#define THROTL_UNSET      -2
#define THROTL_NO_LIMIT   -1
bool throttle_is_quota_valid(int64_t value)
{
    // 复杂的判断条件
    // 请你在三秒内说出 value 如何取值是合法的？
    if (value < 0 && value != THROTL_UNSET && value != THROTL_NO_LIMIT)
    {
        return false;
    }
    return true;
}
bool throttle_is_quota_valid(int64_t value)
{
    // 这是修改后的代码，value 取值合法有三种情况，一目了然
    return value >= 0 || value == THROTL_UNSET || value == THROTL_NO_LIMIT;
}

void RecycleBin::Load(BindCallbackR1<Status>* done)
{
    ......
    FOREACH(iter, fileStats)
    {
        RecycleFile item;
        Status status = ParseDeletedFileName(iter->path, &item.timestamp);
        if (!status.IsOk() { ...... }
        item.fileName = iter->path;
        item.size = iter->size;
        item.physicalSize = iter->refCount > 1 ? 0 : iter->physicalSize;
        ......
        // 这是修改前的代码
        // earliestTimestamp[item.medium] =
        //     item.timestamp != 0 && item.timestamp < earliestTimestamp[item.medium] ?
        //     item.timestamp : earliestTimestamp[item.medium];
        // }
        // 这是修改后的代码
        if (item.timestamp != 0 &&
            item.timestamp < earliestTimestamp[item.medium])
        {
            earliestTimestamp[item.medium] = item.timestamp;
        }
    }
    ......
}

Status Foo()
{
    Status status = Check1();
    if (!status.IsOk())
    {
        return status;
    }
    else
    {
        status = Check2();
        if (!status.IsOk())
        {
            return status;
        }
        else
        {
            status = Check3();
            if (!status.IsOk())
            {
                return status;
            }
            else
            {
                DoSomeRealWork();
                return OK;
            // 四层潜套 if
            }
        }
    }
}

Status Foo()
{
   Status status = Check1();
   if (!status.IsOk())
   {
       return status;
   }
   status = Check2();
   if (!status.IsOk())
   {
       return status;
   }
   status = Check3();
   if (!status.IsOk())
   {
       return status;
   }
   DoSomeRealWork();
   return OK;
}

void Foo(RpcController* ctrl,
         const FooRequest* request,
         FooResponse* response,
         Closure* done)
{
    Status status = Check1(request);
    if (!status.IsOk())
    {
        response->set_errorcode(status.Code());
        // 第一处
        done->Run();
        return;
    }
    status = Check2(request);
    if (!status.IsOk())
    {
        response->set_errorcode(status.Code());
        // 第二处
        done->Run();
        return;
    }
    DoSomeRealWork(...);
    // 第三处
    done->Run();
}

void Foo(RpcController* ctrl,
         const FooRequest* request,
         FooResponse* response,
         Closure* _done)
{
    // 仅一处，不遗漏
    erpc::ScopedCallback done(_done);
    Status status = Check1(request);
    if (!status.IsOk())
    {
         response->set_errorcode(status.Code());
         return;
    }
    status = Check2(request);
    if (!status.IsOk())
    {
         response->set_errorcode(status.Code());
         return;
    }
    DoSomeRealWork(...);
}

void CompactTask::checkFileUtilizationRewrite()
{
    // 此处采取朴素的排序算法，并未采取更高效的 TopK 算法
    std::sort(sealedFilesUsage.begin(), sealedFilesUsage.end(), GarbageCollectionCompare);
    
    int64_t sealedFileMaxSize = INT64_FLAG(lsm_CompactionSealedMaxSize);
    int32_t sealedFileMaxNum = INT32_FLAG(lsm_CompactionSealedMaxFileNum);
    int64_t targetFileSize = 0;
    int32_t sourceFileCnt = 0;                                                                                                                                      
    // 前者简单清淅，并在几十个 File 中选择前几个文件的场景并不算太慢
    FOREACH(itr, sealedFilesUsage)
    {
        LogicalFileId fileId = itr->fileId;
        const FileUsage* usage = baseMap->GetFileUsage(fileId);
        const File* file = fileSet->GetFile(fileId);
        targetFileSize += usage->blocks * mBlockSize;
        sourceFileCnt++;
        if (targetFileSize > sealedFileMaxSize || sourceFileCnt > sealedFileMaxNum)
        {
            break;
        }
        mRewriteSealedFiles[fileId] = true;
    }
    ......
}

