestamp) {
            // the timestamp is necessarily in this buffer
            unsigned short timeOffset = (unsigned short)(timestamp-buffer->m_firstTimestamp);
            unsigned int highBlock;
            item = _findBlock(buffer, timeOffset, &highBlock);
            // now we do a linear search until we find a timestamp that is equal or higher
            // we should normally always find an item but let's put a limit just in case
            limit = CACHE_BLOCK_ITEM_ADDR(this,buffer,highBlock);
            while (item<=limit && item->m_timeOffset < timeOffset )
                item = CACHE_NEXT_ITEM(item);
            assert(item<=limit);
            *rBuffer = buffer;
            return item;
        }
        // search in next buffer
    }
    return NULL;
}
 
CacheItem* CacheChannel::findItemEarlier(unsigned int timestamp, CacheBuffer **rBuffer)
{
    CacheBuffer *buffer, *prevBuffer;
    CacheItem *item, *limit, *prevItem;
    if (!m_busy)
        return NULL;
    if (timestamp == 0)
        return NULL;
    for (prevBuffer=NULL, buffer=m_firstBuffer; buffer; prevBuffer = buffer, buffer = buffer->m_next) {
        if (buffer->m_firstFreePositionW == 0)
            // buffer is empty, this must be the last and we didn't find the timestamp
            return NULL;
        if (timestamp <= buffer->m_firstTimestamp) {
            if (prevBuffer == NULL) {
                // no item before, except the initial item
                *rBuffer = NULL;
                return initItem;
            }
            // the item is necessarily the last one of previous buffer
            *rBuffer = prevBuffer;
            return CACHE_ITEM_ADDR(prevBuffer,prevBuffer->m_lastItemPositionW);
        }
        if (timestamp <= buffer->m_lastTimestamp) {
            // the timestamp is necessarily in this buffer
            unsigned short timeOffset = (unsigned short)(timestamp-buffer->m_firstTimestamp);
            unsigned int highBlock;
            item = _findBlock(buffer, timeOffset, &highBlock);
            // now we do a linear search until we find a timestamp that is equal or higher
            // we should normally always find an item but let's put a limit just in case
            limit = CACHE_BLOCK_ITEM_ADDR(this,buffer,highBlock);
            prevItem = NULL;
            while (item<=limit && item->m_timeOffset < timeOffset) {
                prevItem = item;
                item = CACHE_NEXT_ITEM(item);
            }
            assert(item<=limit && prevItem!=NULL);
            *rBuffer = buffer;
            return prevItem;
        }
        // search in next buffer
    }
    // pass all buffer, the last item is the last item of the last buffer
    if (prevBuffer == NULL) {
        // no item before, except the initial item
        *rBuffer = NULL;
        return initItem;
    }
    // the item is necessarily the last one of previous buffer
    *rBuffer = prevBuffer;
    return CACHE_ITEM_ADDR(prevBuffer,prevBuffer->m_lastItemPositionW);
}
 
 
Cache::Cache()
{
}
 
Cache::~Cache()
{
    CacheMap::iterator it;
    for (it=m_cache.begin(); it!=m_cache.end(); it=m_cache.begin()) {
        deleteDevice(it->first);
    }
}
 
int Cache::addChannel(const void *device, const char *name, unsigned int maxItemSize)
{
    CacheMap::iterator it = m_cache.find(device);
    CacheEntry *entry;
    CacheChannel *channel;
    unsigned int id;
 
    if (maxItemSize > 0x3FFF0)
        return -1;
 
