Use idle time to make progress on scheduled compilation jobs

src/compiler-dispatcher/compiler-dispatcher.cc

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/compiler-dispatcher/compiler-dispatcher.h"
 
+#include "include/v8-platform.h"
+#include "include/v8.h"
+#include "src/base/platform/time.h"
+#include "src/cancelable-task.h"
 #include "src/compiler-dispatcher/compiler-dispatcher-job.h"
 #include "src/compiler-dispatcher/compiler-dispatcher-tracer.h"
 #include "src/objects-inl.h"
 
 namespace v8 {
 namespace internal {
 
 namespace {
 
-bool DoNextStepOnMainThread(CompilerDispatcherJob* job) {
+enum class ExceptionHandling { kSwallow, kKeep };

[rmcilroy, 2016/12/16 12:16:07]

nit - Keep->Throw ?

+
+bool DoNextStepOnMainThread(Isolate* isolate, CompilerDispatcherJob* job,
+                            ExceptionHandling exception_handling) {
+  DCHECK(ThreadId::Current().Equals(isolate->thread_id()));
+  v8::TryCatch try_catch(reinterpret_cast<v8::Isolate*>(isolate));
   switch (job->status()) {
     case CompileJobStatus::kInitial:
       job->PrepareToParseOnMainThread();
       break;
 
     case CompileJobStatus::kReadyToParse:
       job->Parse();
       break;
 
     case CompileJobStatus::kParsed:
@@ skipping 10 matching lines @@
 
     case CompileJobStatus::kCompiled:
       job->FinalizeCompilingOnMainThread();
       break;
 
     case CompileJobStatus::kFailed:
     case CompileJobStatus::kDone:
       break;
   }
 
+  if (exception_handling == ExceptionHandling::kKeep && try_catch.HasCaught()) {
+    DCHECK(job->status() == CompileJobStatus::kFailed);
+    try_catch.ReThrow();
+  }
   return job->status() != CompileJobStatus::kFailed;
 }
 
 bool IsFinished(CompilerDispatcherJob* job) {
   return job->status() == CompileJobStatus::kDone ||
          job->status() == CompileJobStatus::kFailed;
 }
 
+// Theoretically we get 50ms of idle time max, however it's unlikely that
+// we'll get all of it so try to be a conservative.
+const double kMaxIdleTimeToExpectInMs = 40;
+
 }  // namespace
 
-CompilerDispatcher::CompilerDispatcher(Isolate* isolate, size_t max_stack_size)
+class CompilerDispatcher::IdleTask : public CancelableIdleTask {
+ public:
+  IdleTask(Isolate* isolate, CompilerDispatcher* dispatcher);
+  ~IdleTask() override;
+
+  // CancelableIdleTask implementation.
+  void RunInternal(double deadline_in_seconds) override;
+
+ private:
+  CompilerDispatcher* dispatcher_;
+
+  DISALLOW_COPY_AND_ASSIGN(IdleTask);
+};
+
+CompilerDispatcher::IdleTask::IdleTask(Isolate* isolate,
+                                       CompilerDispatcher* dispatcher)
+    : CancelableIdleTask(isolate), dispatcher_(dispatcher) {}
+
+CompilerDispatcher::IdleTask::~IdleTask() {}
+
+void CompilerDispatcher::IdleTask::RunInternal(double deadline_in_seconds) {
+  dispatcher_->DoIdleWork(deadline_in_seconds);
+}
+
+CompilerDispatcher::CompilerDispatcher(Isolate* isolate, Platform* platform,
+                                       size_t max_stack_size)
     : isolate_(isolate),
+      platform_(platform),
       max_stack_size_(max_stack_size),
-      tracer_(new CompilerDispatcherTracer(isolate_)) {}
+      tracer_(new CompilerDispatcherTracer(isolate_)),
+      idle_task_scheduled_(false) {}
 
-CompilerDispatcher::~CompilerDispatcher() {}
+CompilerDispatcher::~CompilerDispatcher() {
+  // To avoid crashing in unit tests due to unfished jobs.
+  AbortAll(BlockingBehavior::kBlock);
+}
 
 bool CompilerDispatcher::Enqueue(Handle<SharedFunctionInfo> function) {
   // We only handle functions (no eval / top-level code / wasm) that are
   // attached to a script.
   if (!function->script()->IsScript() || !function->is_function() ||
       function->asm_function() || function->native()) {
     return false;
   }
 
   if (IsEnqueued(function)) return true;
   std::unique_ptr<CompilerDispatcherJob> job(new CompilerDispatcherJob(
       isolate_, tracer_.get(), function, max_stack_size_));
   std::pair<int, int> key(Script::cast(function->script())->id(),
                           function->function_literal_id());
   jobs_.insert(std::make_pair(key, std::move(job)));
+  ScheduleIdleTaskIfNeeded();
   return true;
 }
 
 bool CompilerDispatcher::IsEnqueued(Handle<SharedFunctionInfo> function) const {
   return GetJobFor(function) != jobs_.end();
 }
 
 bool CompilerDispatcher::FinishNow(Handle<SharedFunctionInfo> function) {
   JobMap::const_iterator job = GetJobFor(function);
   CHECK(job != jobs_.end());
 
