BlobCache.cpp revision 5bed8036644f552210a7cfcbed2d6d20cf2981b0 
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 <inttypes.h>
21#include <stdlib.h>
22#include <string.h>
23
24#include <utils/BlobCache.h>
25#include <utils/Errors.h>
26#include <utils/Log.h>
27
28namespace android {
29
30// BlobCache::Header::mMagicNumber value
31static const uint32_t blobCacheMagic = ('_' << 24) + ('B' << 16) + ('b' << 8) + '$';
32
33// BlobCache::Header::mBlobCacheVersion value
34static const uint32_t blobCacheVersion = 1;
35
36// BlobCache::Header::mDeviceVersion value
37static const uint32_t blobCacheDeviceVersion = 1;
38
39BlobCache::BlobCache(size_t maxKeySize, size_t maxValueSize, size_t maxTotalSize):
40        mMaxKeySize(maxKeySize),
41        mMaxValueSize(maxValueSize),
42        mMaxTotalSize(maxTotalSize),
43        mTotalSize(0) {
44    nsecs_t now = systemTime(SYSTEM_TIME_MONOTONIC);
45#ifdef _WIN32
46    srand(now);
47#else
48    mRandState[0] = (now >> 0) & 0xFFFF;
49    mRandState[1] = (now >> 16) & 0xFFFF;
50    mRandState[2] = (now >> 32) & 0xFFFF;
51#endif
52    ALOGV("initializing random seed using %lld", (unsigned long long)now);
53}
54
55void BlobCache::set(const void* key, size_t keySize, const void* value,
56        size_t valueSize) {
57    if (mMaxKeySize < keySize) {
58        ALOGV("set: not caching because the key is too large: %zu (limit: %zu)",
59                keySize, mMaxKeySize);
60        return;
61    }
62    if (mMaxValueSize < valueSize) {
63        ALOGV("set: not caching because the value is too large: %zu (limit: %zu)",
64                valueSize, mMaxValueSize);
65        return;
66    }
67    if (mMaxTotalSize < keySize + valueSize) {
68        ALOGV("set: not caching because the combined key/value size is too "
69                "large: %zu (limit: %zu)", keySize + valueSize, mMaxTotalSize);
70        return;
71    }
72    if (keySize == 0) {
73        ALOGW("set: not caching because keySize is 0");
74        return;
75    }
76    if (valueSize <= 0) {
77        ALOGW("set: not caching because valueSize is 0");
78        return;
79    }
80
81    sp<Blob> dummyKey(new Blob(key, keySize, false));
82    CacheEntry dummyEntry(dummyKey, NULL);
83
84    while (true) {
85        ssize_t index = mCacheEntries.indexOf(dummyEntry);
86        if (index < 0) {
87            // Create a new cache entry.
88            sp<Blob> keyBlob(new Blob(key, keySize, true));
89            sp<Blob> valueBlob(new Blob(value, valueSize, true));
90            size_t newTotalSize = mTotalSize + keySize + valueSize;
91            if (mMaxTotalSize < newTotalSize) {
92                if (isCleanable()) {
93                    // Clean the cache and try again.
94                    clean();
95                    continue;
96                } else {
97                    ALOGV("set: not caching new key/value pair because the "
98                            "total cache size limit would be exceeded: %zu "
99                            "(limit: %zu)",
100                            keySize + valueSize, mMaxTotalSize);
101                    break;
102                }
103            }
104            mCacheEntries.add(CacheEntry(keyBlob, valueBlob));
105            mTotalSize = newTotalSize;
106            ALOGV("set: created new cache entry with %zu byte key and %zu byte value",
107                    keySize, valueSize);
108        } else {
109            // Update the existing cache entry.
110            sp<Blob> valueBlob(new Blob(value, valueSize, true));
111            sp<Blob> oldValueBlob(mCacheEntries[index].getValue());
112            size_t newTotalSize = mTotalSize + valueSize - oldValueBlob->getSize();
113            if (mMaxTotalSize < newTotalSize) {
114                if (isCleanable()) {
115                    // Clean the cache and try again.
