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