diff --git a/media/libmedia/AudioTrackShared.cpp b/media/libmedia/AudioTrackShared.cpp
new file mode 100644
index 0000000..bee13c8
--- /dev/null
+++ b/media/libmedia/AudioTrackShared.cpp
@@ -0,0 +1,196 @@
+/*
+ * Copyright (C) 2007 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 "AudioTrackShared"
+//#define LOG_NDEBUG 0
+
+#include <private/media/AudioTrackShared.h>
+#include <utils/Log.h>
+
+namespace android {
+
+audio_track_cblk_t::audio_track_cblk_t()
+    : lock(Mutex::SHARED), cv(Condition::SHARED), user(0), server(0),
+    userBase(0), serverBase(0), frameCount_(0),
+    loopStart(UINT_MAX), loopEnd(UINT_MAX), loopCount(0), mVolumeLR(0x10001000),
+    mSendLevel(0), flags(0)
+{
+}
+
+uint32_t audio_track_cblk_t::stepUser(size_t stepCount, size_t frameCount, bool isOut)
+{
+    ALOGV("stepuser %08x %08x %d", user, server, stepCount);
+
+    uint32_t u = user;
+    u += stepCount;
+    // Ensure that user is never ahead of server for AudioRecord
+    if (isOut) {
+        // If stepServer() has been called once, switch to normal obtainBuffer() timeout period
+        if (bufferTimeoutMs == MAX_STARTUP_TIMEOUT_MS-1) {
+            bufferTimeoutMs = MAX_RUN_TIMEOUT_MS;
+        }
+    } else if (u > server) {
+        ALOGW("stepUser occurred after track reset");
+        u = server;
+    }
+
+    if (u >= frameCount) {
+        // common case, user didn't just wrap
+        if (u - frameCount >= userBase ) {
+            userBase += frameCount;
+        }
+    } else if (u >= userBase + frameCount) {
+        // user just wrapped
+        userBase += frameCount;
+    }
+
+    user = u;
+
+    // Clear flow control error condition as new data has been written/read to/from buffer.
+    if (flags & CBLK_UNDERRUN) {
+        android_atomic_and(~CBLK_UNDERRUN, &flags);
+    }
+
+    return u;
+}
+
+bool audio_track_cblk_t::stepServer(size_t stepCount, size_t frameCount, bool isOut)
+{
+    ALOGV("stepserver %08x %08x %d", user, server, stepCount);
+
+    if (!tryLock()) {
+        ALOGW("stepServer() could not lock cblk");
+        return false;
+    }
+
+    uint32_t s = server;
+    bool flushed = (s == user);
+
+    s += stepCount;
+    if (isOut) {
+        // Mark that we have read the first buffer so that next time stepUser() is called
+        // we switch to normal obtainBuffer() timeout period
+        if (bufferTimeoutMs == MAX_STARTUP_TIMEOUT_MS) {
+            bufferTimeoutMs = MAX_STARTUP_TIMEOUT_MS - 1;
+        }
+        // It is possible that we receive a flush()
+        // while the mixer is processing a block: in this case,
+        // stepServer() is called After the flush() has reset u & s and
+        // we have s > u
+        if (flushed) {
+            ALOGW("stepServer occurred after track reset");
+            s = user;
+        }
+    }
+
+    if (s >= loopEnd) {
+        ALOGW_IF(s > loopEnd, "stepServer: s %u > loopEnd %u", s, loopEnd);
+        s = loopStart;
+        if (--loopCount == 0) {
+            loopEnd = UINT_MAX;
+            loopStart = UINT_MAX;
+        }
+    }
+
+    if (s >= frameCount) {
+        // common case, server didn't just wrap
+        if (s - frameCount >= serverBase ) {
+            serverBase += frameCount;
+        }
+    } else if (s >= serverBase + frameCount) {
+        // server just wrapped
+        serverBase += frameCount;
+    }
+
+    server = s;
+
+    if (!(flags & CBLK_INVALID)) {
+        cv.signal();
+    }
+    lock.unlock();
+    return true;
+}
+
+void* audio_track_cblk_t::buffer(void *buffers, size_t frameSize, uint32_t offset) const
+{
+    return (int8_t *)buffers + (offset - userBase) * frameSize;
+}
+
+uint32_t audio_track_cblk_t::framesAvailable(size_t frameCount, bool isOut)
+{
+    Mutex::Autolock _l(lock);
+    return framesAvailable_l(frameCount, isOut);
+}
+
+uint32_t audio_track_cblk_t::framesAvailable_l(size_t frameCount, bool isOut)
+{
+    uint32_t u = user;
+    uint32_t s = server;
+
+    if (isOut) {
+        uint32_t limit = (s < loopStart) ? s : loopStart;
+        return limit + frameCount - u;
+    } else {
+        return frameCount + u - s;
+    }
+}
+
+uint32_t audio_track_cblk_t::framesReady(bool isOut)
+{
+    uint32_t u = user;
+    uint32_t s = server;
+
+    if (isOut) {
+        if (u < loopEnd) {
+            return u - s;
+        } else {
+            // do not block on mutex shared with client on AudioFlinger side
+            if (!tryLock()) {
+                ALOGW("framesReady() could not lock cblk");
+                return 0;
+            }
+            uint32_t frames = UINT_MAX;
+            if (loopCount >= 0) {
+                frames = (loopEnd - loopStart)*loopCount + u - s;
+            }
+            lock.unlock();
+            return frames;
+        }
+    } else {
+        return s - u;
+    }
+}
+
+bool audio_track_cblk_t::tryLock()
+{
+    // the code below simulates lock-with-timeout
+    // we MUST do this to protect the AudioFlinger server
+    // as this lock is shared with the client.
+    status_t err;
+
+    err = lock.tryLock();
+    if (err == -EBUSY) { // just wait a bit
+        usleep(1000);
+        err = lock.tryLock();
+    }
+    if (err != NO_ERROR) {
+        // probably, the client just died.
+        return false;
+    }
+    return true;
+}
+
+}   // namespace android