git-svn-id: https://profuse.googlecode.com/svn/branches/v2@207 aa027e90-d47c-11dd-86d7-074df07e0730

Cache/ConcreteBlockCache.cpp

@@ -0,0 +1,353 @@
+
+#include <algorithm>
+#include <cerrno>
+
+#include <sys/types.h>
+#include <sys/mman.h>
+#include <unistd.h>
+
+#include <Device/BlockDevice.h>
+#include <Cache/ConcreteBlockCache.h>
+
+#include <ProFUSE/Exception.h>
+#include <ProFUSE/auto.h>
+
+
+/*
+ * Note -- everything is assumed to be single-threaded.
+ *
+ */
+
+/*
+ * The primary purpose of the block cache is not as a cache 
+ * (the OS probably does a decent job of that) but rather to
+ * simplify read/writes. Blocks will always be accessed by
+ * pointer, so any updates will be shared.
+ * For memory mapped prodos-order files, MappedBlockCache just
+ * returns a pointer to the memory.
+ * For dos-order, nibblized, or raw devices, ConcreteBlockCache
+ * uses an approach similar to minix (although the buffer pool will 
+ * expand if needed).
+ *
+ * _buffers is a vector of all buffers and only exists to make
+ * freeing them easier.
+ * _hashTable is a simple hashtable of loaded blocks.
+ * _first and _last are a double-linked list of unused blocks, stored
+ * in lru order.
+ *
+ * The Entry struct contains the buffer, the block, a dirty flag, and an in-use
+ * count as well as pointer for the hashtable and lru list.
+ * When a block is loaded, it is stored in the _hashTable.  It remains in the 
+ * hash table when the in-use count goes to 0 (it will also be added to the
+ * end of the lru list).
+ * 
+ * dirty buffers are only written to disk in 3 scenarios:
+ * a) sync() is called
+ * b) the cache is deleted
+ * c) a buffer is re-used from the lru list.
+ */
+
+
+using namespace Device;
+
+using ProFUSE::Exception;
+using ProFUSE::POSIXException;
+
+
+typedef std::vector<BlockCache::Entry *>::iterator EntryIter;
+
+
+
+ConcreteBlockCache::ConcreteBlockCache(BlockDevice *device, unsigned size) :
+    BlockCache(device)
+{
+    if (size < 16) size = 16;
+    
+    std::memset(_hashTable, 0, sizeof(Entry *) * HashTableSize);
+    
+    for (unsigned i = 0; i < size; ++i)
+    {
+        Entry *e = new Entry;
+        
+        std::memset(e, 0, sizeof(Entry));
+        _buffers.push_back(e);
+    }
+    _first = _last = NULL;
+    
+    _first = _buffers.front();
+    _last = _buffers.back();
+    // form a chain....
+    for (unsigned i = 0; i < size; ++i)
+    {
+        Entry *e = _buffers[i];
+        
+        if (i > 0) e->prev = _buffers[i - 1];
+        
+        if (i < size - 1) e->next = _buffers[i + 1];
+    }
+    
+}
+
+ConcreteBlockCache::~ConcreteBlockCache()
+{
+    EntryIter iter;
+    for (iter = _buffers.begin(); iter != _buffers.end(); ++iter)
+    {
+        Entry *e = *iter;
+        
+        if (e->dirty)
+        {
+            _device->write(e->block, e->buffer);
+        }
+        
+        delete e;
+    }
+    _device->sync();
+}
+
+
+ConcreteBlockCache::sync()
+{
+    EntryIter iter;
+    for (iter = _buffers.begin(); iter != _buffers.end(); ++iter)
+    {
+        Entry *e = *iter;
+        
+        if (e->dirty)
+        {
+            _device->write(e->block, e->buffer);
+            e->dirty = false;
+        }
+    }
+    _device->sync();
+}
+
+
+void ConcreteBlockCache::write(unsigned block, const void *bp)
+{
+    FileEntry *e = findEntry();
+    
+    if (e)
+    {
+        e->dirty = true;
+        std::memcpy(e->buffer, bp, 512);
+        return;
+    }
+    
+    // returns a new entry not in the hashtable or the linked list.
+    // we add it to both.
+    e = newEntry(block);
+    
+    e->count = 0;
+    e->dirty = true;
+    
+    std::memcpy(e->buffer, bp, 512);
+    
+    addEntry(e);
+    setLast(e);
+}
+
+void ConcreteBlockCache::markDirty(unsigned block)
+{
+    Entry *e = findEntry(block);
+    
+    if (e) e->dirty = true;
+    // error otherwise?
+}
+
+
+void ConcreteBlockCache::release(unsigned block, int flags)
