Split nblog off from nbaio

nbaio is an acronym for "non-blocking audio I/O", and nblog means
"non-blocking logger" so nblog does not belong with nbaio.

There are a lot of improvements planned for nblog, and having the
restructuring done will make it clearer as more files are added.

Test: builds OK
Change-Id: Ib28bada2566c1d64bdbe9f5d7a5ce40e080178ef
diff --git a/media/libnblog/NBLog.cpp b/media/libnblog/NBLog.cpp
new file mode 100644
index 0000000..c8c7195
--- /dev/null
+++ b/media/libnblog/NBLog.cpp
@@ -0,0 +1,1156 @@
+/*
+ * Copyright (C) 2013 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 "NBLog"
+
+#include <algorithm>
+#include <climits>
+#include <deque>
+#include <fstream>
+#include <iostream>
+#include <math.h>
+#include <numeric>
+#include <vector>
+#include <stdarg.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/prctl.h>
+#include <time.h>
+#include <new>
+#include <audio_utils/roundup.h>
+#include <media/nblog/NBLog.h>
+#include <media/nblog/PerformanceAnalysis.h>
+#include <media/nblog/ReportPerformance.h>
+#include <utils/CallStack.h>
+#include <utils/Log.h>
+#include <utils/String8.h>
+
+#include <queue>
+#include <utility>
+
+namespace android {
+
+int NBLog::Entry::copyEntryDataAt(size_t offset) const
+{
+    // FIXME This is too slow
+    if (offset == 0)
+        return mEvent;
+    else if (offset == 1)
+        return mLength;
+    else if (offset < (size_t) (mLength + 2))
+        return ((char *) mData)[offset - 2];
+    else if (offset == (size_t) (mLength + 2))
+        return mLength;
+    else
+        return 0;
+}
+
+// ---------------------------------------------------------------------------
+
+/*static*/
+std::unique_ptr<NBLog::AbstractEntry> NBLog::AbstractEntry::buildEntry(const uint8_t *ptr) {
+    const uint8_t type = EntryIterator(ptr)->type;
+    switch (type) {
+    case EVENT_START_FMT:
+        return std::make_unique<FormatEntry>(FormatEntry(ptr));
+    case EVENT_AUDIO_STATE:
+    case EVENT_HISTOGRAM_ENTRY_TS:
+        return std::make_unique<HistogramEntry>(HistogramEntry(ptr));
+    default:
+        ALOGW("Tried to create AbstractEntry of type %d", type);
+        return nullptr;
+    }
+}
+
+NBLog::AbstractEntry::AbstractEntry(const uint8_t *entry) : mEntry(entry) {
+}
+
+// ---------------------------------------------------------------------------
+
+NBLog::EntryIterator NBLog::FormatEntry::begin() const {
+    return EntryIterator(mEntry);
+}
+
+const char *NBLog::FormatEntry::formatString() const {
+    return (const char*) mEntry + offsetof(entry, data);
+}
+
+size_t NBLog::FormatEntry::formatStringLength() const {
+    return mEntry[offsetof(entry, length)];
+}
+
+NBLog::EntryIterator NBLog::FormatEntry::args() const {
+    auto it = begin();
+    // skip start fmt
+    ++it;
+    // skip timestamp
+    ++it;
+    // skip hash
+    ++it;
+    // Skip author if present
+    if (it->type == EVENT_AUTHOR) {
+        ++it;
+    }
+    return it;
+}
+
+int64_t NBLog::FormatEntry::timestamp() const {
+    auto it = begin();
+    // skip start fmt
+    ++it;
+    return it.payload<int64_t>();
+}
+
+NBLog::log_hash_t NBLog::FormatEntry::hash() const {
+    auto it = begin();
+    // skip start fmt
+    ++it;
+    // skip timestamp
+    ++it;
+    // unaligned 64-bit read not supported
+    log_hash_t hash;
+    memcpy(&hash, it->data, sizeof(hash));
+    return hash;
+}
+
+int NBLog::FormatEntry::author() const {
+    auto it = begin();
+    // skip start fmt
+    ++it;
+    // skip timestamp
+    ++it;
+    // skip hash
+    ++it;
+    // if there is an author entry, return it, return -1 otherwise
+    if (it->type == EVENT_AUTHOR) {
+        return it.payload<int>();
+    }
+    return -1;
+}
+
+NBLog::EntryIterator NBLog::FormatEntry::copyWithAuthor(
+        std::unique_ptr<audio_utils_fifo_writer> &dst, int author) const {
+    auto it = begin();
+    // copy fmt start entry
+    it.copyTo(dst);
+    // copy timestamp
+    (++it).copyTo(dst);    // copy hash
+    (++it).copyTo(dst);
+    // insert author entry
+    size_t authorEntrySize = NBLog::Entry::kOverhead + sizeof(author);
+    uint8_t authorEntry[authorEntrySize];
+    authorEntry[offsetof(entry, type)] = EVENT_AUTHOR;
+    authorEntry[offsetof(entry, length)] =
+        authorEntry[authorEntrySize + NBLog::Entry::kPreviousLengthOffset] =
+        sizeof(author);
+    *(int*) (&authorEntry[offsetof(entry, data)]) = author;