116                    clean();
117                    continue;
118                } else {
119                    ALOGV("set: not caching new value because the total cache "
120                            "size limit would be exceeded: %zu (limit: %zu)",
121                            keySize + valueSize, mMaxTotalSize);
122                    break;
123                }
124            }
125            mCacheEntries.editItemAt(index).setValue(valueBlob);
126            mTotalSize = newTotalSize;
127            ALOGV("set: updated existing cache entry with %zu byte key and %zu byte "
128                    "value", keySize, valueSize);
129        }
130        break;
131    }
132}
133
134size_t BlobCache::get(const void* key, size_t keySize, void* value,
135        size_t valueSize) {
136    if (mMaxKeySize < keySize) {
137        ALOGV("get: not searching because the key is too large: %zu (limit %zu)",
138                keySize, mMaxKeySize);
139        return 0;
140    }
141    sp<Blob> dummyKey(new Blob(key, keySize, false));
142    CacheEntry dummyEntry(dummyKey, NULL);
143    ssize_t index = mCacheEntries.indexOf(dummyEntry);
144    if (index < 0) {
145        ALOGV("get: no cache entry found for key of size %zu", keySize);
146        return 0;
147    }
148
149    // The key was found. Return the value if the caller's buffer is large
150    // enough.
151    sp<Blob> valueBlob(mCacheEntries[index].getValue());
152    size_t valueBlobSize = valueBlob->getSize();
153    if (valueBlobSize <= valueSize) {
154        ALOGV("get: copying %zu bytes to caller's buffer", valueBlobSize);
155        memcpy(value, valueBlob->getData(), valueBlobSize);
156    } else {
157        ALOGV("get: caller's buffer is too small for value: %zu (needs %zu)",
158                valueSize, valueBlobSize);
159    }
160    return valueBlobSize;
161}
162
163static inline size_t align4(size_t size) {
164    return (size + 3) & ~3;
165}
166
167size_t BlobCache::getFlattenedSize() const {
168    size_t size = sizeof(Header);
169    for (size_t i = 0; i < mCacheEntries.size(); i++) {
170        const CacheEntry& e(mCacheEntries[i]);
171        sp<Blob> keyBlob = e.getKey();
172        sp<Blob> valueBlob = e.getValue();
173        size = align4(size);
174        size += sizeof(EntryHeader) + keyBlob->getSize() +
175                valueBlob->getSize();
176    }
177    return size;
178}
179
180status_t BlobCache::flatten(void* buffer, size_t size) const {
181    // Write the cache header
182    if (size < sizeof(Header)) {
183        ALOGE("flatten: not enough room for cache header");
184        return BAD_VALUE;
185    }
186    Header* header = reinterpret_cast<Header*>(buffer);
187    header->mMagicNumber = blobCacheMagic;
188    header->mBlobCacheVersion = blobCacheVersion;
189    header->mDeviceVersion = blobCacheDeviceVersion;
190    header->mNumEntries = mCacheEntries.size();
191
192    // Write cache entries
193    uint8_t* byteBuffer = reinterpret_cast<uint8_t*>(buffer);
194    off_t byteOffset = align4(sizeof(Header));
195    for (size_t i = 0; i < mCacheEntries.size(); i++) {
196        const CacheEntry& e(mCacheEntries[i]);
197        sp<Blob> keyBlob = e.getKey();
198        sp<Blob> valueBlob = e.getValue();
199        size_t keySize = keyBlob->getSize();
200        size_t valueSize = valueBlob->getSize();
201
202        size_t entrySize = sizeof(EntryHeader) + keySize + valueSize;
203        if (byteOffset + entrySize > size) {
204            ALOGE("flatten: not enough room for cache entries");
205            return BAD_VALUE;
206        }
207
208        EntryHeader* eheader = reinterpret_cast<EntryHeader*>(
209            &byteBuffer[byteOffset]);
210        eheader->mKeySize = keySize;
211        eheader->mValueSize = valueSize;
212
213        memcpy(eheader->mData, keyBlob->getData(), keySize);
214        memcpy(eheader->mData + keySize, valueBlob->getData(), valueSize);
215
216        byteOffset += align4(entrySize);
217    }
218
219    return OK;
220}
221
222status_t BlobCache::unflatten(void const* buffer, size_t size) {
223    // All errors should result in the BlobCache being in an empty state.
224    mCacheEntries.clear();
225
226    // Read the cache header
227    if (size < sizeof(Header)) {
228        ALOGE("unflatten: not enough room for cache header");
229        return BAD_VALUE;
230    }
231    const Header* header = reinterpret_cast<const Header*>(buffer);
232    if (header->mMagicNumber != blobCacheMagic) {
233        ALOGE("unflatten: bad magic number: %" PRIu32, header->mMagicNumber);
234        return BAD_VALUE;
235    }
236    if (header->mBlobCacheVersion != blobCacheVersion ||
237            header->mDeviceVersion != blobCacheDeviceVersion) {
238        // We treat version mismatches as an empty cache.
