Merge "libutils: add a binary blob cache implementation."

1 files changed, 181 insertions, 0 deletions

diff --git a/include/utils/BlobCache.h b/include/utils/BlobCache.h
new file mode 100644
index 0000000..8f76d72
--- /dev/null
+++ b/include/utils/BlobCache.h
@@ -0,0 +1,181 @@
+/*
+ ** Copyright 2011, The Android Open Source Project
+ **
+ ** Licensed under the Apache License, Version 2.0 (the "License");
+ ** you may not use this file except in compliance with the License.
+ ** You may obtain a copy of the License at
+ **
+ **     http://www.apache.org/licenses/LICENSE-2.0
+ **
+ ** Unless required by applicable law or agreed to in writing, software
+ ** distributed under the License is distributed on an "AS IS" BASIS,
+ ** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ ** See the License for the specific language governing permissions and
+ ** limitations under the License.
+ */
+
+#ifndef ANDROID_BLOB_CACHE_H
+#define ANDROID_BLOB_CACHE_H
+
+#include <stddef.h>
+
+#include <utils/RefBase.h>
+#include <utils/SortedVector.h>
+#include <utils/threads.h>
+
+namespace android {
+
+// A BlobCache is an in-memory cache for binary key/value pairs. All the public
+// methods are thread-safe.
+//
+// The cache contents can be serialized to a file and reloaded in a subsequent
+// execution of the program. This serialization is non-portable and should only
+// be loaded by the device that generated it.
+class BlobCache : public RefBase {
+public:
+
+    // Create an empty blob cache. The blob cache will cache key/value pairs
+    // with key and value sizes less than or equal to maxKeySize and
+    // maxValueSize, respectively. The total combined size of ALL cache entries
+    // (key sizes plus value sizes) will not exceed maxTotalSize.
+    BlobCache(size_t maxKeySize, size_t maxValueSize, size_t maxTotalSize);
+
+    // set inserts a new binary value into the cache and associates it with the
+    // given binary key.  If the key or value are too large for the cache then
+    // the cache remains unchanged.  This includes the case where a different
+    // value was previously associated with the given key - the old value will
+    // remain in the cache.  If the given key and value are small enough to be
+    // put in the cache (based on the maxKeySize, maxValueSize, and maxTotalSize
+    // values specified to the BlobCache constructor), then the key/value pair
+    // will be in the cache after set returns.  Note, however, that a subsequent
+    // call to set may evict old key/value pairs from the cache.
+    //
+    // Preconditions:
+    //   key != NULL
+    //   0 < keySize
+    //   value != NULL
+    //   0 < valueSize
+    void set(const void* key, size_t keySize, const void* value,
+            size_t valueSize);
+
+    // The get function retrieves from the cache the binary value associated
+    // with a given binary key.  If the key is present in the cache then the
+    // length of the binary value associated with that key is returned.  If the
+    // value argument is non-NULL and the size of the cached value is less than
+    // valueSize bytes then the cached value is copied into the buffer pointed
+    // to by the value argument.  If the key is not present in the cache then 0
+    // is returned and the buffer pointed to by the value argument is not
+    // modified.
+    //
+    // Note that when calling get multiple times with the same key, the later
+    // calls may fail, returning 0, even if earlier calls succeeded.  The return
+    // value must be checked for each call.
+    //
+    // Preconditions:
+    //   key != NULL
+    //   0 < keySize
+    //   0 <= valueSize
+    size_t get(const void* key, size_t keySize, void* value, size_t valueSize);
+
+private:
+    // Copying is disallowed.
+    BlobCache(const BlobCache&);
+    void operator=(const BlobCache&);
+
+    // clean evicts a randomly chosen set of entries from the cache such that
+    // the total size of all remaining entries is less than mMaxTotalSize/2.
+    void clean();
+
+    // isCleanable returns true if the cache is full enough for the clean method
+    // to have some effect, and false otherwise.
+    bool isCleanable() const;
+
+    // A Blob is an immutable sized unstructured data blob.
+    class Blob : public RefBase {
+    public:
+        Blob(const void* data, size_t size, bool copyData);
+        ~Blob();
+
+        bool operator<(const Blob& rhs) const;
+
+        const void* getData() const;
+        size_t getSize() const;
+
+    private:
+        // Copying is not allowed.
+        Blob(const Blob&);
+        void operator=(const Blob&);
+
+        // mData points to the buffer containing the blob data.
+        const void* mData;
+
+        // mSize is the size of the blob data in bytes.
+        size_t mSize;
+
+        // mOwnsData indicates whether or not this Blob object should free the
+        // memory pointed to by mData when the Blob gets destructed.
+        bool mOwnsData;
+    };
+
+    // A CacheEntry is a single key/value pair in the cache.
+    class CacheEntry {
+    public:
+        CacheEntry();
+        CacheEntry(const sp<Blob>& key, const sp<Blob>& value);
+        CacheEntry(const CacheEntry& ce);
+
+        bool operator<(const CacheEntry& rhs) const;
+        const CacheEntry& operator=(const CacheEntry&);
+
+        sp<Blob> getKey() const;
+        sp<Blob> getValue() const;
+
+        void setValue(const sp<Blob>& value);
+
+    private:
+
+        // mKey is the key that identifies the cache entry.
+        sp<Blob> mKey;
+
+        // mValue is the cached data associated with the key.
+        sp<Blob> mValue;
+    };
+
+    // mMaxKeySize is the maximum key size that will be cached. Calls to
+    // BlobCache::set with a keySize parameter larger than mMaxKeySize will
+    // simply not add the key/value pair to the cache.
+    const size_t mMaxKeySize;
+
+    // mMaxValueSize is the maximum value size that will be cached. Calls to
+    // BlobCache::set with a valueSize parameter larger than mMaxValueSize will
+    // simply not add the key/value pair to the cache.
+    const size_t mMaxValueSize;
+
+    // mMaxTotalSize is the maximum size that all cache entries can occupy. This
+    // includes space for both keys and values. When a call to BlobCache::set
+    // would otherwise cause this limit to be exceeded, either the key/value
+    // pair passed to BlobCache::set will not be cached or other cache entries
+    // will be evicted from the cache to make room for the new entry.
+    const size_t mMaxTotalSize;
+
+    // mTotalSize is the total combined size of all keys and values currently in
+    // the cache.
+    size_t mTotalSize;
+
+    // mRandState is the pseudo-random number generator state. It is passed to
+    // nrand48 to generate random numbers when needed. It must be protected by
+    // mMutex.
+    unsigned short mRandState[3];
+
+    // mCacheEntries stores all the cache entries that are resident in memory.
+    // Cache entries are added to it by the 'set' method.
+    SortedVector<CacheEntry> mCacheEntries;
+
+    // mMutex is used to synchronize access to all member variables.  It must be
+    // locked any time the member variables are written or read.
+    Mutex mMutex;
+};
+
+}
+
+#endif // ANDROID_BLOB_CACHE_H