void UserRequestControl::WaitForPendingIOs()
{
    erpc::ExponentialBackoff delayTimeBackOff;
    delayTimeBackOff.Reset(
            INT64_FLAG(lsm_UnloadWaitingBackoffBaseUs),
            INT64_FLAG(lsm_UnloadWaitingBackoffLimitUs),
            INT64_FLAG(lsm_UnloadWaitingBackoffScaleFactor));
   
    // 轮循等待在途的请求返回
    // 请思考如何用条件变量实现精确的同步
    while (!mWriteQueue.empty()|| !mReadQueue.empty())
    {
        uint64_t delayTime = delayTimeBackOff.Next();
        PGLOG_INFO(sLogger,
                  (__FUNCTION__, "Waiting for inflight requests during segment unload")
                  ("Segment", mSegment->GetName())
                  ("Write Requests", mWriteQueue.size())
                  ("ReadRequests", mReadQueue.size())
                  ("DelayTimeInUs", delayTime));
        easy_coroutine_usleep(delayTime);  // 退避等待
    }
}

pthread_mutex_t mutex;
pthread_cond_t  nonEmptyCondition;
std::list<Task*> queue;
void ConsumerLoop()
{
    pthread_mutex_lock(&mutex);
    while (true)
    {
        while (queue.empty())
        {
            struct timespec ts;
            ts.tv_sec = 1;
            ts.tv_nsec = 0;
            // 使用timewait
            pthread_cond_timedwait(&nonEmptyCondition, &mutex, timespec);
        }
        Task* firstTask = queue.front();
        queue.pop_front();
        consume(firstTask);
    }
    pthread_mutex_unlock(&mutex);
}

// load.cpp
Status LoadTask::Execute()
{
    Status status;
#define RUN_STEP(func) \
    status = func();
    if (!status.IsOk()) { ... }
    // 串行执行下列步骤
    RUN_STEP(doPrepareDirs);
    ...... // 十几步
    RUN_STEP(doTask);
#undef RUN_STEP
    ......
}
// files.cpp
Status FileMap::SealFilesForLiveDevice()
{
    Status status = OK;
    std::vector<SyncClosureR1<Status>*> sealDones;
    STLDeleteElementsGuard<std::vector<SyncClosureR1<Status>*> >
        donesDeleter(&sealDones);
    // 并行 seal 每个文件
    FOREACH(iter, mActiveFiles)
    {
        File* file = iter->second;
        sealDones.push_back(new SyncClosureR1<Status>());
        Closure* work = stone::NewClosure(
                this,
                &FileMap::doSealFileForLiveDevice,
                file,
                static_cast<BindCallbackR1<Status>*>(sealDones.back()));
        InvokeCoroutineInCurrentThread(work);
    }
    // 收集结果
    FOREACH(done, sealDones)
    {
        (*done)->Wait();
        if (!(*done)->GetResult0().IsOk())
        {
            status = (*done)->GetResult0();
        }
    }
    return status;
}

// stream.h
class Stream
{
public:
    Stream();
    ~Stream();
    void Read(ReadArgs* args);
    ......
private:
    // 增加 magic 字段
    // 通常使用 uint32 或 uint64
    uint64_t mObjectMagic;
    ......
};
// stream.cpp
// 定义 magic 常量
// 常量值选择 hexdump 时能识别的字符串，以便在 gdb 查看 coredump 时快速识别
// 此处使用 “STREAM” 的 ASCII 串
static uint64_t STREAM_OBJECT_MAGIC = 0x4e4d474553564544LL; 
Stream::Stream()
  : mObjectMagic(STREAM_OBJECT_MAGIC)  // 在构造函数中赋值
{
    ......
}
Stream::~Stream()
{
    // 在析构函数中检查并破坏 magic 字段，预防 double-free 错误
    easy_assert(mObjectMagic == STREAM_OBJECT_MAGIC);
    mObjectMagic = FREED_OBJECT_MAGIC;
    ......
}
void DeviceSegment::Read(ReadArgs* args)
{
    // 在重要的函数中检查 magic 字段，预防 use-after-free 错误
    easy_assert(mObjectMagic == DEVICE_SEGMENT_OBJECT_MAGIC);
    ......
  }

