Refactor PerfStepTimer to stop on destruct

This eliminates the need to remember to call PERF_TIMER_STOP when a section has
been timed. This allows more useful design with the perf timers and enables
possible return value optimizations. Simplistic example:

class Foo {
  public:
    Foo(int v) : m_v(v);
  private:
    int m_v;
}

Foo makeFrobbedFoo(int *errno)
{
  *errno = 0;
  return Foo();
}

Foo bar(int *errno)
{
  PERF_TIMER_GUARD(some_timer);

  return makeFrobbedFoo(errno);
}

int main(int argc, char[] argv)
{
  Foo f;
  int errno;

  f = bar(&errno);

  if (errno)
    return -1;
  return 0;
}

After bar() is called, perf_context.some_timer would be incremented as if
Stop(&perf_context.some_timer) was called at the end, and the compiler is still
able to produce optimizations on the return value from makeFrobbedFoo() through
to main().

db/db_impl.cc

@@ -3375,7 +3375,7 @@ Status DBImpl::GetImpl(const ReadOptions& options,
                        ColumnFamilyHandle* column_family, const Slice& key,
                        std::string* value, bool* value_found) {
   StopWatch sw(env_, stats_, DB_GET);
-  PERF_TIMER_AUTO(get_snapshot_time);
+  PERF_TIMER_GUARD(get_snapshot_time);
 
   auto cfh = reinterpret_cast<ColumnFamilyHandleImpl*>(column_family);
   auto cfd = cfh->cfd();
@@ -3399,6 +3399,7 @@ Status DBImpl::GetImpl(const ReadOptions& options,
   // merge_operands will contain the sequence of merges in the latter case.
   LookupKey lkey(key, snapshot);
   PERF_TIMER_STOP(get_snapshot_time);
+
   if (sv->mem->Get(lkey, value, &s, merge_context, *cfd->options())) {
     // Done
     RecordTick(stats_, MEMTABLE_HIT);
@@ -3406,20 +3407,19 @@ Status DBImpl::GetImpl(const ReadOptions& options,
     // Done
     RecordTick(stats_, MEMTABLE_HIT);
   } else {
-    PERF_TIMER_START(get_from_output_files_time);
-
+    PERF_TIMER_GUARD(get_from_output_files_time);
     sv->current->Get(options, lkey, value, &s, &merge_context, value_found);
-    PERF_TIMER_STOP(get_from_output_files_time);
     RecordTick(stats_, MEMTABLE_MISS);
   }
 
-  PERF_TIMER_START(get_post_process_time);
+  {
+    PERF_TIMER_GUARD(get_post_process_time);
 
-  ReturnAndCleanupSuperVersion(cfd, sv);
+    ReturnAndCleanupSuperVersion(cfd, sv);
 
-  RecordTick(stats_, NUMBER_KEYS_READ);
-  RecordTick(stats_, BYTES_READ, value->size());
-  PERF_TIMER_STOP(get_post_process_time);
+    RecordTick(stats_, NUMBER_KEYS_READ);
+    RecordTick(stats_, BYTES_READ, value->size());
+  }
   return s;
 }
 
@@ -3429,7 +3429,7 @@ std::vector<Status> DBImpl::MultiGet(
     const std::vector<Slice>& keys, std::vector<std::string>* values) {
 
   StopWatch sw(env_, stats_, DB_MULTIGET);
-  PERF_TIMER_AUTO(get_snapshot_time);
+  PERF_TIMER_GUARD(get_snapshot_time);
 
   SequenceNumber snapshot;
 
@@ -3505,7 +3505,7 @@ std::vector<Status> DBImpl::MultiGet(
   }
 
   // Post processing (decrement reference counts and record statistics)
-  PERF_TIMER_START(get_post_process_time);
+  PERF_TIMER_GUARD(get_post_process_time);
   autovector<SuperVersion*> superversions_to_delete;
 