+    dst->write(authorEntry, authorEntrySize);
+    // copy rest of entries
+    while ((++it)->type != EVENT_END_FMT) {
+        it.copyTo(dst);
+    }
+    it.copyTo(dst);
+    ++it;
+    return it;
+}
+
+void NBLog::EntryIterator::copyTo(std::unique_ptr<audio_utils_fifo_writer> &dst) const {
+    size_t length = ptr[offsetof(entry, length)] + NBLog::Entry::kOverhead;
+    dst->write(ptr, length);
+}
+
+void NBLog::EntryIterator::copyData(uint8_t *dst) const {
+    memcpy((void*) dst, ptr + offsetof(entry, data), ptr[offsetof(entry, length)]);
+}
+
+NBLog::EntryIterator::EntryIterator()
+    : ptr(nullptr) {}
+
+NBLog::EntryIterator::EntryIterator(const uint8_t *entry)
+    : ptr(entry) {}
+
+NBLog::EntryIterator::EntryIterator(const NBLog::EntryIterator &other)
+    : ptr(other.ptr) {}
+
+const NBLog::entry& NBLog::EntryIterator::operator*() const {
+    return *(entry*) ptr;
+}
+
+const NBLog::entry* NBLog::EntryIterator::operator->() const {
+    return (entry*) ptr;
+}
+
+NBLog::EntryIterator& NBLog::EntryIterator::operator++() {
+    ptr += ptr[offsetof(entry, length)] + NBLog::Entry::kOverhead;
+    return *this;
+}
+
+NBLog::EntryIterator& NBLog::EntryIterator::operator--() {
+    ptr -= ptr[NBLog::Entry::kPreviousLengthOffset] + NBLog::Entry::kOverhead;
+    return *this;
+}
+
+NBLog::EntryIterator NBLog::EntryIterator::next() const {
+    EntryIterator aux(*this);
+    return ++aux;
+}
+
+NBLog::EntryIterator NBLog::EntryIterator::prev() const {
+    EntryIterator aux(*this);
+    return --aux;
+}
+
+int NBLog::EntryIterator::operator-(const NBLog::EntryIterator &other) const {
+    return ptr - other.ptr;
+}
+
+bool NBLog::EntryIterator::operator!=(const EntryIterator &other) const {
+    return ptr != other.ptr;
+}
+
+bool NBLog::EntryIterator::hasConsistentLength() const {
+    return ptr[offsetof(entry, length)] == ptr[ptr[offsetof(entry, length)] +
+        NBLog::Entry::kOverhead + NBLog::Entry::kPreviousLengthOffset];
+}
+
+// ---------------------------------------------------------------------------
+
+int64_t NBLog::HistogramEntry::timestamp() const {
+    return EntryIterator(mEntry).payload<HistTsEntry>().ts;
+}
+
+NBLog::log_hash_t NBLog::HistogramEntry::hash() const {
+    return EntryIterator(mEntry).payload<HistTsEntry>().hash;
+}
+
+int NBLog::HistogramEntry::author() const {
+    EntryIterator it(mEntry);
+    if (it->length == sizeof(HistTsEntryWithAuthor)) {
+        return it.payload<HistTsEntryWithAuthor>().author;
+    } else {
+        return -1;
+    }
+}
+
+NBLog::EntryIterator NBLog::HistogramEntry::copyWithAuthor(
+        std::unique_ptr<audio_utils_fifo_writer> &dst, int author) const {
+    // Current histogram entry has {type, length, struct HistTsEntry, length}.
+    // We now want {type, length, struct HistTsEntryWithAuthor, length}
+    uint8_t buffer[Entry::kOverhead + sizeof(HistTsEntryWithAuthor)];
+    // Copy content until the point we want to add the author
+    memcpy(buffer, mEntry, sizeof(entry) + sizeof(HistTsEntry));
+    // Copy the author
+    *(int*) (buffer + sizeof(entry) + sizeof(HistTsEntry)) = author;
+    // Update lengths
+    buffer[offsetof(entry, length)] = sizeof(HistTsEntryWithAuthor);
+    buffer[sizeof(buffer) + Entry::kPreviousLengthOffset] = sizeof(HistTsEntryWithAuthor);
+    // Write new buffer into FIFO
+    dst->write(buffer, sizeof(buffer));
+    return EntryIterator(mEntry).next();
+}
+
+// ---------------------------------------------------------------------------
+
+#if 0   // FIXME see note in NBLog.h
+NBLog::Timeline::Timeline(size_t size, void *shared)
+    : mSize(roundup(size)), mOwn(shared == NULL),
+      mShared((Shared *) (mOwn ? new char[sharedSize(size)] : shared))
+{
+    new (mShared) Shared;
+}
+
+NBLog::Timeline::~Timeline()
+{
+    mShared->~Shared();
+    if (mOwn) {
+        delete[] (char *) mShared;
+    }
+}
+#endif
+
+/*static*/
+size_t NBLog::Timeline::sharedSize(size_t size)
+{
+    // TODO fifo now supports non-power-of-2 buffer sizes, so could remove the roundup
+    return sizeof(Shared) + roundup(size);
+}
+
+// ---------------------------------------------------------------------------
+
+NBLog::Writer::Writer()
+    : mShared(NULL), mFifo(NULL), mFifoWriter(NULL), mEnabled(false), mPidTag(NULL), mPidTagSize(0)
+{
+}
+
+NBLog::Writer::Writer(void *shared, size_t size)
+    : mShared((Shared *) shared),
+      mFifo(mShared != NULL ?
