BlobCache.cpp revision d98e07fdf9c338589f263c47ce5c844ed43efad5 
1/*
2 ** Copyright 2011, The Android Open Source Project
3 **
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
7 **
8 **     http://www.apache.org/licenses/LICENSE-2.0
9 **
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.
15 */
16
17#define LOG_TAG "BlobCache"
18//#define LOG_NDEBUG 0
19
20#include <stdlib.h>
21#include <string.h>
22
23#include <utils/BlobCache.h>
24#include <utils/Errors.h>
25#include <utils/Log.h>
26
27namespace android {
28
29// BlobCache::Header::mMagicNumber value
30static const uint32_t blobCacheMagic = '_Bb$';
31
32// BlobCache::Header::mBlobCacheVersion value
33static const uint32_t blobCacheVersion = 1;
34
35// BlobCache::Header::mDeviceVersion value
36static const uint32_t blobCacheDeviceVersion = 1;
37
38BlobCache::BlobCache(size_t maxKeySize, size_t maxValueSize, size_t maxTotalSize):
39        mMaxKeySize(maxKeySize),
40        mMaxValueSize(maxValueSize),
41        mMaxTotalSize(maxTotalSize),
42        mTotalSize(0) {
43    nsecs_t now = systemTime(SYSTEM_TIME_MONOTONIC);
44#ifdef _WIN32
45    srand(now);
46#else
47    mRandState[0] = (now >> 0) & 0xFFFF;
48    mRandState[1] = (now >> 16) & 0xFFFF;
49    mRandState[2] = (now >> 32) & 0xFFFF;
50#endif
51    ALOGV("initializing random seed using %lld", now);
52}
53
54void BlobCache::set(const void* key, size_t keySize, const void* value,
55        size_t valueSize) {
56    if (mMaxKeySize < keySize) {
57        ALOGV("set: not caching because the key is too large: %d (limit: %d)",
58                keySize, mMaxKeySize);
59        return;
60    }
61    if (mMaxValueSize < valueSize) {
62        ALOGV("set: not caching because the value is too large: %d (limit: %d)",
63                valueSize, mMaxValueSize);
64        return;
65    }
66    if (mMaxTotalSize < keySize + valueSize) {
67        ALOGV("set: not caching because the combined key/value size is too "
68                "large: %d (limit: %d)", keySize + valueSize, mMaxTotalSize);
69        return;
70    }
71    if (keySize == 0) {
72        ALOGW("set: not caching because keySize is 0");
73        return;
74    }
75    if (valueSize <= 0) {
76        ALOGW("set: not caching because valueSize is 0");
77        return;
78    }
79
80    sp<Blob> dummyKey(new Blob(key, keySize, false));
81    CacheEntry dummyEntry(dummyKey, NULL);
82
83    while (true) {
84        ssize_t index = mCacheEntries.indexOf(dummyEntry);
85        if (index < 0) {
86            // Create a new cache entry.
87            sp<Blob> keyBlob(new Blob(key, keySize, true));
88            sp<Blob> valueBlob(new Blob(value, valueSize, true));
89            size_t newTotalSize = mTotalSize + keySize + valueSize;
90            if (mMaxTotalSize < newTotalSize) {
91                if (isCleanable()) {
92                    // Clean the cache and try again.
93                    clean();
94                    continue;
95                } else {
96                    ALOGV("set: not caching new key/value pair because the "
97                            "total cache size limit would be exceeded: %d "
98                            "(limit: %d)",
99                            keySize + valueSize, mMaxTotalSize);
100                    break;
101                }
102            }
103            mCacheEntries.add(CacheEntry(keyBlob, valueBlob));
104            mTotalSize = newTotalSize;
105            ALOGV("set: created new cache entry with %d byte key and %d byte value",
106                    keySize, valueSize);
107        } else {
108            // Update the existing cache entry.
109            sp<Blob> valueBlob(new Blob(value, valueSize, true));
110            sp<Blob> oldValueBlob(mCacheEntries[index].getValue());
111            size_t newTotalSize = mTotalSize + valueSize - oldValueBlob->getSize();
112            if (mMaxTotalSize < newTotalSize) {
113                if (isCleanable()) {
114                    // Clean the cache and try again.