   // TODO(icanadi) do we need lock here or just around Cleanup()?
@@ -3878,7 +3878,7 @@ Status DBImpl::Write(const WriteOptions& options, WriteBatch* my_batch) {
   if (my_batch == nullptr) {
     return Status::Corruption("Batch is nullptr!");
   }
-  PERF_TIMER_AUTO(write_pre_and_post_process_time);
+  PERF_TIMER_GUARD(write_pre_and_post_process_time);
   Writer w(&mutex_);
   w.batch = my_batch;
   w.sync = options.sync;
@@ -4011,7 +4011,7 @@ Status DBImpl::Write(const WriteOptions& options, WriteBatch* my_batch) {
 
       uint64_t log_size = 0;
       if (!options.disableWAL) {
-        PERF_TIMER_START(write_wal_time);
+        PERF_TIMER_GUARD(write_wal_time);
         Slice log_entry = WriteBatchInternal::Contents(updates);
         status = log_->AddRecord(log_entry);
         total_log_size_ += log_entry.size();
@@ -4029,10 +4029,9 @@ Status DBImpl::Write(const WriteOptions& options, WriteBatch* my_batch) {
             status = log_->file()->Sync();
           }
         }
-        PERF_TIMER_STOP(write_wal_time);
       }
       if (status.ok()) {
-        PERF_TIMER_START(write_memtable_time);
+        PERF_TIMER_GUARD(write_memtable_time);
 
         status = WriteBatchInternal::InsertInto(
             updates, column_family_memtables_.get(), false, 0, this, false);
@@ -4044,8 +4043,6 @@ Status DBImpl::Write(const WriteOptions& options, WriteBatch* my_batch) {
         // into the memtable would result in a state that some write ops might
         // have succeeded in memtable but Status reports error for all writes.
 
-        PERF_TIMER_STOP(write_memtable_time);
-
         SetTickerCount(stats_, SEQUENCE_NUMBER, last_sequence);
       }
       PERF_TIMER_START(write_pre_and_post_process_time);
@@ -4079,7 +4076,6 @@ Status DBImpl::Write(const WriteOptions& options, WriteBatch* my_batch) {
     RecordTick(stats_, WRITE_TIMEDOUT);
   }
 
-  PERF_TIMER_STOP(write_pre_and_post_process_time);
   return status;
 }
 

db/db_iter.cc

@@ -194,9 +194,8 @@ void DBIter::Next() {
 // NOTE: In between, saved_key_ can point to a user key that has
 //       a delete marker
 inline void DBIter::FindNextUserEntry(bool skipping) {
-  PERF_TIMER_AUTO(find_next_user_entry_time);
+  PERF_TIMER_GUARD(find_next_user_entry_time);
   FindNextUserEntryInternal(skipping);
-  PERF_TIMER_STOP(find_next_user_entry_time);
 }
 
 // Actual implementation of DBIter::FindNextUserEntry()
@@ -557,9 +556,12 @@ void DBIter::Seek(const Slice& target) {
   saved_key_.Clear();
   // now savved_key is used to store internal key.
   saved_key_.SetInternalKey(target, sequence_);
-  PERF_TIMER_AUTO(seek_internal_seek_time);
-  iter_->Seek(saved_key_.GetKey());
-  PERF_TIMER_STOP(seek_internal_seek_time);
+
+  {
+    PERF_TIMER_GUARD(seek_internal_seek_time);
+    iter_->Seek(saved_key_.GetKey());
+  }
+
   if (iter_->Valid()) {
     direction_ = kForward;
     ClearSavedValue();
@@ -577,9 +579,12 @@ void DBIter::SeekToFirst() {
   }
   direction_ = kForward;
   ClearSavedValue();
-  PERF_TIMER_AUTO(seek_internal_seek_time);
-  iter_->SeekToFirst();
-  PERF_TIMER_STOP(seek_internal_seek_time);
+
+  {
+    PERF_TIMER_GUARD(seek_internal_seek_time);
+    iter_->SeekToFirst();
+  }
+
   if (iter_->Valid()) {
     FindNextUserEntry(false /* not skipping */);
   } else {
@@ -595,9 +600,11 @@ void DBIter::SeekToLast() {
   }
   direction_ = kReverse;
   ClearSavedValue();
-  PERF_TIMER_AUTO(seek_internal_seek_time);
-  iter_->SeekToLast();
-  PERF_TIMER_STOP(seek_internal_seek_time);
+
+  {
+    PERF_TIMER_GUARD(seek_internal_seek_time);
+    iter_->SeekToLast();
+  }
 