+        new audio_utils_fifo(size, sizeof(uint8_t),
+            mShared->mBuffer, mShared->mRear, NULL /*throttlesFront*/) : NULL),
+      mFifoWriter(mFifo != NULL ? new audio_utils_fifo_writer(*mFifo) : NULL),
+      mEnabled(mFifoWriter != NULL)
+{
+    // caching pid and process name
+    pid_t id = ::getpid();
+    char procName[16];
+    int status = prctl(PR_GET_NAME, procName);
+    if (status) {  // error getting process name
+        procName[0] = '\0';
+    }
+    size_t length = strlen(procName);
+    mPidTagSize = length + sizeof(pid_t);
+    mPidTag = new char[mPidTagSize];
+    memcpy(mPidTag, &id, sizeof(pid_t));
+    memcpy(mPidTag + sizeof(pid_t), procName, length);
+}
+
+NBLog::Writer::Writer(const sp<IMemory>& iMemory, size_t size)
+    : Writer(iMemory != 0 ? (Shared *) iMemory->pointer() : NULL, size)
+{
+    mIMemory = iMemory;
+}
+
+NBLog::Writer::~Writer()
+{
+    delete mFifoWriter;
+    delete mFifo;
+    delete[] mPidTag;
+}
+
+void NBLog::Writer::log(const char *string)
+{
+    if (!mEnabled) {
+        return;
+    }
+    LOG_ALWAYS_FATAL_IF(string == NULL, "Attempted to log NULL string");
+    size_t length = strlen(string);
+    if (length > Entry::kMaxLength) {
+        length = Entry::kMaxLength;
+    }
+    log(EVENT_STRING, string, length);
+}
+
+void NBLog::Writer::logf(const char *fmt, ...)
+{
+    if (!mEnabled) {
+        return;
+    }
+    va_list ap;
+    va_start(ap, fmt);
+    Writer::logvf(fmt, ap);     // the Writer:: is needed to avoid virtual dispatch for LockedWriter
+    va_end(ap);
+}
+
+void NBLog::Writer::logvf(const char *fmt, va_list ap)
+{
+    if (!mEnabled) {
+        return;
+    }
+    char buffer[Entry::kMaxLength + 1 /*NUL*/];
+    int length = vsnprintf(buffer, sizeof(buffer), fmt, ap);
+    if (length >= (int) sizeof(buffer)) {
+        length = sizeof(buffer) - 1;
+        // NUL termination is not required
+        // buffer[length] = '\0';
+    }
+    if (length >= 0) {
+        log(EVENT_STRING, buffer, length);
+    }
+}
+
+void NBLog::Writer::logTimestamp()
+{
+    if (!mEnabled) {
+        return;
+    }
+    int64_t ts = get_monotonic_ns();
+    if (ts > 0) {
+        log(EVENT_TIMESTAMP, &ts, sizeof(ts));
+    } else {
+        ALOGE("Failed to get timestamp");
+    }
+}
+
+void NBLog::Writer::logTimestamp(const int64_t ts)
+{
+    if (!mEnabled) {
+        return;
+    }
+    log(EVENT_TIMESTAMP, &ts, sizeof(ts));
+}
+
+void NBLog::Writer::logInteger(const int x)
+{
+    if (!mEnabled) {
+        return;
+    }
+    log(EVENT_INTEGER, &x, sizeof(x));
+}
+
+void NBLog::Writer::logFloat(const float x)
+{
+    if (!mEnabled) {
+        return;
+    }
+    log(EVENT_FLOAT, &x, sizeof(x));
+}
+
+void NBLog::Writer::logPID()
+{
+    if (!mEnabled) {
+        return;
+    }
+    log(EVENT_PID, mPidTag, mPidTagSize);
+}
+
+void NBLog::Writer::logStart(const char *fmt)
+{
+    if (!mEnabled) {
+        return;
+    }
+    size_t length = strlen(fmt);
+    if (length > Entry::kMaxLength) {
+        length = Entry::kMaxLength;
+    }
+    log(EVENT_START_FMT, fmt, length);
+}
+
+void NBLog::Writer::logEnd()
+{
+    if (!mEnabled) {
+        return;
+    }
+    Entry entry = Entry(EVENT_END_FMT, NULL, 0);
+    log(&entry, true);
+}
+
+void NBLog::Writer::logHash(log_hash_t hash)
+{
+    if (!mEnabled) {
+        return;
+    }
+    log(EVENT_HASH, &hash, sizeof(hash));
+}
+
+void NBLog::Writer::logEventHistTs(Event event, log_hash_t hash)
+{
+    if (!mEnabled) {
+        return;
+    }
+    HistTsEntry data;
+    data.hash = hash;
+    data.ts = get_monotonic_ns();
+    if (data.ts > 0) {
+        log(event, &data, sizeof(data));
+    } else {
+        ALOGE("Failed to get timestamp");
+    }
+}
+
+void NBLog::Writer::logFormat(const char *fmt, log_hash_t hash, ...)