115                    clean();
116                    continue;
117                } else {
118                    ALOGV("set: not caching new value because the total cache "
119                            "size limit would be exceeded: %d (limit: %d)",
120                            keySize + valueSize, mMaxTotalSize);
121                    break;
122                }
123            }
124            mCacheEntries.editItemAt(index).setValue(valueBlob);
125            mTotalSize = newTotalSize;
126            ALOGV("set: updated existing cache entry with %d byte key and %d byte "
127                    "value", keySize, valueSize);
128        }
129        break;
130    }
131}
132
133size_t BlobCache::get(const void* key, size_t keySize, void* value,
134        size_t valueSize) {
135    if (mMaxKeySize < keySize) {
136        ALOGV("get: not searching because the key is too large: %d (limit %d)",
137                keySize, mMaxKeySize);
138        return 0;
139    }
140    sp<Blob> dummyKey(new Blob(key, keySize, false));
141    CacheEntry dummyEntry(dummyKey, NULL);
142    ssize_t index = mCacheEntries.indexOf(dummyEntry);
143    if (index < 0) {
144        ALOGV("get: no cache entry found for key of size %d", keySize);
145        return 0;
146    }
147
148    // The key was found. Return the value if the caller's buffer is large
149    // enough.
150    sp<Blob> valueBlob(mCacheEntries[index].getValue());
151    size_t valueBlobSize = valueBlob->getSize();
152    if (valueBlobSize <= valueSize) {
153        ALOGV("get: copying %d bytes to caller's buffer", valueBlobSize);
154        memcpy(value, valueBlob->getData(), valueBlobSize);
155    } else {
156        ALOGV("get: caller's buffer is too small for value: %d (needs %d)",
157                valueSize, valueBlobSize);
158    }
159    return valueBlobSize;
160}
161
162static inline size_t align4(size_t size) {
163    return (size + 3) & ~3;
164}
165
166size_t BlobCache::getFlattenedSize() const {
167    size_t size = sizeof(Header);
168    for (size_t i = 0; i < mCacheEntries.size(); i++) {
169        const CacheEntry& e(mCacheEntries[i]);
170        sp<Blob> keyBlob = e.getKey();
171        sp<Blob> valueBlob = e.getValue();
172        size = align4(size);
173        size += sizeof(EntryHeader) + keyBlob->getSize() +
174                valueBlob->getSize();
175    }
176    return size;
177}
178
179status_t BlobCache::flatten(void* buffer, size_t size) const {
180    // Write the cache header
181    if (size < sizeof(Header)) {
182        ALOGE("flatten: not enough room for cache header");
183        return BAD_VALUE;
184    }
185    Header* header = reinterpret_cast<Header*>(buffer);
186    header->mMagicNumber = blobCacheMagic;
187    header->mBlobCacheVersion = blobCacheVersion;
188    header->mDeviceVersion = blobCacheDeviceVersion;
189    header->mNumEntries = mCacheEntries.size();
190
191    // Write cache entries
192    uint8_t* byteBuffer = reinterpret_cast<uint8_t*>(buffer);
193    off_t byteOffset = align4(sizeof(Header));
194    for (size_t i = 0; i < mCacheEntries.size(); i++) {
195        const CacheEntry& e(mCacheEntries[i]);
196        sp<Blob> keyBlob = e.getKey();
197        sp<Blob> valueBlob = e.getValue();
198        size_t keySize = keyBlob->getSize();
199        size_t valueSize = valueBlob->getSize();
200
201        size_t entrySize = sizeof(EntryHeader) + keySize + valueSize;
202        if (byteOffset + entrySize > size) {
203            ALOGE("flatten: not enough room for cache entries");
204            return BAD_VALUE;
205        }
206
207        EntryHeader* eheader = reinterpret_cast<EntryHeader*>(
208            &byteBuffer[byteOffset]);
209        eheader->mKeySize = keySize;
210        eheader->mValueSize = valueSize;
211
212        memcpy(eheader->mData, keyBlob->getData(), keySize);
213        memcpy(eheader->mData + keySize, valueBlob->getData(), valueSize);
214
215        byteOffset += align4(entrySize);
216    }
217
218    return OK;
219}
220
221status_t BlobCache::unflatten(void const* buffer, size_t size) {
222    // All errors should result in the BlobCache being in an empty state.
