libutils: add a binary blob cache implementation. (58c8dd2a) · Commits · e / os / android_frameworks_native-old

include/utils/BlobCache.h

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		/*
		** 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

libs/utils/Android.mk

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		@@ -21,6 +21,7 @@ commonSources:= \
		Asset.cpp \
		AssetDir.cpp \
		AssetManager.cpp \
		BlobCache.cpp \
		BufferedTextOutput.cpp \
		CallStack.cpp \
		Debug.cpp \

libs/utils/BlobCache.cpp

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		/*
		** 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.
		*/

		#define LOG_TAG "BlobCache"
		//#define LOG_NDEBUG 0

		#include <stdlib.h>
		#include <string.h>

		#include <utils/BlobCache.h>
		#include <utils/Log.h>

		namespace android {

		BlobCache::BlobCache(size_t maxKeySize, size_t maxValueSize, size_t maxTotalSize):
		mMaxKeySize(maxKeySize),
		mMaxValueSize(maxValueSize),
		mMaxTotalSize(maxTotalSize),
		mTotalSize(0) {
		nsecs_t now = systemTime(SYSTEM_TIME_MONOTONIC);
		mRandState[0] = (now >> 0) & 0xFFFF;
		mRandState[1] = (now >> 16) & 0xFFFF;
		mRandState[2] = (now >> 32) & 0xFFFF;
		LOGV("initializing random seed using %lld", now);
		}

		void BlobCache::set(const void* key, size_t keySize, const void* value,
		size_t valueSize) {
		if (mMaxKeySize < keySize) {
		LOGV("set: not caching because the key is too large: %d (limit: %d)",
		keySize, mMaxKeySize);
		return;
		}
		if (mMaxValueSize < valueSize) {
		LOGV("set: not caching because the value is too large: %d (limit: %d)",
		valueSize, mMaxValueSize);
		return;
		}
		if (mMaxTotalSize < keySize + valueSize) {
		LOGV("set: not caching because the combined key/value size is too "
		"large: %d (limit: %d)", keySize + valueSize, mMaxTotalSize);
		return;
		}
		if (keySize == 0) {
		LOGW("set: not caching because keySize is 0");
		return;
		}
		if (valueSize <= 0) {
		LOGW("set: not caching because valueSize is 0");
		return;
		}

		Mutex::Autolock lock(mMutex);
		sp<Blob> dummyKey(new Blob(key, keySize, false));
		CacheEntry dummyEntry(dummyKey, NULL);

		while (true) {

		ssize_t index = mCacheEntries.indexOf(dummyEntry);
		if (index < 0) {
		// Create a new cache entry.
		sp<Blob> keyBlob(new Blob(key, keySize, true));
		sp<Blob> valueBlob(new Blob(value, valueSize, true));
		size_t newTotalSize = mTotalSize + keySize + valueSize;
		if (mMaxTotalSize < newTotalSize) {
		if (isCleanable()) {
		// Clean the cache and try again.
		clean();
		continue;
		} else {
		LOGV("set: not caching new key/value pair because the "
		"total cache size limit would be exceeded: %d "
		"(limit: %d)",
		keySize + valueSize, mMaxTotalSize);
		break;
		}
		}
		mCacheEntries.add(CacheEntry(keyBlob, valueBlob));
		mTotalSize = newTotalSize;
		LOGV("set: created new cache entry with %d byte key and %d byte value",
		keySize, valueSize);
		} else {
		// Update the existing cache entry.
		sp<Blob> valueBlob(new Blob(value, valueSize, true));
		sp<Blob> oldValueBlob(mCacheEntries[index].getValue());
		size_t newTotalSize = mTotalSize + valueSize - oldValueBlob->getSize();
		if (mMaxTotalSize < newTotalSize) {
		if (isCleanable()) {
		// Clean the cache and try again.
		clean();
		continue;
		} else {
		LOGV("set: not caching new value because the total cache "
		"size limit would be exceeded: %d (limit: %d)",
		keySize + valueSize, mMaxTotalSize);
		break;
		}
		}
		mCacheEntries.editItemAt(index).setValue(valueBlob);
		mTotalSize = newTotalSize;
		LOGV("set: updated existing cache entry with %d byte key and %d byte "
		"value", keySize, valueSize);
		}
		break;
		}
		}

