sync with upstream @21706995

Fixed race condition reported by Dave Smit (dizzyd@dizzyd,com)
on the leveldb mailing list.  We were not signalling
waiters after a trivial move from level-0.  The result was
that in some cases (hard to reproduce), a write would get
stuck forever waiting for the number of level-0 files to drop
below its hard limit.

The new code is simpler: there is just one condition variable
instead of two, and the condition variable is signalled after
every piece of background work finishes.  Also, all compaction
work (including for manual compactions) is done in the
background thread, and therefore we can remove the
"compacting_" variable.



git-svn-id: https://leveldb.googlecode.com/svn/trunk@31 62dab493-f737-651d-591e-8d6aee1b9529

db/db_impl.cc

@@ -119,13 +119,12 @@ DBImpl::DBImpl(const Options& options, const std::string& dbname)
       db_lock_(NULL),
       shutting_down_(NULL),
       bg_cv_(&mutex_),
-      compacting_cv_(&mutex_),
       mem_(new MemTable(internal_comparator_)),
       imm_(NULL),
       logfile_(NULL),
       log_(NULL),
       bg_compaction_scheduled_(false),
-      compacting_(false) {
+      manual_compaction_(NULL) {
   mem_->Ref();
   has_imm_.Release_Store(NULL);
 
@@ -141,10 +140,8 @@ DBImpl::~DBImpl() {
   // Wait for background work to finish
   mutex_.Lock();
   shutting_down_.Release_Store(this);  // Any non-NULL value is ok
-  if (bg_compaction_scheduled_) {
-    while (bg_compaction_scheduled_) {
-      bg_cv_.Wait();
-    }
+  while (bg_compaction_scheduled_) {
+    bg_cv_.Wait();
   }
   mutex_.Unlock();
 
@@ -437,7 +434,6 @@ Status DBImpl::WriteLevel0Table(MemTable* mem, VersionEdit* edit) {
 Status DBImpl::CompactMemTable() {
   mutex_.AssertHeld();
   assert(imm_ != NULL);
-  assert(compacting_);
 
   // Save the contents of the memtable as a new Table
   VersionEdit edit;
@@ -457,7 +453,6 @@ Status DBImpl::CompactMemTable() {
     DeleteObsoleteFiles();
   }
 
-  compacting_cv_.SignalAll();  // Wake up waiter even if there was an error
   return s;
 }
 
@@ -466,22 +461,18 @@ void DBImpl::TEST_CompactRange(
     const std::string& begin,
     const std::string& end) {
   MutexLock l(&mutex_);
-  while (compacting_) {
-    compacting_cv_.Wait();
+  while (manual_compaction_ != NULL) {
+    bg_cv_.Wait();
   }
-  Compaction* c = versions_->CompactRange(
-      level,
-      InternalKey(begin, kMaxSequenceNumber, kValueTypeForSeek),
-      InternalKey(end, 0, static_cast<ValueType>(0)));
-
-  if (c != NULL) {
-    CompactionState* compact = new CompactionState(c);
-    DoCompactionWork(compact);  // Ignore error in test compaction
-    CleanupCompaction(compact);
-  }
-
-  // Start any background compaction that may have been delayed by this thread
+  ManualCompaction manual;
+  manual.level = level;
+  manual.begin = begin;
+  manual.end = end;
+  manual_compaction_ = &manual;
   MaybeScheduleCompaction();
+  while (manual_compaction_ == &manual) {
+    bg_cv_.Wait();
+  }
 }
 
 Status DBImpl::TEST_CompactMemTable() {
@@ -490,7 +481,7 @@ Status DBImpl::TEST_CompactMemTable() {
   if (s.ok()) {
     // Wait until the compaction completes
     while (imm_ != NULL && bg_error_.ok()) {
-      compacting_cv_.Wait();
+      bg_cv_.Wait();
     }
     if (imm_ != NULL) {
       s = bg_error_;
@@ -503,11 +494,11 @@ void DBImpl::MaybeScheduleCompaction() {
   mutex_.AssertHeld();
   if (bg_compaction_scheduled_) {
     // Already scheduled
-  } else if (compacting_) {
-    // Some other thread is running a compaction.  Do not conflict with it.
   } else if (shutting_down_.Acquire_Load()) {
     // DB is being deleted; no more background compactions
-  } else if (imm_ == NULL && !versions_->NeedsCompaction()) {
+  } else if (imm_ == NULL &&
+             manual_compaction_ == NULL &&
+             !versions_->NeedsCompaction()) {
     // No work to be done
   } else {
     bg_compaction_scheduled_ = true;
@@ -522,38 +513,41 @@ void DBImpl::BGWork(void* db) {
 void DBImpl::BackgroundCall() {
   MutexLock l(&mutex_);
   assert(bg_compaction_scheduled_);
-  if (!shutting_down_.Acquire_Load() &&
-      !compacting_) {
+  if (!shutting_down_.Acquire_Load()) {
     BackgroundCompaction();
   }
   bg_compaction_scheduled_ = false;
-  bg_cv_.SignalAll();
 