    if (it == m_cache.end()) {
        // device does not exist yet, create a new entry
        entry = new CacheEntry();
        if (entry == NULL)
            return -1;
        if (!m_cache.insert(CacheMap::value_type(device,entry)).second) {
            delete entry;
            return -1;
        }
    } else {
        entry = it->second;
    }
    // locate a channel with the same name and reuse
    for (channel=entry->m_channelArray, id=0; id<entry->m_count; id++, channel++) {
        if (channel->m_busy && !strcmp(name, channel->m_name)) {
            // make this channel free again
            deleteChannel(device, id);
            // there can only be one channel with the same name
            break;
        }
    }
    for (channel=entry->m_channelArray, id=0; id<entry->m_count; id++, channel++) {
        // locate a free channel
        if (!channel->m_busy)
            break;
    }
    if (id == entry->m_count) {
        // no channel free, create new channels
        int newcount = entry->m_count + CACHE_CHANNEL_EXTEND_SIZE;
        channel = (CacheChannel*)realloc(entry->m_channelArray, newcount*sizeof(CacheChannel));
        if (channel == NULL)
            return -1;
        entry->m_channelArray = channel;
        memset(&entry->m_channelArray[entry->m_count], 0, CACHE_CHANNEL_EXTEND_SIZE*sizeof(CacheChannel));
        entry->m_count = newcount;
        channel = &entry->m_channelArray[id];
    }
    // compute the optimal buffer size
    // The buffer size must be selected so that
    // - it does not contain more than 1630 items (=1s of cache assuming 25 items per second)
    // - it contains at least one item
    // - it's not bigger than 256kb and preferably around 32kb
    // - it a multiple of 4
    unsigned int bufSize = 1630*(maxItemSize+4);
    if (bufSize >= CACHE_DEFAULT_BUFFER_SIZE)
        bufSize = CACHE_DEFAULT_BUFFER_SIZE;
    if (bufSize < maxItemSize+16)
        bufSize = maxItemSize+16;
    bufSize = (bufSize + 3) & ~0x3;
    // compute block size and offset bit mask
    // the block size is computed so that
    // - it is a power of 2
    // - there is at least one item per block
    // - there is no more than CACHE_LOOKUP_TABLE_SIZE blocks per buffer
    unsigned int blockSize = bufSize/CACHE_LOOKUP_TABLE_SIZE;
    if (blockSize < maxItemSize+12)
        blockSize = maxItemSize+12;
    // find the power of 2 that is immediately larger than blockSize
    unsigned int m;
    unsigned int pwr2Size = blockSize;
    while ((m = (pwr2Size & (pwr2Size-1))) != 0)
        pwr2Size = m;
    blockSize = (pwr2Size < blockSize) ? pwr2Size<<1 : pwr2Size;
    // convert byte size to word size because all positions and size are expressed in 32 bit words
    blockSize >>= 2;
    channel->m_blockSizeW = blockSize;
    channel->m_bufferSizeW = bufSize>>2;
    channel->m_firstBuffer = NULL;
    channel->m_lastBuffer = NULL;
    channel->m_busy = 1;
    channel->initItem = NULL;
    channel->m_maxItemSizeB = maxItemSize;
    strncpy(channel->m_name, name, sizeof(channel->m_name));
    channel->m_name[sizeof(channel->m_name)-1] = 0;
    channel->m_positionToOffsetMaskW = (blockSize-1);
    for (m=0; blockSize!=1; m++, blockSize>>=1);
    channel->m_positionToBlockShiftW = m;
    return (int)id;
}
 
int Cache::deleteChannel(const void *device, int id)
{
    CacheMap::iterator it = m_cache.find(device);
    CacheEntry *entry;
 
    if (it == m_cache.end()) {
        // device does not exist
        return -1;
    }
    entry = it->second;
    if (id < 0 || id >= (int)entry->m_count || !entry->m_channelArray[id].m_busy)
        return -1;
    entry->m_channelArray[id].clear();
    entry->m_channelArray[id].m_busy = 0;
    return 0;
}
 
int Cache::deleteDevice(const void *device)
{
    CacheMap::iterator it = m_cache.find(device);
    CacheEntry *entry;
 
    if (it == m_cache.end()) {
        // device does not exist
        return -1;
    }
    entry = it->second;
    delete entry;
    m_cache.erase(it);
    return 0;
}
 
void Cache::clearCacheFrom(const void *device, CacheTS timestamp)
{
    CacheMap::iterator it = (device) ? m_cache.find(device) : m_cache.begin();
    CacheEntry *entry;
    CacheChannel *channel;
    CacheBuffer *buffer, *nextBuffer, *prevBuffer;
    CacheItem *item, *prevItem, *nextItem;
    unsigned int positionW, block;
 
