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 "PipeReader"
18 //#define LOG_NDEBUG 0
19
20 #include <cutils/compiler.h>
21 #include <utils/Log.h>
22 #include "PipeReader.h"
23
24 namespace android {
25
PipeReader(Pipe & pipe)26 PipeReader::PipeReader(Pipe& pipe) :
27 NBAIO_Source(pipe.mFormat),
28 mPipe(pipe),
29 // any data already in the pipe is not visible to this PipeReader
30 mFront(android_atomic_acquire_load(&pipe.mRear)),
31 mFramesOverrun(0),
32 mOverruns(0)
33 {
34 android_atomic_inc(&pipe.mReaders);
35 }
36
~PipeReader()37 PipeReader::~PipeReader()
38 {
39 int32_t readers = android_atomic_dec(&mPipe.mReaders);
40 ALOG_ASSERT(readers > 0);
41 }
42
availableToRead()43 ssize_t PipeReader::availableToRead()
44 {
45 if (CC_UNLIKELY(!mNegotiated)) {
46 return NEGOTIATE;
47 }
48 int32_t rear = android_atomic_acquire_load(&mPipe.mRear);
49 // read() is not multi-thread safe w.r.t. itself, so no mutex or atomic op needed to read mFront
50 size_t avail = rear - mFront;
51 if (CC_UNLIKELY(avail > mPipe.mMaxFrames)) {
52 // Discard 1/16 of the most recent data in pipe to avoid another overrun immediately
53 int32_t oldFront = mFront;
54 mFront = rear - mPipe.mMaxFrames + (mPipe.mMaxFrames >> 4);
55 mFramesOverrun += (size_t) (mFront - oldFront);
56 ++mOverruns;
57 return OVERRUN;
58 }
59 return avail;
60 }
61
read(void * buffer,size_t count)62 ssize_t PipeReader::read(void *buffer, size_t count)
63 {
64 ssize_t avail = availableToRead();
65 if (CC_UNLIKELY(avail <= 0)) {
66 return avail;
67 }
68 // An overrun can occur from here on and be silently ignored,
69 // but it will be caught at next read()
70 if (CC_LIKELY(count > (size_t) avail)) {
71 count = avail;
72 }
73 size_t front = mFront & (mPipe.mMaxFrames - 1);
74 size_t red = mPipe.mMaxFrames - front;
75 if (CC_LIKELY(red > count)) {
76 red = count;
77 }
78 // In particular, an overrun during the memcpy will result in reading corrupt data
79 memcpy(buffer, (char *) mPipe.mBuffer + (front << mBitShift), red << mBitShift);
80 // We could re-read the rear pointer here to detect the corruption, but why bother?
81 if (CC_UNLIKELY(front + red == mPipe.mMaxFrames)) {
82 if (CC_UNLIKELY((count -= red) > front)) {
83 count = front;
84 }
85 if (CC_LIKELY(count > 0)) {
86 memcpy((char *) buffer + (red << mBitShift), mPipe.mBuffer, count << mBitShift);
87 red += count;
88 }
89 }
90 mFront += red;
91 mFramesRead += red;
92 return red;
93 }
94
95 } // namespace android
96