   // Previous compaction may have produced too many files in a level,
   // so reschedule another compaction if needed.
   MaybeScheduleCompaction();
+  bg_cv_.SignalAll();
 }
 
 void DBImpl::BackgroundCompaction() {
   mutex_.AssertHeld();
-  assert(!compacting_);
 
   if (imm_ != NULL) {
-    compacting_ = true;
     CompactMemTable();
-    compacting_ = false;
-    compacting_cv_.SignalAll();
     return;
   }
 
-  Compaction* c = versions_->PickCompaction();
-  if (c == NULL) {
-    // Nothing to do
-    return;
+  Compaction* c;
+  bool is_manual = (manual_compaction_ != NULL);
+  if (is_manual) {
+    const ManualCompaction* m = manual_compaction_;
+    c = versions_->CompactRange(
+        m->level,
+        InternalKey(m->begin, kMaxSequenceNumber, kValueTypeForSeek),
+        InternalKey(m->end, 0, static_cast<ValueType>(0)));
+  } else {
+    c = versions_->PickCompaction();
   }
 
   Status status;
-  if (c->IsTrivialMove()) {
+  if (c == NULL) {
+    // Nothing to do
+  } else if (!is_manual && c->IsTrivialMove()) {
     // Move file to next level
     assert(c->num_input_files(0) == 1);
     FileMetaData* f = c->input(0, 0);
@@ -561,11 +555,13 @@ void DBImpl::BackgroundCompaction() {
     c->edit()->AddFile(c->level() + 1, f->number, f->file_size,
                        f->smallest, f->largest);
     status = versions_->LogAndApply(c->edit());
-    Log(env_, options_.info_log, "Moved #%lld to level-%d %lld bytes %s\n",
+    VersionSet::LevelSummaryStorage tmp;
+    Log(env_, options_.info_log, "Moved #%lld to level-%d %lld bytes %s: %s\n",
         static_cast<unsigned long long>(f->number),
         c->level() + 1,
         static_cast<unsigned long long>(f->file_size),
-        status.ToString().c_str());
+        status.ToString().c_str(),
+        versions_->LevelSummary(&tmp));
   } else {
     CompactionState* compact = new CompactionState(c);
     status = DoCompactionWork(compact);
@@ -584,6 +580,11 @@ void DBImpl::BackgroundCompaction() {
       bg_error_ = status;
     }
   }
+
+  if (is_manual) {
+    // Mark it as done
+    manual_compaction_ = NULL;
+  }
 }
 
 void DBImpl::CleanupCompaction(CompactionState* compact) {
@@ -734,7 +735,6 @@ Status DBImpl::DoCompactionWork(CompactionState* compact) {
   }
 
   // Release mutex while we're actually doing the compaction work
-  compacting_ = true;
   mutex_.Unlock();
 
   Iterator* input = versions_->MakeInputIterator(compact->compaction);
@@ -751,7 +751,7 @@ Status DBImpl::DoCompactionWork(CompactionState* compact) {
       mutex_.Lock();
       if (imm_ != NULL) {
         CompactMemTable();
-        compacting_cv_.SignalAll();  // Wakeup MakeRoomForWrite() if necessary
+        bg_cv_.SignalAll();  // Wakeup MakeRoomForWrite() if necessary
       }
       mutex_.Unlock();
       imm_micros += (env_->NowMicros() - imm_start);
@@ -867,8 +867,6 @@ Status DBImpl::DoCompactionWork(CompactionState* compact) {
   if (status.ok()) {
     status = InstallCompactionResults(compact);
   }
-  compacting_ = false;
-  compacting_cv_.SignalAll();
   VersionSet::LevelSummaryStorage tmp;
   Log(env_, options_.info_log,
       "compacted to: %s", versions_->LevelSummary(&tmp));
@@ -1038,10 +1036,11 @@ Status DBImpl::MakeRoomForWrite(bool force) {
     } else if (imm_ != NULL) {
       // We have filled up the current memtable, but the previous
       // one is still being compacted, so we wait.
-      compacting_cv_.Wait();
+      bg_cv_.Wait();
     } else if (versions_->NumLevelFiles(0) >= config::kL0_StopWritesTrigger) {
       // There are too many level-0 files.
-      compacting_cv_.Wait();
+      Log(env_, options_.info_log, "waiting...\n");
+      bg_cv_.Wait();
     } else {
       // Attempt to switch to a new memtable and trigger compaction of old
       assert(versions_->PrevLogNumber() == 0);

db/db_impl.h

@@ -119,8 +119,7 @@ class DBImpl : public DB {
   // State below is protected by mutex_
   port::Mutex mutex_;
   port::AtomicPointer shutting_down_;
-  port::CondVar bg_cv_;          // Signalled when !bg_compaction_scheduled_
-  port::CondVar compacting_cv_;  // Signalled when !compacting_
+  port::CondVar bg_cv_;          // Signalled when background work finishes
   MemTable* mem_;
   MemTable* imm_;                // Memtable being compacted
   port::AtomicPointer has_imm_;  // So bg thread can detect non-NULL imm_
@@ -135,8 +134,13 @@ class DBImpl : public DB {
   // Has a background compaction been scheduled or is running?
   bool bg_compaction_scheduled_;
 
-  // Is there a compaction running?
-  bool compacting_;
+  // Information for a manual compaction
+  struct ManualCompaction {
+    int level;
+    std::string begin;
+    std::string end;
+  };
+  ManualCompaction* manual_compaction_;
 
   VersionSet* versions_;