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author | Pieter Wuille <sipa@ulyssis.org> | 2013-08-20 14:17:45 +0200 |
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committer | Pieter Wuille <sipa@ulyssis.org> | 2013-08-20 14:17:45 +0200 |
commit | cb1e39f0a35cc2b36fb748c26f69cd27e0ed5332 (patch) | |
tree | dd1437e5bb46fbfe1c2bdf7a5bfbfe608761f67d /include/leveldb/cache.h | |
download | bitcoin-cb1e39f0a35cc2b36fb748c26f69cd27e0ed5332.tar.xz |
Squashed 'src/leveldb/' content from commit a02ddf9
git-subtree-dir: src/leveldb
git-subtree-split: a02ddf9b14d145e88185ee209ab8b01d8826663a
Diffstat (limited to 'include/leveldb/cache.h')
-rw-r--r-- | include/leveldb/cache.h | 99 |
1 files changed, 99 insertions, 0 deletions
diff --git a/include/leveldb/cache.h b/include/leveldb/cache.h new file mode 100644 index 0000000000..5e3b47637d --- /dev/null +++ b/include/leveldb/cache.h @@ -0,0 +1,99 @@ +// 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&); +}; + +} // namespace leveldb + +#endif // STORAGE_LEVELDB_UTIL_CACHE_H_ |