class StreamWriter
{
public:
    ......
private:
    struct StreamGroup
    {
        WriteAttemptList failureQueue;
        WriteAttemptList inflightQueue;
        WriteAttemptList pendingQueue;
        uint64_t         commitSeq;
        uint64_t         lastSeq;
    };
    uint32_t     mStreamGroupCount;
    StreamGroup  mStreamGroups[STREAM_GROUP_COUNT];    
    ......
};
void StreamWriter::sanityCheck()
{
#ifndef NDEBUG  // expensive checks
    for (uint32_t i = 0; i < mStreamGroupCount; i++)
    {
        // Check that sequence in "failureQueue", "inflightQueue" and "pendingQueue" are ordered.
        const StreamGroup* group = &mStreamGroups[i];
        uint64_t prevSeq = group->commitSeq;
        const WriteAttemptList* queues[] = {
            &group->failureQueue,
            &group->inflightQueue,
            &group->pendingQueue
        };
        for (size_t k = 0; k < easy_count_of(queues); k++)
        {
            FOREACH(iter, *queues[k])
            {
                const WriteRequest* write = iter->write;
                PANGU_ASSERT(prevSeq <= write->seq); // SanityCheck
                prevSeq = write->seq + write->lbaRange.rangeSize;
            }
        }
        ASSERT(prevSeq == group->lastSeq); // SanityCheck
    }
    ......
#endif  // NDEBUG
}

Status LoadTask::doTailScanFiles()
{
    ......
    for (id = FIRST_REAL_FILE_ID; id < mFileSet->GetTotalFileCount(); id++)
    {
        File* file = mDiskFileSet->GetFile(id);
        if (file->GetLogicalLength() < logicalLengthInIndex)
        {
             const char* msg = “BUG!! Found a data on disk with shorter length ”
                               “than in map. This is probably caused by length reduction of ”
                               “that file.”;   // 记录详细的日志，包括文件名、期望长度、实际长度等
             PGLOG_FATAL(sLogger, (__FUNCTION__, msg)
                         (“Stream”, mStream->GetName())
                         (“File”, file->GetFileName())
                         (“FileId”, file->GetFileId())
                         (“FileLengthOnDisk”, file->GetFileLength())
                         (“FileLengthInIndex”, physicalLengthInIndex)
                         (“LogicalLengthOnDisk”, file->GetLogicalLength())
                         (“LogicalLengthInIndex”, logicalLengthInIndex)
                         (“MissingSize”, physicalLengthInIndex - file->GetFileLength()));
             SERVICE_ADD_COUNTER(“LSM:CriticalIssueCount”, 1);  // 触发电话告警
             return LSM_FILE_CORRUPTED;
        }
    }
}

linux/include/linux/jiffies.h
/** Have the 32 bit jiffies value wrap 5 minutes after boot
* so jiffies wrap bugs show up earlier.
*/
#define INITIAL_JIFFIES ((unsigned long)(unsigned int) (-300*HZ))
/*
* These inlines deal with timer wrapping correctly
You are* strongly encouraged to use them
* 1. Because people otherwise forget
* 2. Because if the timer wrap changes in future you won't have to
* alter your driver code.
*
* time_after(a,b) returns true if the time a is after time b.
*/
#define time_after(a,b) \
    (typecheck(unsigned long, a) && \
    typecheck(unsigned long, b) && \
    ((long)((b) - (a)) < 0))

// easy/src/io/easy_timer.h
// ----------------------------------------------------------------------------------
// following interface, use easy_timer_sched from th(io thread or worker thread),
// ** DON NOT support async call **
//
int easy_timer_start_on_th(easy_baseth_t *th, easy_timer_t *timer);
int easy_timer_stop_on_th(easy_baseth_t *th, easy_timer_t *timer);