   PrevInternal();
 }

db/memtable.cc

@@ -422,7 +422,7 @@ bool MemTable::Get(const LookupKey& key, std::string* value, Status* s,
     // Avoiding recording stats for speed.
     return false;
   }
-  PERF_TIMER_AUTO(get_from_memtable_time);
+  PERF_TIMER_GUARD(get_from_memtable_time);
 
   Slice user_key = key.user_key();
   bool found_final_value = false;
@@ -452,7 +452,6 @@ bool MemTable::Get(const LookupKey& key, std::string* value, Status* s,
   if (!found_final_value && merge_in_progress) {
     *s = Status::MergeInProgress("");
   }
-  PERF_TIMER_STOP(get_from_memtable_time);
   PERF_COUNTER_ADD(get_from_memtable_count, 1);
   return found_final_value;
 }

table/format.cc

@@ -211,10 +211,13 @@ Status ReadBlock(RandomAccessFile* file, const Footer& footer,
                   const ReadOptions& options, const BlockHandle& handle,
                   Slice* contents,  /* result of reading */ char* buf) {
   size_t n = static_cast<size_t>(handle.size());
+  Status s;
+
+  {
+    PERF_TIMER_GUARD(block_read_time);
+    s = file->Read(handle.offset(), n + kBlockTrailerSize, contents, buf);
+  }
 
-  PERF_TIMER_AUTO(block_read_time);
-  Status s = file->Read(handle.offset(), n + kBlockTrailerSize, contents, buf);
-  PERF_TIMER_MEASURE(block_read_time);
   PERF_COUNTER_ADD(block_read_count, 1);
   PERF_COUNTER_ADD(block_read_byte, n + kBlockTrailerSize);
 
@@ -228,6 +231,7 @@ Status ReadBlock(RandomAccessFile* file, const Footer& footer,
   // Check the crc of the type and the block contents
   const char* data = contents->data();  // Pointer to where Read put the data
   if (options.verify_checksums) {
+    PERF_TIMER_GUARD(block_checksum_time);
     uint32_t value = DecodeFixed32(data + n + 1);
     uint32_t actual = 0;
     switch (footer.checksum()) {
@@ -247,7 +251,6 @@ Status ReadBlock(RandomAccessFile* file, const Footer& footer,
     if (!s.ok()) {
       return s;
     }
-    PERF_TIMER_STOP(block_checksum_time);
   }
   return s;
 }
@@ -265,7 +268,7 @@ Status DecompressBlock(BlockContents* result, size_t block_size,
   result->cachable = false;
   result->heap_allocated = false;
 
-  PERF_TIMER_AUTO(block_decompress_time);
+  PERF_TIMER_GUARD(block_decompress_time);
   rocksdb::CompressionType compression_type =
       static_cast<rocksdb::CompressionType>(data[n]);
   // If the caller has requested that the block not be uncompressed
@@ -295,7 +298,6 @@ Status DecompressBlock(BlockContents* result, size_t block_size,
   } else {
     s = UncompressBlockContents(data, n, result);
   }
-  PERF_TIMER_STOP(block_decompress_time);
   return s;
 }
 

table/merger.cc

@@ -116,12 +116,12 @@ class MergingIterator : public Iterator {
     // Invalidate the heap.
     use_heap_ = false;
     IteratorWrapper* first_child = nullptr;
-    PERF_TIMER_DECLARE();
 
     for (auto& child : children_) {
-      PERF_TIMER_START(seek_child_seek_time);
-      child.Seek(target);
-      PERF_TIMER_STOP(seek_child_seek_time);
+      {
+        PERF_TIMER_GUARD(seek_child_seek_time);
+        child.Seek(target);
+      }
       PERF_COUNTER_ADD(seek_child_seek_count, 1);
 
