StateQueue.cpp revision dc998c809e084b617990b281e2ed5271830cc2e0 
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
25namespace android {
26
27// Constructor and destructor
28
29template<typename T> StateQueue<T>::StateQueue() :
30    mNext(NULL), mAck(NULL), mCurrent(NULL),
31    mMutating(&mStates[0]), mExpecting(NULL),
32    mInMutation(false), mIsDirty(false), mIsInitialized(false)
33{
34}
35
36template<typename T> StateQueue<T>::~StateQueue()
37{
38}
39
40// Observer APIs
41
42template<typename T> const T* StateQueue<T>::poll()
43{
44    const T *next = (const T *) android_atomic_acquire_load((volatile int32_t *) &mNext);
45    if (next != mCurrent) {
46        mAck = next;    // no additional barrier needed
47        mCurrent = next;
48    }
49    return next;
50}
51
52// Mutator APIs
53
54template<typename T> T* StateQueue<T>::begin()
55{
56    ALOG_ASSERT(!mInMutation, "begin() called when in a mutation");
57    mInMutation = true;
58    return mMutating;
59}
60
61template<typename T> void StateQueue<T>::end(bool didModify)
62{
63    ALOG_ASSERT(mInMutation, "end() called when not in a mutation");
64    ALOG_ASSERT(mIsInitialized || didModify, "first end() must modify for initialization");
65    if (didModify) {
66        mIsDirty = true;
67        mIsInitialized = true;
68    }
69    mInMutation = false;
70}
71
72template<typename T> bool StateQueue<T>::push(StateQueue<T>::block_t block)
73{
74#define PUSH_BLOCK_ACK_NS    3000000L   // 3 ms: time between checks for ack in push()
75                                        //       FIXME should be configurable
76    static const struct timespec req = {0, PUSH_BLOCK_ACK_NS};
77
78    ALOG_ASSERT(!mInMutation, "push() called when in a mutation");
79
80    if (mIsDirty) {
81
82        // wait for prior push to be acknowledged
83        if (mExpecting != NULL) {
84            for (;;) {
85                const T *ack = (const T *) mAck;    // no additional barrier needed
86                if (ack == mExpecting) {
87                    // unnecessary as we're about to rewrite
88                    //mExpecting = NULL;
89                    break;
90                }
91                if (block == BLOCK_NEVER) {
92                    return false;
93                }
94                nanosleep(&req, NULL);
95            }
96        }
97
98        // publish
99        android_atomic_release_store((int32_t) mMutating, (volatile int32_t *) &mNext);
100        mExpecting = mMutating;
101
102        // copy with circular wraparound
103        if (++mMutating >= &mStates[kN]) {
104            mMutating = &mStates[0];
105        }
106        *mMutating = *mExpecting;
107        mIsDirty = false;
108
109    }
110
111    // optionally wait for this push or a prior push to be acknowledged
112    if (block == BLOCK_UNTIL_ACKED) {
113        if (mExpecting != NULL) {
114            for (;;) {
115                const T *ack = (const T *) mAck;    // no additional barrier needed
116                if (ack == mExpecting) {
117                    mExpecting = NULL;
118                    break;
119                }
120                nanosleep(&req, NULL);
121            }
122        }
123    }
124
125    return true;
126}
127
128}   // namespace android
129
130// hack for gcc
131#ifdef STATE_QUEUE_INSTANTIATIONS
132#include STATE_QUEUE_INSTANTIATIONS
133#endif
134