		size_t BlobCache::get(const void* key, size_t keySize, void* value,
		size_t valueSize) {
		if (mMaxKeySize < keySize) {
		LOGV("get: not searching because the key is too large: %d (limit %d)",
		keySize, mMaxKeySize);
		return 0;
		}
		Mutex::Autolock lock(mMutex);
		sp<Blob> dummyKey(new Blob(key, keySize, false));
		CacheEntry dummyEntry(dummyKey, NULL);
		ssize_t index = mCacheEntries.indexOf(dummyEntry);
		if (index < 0) {
		LOGV("get: no cache entry found for key of size %d", keySize);
		return 0;
		}

		// The key was found. Return the value if the caller's buffer is large
		// enough.
		sp<Blob> valueBlob(mCacheEntries[index].getValue());
		size_t valueBlobSize = valueBlob->getSize();
		if (valueBlobSize <= valueSize) {
		LOGV("get: copying %d bytes to caller's buffer", valueBlobSize);
		memcpy(value, valueBlob->getData(), valueBlobSize);
		} else {
		LOGV("get: caller's buffer is too small for value: %d (needs %d)",
		valueSize, valueBlobSize);
		}
		return valueBlobSize;
		}

		void BlobCache::clean() {
		// Remove a random cache entry until the total cache size gets below half
		// the maximum total cache size.
		while (mTotalSize > mMaxTotalSize / 2) {
		size_t i = size_t(nrand48(mRandState) % (mCacheEntries.size()));
		const CacheEntry& entry(mCacheEntries[i]);
		mTotalSize -= entry.getKey()->getSize() + entry.getValue()->getSize();
		mCacheEntries.removeAt(i);
		}
		}

		bool BlobCache::isCleanable() const {
		return mTotalSize > mMaxTotalSize / 2;
		}

		BlobCache::Blob::Blob(const void* data, size_t size, bool copyData):
		mData(copyData ? malloc(size) : data),
		mSize(size),
		mOwnsData(copyData) {
		if (copyData) {
		memcpy(const_cast<void*>(mData), data, size);
		}
		}

		BlobCache::Blob::~Blob() {
		if (mOwnsData) {
		free(const_cast<void*>(mData));
		}
		}

		bool BlobCache::Blob::operator<(const Blob& rhs) const {
		if (mSize == rhs.mSize) {
		return memcmp(mData, rhs.mData, mSize) < 0;
		} else {
		return mSize < rhs.mSize;
		}
		}

		const void* BlobCache::Blob::getData() const {
		return mData;
		}

		size_t BlobCache::Blob::getSize() const {
		return mSize;
		}

		BlobCache::CacheEntry::CacheEntry() {
		}

		BlobCache::CacheEntry::CacheEntry(const sp<Blob>& key, const sp<Blob>& value):
		mKey(key),
		mValue(value) {
		}

		BlobCache::CacheEntry::CacheEntry(const CacheEntry& ce):
		mKey(ce.mKey),
		mValue(ce.mValue) {
		}

		bool BlobCache::CacheEntry::operator<(const CacheEntry& rhs) const {
		return mKey < rhs.mKey;
		}

		const BlobCache::CacheEntry& BlobCache::CacheEntry::operator=(const CacheEntry& rhs) {
		mKey = rhs.mKey;
		mValue = rhs.mValue;
		return *this;
		}

		sp<BlobCache::Blob> BlobCache::CacheEntry::getKey() const {
		return mKey;
		}

		sp<BlobCache::Blob> BlobCache::CacheEntry::getValue() const {
		return mValue;
		}

		void BlobCache::CacheEntry::setValue(const sp<Blob>& value) {
		mValue = value;
		}