   // TODO(jochen): Check if there's an in-flight background task working on this
   // job.
   while (!IsFinished(job->second.get())) {
-    DoNextStepOnMainThread(job->second.get());
+    DoNextStepOnMainThread(isolate_, job->second.get(),
+                           ExceptionHandling::kKeep);
   }
   bool result = job->second->status() != CompileJobStatus::kFailed;
+  job->second->ResetOnMainThread();
   jobs_.erase(job);
   return result;
 }
 
 void CompilerDispatcher::Abort(Handle<SharedFunctionInfo> function,
                                BlockingBehavior blocking) {
   USE(blocking);
   JobMap::const_iterator job = GetJobFor(function);
   CHECK(job != jobs_.end());
 
   // TODO(jochen): Check if there's an in-flight background task working on this
   // job.
+  job->second->ResetOnMainThread();
   jobs_.erase(job);
 }
 
 void CompilerDispatcher::AbortAll(BlockingBehavior blocking) {
   USE(blocking);
   // TODO(jochen): Check if there's an in-flight background task working on this
   // job.
+  for (auto& kv : jobs_) {
+    kv.second->ResetOnMainThread();
+  }
   jobs_.clear();
 }
 
 CompilerDispatcher::JobMap::const_iterator CompilerDispatcher::GetJobFor(
     Handle<SharedFunctionInfo> shared) const {
   if (!shared->script()->IsScript()) return jobs_.end();
   std::pair<int, int> key(Script::cast(shared->script())->id(),
                           shared->function_literal_id());
   auto range = jobs_.equal_range(key);
   for (auto job = range.first; job != range.second; ++job) {
     if (job->second->IsAssociatedWith(shared)) return job;
   }
   return jobs_.end();
 }
 
+void CompilerDispatcher::ScheduleIdleTaskIfNeeded() {
+  v8::Isolate* v8_isolate = reinterpret_cast<v8::Isolate*>(isolate_);
+  if (!platform_->IdleTasksEnabled(v8_isolate)) return;
+  if (idle_task_scheduled_) return;
+  if (jobs_.empty()) return;
+  idle_task_scheduled_ = true;
+  platform_->CallIdleOnForegroundThread(v8_isolate,
+                                        new IdleTask(isolate_, this));
+}
+
+void CompilerDispatcher::DoIdleWork(double deadline_in_seconds) {
+  idle_task_scheduled_ = false;
+
+  // Number of jobs that are unlikely to make progress during any idle callback
+  // due to their estimated duration.
+  size_t too_long_jobs = 0;
+
+  // Iterate over all available jobs & remaining time. For each job, decide
+  // whether to 1) skip it (if it would take too long), 2) erase it (if it's
+  // finished), or 3) make progress on it.
+  double idle_time_in_seconds =
+      deadline_in_seconds - platform_->MonotonicallyIncreasingTime();
+  for (auto job = jobs_.begin();
+       job != jobs_.end() && idle_time_in_seconds > 0.0;
+       idle_time_in_seconds =
+           deadline_in_seconds - platform_->MonotonicallyIncreasingTime()) {
+    double estimate_in_ms = job->second->EstimateRuntimeOfNextStepInMs();
+    if (idle_time_in_seconds <
+        (estimate_in_ms /
+         static_cast<double>(base::Time::kMillisecondsPerSecond))) {
+      // If there's not enough time left, try to estimate whether we would
+      // have managed to finish the job in a large idle task to assess
+      // whether we should ask for another idle callback.
+      if (estimate_in_ms > kMaxIdleTimeToExpectInMs) ++too_long_jobs;
+      ++job;
+    } else if (IsFinished(job->second.get())) {

[rmcilroy, 2016/12/16 12:16:07]

Question - do we always estimate that finishing a job takes zero time? Just
wondering whether finishing jobs shouldn't care about idle time remaining?

[jochen (gone - plz use gerrit), 2016/12/16 12:22:50]

you mean the "ResetOnMainThread" operation (IsFinished() just checks the
status). That just frees the memory held by the job. Of course that can take
arbitrarily long if the system is swapping, but then you got bigger problems...

[rmcilroy, 2016/12/16 12:37:38]

i was more worried about us estimaring a time and never getting to finalize the
job. i see now you always estinate 0.0 for these phases so this is good (hard to
jump about CL reviewing on a phone....)
.

+      job->second->ResetOnMainThread();
+      job = jobs_.erase(job);
+      break;
+    } else {
+      // Do one step, and keep processing the job (as we don't advance the
+      // iterator).
+      DoNextStepOnMainThread(isolate_, job->second.get(),
+                             ExceptionHandling::kSwallow);

[rmcilroy, 2016/12/16 12:16:07]

Do we loose the exception here or rethrow when finalising? 

[jochen (gone - plz use gerrit), 2016/12/16 12:22:50]

we lose it. DoNextStepOnMainThread also finalizes. That means that the SFI still
has the CompileLazy stub, and once we execute it, we compile on the main thread
and throw again.

[rmcilroy, 2016/12/16 12:37:39]

Acknowledged.

+    }
+  }
+  if (jobs_.size() > too_long_jobs) ScheduleIdleTaskIfNeeded();
+}
+
 }  // namespace internal
 }  // namespace v8