Make TimelineEventBlocks reclaimable

runtime/vm/timeline.cc

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include <cstdlib>
 
 #include "vm/atomic.h"
 #include "vm/isolate.h"
 #include "vm/json_stream.h"
 #include "vm/lockers.h"
 #include "vm/log.h"
 #include "vm/object.h"
 #include "vm/thread.h"
 #include "vm/timeline.h"
 
 namespace dart {
 
 DEFINE_FLAG(bool, complete_timeline, false, "Record the complete timeline");
 DEFINE_FLAG(bool, trace_timeline, false,
             "Trace timeline backend");
 DEFINE_FLAG(bool, trace_timeline_analysis, false,
             "Trace timeline analysis backend");
 DEFINE_FLAG(bool, timing, false,
             "Dump isolate timing information from timeline.");
 DEFINE_FLAG(charp, timeline_dir, NULL,
             "Enable all timeline trace streams and output VM global trace "
             "into specified directory.");
 
+// Implementation notes:
+//
+// Writing events:
+// |TimelineEvent|s are written into |TimelineEventBlock|s. Each |Thread| caches
+// a |TimelineEventBlock| in TLS so that it can write events without
+// synchronizing with other threads in the system. Even though the |Thread| owns
+// the |TimelineEventBlock| the block may need to be reclaimed by the reporting
+// system. To support that, a |Thread| must hold its |timeline_block_lock_|
+// when operating on the |TimelineEventBlock|. This lock will only ever be
+// busy if blocks are being reclaimed by the reporting system.
+//
+// Reporting:
+// When requested, the timeline is serialized in the trace-event format
+// (https://goo.gl/hDZw5M). The request can be for a VM-wide timeline or an
+// isolate specific timeline. In both cases it may be that a thread has
+// a |TimelineEventBlock| cached in TLS. In order to report a complete timeline
+// the cached |TimelineEventBlock|s need to be reclaimed.
+//
+// Reclaiming open |TimelineEventBlock|s for an isolate:
+//
+// Cached |TimelineEventBlock|s can be in two places:
+// 1) In a |Thread| (Thread currently in an |Isolate|)
+// 2) In a |Thread::State| (Thread not currently in an |Isolate|).
+//
+// As a |Thread| enters and exits an |Isolate|, a |TimelineEventBlock|
+// will move between (1) and (2).
+//
+// The first case occurs for |Thread|s that are currently running inside an
+// isolate. The second case occurs for |Thread|s that are not currently
+// running inside an isolate.
+//
+// To reclaim the first case, we take the |Thread|'s |timeline_block_lock_|
+// and reclaim the cached block.
+//
+// To reclaim the second case, we can take the |ThreadRegistry| lock and
+// reclaim these blocks.
+//
+// |Timeline::ReclaimIsolateBlocks| and |Timeline::ReclaimAllBlocks| are
+// the two utility methods used to reclaim blocks before reporting.
+//
+// Locking notes:
+// The following locks are used by the timeline system:
+// - |TimelineEventRecorder::lock_| This lock is held whenever a
+// |TimelineEventBlock| is being requested or reclaimed.
+// - |Thread::timeline_block_lock_| This lock is held whenever a |Thread|'s
+// cached block is being operated on.
+// - |ThreadRegistry::monitor_| This lock protects the cached block for
+// unscheduled threads of an isolate.
+// - |Isolate::isolates_list_monitor_| This lock protects the list of
+// isolates in the system.
+//
+// Locks must always be taken in the following order:
+// |Isolate::isolates_list_monitor_|
+//   |ThreadRegistry::monitor_|
+//     |Thread::timeline_block_lock_|
+//       |TimelineEventRecorder::lock_|
+//
+
 void Timeline::InitOnce() {
   ASSERT(recorder_ == NULL);
   // Default to ring recorder being enabled.
   const bool use_ring_recorder = true;
   // Some flags require that we use the endless recorder.
   const bool use_endless_recorder =
       (FLAG_timeline_dir != NULL) || FLAG_timing;
   if (use_endless_recorder) {
     recorder_ = new TimelineEventEndlessRecorder();
   } else if (use_ring_recorder) {
@@ skipping 31 matching lines @@
   return (FLAG_timeline_dir != NULL) || FLAG_timing;
 }
 
 
 TimelineStream* Timeline::GetVMStream() {
   ASSERT(vm_stream_ != NULL);
   return vm_stream_;
 }
 
 
+void Timeline::ReclaimIsolateBlocks() {
+  if (recorder() == NULL) {
+    return;
+  }

[turnidge, 2015/09/24 17:05:52]

This check is redundant (also in callee).

