2 ** Copyright 2011, The Android Open Source Project
4 ** Licensed under the Apache License, Version 2.0 (the "License");
5 ** you may not use this file except in compliance with the License.
6 ** You may obtain a copy of the License at
8 ** http://www.apache.org/licenses/LICENSE-2.0
10 ** Unless required by applicable law or agreed to in writing, software
11 ** distributed under the License is distributed on an "AS IS" BASIS,
12 ** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 ** See the License for the specific language governing permissions and
14 ** limitations under the License.
17 #ifndef ANDROID_BLOB_CACHE_H
18 #define ANDROID_BLOB_CACHE_H
22 #include <utils/Flattenable.h>
23 #include <utils/RefBase.h>
24 #include <utils/SortedVector.h>
25 #include <utils/threads.h>
29 // A BlobCache is an in-memory cache for binary key/value pairs. A BlobCache
30 // does NOT provide any thread-safety guarantees.
32 // The cache contents can be serialized to an in-memory buffer or mmap'd file
33 // and then reloaded in a subsequent execution of the program. This
34 // serialization is non-portable and the data should only be used by the device
36 class BlobCache : public RefBase {
40 // Create an empty blob cache. The blob cache will cache key/value pairs
41 // with key and value sizes less than or equal to maxKeySize and
42 // maxValueSize, respectively. The total combined size of ALL cache entries
43 // (key sizes plus value sizes) will not exceed maxTotalSize.
44 BlobCache(size_t maxKeySize, size_t maxValueSize, size_t maxTotalSize);
46 // set inserts a new binary value into the cache and associates it with the
47 // given binary key. If the key or value are too large for the cache then
48 // the cache remains unchanged. This includes the case where a different
49 // value was previously associated with the given key - the old value will
50 // remain in the cache. If the given key and value are small enough to be
51 // put in the cache (based on the maxKeySize, maxValueSize, and maxTotalSize
52 // values specified to the BlobCache constructor), then the key/value pair
53 // will be in the cache after set returns. Note, however, that a subsequent
54 // call to set may evict old key/value pairs from the cache.
61 void set(const void* key, size_t keySize, const void* value,
64 // get retrieves from the cache the binary value associated with a given
65 // binary key. If the key is present in the cache then the length of the
66 // binary value associated with that key is returned. If the value argument
67 // is non-NULL and the size of the cached value is less than valueSize bytes
68 // then the cached value is copied into the buffer pointed to by the value
69 // argument. If the key is not present in the cache then 0 is returned and
70 // the buffer pointed to by the value argument is not modified.
72 // Note that when calling get multiple times with the same key, the later
73 // calls may fail, returning 0, even if earlier calls succeeded. The return
74 // value must be checked for each call.
80 size_t get(const void* key, size_t keySize, void* value, size_t valueSize);
83 // getFlattenedSize returns the number of bytes needed to store the entire
85 size_t getFlattenedSize() const;
87 // flatten serializes the current contents of the cache into the memory
88 // pointed to by 'buffer'. The serialized cache contents can later be
89 // loaded into a BlobCache object using the unflatten method. The contents
90 // of the BlobCache object will not be modified.
93 // size >= this.getFlattenedSize()
94 status_t flatten(void* buffer, size_t size) const;
96 // unflatten replaces the contents of the cache with the serialized cache
97 // contents in the memory pointed to by 'buffer'. The previous contents of
98 // the BlobCache will be evicted from the cache. If an error occurs while
99 // unflattening the serialized cache contents then the BlobCache will be
100 // left in an empty state.
102 status_t unflatten(void const* buffer, size_t size);
105 // Copying is disallowed.
106 BlobCache(const BlobCache&);
107 void operator=(const BlobCache&);
109 // A random function helper to get around MinGW not having nrand48()
110 long int blob_random();
112 // clean evicts a randomly chosen set of entries from the cache such that
113 // the total size of all remaining entries is less than mMaxTotalSize/2.
116 // isCleanable returns true if the cache is full enough for the clean method
117 // to have some effect, and false otherwise.
118 bool isCleanable() const;
120 // A Blob is an immutable sized unstructured data blob.
121 class Blob : public RefBase {
123 Blob(const void* data, size_t size, bool copyData);
126 bool operator<(const Blob& rhs) const;
128 const void* getData() const;
129 size_t getSize() const;
132 // Copying is not allowed.
134 void operator=(const Blob&);
136 // mData points to the buffer containing the blob data.
139 // mSize is the size of the blob data in bytes.
142 // mOwnsData indicates whether or not this Blob object should free the
143 // memory pointed to by mData when the Blob gets destructed.
147 // A CacheEntry is a single key/value pair in the cache.
151 CacheEntry(const sp<Blob>& key, const sp<Blob>& value);
152 CacheEntry(const CacheEntry& ce);
154 bool operator<(const CacheEntry& rhs) const;
155 const CacheEntry& operator=(const CacheEntry&);
157 sp<Blob> getKey() const;
158 sp<Blob> getValue() const;
160 void setValue(const sp<Blob>& value);
164 // mKey is the key that identifies the cache entry.
167 // mValue is the cached data associated with the key.
171 // A Header is the header for the entire BlobCache serialization format. No
172 // need to make this portable, so we simply write the struct out.
174 // mMagicNumber is the magic number that identifies the data as
175 // serialized BlobCache contents. It must always contain 'Blb$'.
176 uint32_t mMagicNumber;
178 // mBlobCacheVersion is the serialization format version.
179 uint32_t mBlobCacheVersion;
181 // mDeviceVersion is the device-specific version of the cache. This can
182 // be used to invalidate the cache.
183 uint32_t mDeviceVersion;
185 // mNumEntries is number of cache entries following the header in the
190 // An EntryHeader is the header for a serialized cache entry. No need to
191 // make this portable, so we simply write the struct out. Each EntryHeader
192 // is followed imediately by the key data and then the value data.
194 // The beginning of each serialized EntryHeader is 4-byte aligned, so the
195 // number of bytes that a serialized cache entry will occupy is:
197 // ((sizeof(EntryHeader) + keySize + valueSize) + 3) & ~3
200 // mKeySize is the size of the entry key in bytes.
203 // mValueSize is the size of the entry value in bytes.
206 // mData contains both the key and value data for the cache entry. The
207 // key comes first followed immediately by the value.
211 // mMaxKeySize is the maximum key size that will be cached. Calls to
212 // BlobCache::set with a keySize parameter larger than mMaxKeySize will
213 // simply not add the key/value pair to the cache.
214 const size_t mMaxKeySize;
216 // mMaxValueSize is the maximum value size that will be cached. Calls to
217 // BlobCache::set with a valueSize parameter larger than mMaxValueSize will
218 // simply not add the key/value pair to the cache.
219 const size_t mMaxValueSize;
221 // mMaxTotalSize is the maximum size that all cache entries can occupy. This
222 // includes space for both keys and values. When a call to BlobCache::set
223 // would otherwise cause this limit to be exceeded, either the key/value
224 // pair passed to BlobCache::set will not be cached or other cache entries
225 // will be evicted from the cache to make room for the new entry.
226 const size_t mMaxTotalSize;
228 // mTotalSize is the total combined size of all keys and values currently in
232 // mRandState is the pseudo-random number generator state. It is passed to
233 // nrand48 to generate random numbers when needed.
234 unsigned short mRandState[3];
236 // mCacheEntries stores all the cache entries that are resident in memory.
237 // Cache entries are added to it by the 'set' method.
238 SortedVector<CacheEntry> mCacheEntries;
243 #endif // ANDROID_BLOB_CACHE_H