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/*
* Copyright (C) 2012 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#define LOG_TAG "StateQueue"
//#define LOG_NDEBUG 0
#include <time.h>
#include <cutils/atomic.h>
#include <utils/Log.h>
#include "StateQueue.h"
namespace android {
#ifdef STATE_QUEUE_DUMP
void StateQueueObserverDump::dump(int fd)
{
fdprintf(fd, "State queue observer: stateChanges=%u\n", mStateChanges);
}
void StateQueueMutatorDump::dump(int fd)
{
fdprintf(fd, "State queue mutator: pushDirty=%u pushAck=%u blockedSequence=%u\n",
mPushDirty, mPushAck, mBlockedSequence);
}
#endif
// Constructor and destructor
template<typename T> StateQueue<T>::StateQueue() :
mNext(NULL), mAck(NULL), mCurrent(NULL),
mMutating(&mStates[0]), mExpecting(NULL),
mInMutation(false), mIsDirty(false), mIsInitialized(false)
#ifdef STATE_QUEUE_DUMP
, mObserverDump(&mObserverDummyDump), mMutatorDump(&mMutatorDummyDump)
#endif
{
}
template<typename T> StateQueue<T>::~StateQueue()
{
}
// Observer APIs
template<typename T> const T* StateQueue<T>::poll()
{
const T *next = (const T *) android_atomic_acquire_load((volatile int32_t *) &mNext);
if (next != mCurrent) {
mAck = next; // no additional barrier needed
mCurrent = next;
#ifdef STATE_QUEUE_DUMP
mObserverDump->mStateChanges++;
#endif
}
return next;
}
// Mutator APIs
template<typename T> T* StateQueue<T>::begin()
{
ALOG_ASSERT(!mInMutation, "begin() called when in a mutation");
mInMutation = true;
return mMutating;
}
template<typename T> void StateQueue<T>::end(bool didModify)
{
ALOG_ASSERT(mInMutation, "end() called when not in a mutation");
ALOG_ASSERT(mIsInitialized || didModify, "first end() must modify for initialization");
if (didModify) {
mIsDirty = true;
mIsInitialized = true;
}
mInMutation = false;
}
template<typename T> bool StateQueue<T>::push(StateQueue<T>::block_t block)
{
#define PUSH_BLOCK_ACK_NS 3000000L // 3 ms: time between checks for ack in push()
// FIXME should be configurable
static const struct timespec req = {0, PUSH_BLOCK_ACK_NS};
ALOG_ASSERT(!mInMutation, "push() called when in a mutation");
#ifdef STATE_QUEUE_DUMP
if (block == BLOCK_UNTIL_ACKED) {
mMutatorDump->mPushAck++;
}
#endif
if (mIsDirty) {
#ifdef STATE_QUEUE_DUMP
mMutatorDump->mPushDirty++;
#endif
// wait for prior push to be acknowledged
if (mExpecting != NULL) {
#ifdef STATE_QUEUE_DUMP
unsigned count = 0;
#endif
for (;;) {
const T *ack = (const T *) mAck; // no additional barrier needed
if (ack == mExpecting) {
// unnecessary as we're about to rewrite
//mExpecting = NULL;
break;
}
if (block == BLOCK_NEVER) {
return false;
}
#ifdef STATE_QUEUE_DUMP
if (count == 1) {
mMutatorDump->mBlockedSequence++;
}
++count;
#endif
nanosleep(&req, NULL);
}
#ifdef STATE_QUEUE_DUMP
if (count > 1) {
mMutatorDump->mBlockedSequence++;
}
#endif
}
// publish
android_atomic_release_store((int32_t) mMutating, (volatile int32_t *) &mNext);
mExpecting = mMutating;
// copy with circular wraparound
if (++mMutating >= &mStates[kN]) {
mMutating = &mStates[0];
}
*mMutating = *mExpecting;
mIsDirty = false;
}
// optionally wait for this push or a prior push to be acknowledged
if (block == BLOCK_UNTIL_ACKED) {
if (mExpecting != NULL) {
#ifdef STATE_QUEUE_DUMP
unsigned count = 0;
#endif
for (;;) {
const T *ack = (const T *) mAck; // no additional barrier needed
if (ack == mExpecting) {
mExpecting = NULL;
break;
}
#ifdef STATE_QUEUE_DUMP
if (count == 1) {
mMutatorDump->mBlockedSequence++;
}
++count;
#endif
nanosleep(&req, NULL);
}
#ifdef STATE_QUEUE_DUMP
if (count > 1) {
mMutatorDump->mBlockedSequence++;
}
#endif
}
}
return true;
}
} // namespace android
// hack for gcc
#ifdef STATE_QUEUE_INSTANTIATIONS
#include STATE_QUEUE_INSTANTIATIONS
#endif
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