       if (child.Valid()) {
@@ -134,24 +134,21 @@ class MergingIterator : public Iterator {
           } else {
             // We have more than one children with valid keys. Initialize
             // the heap and put the first child into the heap.
-            PERF_TIMER_START(seek_min_heap_time);
+            PERF_TIMER_GUARD(seek_min_heap_time);
             ClearHeaps();
             minHeap_.push(first_child);
-            PERF_TIMER_STOP(seek_min_heap_time);
           }
         }
         if (use_heap_) {
-          PERF_TIMER_START(seek_min_heap_time);
+          PERF_TIMER_GUARD(seek_min_heap_time);
           minHeap_.push(&child);
-          PERF_TIMER_STOP(seek_min_heap_time);
         }
       }
     }
     if (use_heap_) {
       // If heap is valid, need to put the smallest key to curent_.
-      PERF_TIMER_START(seek_min_heap_time);
+      PERF_TIMER_GUARD(seek_min_heap_time);
       FindSmallest();
-      PERF_TIMER_STOP(seek_min_heap_time);
     } else {
       // The heap is not valid, then the current_ iterator is the first
       // one, or null if there is no first child.

util/perf_context_imp.h

@@ -11,11 +11,10 @@ namespace rocksdb {
 
 #if defined(NPERF_CONTEXT) || defined(IOS_CROSS_COMPILE)
 
-#define PERF_TIMER_DECLARE()
-#define PERF_TIMER_START(metric)
-#define PERF_TIMER_AUTO(metric)
+#define PERF_TIMER_GUARD(metric)
 #define PERF_TIMER_MEASURE(metric)
 #define PERF_TIMER_STOP(metric)
+#define PERF_TIMER_START(metric)
 #define PERF_COUNTER_ADD(metric, value)
 
 #else
@@ -24,10 +23,15 @@ extern __thread PerfLevel perf_level;
 
 class PerfStepTimer {
  public:
-  PerfStepTimer()
+  PerfStepTimer(uint64_t* metric)
     : enabled_(perf_level >= PerfLevel::kEnableTime),
       env_(enabled_ ? Env::Default() : nullptr),
-      start_(0) {
+      start_(0),
+      metric_(metric) {
+  }
+
+  ~PerfStepTimer() {
+    Stop();
   }
 
   void Start() {
@@ -36,17 +40,17 @@ class PerfStepTimer {
     }
   }
 
-  void Measure(uint64_t* metric) {
+  void Measure() {
     if (start_) {
       uint64_t now = env_->NowNanos();
-      *metric += now - start_;
+      *metric_ += now - start_;
       start_ = now;
     }
   }
 
-  void Stop(uint64_t* metric) {
+  void Stop() {
     if (start_) {
-      *metric += env_->NowNanos() - start_;
+      *metric_ += env_->NowNanos() - start_;
       start_ = 0;
     }
   }
@@ -55,29 +59,25 @@ class PerfStepTimer {
   const bool enabled_;
   Env* const env_;
   uint64_t start_;
+  uint64_t* metric_;
 };
 
-// Declare the local timer object to be used later on
-#define PERF_TIMER_DECLARE()           \
-  PerfStepTimer perf_step_timer;
+// Stop the timer and update the metric
+#define PERF_TIMER_STOP(metric)          \
+  perf_step_timer_ ## metric.Stop();
 
-// Set start time of the timer
 #define PERF_TIMER_START(metric)          \
-  perf_step_timer.Start();
+  perf_step_timer_ ## metric.Start();
 
 // Declare and set start time of the timer
-#define PERF_TIMER_AUTO(metric)           \
-  PerfStepTimer perf_step_timer;          \
-  perf_step_timer.Start();
+#define PERF_TIMER_GUARD(metric)           \
+  PerfStepTimer perf_step_timer_ ## metric(&(perf_context.metric));          \
+  perf_step_timer_ ## metric.Start();
 
 // Update metric with time elapsed since last START. start time is reset
 // to current timestamp.
 #define PERF_TIMER_MEASURE(metric)        \
-  perf_step_timer.Measure(&(perf_context.metric));
-
-// Update metric with time elapsed since last START. But start time is not set.
-#define PERF_TIMER_STOP(metric)        \
-  perf_step_timer.Stop(&(perf_context.metric));
+  perf_step_timer_ ## metric.Measure();
 
 // Increase metric value
 #define PERF_COUNTER_ADD(metric, value)     \