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authorjorlow@chromium.org <jorlow@chromium.org@62dab493-f737-651d-591e-8d6aee1b9529>2011-03-30 18:49:03 +0000
committerjorlow@chromium.org <jorlow@chromium.org@62dab493-f737-651d-591e-8d6aee1b9529>2011-03-30 18:49:03 +0000
commit9e33808a26cbbb38008fcd10b74c4d05d78d0aa1 (patch)
treeaa5b999df95bf5949265ae55e167a82033a959d7 /include/leveldb/cache.h
parent4671a695fca3a8fb00cdf4609cd8238cf12ed13d (diff)
downloadleveldb-9e33808a26cbbb38008fcd10b74c4d05d78d0aa1.tar.gz
Fix last commit
git-svn-id: https://leveldb.googlecode.com/svn/trunk@19 62dab493-f737-651d-591e-8d6aee1b9529
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+// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file. See the AUTHORS file for names of contributors.
+//
+// A Cache is an interface that maps keys to values. It has internal
+// synchronization and may be safely accessed concurrently from
+// multiple threads. It may automatically evict entries to make room
+// for new entries. Values have a specified charge against the cache
+// capacity. For example, a cache where the values are variable
+// length strings, may use the length of the string as the charge for
+// the string.
+//
+// A builtin cache implementation with a least-recently-used eviction
+// policy is provided. Clients may use their own implementations if
+// they want something more sophisticated (like scan-resistance, a
+// custom eviction policy, variable cache sizing, etc.)
+
+#ifndef STORAGE_LEVELDB_INCLUDE_CACHE_H_
+#define STORAGE_LEVELDB_INCLUDE_CACHE_H_
+
+#include <stdint.h>
+#include "leveldb/slice.h"
+
+namespace leveldb {
+
+class Cache;
+
+// Create a new cache with a fixed size capacity. This implementation
+// of Cache uses a least-recently-used eviction policy.
+extern Cache* NewLRUCache(size_t capacity);
+
+class Cache {
+ public:
+ Cache() { }
+
+ // Destroys all existing entries by calling the "deleter"
+ // function that was passed to the constructor.
+ virtual ~Cache();
+
+ // Opaque handle to an entry stored in the cache.
+ struct Handle { };
+
+ // Insert a mapping from key->value into the cache and assign it
+ // the specified charge against the total cache capacity.
+ //
+ // Returns a handle that corresponds to the mapping. The caller
+ // must call this->Release(handle) when the returned mapping is no
+ // longer needed.
+ //
+ // When the inserted entry is no longer needed, the key and
+ // value will be passed to "deleter".
+ virtual Handle* Insert(const Slice& key, void* value, size_t charge,
+ void (*deleter)(const Slice& key, void* value)) = 0;
+
+ // If the cache has no mapping for "key", returns NULL.
+ //
+ // Else return a handle that corresponds to the mapping. The caller
+ // must call this->Release(handle) when the returned mapping is no
+ // longer needed.
+ virtual Handle* Lookup(const Slice& key) = 0;
+
+ // Release a mapping returned by a previous Lookup().
+ // REQUIRES: handle must not have been released yet.
+ // REQUIRES: handle must have been returned by a method on *this.
+ virtual void Release(Handle* handle) = 0;
+
+ // Return the value encapsulated in a handle returned by a
+ // successful Lookup().
+ // REQUIRES: handle must not have been released yet.
+ // REQUIRES: handle must have been returned by a method on *this.
+ virtual void* Value(Handle* handle) = 0;
+
+ // If the cache contains entry for key, erase it. Note that the
+ // underlying entry will be kept around until all existing handles
+ // to it have been released.
+ virtual void Erase(const Slice& key) = 0;
+
+ // Return a new numeric id. May be used by multiple clients who are
+ // sharing the same cache to partition the key space. Typically the
+ // client will allocate a new id at startup and prepend the id to
+ // its cache keys.
+ virtual uint64_t NewId() = 0;
+
+ private:
+ void LRU_Remove(Handle* e);
+ void LRU_Append(Handle* e);
+ void Unref(Handle* e);
+
+ struct Rep;
+ Rep* rep_;
+
+ // No copying allowed
+ Cache(const Cache&);
+ void operator=(const Cache&);
+};
+
+}
+
+#endif // STORAGE_LEVELDB_UTIL_CACHE_H_