+{
+    Entry *e = findEntry(block);
+    bool dirty = flags & (kBlockDirty | kBlockCommitNow);
+    
+    if (e)
+    {
+        if (dirty) e->dirty = true;    
+        
+        decrementCount(e);
+        
+        if (flags & kCommitNow)
+        {
+            _device->write(block, e->buffer);
+            e->dirty = false;
+        }
+        
+    }
+    // error otherwise?
+}
+
+void *ConcreteBlockCache::acquire(unsigned block)
+{
+    Entry *e = findEntry(block);
+    
+    if (e)
+    {
+        incrementCount(e);
+        return e->buffer;
+    }
+    
+    // returns a new entry, not in hash table, not in free list.
+    e = newEntry(block);
+    
+    _device->read(block, e->buffer);
+    
+    addEntry(e);
+    
+    return e->buffer;
+}
+
+unsigned ConcreteBlockCache::hashFunction(unsigned block)
+{
+    return block % HashTableSize;
+}
+
+/*
+ * remove a block from the hashtable
+ * and write to dick if dirty.
+ */
+void removeEntry(unsigned block)
+{
+    Entry *e;
+    Entry *prev;
+    unsigned hash = hashFunction(block);
+    
+    e = _hashTable[hash];
+    if (!e) return;
+    
+    // head pointer, special case.
+    if (e->block == block)
+    {
+        _hashTable[hash] = e->nextHash;
+        e->nextHash = NULL;
+        
+        return;
+    }
+    
+    for(;;)
+    {
+        prev = e;
+        e = e->next;
+        
+        if (!e) break;
+        if (e->block == block)
+        {
+            prev->nextHash = e->nextHash;
+            e->nextHash = NULL;
+            
+            break;
+        }    
+    }
+}
+
+
+void ConcreteBlockCache::addEntry(Entry *e)
+{
+    unsigned hash = hashFunction(e->block);
+    
+    e->nextHash = _hashTable[hash];
+    _hashTable[hash] = e;
+}
+
+// increment the count and remove from the free list
+// if necessary.
+void ConcreteBlockCache::incrementCount(Entry *e)
+{
+
+    if (e->count == 0)
+    {
+        Entry *prev = e->prev;
+        Entry *next = e->next;
+        
+        e->prev = e->next = NULL;
+
+        if (prev) prev->next = next;
+        if (next) next->prev = prev;
+        
+        if (_first == e) _first = next;
+        if (_last == e) _last = prev;
+    }
+    
+    e->count = e->count + 1;
+    
+}
+
+// decrement the count.  If it goes to 0,
+// add it as the last block entry.
+void ConcreteBlockCache::decrementCount(Entry *e)
+{
+    e->count = e->count - 1;
+    if (e->count == 0)
+    {
+        setLast(e);
+    }
+}
+
+Entry *ConcreteBlockCache::newEntry(unsigned block)
+{
+    Entry *e;
+    
+    if (_first)
+    {
+        e = _first;
+        if (_first == _last)
+        {
+            _first = _last = NULL;
+        }
+        else
+        {
+            _first = e->next;
+            _first->prev = NULL; 
+        }
+
+
+        if (e->dirty)
+        {
+            _device->write(e->block, e->buffer);
+            e->dirty = false;
+        }
+        removeEntry(e->block);
+    }
+    else
+    {
+        e = new Entry;
+        _buffers.push_back(e);
+    }
+    
+    e->next = NULL;
+    e->prev= NULL;
+    e->nextHash = NULL;
+    e->count = 1;
+    e->block = block;
+    e->dirty = false;
+
+    return e;
+}
+
+
+void ConcreteBlockCache::setLast(Entry *e)
+{
+    if (_last == NULL)
+    {
+        _first = _last = e;
+        return;
+    }
+    
+    e->prev = _last;
+    _last->next = e;
+    _last = e;
+}
+
+
+void ConcreteBlockCache::setFirst(Entry *e)
+{
+    if (_first == NULL)
+    {
+        _first = _last = e;
+        return;
+    }
+    
+    e->next = _first;
+    _first->prev = e;
+    _first = e;
+}

Cache/ConcreteBlockCache.h

@@ -3,7 +3,7 @@
 
 #include <vector>
 
-#include <BlockCache.h>
+#include <Cache/BlockCache.h>
 
 namespace Device {
 
@@ -56,6 +56,7 @@ private:
     void pushEntry(Entry *);
 
     void setLast(Entry *);
+    void setFirst(Entry *);
     
     incrementCount(Entry *);
     decrementCount(Entry *);