From 2dd4bdd715f586d4d30cf90cc6fc2bbfbce60fe0 Mon Sep 17 00:00:00 2001
From: Glenn Kasten <gkasten@google.com>
Date: Wed, 29 Aug 2012 11:10:32 -0700
Subject: Move libnbaio out of AudioFlinger

libnbaio is now a separate shared library from AudioFlinger, rather
than a static library used only by AudioFlinger.

AudioBufferProvider interface is now also independent of AudioFlinger,
moved to include/media/

Change-Id: I9bb62ffbc38d42a38b0af76e66da5e9ab1e0e21b
---
 media/libnbaio/PipeReader.cpp | 95 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 95 insertions(+)
 create mode 100644 media/libnbaio/PipeReader.cpp

(limited to 'media/libnbaio/PipeReader.cpp')

diff --git a/media/libnbaio/PipeReader.cpp b/media/libnbaio/PipeReader.cpp
new file mode 100644
index 0000000..d786b84
--- /dev/null
+++ b/media/libnbaio/PipeReader.cpp
@@ -0,0 +1,95 @@
+/*
+ * 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 "PipeReader"
+//#define LOG_NDEBUG 0
+
+#include <cutils/compiler.h>
+#include <utils/Log.h>
+#include <media/nbaio/PipeReader.h>
+
+namespace android {
+
+PipeReader::PipeReader(Pipe& pipe) :
+        NBAIO_Source(pipe.mFormat),
+        mPipe(pipe),
+        // any data already in the pipe is not visible to this PipeReader
+        mFront(android_atomic_acquire_load(&pipe.mRear)),
+        mFramesOverrun(0),
+        mOverruns(0)
+{
+    android_atomic_inc(&pipe.mReaders);
+}
+
+PipeReader::~PipeReader()
+{
+    int32_t readers = android_atomic_dec(&mPipe.mReaders);
+    ALOG_ASSERT(readers > 0);
+}
+
+ssize_t PipeReader::availableToRead()
+{
+    if (CC_UNLIKELY(!mNegotiated)) {
+        return NEGOTIATE;
+    }
+    int32_t rear = android_atomic_acquire_load(&mPipe.mRear);
+    // read() is not multi-thread safe w.r.t. itself, so no mutex or atomic op needed to read mFront
+    size_t avail = rear - mFront;
+    if (CC_UNLIKELY(avail > mPipe.mMaxFrames)) {
+        // Discard 1/16 of the most recent data in pipe to avoid another overrun immediately
+        int32_t oldFront = mFront;
+        mFront = rear - mPipe.mMaxFrames + (mPipe.mMaxFrames >> 4);
+        mFramesOverrun += (size_t) (mFront - oldFront);
+        ++mOverruns;
+        return OVERRUN;
+    }
+    return avail;
+}
+
+ssize_t PipeReader::read(void *buffer, size_t count, int64_t readPTS)
+{
+    ssize_t avail = availableToRead();
+    if (CC_UNLIKELY(avail <= 0)) {
+        return avail;
+    }
+    // An overrun can occur from here on and be silently ignored,
+    // but it will be caught at next read()
+    if (CC_LIKELY(count > (size_t) avail)) {
+        count = avail;
+    }
+    size_t front = mFront & (mPipe.mMaxFrames - 1);
+    size_t red = mPipe.mMaxFrames - front;
+    if (CC_LIKELY(red > count)) {
+        red = count;
+    }
+    // In particular, an overrun during the memcpy will result in reading corrupt data
+    memcpy(buffer, (char *) mPipe.mBuffer + (front << mBitShift), red << mBitShift);
+    // We could re-read the rear pointer here to detect the corruption, but why bother?
+    if (CC_UNLIKELY(front + red == mPipe.mMaxFrames)) {
+        if (CC_UNLIKELY((count -= red) > front)) {
+            count = front;
+        }
+        if (CC_LIKELY(count > 0)) {
+            memcpy((char *) buffer + (red << mBitShift), mPipe.mBuffer, count << mBitShift);
+            red += count;
+        }
+    }
+    mFront += red;
+    mFramesRead += red;
+    return red;
+}
+
+}   // namespace android
-- 
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