TEST_F(..., SharedDisk_StopOneBs)(...) 
{
    BenchMarkStart(mOption);
    // for循环反复注入
    mCluster->StopServer(0);
    mCluster->StartServer(0);
    // 修复前无第12行无代码，无下限检查，全部失败时Case PASS
    // 共享盘开盘后线程死锁必IO Hang，有测试无断言遗漏Bug导致P1故障
    EXPECT_GT(mIoBench->GetLastPrintIops(), 0);
    EXPECT_GT(mIoBench->GetMaxLatency(), 0);
    // 断言检查，边界上限
    EXPECT_GT(20 * 1000000, mIoBench->GetMaxLatency());
    // Do something below
}
Status PRConfig::Register )(...)
{
     assertIoThread();
     // 修复前缺少=，导致Sever Crash
     if (unlikely(mRegistrants.size() >= MAX_REGISTRANT_NUM))
    {
        LOG_ERROR(...);
        return SC_RESERVATION_CONFLICT;
    }
    // Do something below
}

void WalStreamWriterPool::tryCreateWalWriter()
{
    AssertCoroutine();
    ASSERT_DEBUG(mIsCreating);
    Status status = OK;
    while (...)
    {
        WalStreamWriter *writer = mWalManager->CreateWalWriter();
        status = writer->Open();
        // 修复前无第14行代码部分，未处理Commit，失败导致丢掉WAL文件，进而丢数据
        if (status.IsOk())
        {
            status = mWalManager->Commit();
        }
        // Do something below
}
void RPCController::StartCancel()
{
    if (_session) {
        if (_pendingRpc != NULL) {
            // 修复前无第29行代码，线程Hang进而IOHang
            // 未测试覆盖call StartCancel  before handshake
            _session->need_cancel = true;
        } else {
            easy_session_cancel(_session);
        }
    } else {
        easy_error_log(...);
    }
}

Status CompressOffsetTable::Seal()
{
    // Do something before
    status = mTableFile->Seal();
    if (!status.IsOk())
    {
        PGLOG_ERROR(...);
        return status;
    }
    mIsSealed = true;
    // 修复前无第14行代码，文件写入已完成，清空缓存，释放内存
    mEasyPool.reset();
    // Do something below
}

void ActiveManager::SubmitIO(
{
     // 【版本兼容性】 SDK 和 Server线程不对齐，旧版本SDK不支持切线程
     if (UNLIKELY(GetCurrentThread() != serverThread))
     PGLOG_WARNING(...  "Server thread mismatch");
     response->ErrorCode = SERVER_BUSY;
     done->Run();
}
void ChunkListAccessor::SetChunkInfoAndLocations()
{
    uint8_t flags = mFileNodePtr->fileFlags;
    bool isLogFile = IsFlatLogFile(flags);
    ASSERT(
        //【协议兼容性】Master 和 SDK异常场景定长误判
        (isLogFile && vecChunkInfoNode[0].version <= masterChunkInfo.version) ||
        !isLogFile);
         // Do something below
}
// 【API兼容性】 Server 和 Master的错误码不一致，数据分片反复加载/卸载
// Master侧，device_load.cpp
// if(status.Code() == LSM_SEGMENT_EXIST_OTHER_VERSION))
// Server侧，device_load.cpp
// return LSM_NOT_OWN_SEGMENT;

TEST_F(FastPathSmokeTestFixture, Resize)
{
    // ... Do something
    ResizeVolume(uri, DEVICE_SIZE * 2);
    Status status = OK;
    do {
        // 状态依赖，未检查resize 是否成功，导致错误的认为是越界io处理
        status = Write(handle, wbuf.get(), 0, 4096);
        if (status.Code() == OK)
        {
            break;
        }
        easy_coroutine_usleep(100*1000);
    } while(1);
    // ... Do something
}
// volume_iov_split_test.cpp
TEST(VolumeIovSplitTest, Iovsplit_Random)
{
    // ... Do something
    size_t totalLength = 0;
    // 修改前无+1，0是非法随机值，造成Case低概率失败
    totalLength = rand() % (10*1024*1024) + 1
    // ... Do something
}