+{
+    if (!mEnabled) {
+        return;
+    }
+
+    va_list ap;
+    va_start(ap, hash);
+    Writer::logVFormat(fmt, hash, ap);
+    va_end(ap);
+}
+
+void NBLog::Writer::logVFormat(const char *fmt, log_hash_t hash, va_list argp)
+{
+    if (!mEnabled) {
+        return;
+    }
+    Writer::logStart(fmt);
+    int i;
+    double f;
+    char* s;
+    int64_t t;
+    Writer::logTimestamp();
+    Writer::logHash(hash);
+    for (const char *p = fmt; *p != '\0'; p++) {
+        // TODO: implement more complex formatting such as %.3f
+        if (*p != '%') {
+            continue;
+        }
+        switch(*++p) {
+        case 's': // string
+            s = va_arg(argp, char *);
+            Writer::log(s);
+            break;
+
+        case 't': // timestamp
+            t = va_arg(argp, int64_t);
+            Writer::logTimestamp(t);
+            break;
+
+        case 'd': // integer
+            i = va_arg(argp, int);
+            Writer::logInteger(i);
+            break;
+
+        case 'f': // float
+            f = va_arg(argp, double); // float arguments are promoted to double in vararg lists
+            Writer::logFloat((float)f);
+            break;
+
+        case 'p': // pid
+            Writer::logPID();
+            break;
+
+        // the "%\0" case finishes parsing
+        case '\0':
+            --p;
+            break;
+
+        case '%':
+            break;
+
+        default:
+            ALOGW("NBLog Writer parsed invalid format specifier: %c", *p);
+            break;
+        }
+    }
+    Writer::logEnd();
+}
+
+void NBLog::Writer::log(Event event, const void *data, size_t length)
+{
+    if (!mEnabled) {
+        return;
+    }
+    if (data == NULL || length > Entry::kMaxLength) {
+        // TODO Perhaps it makes sense to display truncated data or at least a
+        //      message that the data is too long?  The current behavior can create
+        //      a confusion for a programmer debugging their code.
+        return;
+    }
+    // Ignore if invalid event
+    if (event == EVENT_RESERVED || event >= EVENT_UPPER_BOUND) {
+        return;
+    }
+    Entry etr(event, data, length);
+    log(&etr, true /*trusted*/);
+}
+
+void NBLog::Writer::log(const NBLog::Entry *etr, bool trusted)
+{
+    if (!mEnabled) {
+        return;
+    }
+    if (!trusted) {
+        log(etr->mEvent, etr->mData, etr->mLength);
+        return;
+    }
+    size_t need = etr->mLength + Entry::kOverhead;    // mEvent, mLength, data[mLength], mLength
+                                                      // need = number of bytes written to FIFO
+
+    // FIXME optimize this using memcpy for the data part of the Entry.
+    // The Entry could have a method copyTo(ptr, offset, size) to optimize the copy.
+    // checks size of a single log Entry: type, length, data pointer and ending
+    uint8_t temp[Entry::kMaxLength + Entry::kOverhead];
+    // write this data to temp array
+    for (size_t i = 0; i < need; i++) {
+        temp[i] = etr->copyEntryDataAt(i);
+    }
+    // write to circular buffer
+    mFifoWriter->write(temp, need);
+}
+
+bool NBLog::Writer::isEnabled() const
+{
+    return mEnabled;
+}
+
+bool NBLog::Writer::setEnabled(bool enabled)
+{
+    bool old = mEnabled;
+    mEnabled = enabled && mShared != NULL;
+    return old;
+}
+
+// ---------------------------------------------------------------------------
+
+NBLog::LockedWriter::LockedWriter()
+    : Writer()
+{
+}
+
+NBLog::LockedWriter::LockedWriter(void *shared, size_t size)
+    : Writer(shared, size)
+{
+}
+
+void NBLog::LockedWriter::log(const char *string)
+{
+    Mutex::Autolock _l(mLock);
+    Writer::log(string);
+}
+
+void NBLog::LockedWriter::logf(const char *fmt, ...)