    while (it != m_cache.end()) {
        entry = it->second;
        for (unsigned int ch=0; ch<entry->m_count; ch++) {
            channel = &entry->m_channelArray[ch];
            if (channel->m_busy) {
                item = channel->findItemOrLater(timestamp, &buffer);
                if (item ) {
                    if (!buffer) {
                        // this is possible if we return the special timestamp=0 item, delete all buffers
                        channel->clear();
                    } else {
                        // this item and all later items will be removed, clear any later buffer
                        while ((nextBuffer = buffer->m_next) != NULL) {
                            buffer->m_next = nextBuffer->m_next;
                            free(nextBuffer);
                        }
                        positionW = CACHE_ITEM_POSITIONW(buffer,item);
                        if (positionW == 0) {
                            // this item is the first one of the buffer, remove the buffer completely
                            // first find the buffer just before it
                            nextBuffer = channel->m_firstBuffer;
                            prevBuffer = NULL;
                            while (nextBuffer != buffer) {
                                prevBuffer = nextBuffer;
                                nextBuffer = nextBuffer->m_next;
                                // we must quit this loop before reaching the end of the list
                                assert(nextBuffer);
                            }
                            free(buffer);
                            buffer = prevBuffer;
                            if (buffer == NULL)
                                // this was also the first buffer
                                channel->m_firstBuffer = NULL;
                        } else {
                            // removing this item means finding the previous item to make it the last one
                            block = positionW>>channel->m_positionToBlockShiftW;
                            if (block == 0) {
                                // start from first item, we know it is not our item because positionW > 0
                                prevItem = &buffer->m_firstItem;
                            } else {
                                // no need to check the current block, it will point to our item or a later one
                                // but the previous block will be a good start for sure.
                                block--;
                                prevItem = CACHE_BLOCK_ITEM_ADDR(channel,buffer,block);
                            }
                            while ((nextItem = CACHE_NEXT_ITEM(prevItem)) < item)
                                prevItem = nextItem;
                            // we must have found our item
                            assert(nextItem==item);
                            // now set the buffer
                            buffer->m_lastItemPositionW = CACHE_ITEM_POSITIONW(buffer,prevItem);
                            buffer->m_firstFreePositionW = positionW;
                            buffer->m_lastTimestamp = buffer->m_firstTimestamp + prevItem->m_timeOffset;
                            block = buffer->m_lastItemPositionW>>channel->m_positionToBlockShiftW;
                            buffer->lookup[block].m_offsetW = buffer->m_lastItemPositionW&channel->m_positionToOffsetMaskW;
                            buffer->lookup[block].m_timeOffset = prevItem->m_timeOffset;
                        }
                        // set the channel
                        channel->m_lastBuffer = buffer;
                        if (buffer) {
                            channel->m_lastTimestamp = buffer->m_lastTimestamp;
                            channel->m_lastItemPositionW = buffer->m_lastItemPositionW;
                        }
                    }
                }
            }
        }
        if (device)
            break;
        ++it;
    }
}
 
void *Cache::addCacheItem(const void *device, int id, unsigned int timestamp, void *data, unsigned int length)
{
    CacheMap::iterator it = m_cache.find(device);
    CacheEntry *entry;
    CacheChannel *channel;
    CacheBuffer *buffer, *next;
    CacheItem *item;
    unsigned int positionW, sizeW, block;
 