		} // namespace android

libs/utils/tests/Android.mk

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		@@ -6,6 +6,7 @@ ifneq ($(TARGET_SIMULATOR),true)

		# Build the unit tests.
		test_src_files := \
		BlobCache_test.cpp \
		ObbFile_test.cpp \
		Looper_test.cpp \
		String8_test.cpp \

libs/utils/tests/BlobCache_test.cpp

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		/*
		** 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.
		*/

		#include <gtest/gtest.h>

		#include <utils/BlobCache.h>

		namespace android {

		class BlobCacheTest : public ::testing::Test {
		protected:
		enum {
		MAX_KEY_SIZE = 6,
		MAX_VALUE_SIZE = 8,
		MAX_TOTAL_SIZE = 13,
		};

		virtual void SetUp() {
		mBC = new BlobCache(MAX_KEY_SIZE, MAX_VALUE_SIZE, MAX_TOTAL_SIZE);
		}

		virtual void TearDown() {
		mBC.clear();
		}

		sp<BlobCache> mBC;
		};

		TEST_F(BlobCacheTest, CacheSingleValueSucceeds) {
		char buf[4] = { 0xee, 0xee, 0xee, 0xee };
		mBC->set("abcd", 4, "efgh", 4);
		ASSERT_EQ(size_t(4), mBC->get("abcd", 4, buf, 4));
		ASSERT_EQ('e', buf[0]);
		ASSERT_EQ('f', buf[1]);
		ASSERT_EQ('g', buf[2]);
		ASSERT_EQ('h', buf[3]);
		}

		TEST_F(BlobCacheTest, CacheTwoValuesSucceeds) {
		char buf[2] = { 0xee, 0xee };
		mBC->set("ab", 2, "cd", 2);
		mBC->set("ef", 2, "gh", 2);
		ASSERT_EQ(size_t(2), mBC->get("ab", 2, buf, 2));
		ASSERT_EQ('c', buf[0]);
		ASSERT_EQ('d', buf[1]);
		ASSERT_EQ(size_t(2), mBC->get("ef", 2, buf, 2));
		ASSERT_EQ('g', buf[0]);
		ASSERT_EQ('h', buf[1]);
		}

		TEST_F(BlobCacheTest, GetOnlyWritesInsideBounds) {
		char buf[6] = { 0xee, 0xee, 0xee, 0xee, 0xee, 0xee };
		mBC->set("abcd", 4, "efgh", 4);
		ASSERT_EQ(size_t(4), mBC->get("abcd", 4, buf+1, 4));
		ASSERT_EQ(0xee, buf[0]);
		ASSERT_EQ('e', buf[1]);
		ASSERT_EQ('f', buf[2]);
		ASSERT_EQ('g', buf[3]);
		ASSERT_EQ('h', buf[4]);
		ASSERT_EQ(0xee, buf[5]);
		}

		TEST_F(BlobCacheTest, GetOnlyWritesIfBufferIsLargeEnough) {
		char buf[3] = { 0xee, 0xee, 0xee };
		mBC->set("abcd", 4, "efgh", 4);
		ASSERT_EQ(size_t(4), mBC->get("abcd", 4, buf, 3));
		ASSERT_EQ(0xee, buf[0]);
		ASSERT_EQ(0xee, buf[1]);
		ASSERT_EQ(0xee, buf[2]);
		}

		TEST_F(BlobCacheTest, GetDoesntAccessNullBuffer) {
		mBC->set("abcd", 4, "efgh", 4);
		ASSERT_EQ(size_t(4), mBC->get("abcd", 4, NULL, 0));
		}