+{
+    // FIXME should not take the lock until after formatting is done
+    Mutex::Autolock _l(mLock);
+    va_list ap;
+    va_start(ap, fmt);
+    Writer::logvf(fmt, ap);
+    va_end(ap);
+}
+
+void NBLog::LockedWriter::logvf(const char *fmt, va_list ap)
+{
+    // FIXME should not take the lock until after formatting is done
+    Mutex::Autolock _l(mLock);
+    Writer::logvf(fmt, ap);
+}
+
+void NBLog::LockedWriter::logTimestamp()
+{
+    // FIXME should not take the lock until after the clock_gettime() syscall
+    Mutex::Autolock _l(mLock);
+    Writer::logTimestamp();
+}
+
+void NBLog::LockedWriter::logTimestamp(const int64_t ts)
+{
+    Mutex::Autolock _l(mLock);
+    Writer::logTimestamp(ts);
+}
+
+void NBLog::LockedWriter::logInteger(const int x)
+{
+    Mutex::Autolock _l(mLock);
+    Writer::logInteger(x);
+}
+
+void NBLog::LockedWriter::logFloat(const float x)
+{
+    Mutex::Autolock _l(mLock);
+    Writer::logFloat(x);
+}
+
+void NBLog::LockedWriter::logPID()
+{
+    Mutex::Autolock _l(mLock);
+    Writer::logPID();
+}
+
+void NBLog::LockedWriter::logStart(const char *fmt)
+{
+    Mutex::Autolock _l(mLock);
+    Writer::logStart(fmt);
+}
+
+
+void NBLog::LockedWriter::logEnd()
+{
+    Mutex::Autolock _l(mLock);
+    Writer::logEnd();
+}
+
+void NBLog::LockedWriter::logHash(log_hash_t hash)
+{
+    Mutex::Autolock _l(mLock);
+    Writer::logHash(hash);
+}
+
+bool NBLog::LockedWriter::isEnabled() const
+{
+    Mutex::Autolock _l(mLock);
+    return Writer::isEnabled();
+}
+
+bool NBLog::LockedWriter::setEnabled(bool enabled)
+{
+    Mutex::Autolock _l(mLock);
+    return Writer::setEnabled(enabled);
+}
+
+// ---------------------------------------------------------------------------
+
+const std::set<NBLog::Event> NBLog::Reader::startingTypes {NBLog::Event::EVENT_START_FMT,
+        NBLog::Event::EVENT_HISTOGRAM_ENTRY_TS,
+        NBLog::Event::EVENT_AUDIO_STATE};
+const std::set<NBLog::Event> NBLog::Reader::endingTypes   {NBLog::Event::EVENT_END_FMT,
+        NBLog::Event::EVENT_HISTOGRAM_ENTRY_TS,
+        NBLog::Event::EVENT_AUDIO_STATE};
+
+NBLog::Reader::Reader(const void *shared, size_t size)
+    : mFd(-1), mIndent(0), mLost(0),
+      mShared((/*const*/ Shared *) shared), /*mIMemory*/
+      mFifo(mShared != NULL ?
+        new audio_utils_fifo(size, sizeof(uint8_t),
+            mShared->mBuffer, mShared->mRear, NULL /*throttlesFront*/) : NULL),
+      mFifoReader(mFifo != NULL ? new audio_utils_fifo_reader(*mFifo) : NULL)
+{
+}
+
+NBLog::Reader::Reader(const sp<IMemory>& iMemory, size_t size)
+    : Reader(iMemory != 0 ? (Shared *) iMemory->pointer() : NULL, size)
+{
+    mIMemory = iMemory;
+}
+
+NBLog::Reader::~Reader()
+{
+    delete mFifoReader;
+    delete mFifo;
+}
+
+const uint8_t *NBLog::Reader::findLastEntryOfTypes(const uint8_t *front, const uint8_t *back,
+                                            const std::set<Event> &types) {
+    while (back + Entry::kPreviousLengthOffset >= front) {
+        const uint8_t *prev = back - back[Entry::kPreviousLengthOffset] - Entry::kOverhead;
+        if (prev < front || prev + prev[offsetof(entry, length)] +
+                            Entry::kOverhead != back) {
+
+            // prev points to an out of limits or inconsistent entry
+            return nullptr;
+        }
+        if (types.find((const Event) prev[offsetof(entry, type)]) != types.end()) {
+            return prev;
+        }
+        back = prev;
+    }
+    return nullptr; // no entry found
+}
+
+// Copies content of a Reader FIFO into its Snapshot
+// The Snapshot has the same raw data, but represented as a sequence of entries
+// and an EntryIterator making it possible to process the data.
+std::unique_ptr<NBLog::Reader::Snapshot> NBLog::Reader::getSnapshot()
+{
+    if (mFifoReader == NULL) {
+        return std::unique_ptr<NBLog::Reader::Snapshot>(new Snapshot());
+    }
+    // make a copy to avoid race condition with writer
+    size_t capacity = mFifo->capacity();
+
+    // This emulates the behaviour of audio_utils_fifo_reader::read, but without incrementing the
+    // reader index. The index is incremented after handling corruption, to after the last complete
+    // entry of the buffer
+    size_t lost;
+    audio_utils_iovec iovec[2];
+    ssize_t availToRead = mFifoReader->obtain(iovec, capacity, NULL /*timeout*/, &lost);
+    if (availToRead <= 0) {
+        return std::unique_ptr<NBLog::Reader::Snapshot>(new Snapshot());
+    }
+
+    std::unique_ptr<Snapshot> snapshot(new Snapshot(availToRead));
+    memcpy(snapshot->mData, (const char *) mFifo->buffer() + iovec[0].mOffset, iovec[0].mLength);
+    if (iovec[1].mLength > 0) {
+        memcpy(snapshot->mData + (iovec[0].mLength),
+            (const char *) mFifo->buffer() + iovec[1].mOffset, iovec[1].mLength);
+    }
+
+    // Handle corrupted buffer
+    // Potentially, a buffer has corrupted data on both beginning (due to overflow) and end
+    // (due to incomplete format entry). But even if the end format entry is incomplete,
+    // it ends in a complete entry (which is not an END_FMT). So is safe to traverse backwards.