    if (it == m_cache.end()) {
        // device does not exist
        return NULL;
    }
    entry = it->second;
    if (id < 0 || id >= (int) entry->m_count || !entry->m_channelArray[id].m_busy)
        return NULL;
    channel = &entry->m_channelArray[id];
    if (length > channel->m_maxItemSizeB)
        return NULL;
    if (timestamp == 0) {
        // initial item, delete all buffers
        channel->clear();
        // and create initial item
        item = NULL;
        // we will allocate the memory, which is always pointer aligned => compute size
        // with NULL will give same result.
        sizeW = CACHE_ITEM_SIZEW(item,length);
        item = (CacheItem*)calloc(sizeW, 4);
        item->m_sizeW = sizeW;
        channel->initItem = item;
    } else {
        if (!channel->m_lastBuffer) {
            // no item in buffer, insert item at first position of first buffer
            positionW = 0;
            if ((buffer = channel->m_firstBuffer) == NULL) {
                buffer = channel->allocBuffer();
                channel->m_firstBuffer = buffer;
            }
        } else if (timestamp > channel->m_lastTimestamp) {
            // this is the normal case: we are writing past lastest timestamp
            buffer = channel->m_lastBuffer;
            positionW = buffer->m_firstFreePositionW;
        } else if (timestamp == channel->m_lastTimestamp) {
            // common case, rewriting the last timestamp, just reuse the last position
            buffer = channel->m_lastBuffer;
            positionW = channel->m_lastItemPositionW;
        } else {
            // general case, write in the middle of the buffer, locate the timestamp
            // (or the timestamp just after), clear this item and all future items,
            // and write at that position
            item = channel->findItemOrLater(timestamp, &buffer);
            if (item == NULL) {
                // this should not happen
                return NULL;
            }
            // this item will become the last one of this channel, clear any later buffer
            while ((next = buffer->m_next) != NULL) {
                buffer->m_next = next->m_next;
                free(next);
            }
            // no need to update the buffer, this will be done when the item is written
            positionW = CACHE_ITEM_POSITIONW(buffer,item);
        }
        item = CACHE_ITEM_ADDR(buffer,positionW);
        sizeW = CACHE_ITEM_SIZEW(item,length);
        // we have positionW pointing where we can put the item
        // before we do that we have to check if we can:
        // - enough room
        // - timestamp not too late
        if ((positionW+sizeW > channel->m_bufferSizeW) ||
            (positionW > 0 && timestamp >= buffer->m_firstTimestamp+0x10000)) {
            // we must allocate a new buffer to store this item
            // but before we must make sure that the current buffer is consistent
            if (positionW != buffer->m_firstFreePositionW) {
                // This means that we were trying to write in the middle of the buffer.
                // We must set the buffer right with positionW being the last position
                // and find the item before positionW to make it the last.
                block = positionW>>channel->m_positionToBlockShiftW;
                CacheItem *previousItem, *nextItem;
                if (block == 0) {
                    // start from first item, we know it is not our item because positionW > 0
                    previousItem = &buffer->m_firstItem;
                } else {
                    // no need to check the current block, it will point to our item or a later one
                    // but the previous block will be a good start for sure.
                    block--;
                    previousItem = CACHE_BLOCK_ITEM_ADDR(channel,buffer,block);
                }
                while ((nextItem = CACHE_NEXT_ITEM(previousItem)) < item)
                    previousItem = nextItem;
                // we must have found our item
                assert(nextItem==item);
                // now set the buffer
                buffer->m_lastItemPositionW = CACHE_ITEM_POSITIONW(buffer,previousItem);
                buffer->m_firstFreePositionW = positionW;
                buffer->m_lastTimestamp = buffer->m_firstTimestamp + previousItem->m_timeOffset;
                block = buffer->m_lastItemPositionW>>channel->m_positionToBlockShiftW;
                buffer->lookup[block].m_offsetW = buffer->m_lastItemPositionW&channel->m_positionToOffsetMaskW;
                buffer->lookup[block].m_timeOffset = previousItem->m_timeOffset;
                // and also the channel, just in case
                channel->m_lastBuffer = buffer;
                channel->m_lastTimestamp = buffer->m_lastTimestamp;
                channel->m_lastItemPositionW = buffer->m_lastItemPositionW;
            }
            // now allocate a new buffer
            buffer->m_next = channel->allocBuffer();
            if (buffer->m_next == NULL)
                return NULL;
            buffer = buffer->m_next;
            positionW = 0;
            item = &buffer->m_firstItem;
            sizeW = CACHE_ITEM_SIZEW(item,length);
        }
        // all check passed, ready to write the item
        item->m_sizeW = sizeW;
        if (positionW == 0) {
            item->m_timeOffset = 0;
            buffer->m_firstTimestamp = timestamp;
        } else {
            item->m_timeOffset = (unsigned short)(timestamp-buffer->m_firstTimestamp);
        }
        buffer->m_lastItemPositionW = positionW;
        buffer->m_firstFreePositionW = positionW+sizeW;
        buffer->m_lastTimestamp = timestamp;
        block = positionW>>channel->m_positionToBlockShiftW;
        buffer->lookup[block].m_offsetW = positionW&channel->m_positionToOffsetMaskW;
        buffer->lookup[block].m_timeOffset = item->m_timeOffset;
        buffer->m_lastItemPositionW = CACHE_ITEM_POSITIONW(buffer,item);
        buffer->m_firstFreePositionW = buffer->m_lastItemPositionW+item->m_sizeW;
        channel->m_lastBuffer = buffer;
        channel->m_lastItemPositionW = positionW;
        channel->m_lastTimestamp = timestamp;
    }
    // now copy the item
    void *itemData = CACHE_ITEM_DATA_POINTER(item);
    if (data)
        memcpy(itemData, data, length);
    return itemData;
}
 