		TEST_F(BlobCacheTest, MultipleSetsCacheLatestValue) {
		char buf[4] = { 0xee, 0xee, 0xee, 0xee };
		mBC->set("abcd", 4, "efgh", 4);
		mBC->set("abcd", 4, "ijkl", 4);
		ASSERT_EQ(size_t(4), mBC->get("abcd", 4, buf, 4));
		ASSERT_EQ('i', buf[0]);
		ASSERT_EQ('j', buf[1]);
		ASSERT_EQ('k', buf[2]);
		ASSERT_EQ('l', buf[3]);
		}

		TEST_F(BlobCacheTest, SecondSetKeepsFirstValueIfTooLarge) {
		char buf[MAX_VALUE_SIZE+1] = { 0xee, 0xee, 0xee, 0xee };
		mBC->set("abcd", 4, "efgh", 4);
		mBC->set("abcd", 4, buf, MAX_VALUE_SIZE+1);
		ASSERT_EQ(size_t(4), mBC->get("abcd", 4, buf, 4));
		ASSERT_EQ('e', buf[0]);
		ASSERT_EQ('f', buf[1]);
		ASSERT_EQ('g', buf[2]);
		ASSERT_EQ('h', buf[3]);
		}

		TEST_F(BlobCacheTest, DoesntCacheIfKeyIsTooBig) {
		char key[MAX_KEY_SIZE+1];
		char buf[4] = { 0xee, 0xee, 0xee, 0xee };
		for (int i = 0; i < MAX_KEY_SIZE+1; i++) {
		key[i] = 'a';
		}
		mBC->set(key, MAX_KEY_SIZE+1, "bbbb", 4);
		ASSERT_EQ(size_t(0), mBC->get(key, MAX_KEY_SIZE+1, buf, 4));
		ASSERT_EQ(0xee, buf[0]);
		ASSERT_EQ(0xee, buf[1]);
		ASSERT_EQ(0xee, buf[2]);
		ASSERT_EQ(0xee, buf[3]);
		}

		TEST_F(BlobCacheTest, DoesntCacheIfValueIsTooBig) {
		char buf[MAX_VALUE_SIZE+1];
		for (int i = 0; i < MAX_VALUE_SIZE+1; i++) {
		buf[i] = 'b';
		}
		mBC->set("abcd", 4, buf, MAX_VALUE_SIZE+1);
		for (int i = 0; i < MAX_VALUE_SIZE+1; i++) {
		buf[i] = 0xee;
		}
		ASSERT_EQ(size_t(0), mBC->get("abcd", 4, buf, MAX_VALUE_SIZE+1));
		for (int i = 0; i < MAX_VALUE_SIZE+1; i++) {
		SCOPED_TRACE(i);
		ASSERT_EQ(0xee, buf[i]);
		}
		}

		TEST_F(BlobCacheTest, DoesntCacheIfKeyValuePairIsTooBig) {
		// Check a testing assumptions
		ASSERT_TRUE(MAX_TOTAL_SIZE < MAX_KEY_SIZE + MAX_VALUE_SIZE);
		ASSERT_TRUE(MAX_KEY_SIZE < MAX_TOTAL_SIZE);

		enum { bufSize = MAX_TOTAL_SIZE - MAX_KEY_SIZE + 1 };

		char key[MAX_KEY_SIZE];
		char buf[bufSize];
		for (int i = 0; i < MAX_KEY_SIZE; i++) {
		key[i] = 'a';
		}
		for (int i = 0; i < bufSize; i++) {
		buf[i] = 'b';
		}

		mBC->set(key, MAX_KEY_SIZE, buf, MAX_VALUE_SIZE);
		ASSERT_EQ(size_t(0), mBC->get(key, MAX_KEY_SIZE, NULL, 0));
		}