[Cutch, 2015/09/24 18:14:16]

Done.

+  ReclaimBlocksForIsolate(Isolate::Current());
+}
+
+
+class ReclaimBlocksIsolateVisitor : public IsolateVisitor {
+ public:
+  ReclaimBlocksIsolateVisitor() {}
+
+  virtual void VisitIsolate(Isolate* isolate) {
+    Timeline::ReclaimBlocksForIsolate(isolate);
+  }
+
+ private:
+};
+
+
+void Timeline::ReclaimAllBlocks() {
+  if (recorder() == NULL) {
+    return;
+  }
+  // Reclaim all blocks cached for all isolates.
+  ReclaimBlocksIsolateVisitor visitor;
+  Isolate::VisitIsolates(&visitor);
+  // Reclaim the global VM block.
+  recorder()->ReclaimGlobalBlock();
+}
+
+
+void Timeline::ReclaimBlocksForIsolate(Isolate* isolate) {
+  if (recorder() == NULL) {
+    return;
+  }
+  if (isolate == NULL) {
+    return;
+  }

[turnidge, 2015/09/24 17:05:52]

Consider an ASSERT for isolate != NULL?

[Cutch, 2015/09/24 18:14:16]

Done.

+  isolate->ReclaimTimelineBlocks();
+}
+
+
 TimelineEventRecorder* Timeline::recorder_ = NULL;
 TimelineStream* Timeline::vm_stream_ = NULL;
 
 #define ISOLATE_TIMELINE_STREAM_DEFINE_FLAG(name, enabled_by_default)          \
   bool Timeline::stream_##name##_enabled_ = false;
   ISOLATE_TIMELINE_STREAM_LIST(ISOLATE_TIMELINE_STREAM_DEFINE_FLAG)
 #undef ISOLATE_TIMELINE_STREAM_DEFINE_FLAG
 
 TimelineEvent::TimelineEvent()
     : timestamp0_(0),
@@ skipping 297 matching lines @@
     : global_block_(NULL),
       async_id_(0) {
 }
 
 
 void TimelineEventRecorder::PrintJSONMeta(JSONArray* events) const {
 }
 
 
 TimelineEvent* TimelineEventRecorder::ThreadBlockStartEvent() {
-  // Grab the thread's timeline event block.
+  // Grab the current thread.
   Thread* thread = Thread::Current();
   ASSERT(thread != NULL);
+  // We are accessing the thread's timeline block- so take the lock.
+  MutexLocker ml(thread->timeline_block_lock());
 
   if (thread->isolate() == NULL) {
     // Non-isolate thread case. This should be infrequent.
     return GlobalBlockStartEvent();
   }
 
   TimelineEventBlock* thread_block = thread->timeline_block();
 
   if ((thread_block != NULL) && thread_block->IsFull()) {
     MutexLocker ml(&lock_);
@@ skipping 43 matching lines @@
 
 
 void TimelineEventRecorder::WriteTo(const char* directory) {
   Dart_FileOpenCallback file_open = Isolate::file_open_callback();
   Dart_FileWriteCallback file_write = Isolate::file_write_callback();
   Dart_FileCloseCallback file_close = Isolate::file_close_callback();
   if ((file_open == NULL) || (file_write == NULL) || (file_close == NULL)) {
     return;
   }
 
-  FinishGlobalBlock();
+  Timeline::ReclaimAllBlocks();
 
   JSONStream js;
   TimelineEventFilter filter;
   PrintJSON(&js, &filter);
 
   intptr_t pid = OS::ProcessId();
   char* filename = OS::SCreate(NULL,
       "%s/dart-timeline-%" Pd ".json", directory, pid);
   void* file = (*file_open)(filename, true);
   if (file == NULL) {
     OS::Print("Failed to write timeline file: %s\n", filename);
     free(filename);
     return;
   }
   free(filename);
   (*file_write)(js.buffer()->buf(), js.buffer()->length(), file);
   (*file_close)(file);
 }
 
 
-void TimelineEventRecorder::FinishGlobalBlock() {
+void TimelineEventRecorder::ReclaimGlobalBlock() {
   MutexLocker ml(&lock_);
   if (global_block_ != NULL) {
     global_block_->Finish();
     global_block_ = NULL;
   }
 }
 
 
 int64_t TimelineEventRecorder::GetNextAsyncId() {
   // TODO(johnmccutchan): Gracefully handle wrap around.
@@ skipping 368 matching lines @@
 
 
 TimelineEventBlock* TimelineEventBlockIterator::Next() {
   ASSERT(current_ != NULL);
   TimelineEventBlock* r = current_;
   current_ = current_->next();
   return r;
 }
 
 }  // namespace dart