const void *Cache::getPreviousCacheItem(const void *device, int id, unsigned int *timestamp)
{
    CacheMap::iterator it;
    CacheEntry *entry;
    CacheChannel *channel;
    CacheBuffer *buffer;
    CacheItem *item;
 
    if (device) {
        it = m_cache.find(device);  
    } else {
        it = m_cache.begin();
    }
    if (it == m_cache.end()) {
        // device does not exist
        return NULL;
    }
    entry = it->second;
    if (id < 0 || id >= (int) entry->m_count || !entry->m_channelArray[id].m_busy)
        return NULL;
    channel = &entry->m_channelArray[id];
    if ((item = channel->findItemEarlier(*timestamp,&buffer)) == NULL)
        return NULL;
    *timestamp = (buffer) ? buffer->m_firstTimestamp+item->m_timeOffset : 0;
    return CACHE_ITEM_DATA_POINTER(item);
}
 
const CacheItem *Cache::getCurrentCacheItemInternal(const void *device, int id, CacheTS timestamp)
{
    CacheMap::iterator it = m_cache.find(device);
    CacheEntry *entry;
    CacheChannel *channel;
    CacheBuffer *buffer;
    CacheItem *item;
 
    if (it == m_cache.end()) {
        // device does not exist
        return NULL;
    }
    entry = it->second;
    if (id < 0 || id >= (int) entry->m_count || !entry->m_channelArray[id].m_busy)
        return NULL;
    channel = &entry->m_channelArray[id];
    if ((item = channel->findItemOrLater(timestamp,&buffer)) == NULL)
        return NULL;
    if (buffer && buffer->m_firstTimestamp+item->m_timeOffset != timestamp)
        return NULL;
    return item;
}
 
const void *Cache::getCurrentCacheItem(const void *device, int channel, unsigned int timestamp)
{
    const CacheItem *item = getCurrentCacheItemInternal(device, channel, timestamp);
    return (item) ? CACHE_ITEM_DATA_POINTER(item) : NULL;
}
 
double *Cache::addCacheVectorIfDifferent(const void *device, int channel, CacheTS timestamp, double *newdata, unsigned int length, double threshold)
{
    const CacheItem *item = getCurrentCacheItemInternal(device, channel, timestamp);
    unsigned int sizeW = CACHE_ITEM_SIZEW(item,length*sizeof(double));
    if (!item || item->m_sizeW != sizeW)
        return (double*)addCacheItem(device, channel, timestamp, newdata, length*sizeof(double));
    double *olddata = (double*)CACHE_ITEM_DATA_POINTER(item);
    if (!length)
        return olddata;
    double *ref = olddata;
    double *v = newdata;
    unsigned int i;
    for (i=length; i>0; --i) {
        if (fabs(*v-*ref) > threshold)
            break;
        *ref++ = *v++;
    }
    if (i) 
        olddata = (double*)addCacheItem(device, channel, timestamp, newdata, length*sizeof(double));
    return olddata;
}
 
}