+    // TODO: handle client corruption (in the middle of a buffer)
+
+    const uint8_t *back = snapshot->mData + availToRead;
+    const uint8_t *front = snapshot->mData;
+
+    // Find last END_FMT. <back> is sitting on an entry which might be the middle of a FormatEntry.
+    // We go backwards until we find an EVENT_END_FMT.
+    const uint8_t *lastEnd = findLastEntryOfTypes(front, back, endingTypes);
+    if (lastEnd == nullptr) {
+        snapshot->mEnd = snapshot->mBegin = EntryIterator(front);
+    } else {
+        // end of snapshot points to after last END_FMT entry
+        snapshot->mEnd = EntryIterator(lastEnd).next();
+        // find first START_FMT
+        const uint8_t *firstStart = nullptr;
+        const uint8_t *firstStartTmp = snapshot->mEnd;
+        while ((firstStartTmp = findLastEntryOfTypes(front, firstStartTmp, startingTypes))
+                != nullptr) {
+            firstStart = firstStartTmp;
+        }
+        // firstStart is null if no START_FMT entry was found before lastEnd
+        if (firstStart == nullptr) {
+            snapshot->mBegin = snapshot->mEnd;
+        } else {
+            snapshot->mBegin = EntryIterator(firstStart);
+        }
+    }
+
+    // advance fifo reader index to after last entry read.
+    mFifoReader->release(snapshot->mEnd - front);
+
+    snapshot->mLost = lost;
+    return snapshot;
+
+}
+
+// Takes raw content of the local merger FIFO, processes log entries, and
+// writes the data to a map of class PerformanceAnalysis, based on their thread ID.
+void NBLog::MergeReader::getAndProcessSnapshot(NBLog::Reader::Snapshot &snapshot)
+{
+    String8 timestamp, body;
+
+    for (auto entry = snapshot.begin(); entry != snapshot.end();) {
+        switch (entry->type) {
+        case EVENT_START_FMT:
+            entry = handleFormat(FormatEntry(entry), &timestamp, &body);
+            break;
+        case EVENT_HISTOGRAM_ENTRY_TS: {
+            HistTsEntryWithAuthor *data = (HistTsEntryWithAuthor *) (entry->data);
+            // TODO This memcpies are here to avoid unaligned memory access crash.
+            // There's probably a more efficient way to do it
+            log_hash_t hash;
+            memcpy(&hash, &(data->hash), sizeof(hash));
+            int64_t ts;
+            memcpy(&ts, &data->ts, sizeof(ts));
+            // TODO: hash for histogram ts and audio state need to match
+            // and correspond to audio production source file location
+            mThreadPerformanceAnalysis[data->author][0 /*hash*/].logTsEntry(ts);
+            ++entry;
+            break;
+        }
+        case EVENT_AUDIO_STATE: {
+            HistTsEntryWithAuthor *data = (HistTsEntryWithAuthor *) (entry->data);
+            // TODO This memcpies are here to avoid unaligned memory access crash.
+            // There's probably a more efficient way to do it
+            log_hash_t hash;
+            memcpy(&hash, &(data->hash), sizeof(hash));
+            // TODO: remove ts if unused
+            int64_t ts;
+            memcpy(&ts, &data->ts, sizeof(ts));
+            mThreadPerformanceAnalysis[data->author][0 /*hash*/].handleStateChange();
+            ++entry;
+            break;
+        }
+        case EVENT_END_FMT:
+            body.appendFormat("warning: got to end format event");
+            ++entry;
+            break;
+        case EVENT_RESERVED:
+        default:
+            body.appendFormat("warning: unexpected event %d", entry->type);
+            ++entry;
+            break;
+        }
+    }
+    // FIXME: decide whether to print the warnings here or elsewhere
+    if (!body.isEmpty()) {
+        dumpLine(timestamp, body);
+    }
+}
+
+void NBLog::MergeReader::getAndProcessSnapshot()
+{
+    // get a snapshot, process it
+    std::unique_ptr<Snapshot> snap = getSnapshot();
+    getAndProcessSnapshot(*snap);
+}
+
+void NBLog::MergeReader::dump(int fd, int indent) {
+    // TODO: add a mutex around media.log dump
+    ReportPerformance::dump(fd, indent, mThreadPerformanceAnalysis);
+}
+
+// Writes a string to the console
+void NBLog::Reader::dumpLine(const String8 &timestamp, String8 &body)
+{
+    if (mFd >= 0) {
+        dprintf(mFd, "%.*s%s %s\n", mIndent, "", timestamp.string(), body.string());
+    } else {
+        ALOGI("%.*s%s %s", mIndent, "", timestamp.string(), body.string());
+    }
+    body.clear();
+}
+
+bool NBLog::Reader::isIMemory(const sp<IMemory>& iMemory) const
+{
+    return iMemory != 0 && mIMemory != 0 && iMemory->pointer() == mIMemory->pointer();
+}
+
+// ---------------------------------------------------------------------------
+
+void NBLog::appendTimestamp(String8 *body, const void *data) {
+    int64_t ts;
+    memcpy(&ts, data, sizeof(ts));
+    body->appendFormat("[%d.%03d]", (int) (ts / (1000 * 1000 * 1000)),
