BlobCache.cpp revision 5f549b2089442cb80e8d7f4bd00ac69560375b2c 
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 <utils/BlobCache.h>
21#include <utils/Timers.h>
22
23#include <inttypes.h>
24
25#include <cutils/properties.h>
26
27namespace android {
28
29// BlobCache::Header::mMagicNumber value
30static const uint32_t blobCacheMagic = ('_' << 24) + ('B' << 16) + ('b' << 8) + '$';
31
32// BlobCache::Header::mBlobCacheVersion value
33static const uint32_t blobCacheVersion = 3;
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", (unsigned long long)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: %zu (limit: %zu)",
58                keySize, mMaxKeySize);
59        return;
60    }
61    if (mMaxValueSize < valueSize) {
62        ALOGV("set: not caching because the value is too large: %zu (limit: %zu)",
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: %zu (limit: %zu)", 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: %zu "
98                            "(limit: %zu)",
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 %zu byte key and %zu 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: %zu (limit: %zu)",
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 %zu byte key and %zu 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: %zu (limit %zu)",
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 %zu", 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 %zu 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: %zu (needs %zu)",
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 = align4(sizeof(Header) + PROPERTY_VALUE_MAX);
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(sizeof(EntryHeader) + keyBlob->getSize() +
173                       valueBlob->getSize());
174    }
175    return size;
176}
177
178status_t BlobCache::flatten(void* buffer, size_t size) const {
179    // Write the cache header
180    if (size < sizeof(Header)) {
181        ALOGE("flatten: not enough room for cache header");
182        return BAD_VALUE;
183    }
184    Header* header = reinterpret_cast<Header*>(buffer);
185    header->mMagicNumber = blobCacheMagic;
186    header->mBlobCacheVersion = blobCacheVersion;
187    header->mDeviceVersion = blobCacheDeviceVersion;
188    header->mNumEntries = mCacheEntries.size();
189    char buildId[PROPERTY_VALUE_MAX];
190    header->mBuildIdLength = property_get("ro.build.id", buildId, "");
191    memcpy(header->mBuildId, buildId, header->mBuildIdLength);
192
193    // Write cache entries
194    uint8_t* byteBuffer = reinterpret_cast<uint8_t*>(buffer);
195    off_t byteOffset = align4(sizeof(Header) + header->mBuildIdLength);
196    for (size_t i = 0; i < mCacheEntries.size(); i++) {
197        const CacheEntry& e(mCacheEntries[i]);
198        sp<Blob> keyBlob = e.getKey();
199        sp<Blob> valueBlob = e.getValue();
200        size_t keySize = keyBlob->getSize();
201        size_t valueSize = valueBlob->getSize();
202
203        size_t entrySize = sizeof(EntryHeader) + keySize + valueSize;
204        size_t totalSize = align4(entrySize);
205        if (byteOffset + totalSize > size) {
206            ALOGE("flatten: not enough room for cache entries");
207            return BAD_VALUE;
208        }
209
210        EntryHeader* eheader = reinterpret_cast<EntryHeader*>(
211            &byteBuffer[byteOffset]);
212        eheader->mKeySize = keySize;
213        eheader->mValueSize = valueSize;
214
215        memcpy(eheader->mData, keyBlob->getData(), keySize);
216        memcpy(eheader->mData + keySize, valueBlob->getData(), valueSize);
217
218        if (totalSize > entrySize) {
219            // We have padding bytes. Those will get written to storage, and contribute to the CRC,
220            // so make sure we zero-them to have reproducible results.
221            memset(eheader->mData + keySize + valueSize, 0, totalSize - entrySize);
222        }
223
224        byteOffset += totalSize;
225    }
226
227    return OK;
228}
229
230status_t BlobCache::unflatten(void const* buffer, size_t size) {
231    // All errors should result in the BlobCache being in an empty state.
232    mCacheEntries.clear();
233
234    // Read the cache header
235    if (size < sizeof(Header)) {
236        ALOGE("unflatten: not enough room for cache header");
237        return BAD_VALUE;
238    }
239    const Header* header = reinterpret_cast<const Header*>(buffer);
240    if (header->mMagicNumber != blobCacheMagic) {
241        ALOGE("unflatten: bad magic number: %" PRIu32, header->mMagicNumber);
242        return BAD_VALUE;
243    }
244    char buildId[PROPERTY_VALUE_MAX];
245    int len = property_get("ro.build.id", buildId, "");
246    if (header->mBlobCacheVersion != blobCacheVersion ||
247            header->mDeviceVersion != blobCacheDeviceVersion ||
248            len != header->mBuildIdLength ||
249            strncmp(buildId, header->mBuildId, len)) {
250        // We treat version mismatches as an empty cache.