		TEST_F(BlobCacheTest, CacheMaxKeySizeSucceeds) {
		char key[MAX_KEY_SIZE];
		char buf[4] = { 0xee, 0xee, 0xee, 0xee };
		for (int i = 0; i < MAX_KEY_SIZE; i++) {
		key[i] = 'a';
		}
		mBC->set(key, MAX_KEY_SIZE, "wxyz", 4);
		ASSERT_EQ(size_t(4), mBC->get(key, MAX_KEY_SIZE, buf, 4));
		ASSERT_EQ('w', buf[0]);
		ASSERT_EQ('x', buf[1]);
		ASSERT_EQ('y', buf[2]);
		ASSERT_EQ('z', buf[3]);
		}

		TEST_F(BlobCacheTest, CacheMaxValueSizeSucceeds) {
		char buf[MAX_VALUE_SIZE];
		for (int i = 0; i < MAX_VALUE_SIZE; i++) {
		buf[i] = 'b';
		}
		mBC->set("abcd", 4, buf, MAX_VALUE_SIZE);
		for (int i = 0; i < MAX_VALUE_SIZE; i++) {
		buf[i] = 0xee;
		}
		ASSERT_EQ(size_t(MAX_VALUE_SIZE), mBC->get("abcd", 4, buf,
		MAX_VALUE_SIZE));
		for (int i = 0; i < MAX_VALUE_SIZE; i++) {
		SCOPED_TRACE(i);
		ASSERT_EQ('b', buf[i]);
		}
		}

		TEST_F(BlobCacheTest, CacheMaxKeyValuePairSizeSucceeds) {
		// Check a testing assumption
		ASSERT_TRUE(MAX_KEY_SIZE < MAX_TOTAL_SIZE);

		enum { bufSize = MAX_TOTAL_SIZE - MAX_KEY_SIZE };

		char key[MAX_KEY_SIZE];
		char buf[bufSize];
		for (int i = 0; i < MAX_KEY_SIZE; i++) {
		key[i] = 'a';
		}
		for (int i = 0; i < bufSize; i++) {
		buf[i] = 'b';
		}

		mBC->set(key, MAX_KEY_SIZE, buf, bufSize);
		ASSERT_EQ(size_t(bufSize), mBC->get(key, MAX_KEY_SIZE, NULL, 0));
		}

		TEST_F(BlobCacheTest, CacheMinKeyAndValueSizeSucceeds) {
		char buf[1] = { 0xee };
		mBC->set("x", 1, "y", 1);
		ASSERT_EQ(size_t(1), mBC->get("x", 1, buf, 1));
		ASSERT_EQ('y', buf[0]);
		}

		TEST_F(BlobCacheTest, CacheSizeDoesntExceedTotalLimit) {
		for (int i = 0; i < 256; i++) {
		uint8_t k = i;
		mBC->set(&k, 1, "x", 1);
		}
		int numCached = 0;
		for (int i = 0; i < 256; i++) {
		uint8_t k = i;
		if (mBC->get(&k, 1, NULL, 0) == 1) {
		numCached++;
		}
		}
		ASSERT_GE(MAX_TOTAL_SIZE / 2, numCached);
		}

		TEST_F(BlobCacheTest, ExceedingTotalLimitHalvesCacheSize) {
		// Fill up the entire cache with 1 char key/value pairs.
		const int maxEntries = MAX_TOTAL_SIZE / 2;
		for (int i = 0; i < maxEntries; i++) {
		uint8_t k = i;
		mBC->set(&k, 1, "x", 1);
		}
		// Insert one more entry, causing a cache overflow.
		{
		uint8_t k = maxEntries;
		mBC->set(&k, 1, "x", 1);
		}
		// Count the number of entries in the cache.
		int numCached = 0;
		for (int i = 0; i < maxEntries+1; i++) {
		uint8_t k = i;
		if (mBC->get(&k, 1, NULL, 0) == 1) {
		numCached++;
		}
		}
		ASSERT_EQ(maxEntries/2 + 1, numCached);
		}

		} // namespace android