1 /*
2 * Copyright (C) 2012 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 "StateQueue"
18 //#define LOG_NDEBUG 0
19
20 #include <time.h>
21 #include <cutils/atomic.h>
22 #include <utils/Log.h>
23 #include "StateQueue.h"
24
25 namespace android {
26
27 #ifdef STATE_QUEUE_DUMP
dump(int fd)28 void StateQueueObserverDump::dump(int fd)
29 {
30 fdprintf(fd, "State queue observer: stateChanges=%u\n", mStateChanges);
31 }
32
dump(int fd)33 void StateQueueMutatorDump::dump(int fd)
34 {
35 fdprintf(fd, "State queue mutator: pushDirty=%u pushAck=%u blockedSequence=%u\n",
36 mPushDirty, mPushAck, mBlockedSequence);
37 }
38 #endif
39
40 // Constructor and destructor
41
StateQueue()42 template<typename T> StateQueue<T>::StateQueue() :
43 mNext(NULL), mAck(NULL), mCurrent(NULL),
44 mMutating(&mStates[0]), mExpecting(NULL),
45 mInMutation(false), mIsDirty(false), mIsInitialized(false)
46 #ifdef STATE_QUEUE_DUMP
47 , mObserverDump(&mObserverDummyDump), mMutatorDump(&mMutatorDummyDump)
48 #endif
49 {
50 }
51
~StateQueue()52 template<typename T> StateQueue<T>::~StateQueue()
53 {
54 }
55
56 // Observer APIs
57
poll()58 template<typename T> const T* StateQueue<T>::poll()
59 {
60 const T *next = (const T *) android_atomic_acquire_load((volatile int32_t *) &mNext);
61 if (next != mCurrent) {
62 mAck = next; // no additional barrier needed
63 mCurrent = next;
64 #ifdef STATE_QUEUE_DUMP
65 mObserverDump->mStateChanges++;
66 #endif
67 }
68 return next;
69 }
70
71 // Mutator APIs
72
begin()73 template<typename T> T* StateQueue<T>::begin()
74 {
75 ALOG_ASSERT(!mInMutation, "begin() called when in a mutation");
76 mInMutation = true;
77 return mMutating;
78 }
79
end(bool didModify)80 template<typename T> void StateQueue<T>::end(bool didModify)
81 {
82 ALOG_ASSERT(mInMutation, "end() called when not in a mutation");
83 ALOG_ASSERT(mIsInitialized || didModify, "first end() must modify for initialization");
84 if (didModify) {
85 mIsDirty = true;
86 mIsInitialized = true;
87 }
88 mInMutation = false;
89 }
90
push(StateQueue<T>::block_t block)91 template<typename T> bool StateQueue<T>::push(StateQueue<T>::block_t block)
92 {
93 #define PUSH_BLOCK_ACK_NS 3000000L // 3 ms: time between checks for ack in push()
94 // FIXME should be configurable
95 static const struct timespec req = {0, PUSH_BLOCK_ACK_NS};
96
97 ALOG_ASSERT(!mInMutation, "push() called when in a mutation");
98
99 #ifdef STATE_QUEUE_DUMP
100 if (block == BLOCK_UNTIL_ACKED) {
101 mMutatorDump->mPushAck++;
102 }
103 #endif
104
105 if (mIsDirty) {
106
107 #ifdef STATE_QUEUE_DUMP
108 mMutatorDump->mPushDirty++;
109 #endif
110
111 // wait for prior push to be acknowledged
112 if (mExpecting != NULL) {
113 #ifdef STATE_QUEUE_DUMP
114 unsigned count = 0;
115 #endif
116 for (;;) {
117 const T *ack = (const T *) mAck; // no additional barrier needed
118 if (ack == mExpecting) {
119 // unnecessary as we're about to rewrite
120 //mExpecting = NULL;
121 break;
122 }
123 if (block == BLOCK_NEVER) {
124 return false;
125 }
126 #ifdef STATE_QUEUE_DUMP
127 if (count == 1) {
128 mMutatorDump->mBlockedSequence++;
129 }
130 ++count;
131 #endif
132 nanosleep(&req, NULL);
133 }
134 #ifdef STATE_QUEUE_DUMP
135 if (count > 1) {
136 mMutatorDump->mBlockedSequence++;
137 }
138 #endif
139 }
140
141 // publish
142 android_atomic_release_store((int32_t) mMutating, (volatile int32_t *) &mNext);
143 mExpecting = mMutating;
144
145 // copy with circular wraparound
146 if (++mMutating >= &mStates[kN]) {
147 mMutating = &mStates[0];
148 }
149 *mMutating = *mExpecting;
150 mIsDirty = false;
151
152 }
153
154 // optionally wait for this push or a prior push to be acknowledged
155 if (block == BLOCK_UNTIL_ACKED) {
156 if (mExpecting != NULL) {
157 #ifdef STATE_QUEUE_DUMP
158 unsigned count = 0;
159 #endif
160 for (;;) {
161 const T *ack = (const T *) mAck; // no additional barrier needed
162 if (ack == mExpecting) {
163 mExpecting = NULL;
164 break;
165 }
166 #ifdef STATE_QUEUE_DUMP
167 if (count == 1) {
168 mMutatorDump->mBlockedSequence++;
169 }
170 ++count;
171 #endif
172 nanosleep(&req, NULL);
173 }
174 #ifdef STATE_QUEUE_DUMP
175 if (count > 1) {
176 mMutatorDump->mBlockedSequence++;
177 }
178 #endif
179 }
180 }
181
182 return true;
183 }
184
185 } // namespace android
186
187 // hack for gcc
188 #ifdef STATE_QUEUE_INSTANTIATIONS
189 #include STATE_QUEUE_INSTANTIATIONS
190 #endif
191