From 9fc279ef643a093c2cbe4c5b5f57944f30fed833 Mon Sep 17 00:00:00 2001
From: ksherlock <ksherlock@aa027e90-d47c-11dd-86d7-074df07e0730>
Date: Tue, 8 Dec 2009 00:01:24 +0000
Subject: [PATCH] git-svn-id:
 https://profuse.googlecode.com/svn/branches/v2@127
 aa027e90-d47c-11dd-86d7-074df07e0730

---
 BlockCache.cpp      | 120 ++++++++++++++++++++++++++++++++++++++++++++
 BlockCache.h        |  37 ++++++++++++++
 VolumeDirectory.cpp |   1 +
 3 files changed, 158 insertions(+)
 create mode 100644 BlockCache.cpp
 create mode 100644 BlockCache.h

diff --git a/BlockCache.cpp b/BlockCache.cpp
new file mode 100644
index 0000000..b0d4c74
--- /dev/null
+++ b/BlockCache.cpp
@@ -0,0 +1,120 @@
+#include "BlockCache.h"
+#include "BlockDevice.h"
+#include "auto.h"
+
+#include <algorithm>
+
+
+
+/*
+ * Note -- everything is assumed to be single-threaded.
+ *
+ */
+
+
+
+using namespace ProFUSE;
+
+typedef std::vector<BlockDescriptor>::iterator BDIter;
+
+const unsigned CacheSize = 16; 
+
+BlockCache::BlockCache(BlockDevice *device)
+{
+    _device = device;
+    _ts = 0;
+    _blocks.reserve(CacheSize);
+}
+
+BlockCache::~BlockCache()
+{
+    for (BDIter iter = _blocks.begin(); iter != _blocks.end(); ++iter)
+    {
+        if (iter->data) delete[] iter->data;
+    }
+}
+
+
+void *BlockCache::acquire(unsigned block)
+{
+    unsigned mints = -1;
+    unsigned freeCount = 0;
+    
+    BDIter oldest;
+
+
+    ++_ts;
+
+    /*
+     * keep a pointer to the oldest free entry (according to ts).
+     * and re-use if >= 16 entries. 
+     */
+ 
+    
+    for (BDIter iter = _blocks.begin(); iter != _blocks.end(); ++iter)
+    {
+        if (iter->block == block)
+        {
+            ++iter->count;
+            iter->ts = _ts;
+            return iter->data;
+        }
+        
+        if (iter->count == 0)
+        {
+            ++freeCount;
+            if (iter->ts < mints)
+            {
+                mints = iter->ts;
+                oldest = iter;
+            }
+        }
+    }
+    
+    
+    if (freeCount && (_blocks.size() >= CacheSize))
+    {
+        oldest->block = block;
+        oldest->count = 1;
+        oldest->ts = _ts;
+        
+        _device->read(block, oldest->data);
+        return oldest->data;
+    }
+    
+
+    auto_array<uint8_t> buffer(new uint8_t[512]);
+    BlockDescriptor bd = { block, 1, _ts, buffer.get() };
+    
+    _device->read(block, buffer.get());    
+
+    _blocks.push_back(bd);
+
+    
+    return buffer.release();
+}
+
+
+void BlockCache::release(unsigned block)
+{
+
+    for (BDIter iter = _blocks.begin(); iter != _blocks.end(); ++iter)
+    {
+        if (iter->block == block)
+        {
+            if (!--iter->count)
+            {
+                _device->write(block, iter->data);
+                
+                // trim back if too many entries.
+                
+                if (_blocks.size() > CacheSize)
+                {
+                    delete[] iter->data;
+                    _blocks.erase(iter);
+                }                
+            }            
+            return;
+        }
+    }
+}
\ No newline at end of file
diff --git a/BlockCache.h b/BlockCache.h
new file mode 100644
index 0000000..4e65719
--- /dev/null
+++ b/BlockCache.h
@@ -0,0 +1,37 @@
+#ifndef __BLOCKCACHE_H__
+#define __BLOCKCACHE_H__
+
+#include <stdint.h>
+#include <vector>
+
+namespace ProFUSE {
+
+class BlockDevice;
+
+struct BlockDescriptor {
+    unsigned block;
+    unsigned count;
+    unsigned ts;
+    uint8_t *data;
+};
+
+
+
+class BlockCache {
+    BlockCache(BlockDevice *device);
+    ~BlockCache();
+    
+    void write();
+    
+    void *acquire(unsigned block);
+    void release(unsigned block);
+    
+private:
+    std::vector<BlockDescriptor> _blocks;
+    BlockDevice *_device;
+    unsigned _ts;
+};
+
+}
+
+#endif
\ No newline at end of file
diff --git a/VolumeDirectory.cpp b/VolumeDirectory.cpp
index dd67bdb..fe1e94e 100644
--- a/VolumeDirectory.cpp
+++ b/VolumeDirectory.cpp
@@ -16,6 +16,7 @@ using namespace LittleEndian;
 #pragma mark VolumeDirectory
 
 
+
 VolumeDirectory *VolumeDirectory::Create(const char *name, BlockDevice *device)
 {
     return new VolumeDirectory(name, device);