+                    (int) ((ts / (1000 * 1000)) % 1000));
+}
+
+void NBLog::appendInt(String8 *body, const void *data) {
+    int x = *((int*) data);
+    body->appendFormat("<%d>", x);
+}
+
+void NBLog::appendFloat(String8 *body, const void *data) {
+    float f;
+    memcpy(&f, data, sizeof(float));
+    body->appendFormat("<%f>", f);
+}
+
+void NBLog::appendPID(String8 *body, const void* data, size_t length) {
+    pid_t id = *((pid_t*) data);
+    char * name = &((char*) data)[sizeof(pid_t)];
+    body->appendFormat("<PID: %d, name: %.*s>", id, (int) (length - sizeof(pid_t)), name);
+}
+
+String8 NBLog::bufferDump(const uint8_t *buffer, size_t size)
+{
+    String8 str;
+    str.append("[ ");
+    for(size_t i = 0; i < size; i++)
+    {
+        str.appendFormat("%d ", buffer[i]);
+    }
+    str.append("]");
+    return str;
+}
+
+String8 NBLog::bufferDump(const EntryIterator &it)
+{
+    return bufferDump(it, it->length + Entry::kOverhead);
+}
+
+NBLog::EntryIterator NBLog::Reader::handleFormat(const FormatEntry &fmtEntry,
+                                                         String8 *timestamp,
+                                                         String8 *body) {
+    // log timestamp
+    int64_t ts = fmtEntry.timestamp();
+    timestamp->clear();
+    timestamp->appendFormat("[%d.%03d]", (int) (ts / (1000 * 1000 * 1000)),
+                    (int) ((ts / (1000 * 1000)) % 1000));
+
+    // log unique hash
+    log_hash_t hash = fmtEntry.hash();
+    // print only lower 16bit of hash as hex and line as int to reduce spam in the log
+    body->appendFormat("%.4X-%d ", (int)(hash >> 16) & 0xFFFF, (int) hash & 0xFFFF);
+
+    // log author (if present)
+    handleAuthor(fmtEntry, body);
+
+    // log string
+    NBLog::EntryIterator arg = fmtEntry.args();
+
+    const char* fmt = fmtEntry.formatString();
+    size_t fmt_length = fmtEntry.formatStringLength();
+
+    for (size_t fmt_offset = 0; fmt_offset < fmt_length; ++fmt_offset) {
+        if (fmt[fmt_offset] != '%') {
+            body->append(&fmt[fmt_offset], 1); // TODO optimize to write consecutive strings at once
+            continue;
+        }
+        // case "%%""
+        if (fmt[++fmt_offset] == '%') {
+            body->append("%");
+            continue;
+        }
+        // case "%\0"
+        if (fmt_offset == fmt_length) {
+            continue;
+        }
+
+        NBLog::Event event = (NBLog::Event) arg->type;
+        size_t length = arg->length;
+
+        // TODO check length for event type is correct
+
+        if (event == EVENT_END_FMT) {
+            break;
+        }
+
+        // TODO: implement more complex formatting such as %.3f
+        const uint8_t *datum = arg->data; // pointer to the current event args
+        switch(fmt[fmt_offset])
+        {
+        case 's': // string
+            ALOGW_IF(event != EVENT_STRING,
+                "NBLog Reader incompatible event for string specifier: %d", event);
+            body->append((const char*) datum, length);
+            break;
+
+        case 't': // timestamp
+            ALOGW_IF(event != EVENT_TIMESTAMP,
+                "NBLog Reader incompatible event for timestamp specifier: %d", event);
+            appendTimestamp(body, datum);
+            break;
+
+        case 'd': // integer
+            ALOGW_IF(event != EVENT_INTEGER,
+                "NBLog Reader incompatible event for integer specifier: %d", event);
+            appendInt(body, datum);
+            break;
+
+        case 'f': // float
+            ALOGW_IF(event != EVENT_FLOAT,
+                "NBLog Reader incompatible event for float specifier: %d", event);
+            appendFloat(body, datum);
+            break;
+
+        case 'p': // pid
+            ALOGW_IF(event != EVENT_PID,
+                "NBLog Reader incompatible event for pid specifier: %d", event);
+            appendPID(body, datum, length);
+            break;
+
+        default:
+            ALOGW("NBLog Reader encountered unknown character %c", fmt[fmt_offset]);
+        }
+        ++arg;
+    }
+    ALOGW_IF(arg->type != EVENT_END_FMT, "Expected end of format, got %d", arg->type);
+    ++arg;
+    return arg;
+}
+
+NBLog::Merger::Merger(const void *shared, size_t size):
+      mShared((Shared *) shared),
+      mFifo(mShared != NULL ?
+        new audio_utils_fifo(size, sizeof(uint8_t),
+            mShared->mBuffer, mShared->mRear, NULL /*throttlesFront*/) : NULL),
+      mFifoWriter(mFifo != NULL ? new audio_utils_fifo_writer(*mFifo) : NULL)
+      {}
+
+void NBLog::Merger::addReader(const NBLog::NamedReader &reader) {
+
+    // FIXME This is called by binder thread in MediaLogService::registerWriter
+    //       but the access to shared variable mNamedReaders is not yet protected by a lock.