223    mCacheEntries.clear();
224
225    // Read the cache header
226    if (size < sizeof(Header)) {
227        ALOGE("unflatten: not enough room for cache header");
228        return BAD_VALUE;
229    }
230    const Header* header = reinterpret_cast<const Header*>(buffer);
231    if (header->mMagicNumber != blobCacheMagic) {
232        ALOGE("unflatten: bad magic number: %d", header->mMagicNumber);
233        return BAD_VALUE;
234    }
235    if (header->mBlobCacheVersion != blobCacheVersion ||
236            header->mDeviceVersion != blobCacheDeviceVersion) {
237        // We treat version mismatches as an empty cache.
238        return OK;
239    }
240
241    // Read cache entries
242    const uint8_t* byteBuffer = reinterpret_cast<const uint8_t*>(buffer);
243    off_t byteOffset = align4(sizeof(Header));
244    size_t numEntries = header->mNumEntries;
245    for (size_t i = 0; i < numEntries; i++) {
246        if (byteOffset + sizeof(EntryHeader) > size) {
247            mCacheEntries.clear();
248            ALOGE("unflatten: not enough room for cache entry headers");
249            return BAD_VALUE;
250        }
251
252        const EntryHeader* eheader = reinterpret_cast<const EntryHeader*>(
253                &byteBuffer[byteOffset]);
254        size_t keySize = eheader->mKeySize;
255        size_t valueSize = eheader->mValueSize;
256        size_t entrySize = sizeof(EntryHeader) + keySize + valueSize;
257
258        if (byteOffset + entrySize > size) {
259            mCacheEntries.clear();
260            ALOGE("unflatten: not enough room for cache entry headers");
261            return BAD_VALUE;
262        }
263
264        const uint8_t* data = eheader->mData;
265        set(data, keySize, data + keySize, valueSize);
266
267        byteOffset += align4(entrySize);
268    }
269
270    return OK;
271}
272
273long int BlobCache::blob_random() {
274#ifdef _WIN32
275    return rand();
276#else
277    return nrand48(mRandState);
278#endif
279}
280
281void BlobCache::clean() {
282    // Remove a random cache entry until the total cache size gets below half
283    // the maximum total cache size.
284    while (mTotalSize > mMaxTotalSize / 2) {
285        size_t i = size_t(blob_random() % (mCacheEntries.size()));
286        const CacheEntry& entry(mCacheEntries[i]);
287        mTotalSize -= entry.getKey()->getSize() + entry.getValue()->getSize();
288        mCacheEntries.removeAt(i);
289    }
290}
291
292bool BlobCache::isCleanable() const {
293    return mTotalSize > mMaxTotalSize / 2;
294}
295
296BlobCache::Blob::Blob(const void* data, size_t size, bool copyData):
297        mData(copyData ? malloc(size) : data),
298        mSize(size),
299        mOwnsData(copyData) {
300    if (data != NULL && copyData) {
301        memcpy(const_cast<void*>(mData), data, size);
302    }
303}
304
305BlobCache::Blob::~Blob() {
306    if (mOwnsData) {
307        free(const_cast<void*>(mData));
308    }
309}
310
311bool BlobCache::Blob::operator<(const Blob& rhs) const {
312    if (mSize == rhs.mSize) {
313        return memcmp(mData, rhs.mData, mSize) < 0;
314    } else {
315        return mSize < rhs.mSize;
316    }
317}
318
319const void* BlobCache::Blob::getData() const {
320    return mData;
321}
322
323size_t BlobCache::Blob::getSize() const {
324    return mSize;
325}
326
327BlobCache::CacheEntry::CacheEntry() {
328}
329
330BlobCache::CacheEntry::CacheEntry(const sp<Blob>& key, const sp<Blob>& value):
331        mKey(key),
332        mValue(value) {
333}
334
335BlobCache::CacheEntry::CacheEntry(const CacheEntry& ce):
336        mKey(ce.mKey),
337        mValue(ce.mValue) {
338}
339
340bool BlobCache::CacheEntry::operator<(const CacheEntry& rhs) const {
341    return *mKey < *rhs.mKey;
342}
343
344const BlobCache::CacheEntry& BlobCache::CacheEntry::operator=(const CacheEntry& rhs) {
345    mKey = rhs.mKey;
346    mValue = rhs.mValue;
347    return *this;
348}
349
350sp<BlobCache::Blob> BlobCache::CacheEntry::getKey() const {
351    return mKey;
352}
353
354sp<BlobCache::Blob> BlobCache::CacheEntry::getValue() const {
355    return mValue;
356}
357
358void BlobCache::CacheEntry::setValue(const sp<Blob>& value) {
359    mValue = value;
360}
361
362} // namespace android
363