blob: 8835fb0130a3d9847004482c31648a022611d2ff [file] [log] [blame]
Adam Lesinski282e1812014-01-23 18:17:42 -08001//
2// Copyright 2012 The Android Open Source Project
3//
4// Manage a resource ID cache.
5
6#define LOG_TAG "ResourceIdCache"
7
8#include <utils/String16.h>
9#include <utils/Log.h>
10#include "ResourceIdCache.h"
11#include <map>
Adam Lesinski282e1812014-01-23 18:17:42 -080012
13static size_t mHits = 0;
14static size_t mMisses = 0;
15static size_t mCollisions = 0;
16
17static const size_t MAX_CACHE_ENTRIES = 2048;
18static const android::String16 TRUE16("1");
19static const android::String16 FALSE16("0");
20
21struct CacheEntry {
22 // concatenation of the relevant strings into a single instance
23 android::String16 hashedName;
24 uint32_t id;
25
26 CacheEntry() {}
27 CacheEntry(const android::String16& name, uint32_t resId) : hashedName(name), id(resId) { }
28};
29
Adam Lesinski40e8eef2014-09-16 14:43:29 -070030static std::map< uint32_t, CacheEntry > mIdMap;
Adam Lesinski282e1812014-01-23 18:17:42 -080031
32
33// djb2; reasonable choice for strings when collisions aren't particularly important
34static inline uint32_t hashround(uint32_t hash, int c) {
35 return ((hash << 5) + hash) + c; /* hash * 33 + c */
36}
37
38static uint32_t hash(const android::String16& hashableString) {
39 uint32_t hash = 5381;
40 const char16_t* str = hashableString.string();
41 while (int c = *str++) hash = hashround(hash, c);
42 return hash;
43}
44
45namespace android {
46
47static inline String16 makeHashableName(const android::String16& package,
48 const android::String16& type,
49 const android::String16& name,
50 bool onlyPublic) {
51 String16 hashable = String16(name);
52 hashable += type;
53 hashable += package;
54 hashable += (onlyPublic ? TRUE16 : FALSE16);
55 return hashable;
56}
57
58uint32_t ResourceIdCache::lookup(const android::String16& package,
59 const android::String16& type,
60 const android::String16& name,
61 bool onlyPublic) {
62 const String16 hashedName = makeHashableName(package, type, name, onlyPublic);
63 const uint32_t hashcode = hash(hashedName);
Adam Lesinski40e8eef2014-09-16 14:43:29 -070064 std::map<uint32_t, CacheEntry>::iterator item = mIdMap.find(hashcode);
Adam Lesinski282e1812014-01-23 18:17:42 -080065 if (item == mIdMap.end()) {
66 // cache miss
67 mMisses++;
68 return 0;
69 }
70
71 // legit match?
72 if (hashedName == (*item).second.hashedName) {
73 mHits++;
74 return (*item).second.id;
75 }
76
77 // collision
78 mCollisions++;
79 mIdMap.erase(hashcode);
80 return 0;
81}
82
83// returns the resource ID being stored, for callsite convenience
84uint32_t ResourceIdCache::store(const android::String16& package,
85 const android::String16& type,
86 const android::String16& name,
87 bool onlyPublic,
88 uint32_t resId) {
89 if (mIdMap.size() < MAX_CACHE_ENTRIES) {
90 const String16 hashedName = makeHashableName(package, type, name, onlyPublic);
91 const uint32_t hashcode = hash(hashedName);
92 mIdMap[hashcode] = CacheEntry(hashedName, resId);
93 }
94 return resId;
95}
96
97void ResourceIdCache::dump() {
98 printf("ResourceIdCache dump:\n");
Adam Lesinskide898ff2014-01-29 18:20:45 -080099 printf("Size: %zd\n", mIdMap.size());
100 printf("Hits: %zd\n", mHits);
101 printf("Misses: %zd\n", mMisses);
102 printf("(Collisions: %zd)\n", mCollisions);
Adam Lesinski282e1812014-01-23 18:17:42 -0800103}
104
105}