251        return OK;
252    }
253
254    // Read cache entries
255    const uint8_t* byteBuffer = reinterpret_cast<const uint8_t*>(buffer);
256    off_t byteOffset = align4(sizeof(Header) + header->mBuildIdLength);
257    size_t numEntries = header->mNumEntries;
258    for (size_t i = 0; i < numEntries; i++) {
259        if (byteOffset + sizeof(EntryHeader) > size) {
260            mCacheEntries.clear();
261            ALOGE("unflatten: not enough room for cache entry headers");
262            return BAD_VALUE;
263        }
264
265        const EntryHeader* eheader = reinterpret_cast<const EntryHeader*>(
266                &byteBuffer[byteOffset]);
267        size_t keySize = eheader->mKeySize;
268        size_t valueSize = eheader->mValueSize;
269        size_t entrySize = sizeof(EntryHeader) + keySize + valueSize;
270
271        size_t totalSize = align4(entrySize);
272        if (byteOffset + totalSize > size) {
273            mCacheEntries.clear();
274            ALOGE("unflatten: not enough room for cache entry headers");
275            return BAD_VALUE;
276        }
277
278        const uint8_t* data = eheader->mData;
279        set(data, keySize, data + keySize, valueSize);
280
281        byteOffset += totalSize;
282    }
283
284    return OK;
285}
286
287long int BlobCache::blob_random() {
288#ifdef _WIN32
289    return rand();
290#else
291    return nrand48(mRandState);
292#endif
293}
294
295void BlobCache::clean() {
296    // Remove a random cache entry until the total cache size gets below half
297    // the maximum total cache size.
298    while (mTotalSize > mMaxTotalSize / 2) {
299        size_t i = size_t(blob_random() % (mCacheEntries.size()));
300        const CacheEntry& entry(mCacheEntries[i]);
301        mTotalSize -= entry.getKey()->getSize() + entry.getValue()->getSize();
302        mCacheEntries.removeAt(i);
303    }
304}
305
306bool BlobCache::isCleanable() const {
307    return mTotalSize > mMaxTotalSize / 2;
308}
309
310BlobCache::Blob::Blob(const void* data, size_t size, bool copyData):
311        mData(copyData ? malloc(size) : data),
312        mSize(size),
313        mOwnsData(copyData) {
314    if (data != NULL && copyData) {
315        memcpy(const_cast<void*>(mData), data, size);
316    }
317}
318
319BlobCache::Blob::~Blob() {
320    if (mOwnsData) {
321        free(const_cast<void*>(mData));
322    }
323}
324
325bool BlobCache::Blob::operator<(const Blob& rhs) const {
326    if (mSize == rhs.mSize) {
327        return memcmp(mData, rhs.mData, mSize) < 0;
328    } else {
329        return mSize < rhs.mSize;
330    }
331}
332
333const void* BlobCache::Blob::getData() const {
334    return mData;
335}
336
337size_t BlobCache::Blob::getSize() const {
338    return mSize;
339}
340
341BlobCache::CacheEntry::CacheEntry() {
342}
343
344BlobCache::CacheEntry::CacheEntry(const sp<Blob>& key, const sp<Blob>& value):
345        mKey(key),
346        mValue(value) {
347}
348
349BlobCache::CacheEntry::CacheEntry(const CacheEntry& ce):
350        mKey(ce.mKey),
351        mValue(ce.mValue) {
352}
353
354bool BlobCache::CacheEntry::operator<(const CacheEntry& rhs) const {
355    return *mKey < *rhs.mKey;
356}
357
358const BlobCache::CacheEntry& BlobCache::CacheEntry::operator=(const CacheEntry& rhs) {
359    mKey = rhs.mKey;
360    mValue = rhs.mValue;
361    return *this;
362}
363
364sp<BlobCache::Blob> BlobCache::CacheEntry::getKey() const {
365    return mKey;
366}
367
368sp<BlobCache::Blob> BlobCache::CacheEntry::getValue() const {
369    return mValue;
370}
371
372void BlobCache::CacheEntry::setValue(const sp<Blob>& value) {
373    mValue = value;
374}
375
376} // namespace android
377