+    mNamedReaders.push_back(reader);
+}
+
+// items placed in priority queue during merge
+// composed by a timestamp and the index of the snapshot where the timestamp came from
+struct MergeItem
+{
+    int64_t ts;
+    int index;
+    MergeItem(int64_t ts, int index): ts(ts), index(index) {}
+};
+
+// operators needed for priority queue in merge
+// bool operator>(const int64_t &t1, const int64_t &t2) {
+//     return t1.tv_sec > t2.tv_sec || (t1.tv_sec == t2.tv_sec && t1.tv_nsec > t2.tv_nsec);
+// }
+
+bool operator>(const struct MergeItem &i1, const struct MergeItem &i2) {
+    return i1.ts > i2.ts || (i1.ts == i2.ts && i1.index > i2.index);
+}
+
+// Merge registered readers, sorted by timestamp, and write data to a single FIFO in local memory
+void NBLog::Merger::merge() {
+    // FIXME This is called by merge thread
+    //       but the access to shared variable mNamedReaders is not yet protected by a lock.
+    int nLogs = mNamedReaders.size();
+    std::vector<std::unique_ptr<NBLog::Reader::Snapshot>> snapshots(nLogs);
+    std::vector<NBLog::EntryIterator> offsets(nLogs);
+    for (int i = 0; i < nLogs; ++i) {
+        snapshots[i] = mNamedReaders[i].reader()->getSnapshot();
+        offsets[i] = snapshots[i]->begin();
+    }
+    // initialize offsets
+    // TODO custom heap implementation could allow to update top, improving performance
+    // for bursty buffers
+    std::priority_queue<MergeItem, std::vector<MergeItem>, std::greater<MergeItem>> timestamps;
+    for (int i = 0; i < nLogs; ++i)
+    {
+        if (offsets[i] != snapshots[i]->end()) {
+            int64_t ts = AbstractEntry::buildEntry(offsets[i])->timestamp();
+            timestamps.emplace(ts, i);
+        }
+    }
+
+    while (!timestamps.empty()) {
+        // find minimum timestamp
+        int index = timestamps.top().index;
+        // copy it to the log, increasing offset
+        offsets[index] = AbstractEntry::buildEntry(offsets[index])->copyWithAuthor(mFifoWriter,
+                                                                                   index);
+        // update data structures
+        timestamps.pop();
+        if (offsets[index] != snapshots[index]->end()) {
+            int64_t ts = AbstractEntry::buildEntry(offsets[index])->timestamp();
+            timestamps.emplace(ts, index);
+        }
+    }
+}
+
+const std::vector<NBLog::NamedReader>& NBLog::Merger::getNamedReaders() const {
+    // FIXME This is returning a reference to a shared variable that needs a lock
+    return mNamedReaders;
+}
+
+// ---------------------------------------------------------------------------
+
+NBLog::MergeReader::MergeReader(const void *shared, size_t size, Merger &merger)
+    : Reader(shared, size), mNamedReaders(merger.getNamedReaders()) {}
+
+void NBLog::MergeReader::handleAuthor(const NBLog::AbstractEntry &entry, String8 *body) {
+    int author = entry.author();
+    // FIXME Needs a lock
+    const char* name = mNamedReaders[author].name();
+    body->appendFormat("%s: ", name);
+}
+
+// ---------------------------------------------------------------------------
+
+NBLog::MergeThread::MergeThread(NBLog::Merger &merger, NBLog::MergeReader &mergeReader)
+    : mMerger(merger),
+      mMergeReader(mergeReader),
+      mTimeoutUs(0) {}
+
+NBLog::MergeThread::~MergeThread() {
+    // set exit flag, set timeout to 0 to force threadLoop to exit and wait for the thread to join
+    requestExit();
+    setTimeoutUs(0);
+    join();
+}
+
+bool NBLog::MergeThread::threadLoop() {
+    bool doMerge;
+    {
+        AutoMutex _l(mMutex);
+        // If mTimeoutUs is negative, wait on the condition variable until it's positive.
+        // If it's positive, wait kThreadSleepPeriodUs and then merge
+        nsecs_t waitTime = mTimeoutUs > 0 ? kThreadSleepPeriodUs * 1000 : LLONG_MAX;
+        mCond.waitRelative(mMutex, waitTime);
+        doMerge = mTimeoutUs > 0;
+        mTimeoutUs -= kThreadSleepPeriodUs;
+    }
+    if (doMerge) {
+        // Merge data from all the readers
+        mMerger.merge();
+        // Process the data collected by mMerger and write it to PerformanceAnalysis
+        // FIXME: decide whether to call getAndProcessSnapshot every time
+        // or whether to have a separate thread that calls it with a lower frequency
+        mMergeReader.getAndProcessSnapshot();
+    }
+    return true;
+}
+
+void NBLog::MergeThread::wakeup() {
+    setTimeoutUs(kThreadWakeupPeriodUs);
+}
+
+void NBLog::MergeThread::setTimeoutUs(int time) {
+    AutoMutex _l(mMutex);
+    mTimeoutUs = time;
+    mCond.signal();
+}
+
+}   // namespace android