239        return OK;
240    }
241
242    // Read cache entries
243    const uint8_t* byteBuffer = reinterpret_cast<const uint8_t*>(buffer);
244    off_t byteOffset = align4(sizeof(Header));
245    size_t numEntries = header->mNumEntries;
246    for (size_t i = 0; i < numEntries; i++) {
247        if (byteOffset + sizeof(EntryHeader) > size) {
248            mCacheEntries.clear();
249            ALOGE("unflatten: not enough room for cache entry headers");
250            return BAD_VALUE;
251        }
252
253        const EntryHeader* eheader = reinterpret_cast<const EntryHeader*>(
254                &byteBuffer[byteOffset]);
255        size_t keySize = eheader->mKeySize;
256        size_t valueSize = eheader->mValueSize;
257        size_t entrySize = sizeof(EntryHeader) + keySize + valueSize;
258
259        if (byteOffset + entrySize > size) {
260            mCacheEntries.clear();
261            ALOGE("unflatten: not enough room for cache entry headers");
262            return BAD_VALUE;
263        }
264
265        const uint8_t* data = eheader->mData;
266        set(data, keySize, data + keySize, valueSize);
267
268        byteOffset += align4(entrySize);
269    }
270
271    return OK;
272}
273
274long int BlobCache::blob_random() {
275#ifdef _WIN32
276    return rand();
277#else
278    return nrand48(mRandState);
279#endif
280}
281
282void BlobCache::clean() {
283    // Remove a random cache entry until the total cache size gets below half
284    // the maximum total cache size.
285    while (mTotalSize > mMaxTotalSize / 2) {
286        size_t i = size_t(blob_random() % (mCacheEntries.size()));
287        const CacheEntry& entry(mCacheEntries[i]);
288        mTotalSize -= entry.getKey()->getSize() + entry.getValue()->getSize();
289        mCacheEntries.removeAt(i);
290    }
291}
292
293bool BlobCache::isCleanable() const {
294    return mTotalSize > mMaxTotalSize / 2;
295}
296
297BlobCache::Blob::Blob(const void* data, size_t size, bool copyData):
298        mData(copyData ? malloc(size) : data),
299        mSize(size),
300        mOwnsData(copyData) {
301    if (data != NULL && copyData) {
302        memcpy(const_cast<void*>(mData), data, size);
303    }
304}
305
306BlobCache::Blob::~Blob() {
307    if (mOwnsData) {
308        free(const_cast<void*>(mData));
309    }
310}
311
312bool BlobCache::Blob::operator<(const Blob& rhs) const {
313    if (mSize == rhs.mSize) {
314        return memcmp(mData, rhs.mData, mSize) < 0;
315    } else {
316        return mSize < rhs.mSize;
317    }
318}
319
320const void* BlobCache::Blob::getData() const {
321    return mData;
322}
323
324size_t BlobCache::Blob::getSize() const {
325    return mSize;
326}
327
328BlobCache::CacheEntry::CacheEntry() {
329}
330
331BlobCache::CacheEntry::CacheEntry(const sp<Blob>& key, const sp<Blob>& value):
332        mKey(key),
333        mValue(value) {
334}
335
336BlobCache::CacheEntry::CacheEntry(const CacheEntry& ce):
337        mKey(ce.mKey),
338        mValue(ce.mValue) {
339}
340
341bool BlobCache::CacheEntry::operator<(const CacheEntry& rhs) const {
342    return *mKey < *rhs.mKey;
343}
344
345const BlobCache::CacheEntry& BlobCache::CacheEntry::operator=(const CacheEntry& rhs) {
346    mKey = rhs.mKey;
347    mValue = rhs.mValue;
348    return *this;
349}
350
351sp<BlobCache::Blob> BlobCache::CacheEntry::getKey() const {
352    return mKey;
353}
354
355sp<BlobCache::Blob> BlobCache::CacheEntry::getValue() const {
356    return mValue;
357}
358
359void BlobCache::CacheEntry::setValue(const sp<Blob>& value) {
360    mValue = value;
361}
362
363} // namespace android
364