Workaround for glibc semaphore bug.

src/heap/page-parallel-job.h

 // 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.
 
 #ifndef V8_HEAP_PAGE_PARALLEL_JOB_
 #define V8_HEAP_PAGE_PARALLEL_JOB_
 
 #include "src/allocation.h"
 #include "src/cancelable-task.h"
 #include "src/utils.h"
@@ skipping 15 matching lines @@
 //                                     PerPageData page_data)
 //   The function should return true iff processing succeeded.
 // - static const bool NeedSequentialFinalization
 // - static void FinalizePageSequentially(Heap* heap,
 //                                        bool processing_succeeded,
 //                                        MemoryChunk* page,
 //                                        PerPageData page_data)
 template <typename JobTraits>
 class PageParallelJob {
  public:
-  PageParallelJob(Heap* heap, CancelableTaskManager* cancelable_task_manager)
+  // PageParallelJob cannot dynamically create a semaphore because of a bug in
+  // glibc. See http://crbug.com/609249 and
+  // https://sourceware.org/bugzilla/show_bug.cgi?id=12674.
+  // The caller must provide a semaphore with value 0 and ensure that
+  // the lifetime of the semaphore is the same as the lifetime of the Isolate.
+  // It is guaranteed that the semaphore value will be 0 after Run() call.
+  PageParallelJob(Heap* heap, CancelableTaskManager* cancelable_task_manager,
+                  base::Semaphore* semaphore)
       : heap_(heap),
         cancelable_task_manager_(cancelable_task_manager),
         items_(nullptr),
         num_items_(0),
         num_tasks_(0),
-        pending_tasks_(new base::Semaphore(0)),
-        finished_tasks_(new base::AtomicNumber<int>(0)) {}
+        pending_tasks_(semaphore) {}
 
   ~PageParallelJob() {
     Item* item = items_;
     while (item != nullptr) {
       Item* next = item->next;
       delete item;
       item = next;
     }
-    delete pending_tasks_;
-    delete finished_tasks_;
   }
 
   void AddPage(MemoryChunk* chunk, typename JobTraits::PerPageData data) {
     Item* item = new Item(chunk, data, items_);
     items_ = item;
     ++num_items_;
   }
 
   int NumberOfPages() { return num_items_; }
 
@@ skipping 14 matching lines @@
             V8::GetCurrentPlatform()->NumberOfAvailableBackgroundThreads()));
     num_tasks_ = Max(1, Min(num_tasks, max_num_tasks));
     int items_per_task = (num_items_ + num_tasks_ - 1) / num_tasks_;
     int start_index = 0;
     Task* main_task = nullptr;
     for (int i = 0; i < num_tasks_; i++, start_index += items_per_task) {
       if (start_index >= num_items_) {
         start_index -= num_items_;
       }
       Task* task = new Task(heap_, items_, num_items_, start_index,
-                            pending_tasks_, per_task_data_callback(i), this);
+                            pending_tasks_, per_task_data_callback(i));
       task_ids[i] = task->id();
       if (i > 0) {
         V8::GetCurrentPlatform()->CallOnBackgroundThread(
             task, v8::Platform::kShortRunningTask);
       } else {
         main_task = task;
       }
     }
     // Contribute on main thread.
     main_task->Run();
     delete main_task;
-    int aborted_tasks = 0;

[ulan, 2016/05/20 11:28:24]

All removed lines below are instrumentation code.

     // Wait for background tasks.
     for (int i = 0; i < num_tasks_; i++) {
       if (!cancelable_task_manager_->TryAbort(task_ids[i])) {
         pending_tasks_->Wait();
-      } else {
-        ++aborted_tasks;
       }
     }
-    int finished_tasks = finished_tasks_->Value();
-    // TODO(ulan): Remove this check after investigation of crbug.com/609249.
-    CHECK_EQ(aborted_tasks + finished_tasks, num_tasks_);
     if (JobTraits::NeedSequentialFinalization) {
       Item* item = items_;
       while (item != nullptr) {
         bool success = (item->state.Value() == kFinished);
         JobTraits::FinalizePageSequentially(heap_, item->chunk, success,
                                             item->data);
         item = item->next;
       }
     }
   }
 
-  void NotifyFinishedTask() { finished_tasks_->Increment(1); }
-
  private:
   static const int kMaxNumberOfTasks = 10;
 
   enum ProcessingState { kAvailable, kProcessing, kFinished, kFailed };
 
   struct Item : public Malloced {
     Item(MemoryChunk* chunk, typename JobTraits::PerPageData data, Item* next)
         : chunk(chunk), state(kAvailable), data(data), next(next) {}
     MemoryChunk* chunk;
     base::AtomicValue<ProcessingState> state;
     typename JobTraits::PerPageData data;
     Item* next;
   };
 
   class Task : public CancelableTask {
    public:
     Task(Heap* heap, Item* items, int num_items, int start_index,
-         base::Semaphore* on_finish, typename JobTraits::PerTaskData data,
-         PageParallelJob<JobTraits>* job)
+         base::Semaphore* on_finish, typename JobTraits::PerTaskData data)
         : CancelableTask(heap->isolate()),
           heap_(heap),
           items_(items),
           num_items_(num_items),
           start_index_(start_index),
           on_finish_(on_finish),
-          data_(data),
-          job_(job) {}
+          data_(data) {}
 
     virtual ~Task() {}
 
    private:
     // v8::internal::CancelableTask overrides.
     void RunInternal() override {
       // Each task starts at a different index to improve parallelization.
       Item* current = items_;
       int skip = start_index_;
       while (skip-- > 0) {
         current = current->next;
       }
       for (int i = 0; i < num_items_; i++) {
         if (current->state.TrySetValue(kAvailable, kProcessing)) {
           bool success = JobTraits::ProcessPageInParallel(
               heap_, data_, current->chunk, current->data);
           current->state.SetValue(success ? kFinished : kFailed);
         }
         current = current->next;
         // Wrap around if needed.
         if (current == nullptr) {
           current = items_;
         }
       }
-      job_->NotifyFinishedTask();
-      on_finish_->Signal("PageParallelJob::Task::RunInternal");
+      on_finish_->Signal();
     }
 
     Heap* heap_;
     Item* items_;
     int num_items_;
     int start_index_;
     base::Semaphore* on_finish_;
     typename JobTraits::PerTaskData data_;
-    PageParallelJob<JobTraits>* job_;
     DISALLOW_COPY_AND_ASSIGN(Task);
   };
 
   Heap* heap_;
   CancelableTaskManager* cancelable_task_manager_;
   Item* items_;
   int num_items_;
   int num_tasks_;
   base::Semaphore* pending_tasks_;
-  base::AtomicNumber<int>* finished_tasks_;
   DISALLOW_COPY_AND_ASSIGN(PageParallelJob);
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_HEAP_PAGE_PARALLEL_JOB_