Reland "Second try at using LazilyDeallocatedDeque instead of circular_deque in TaskQueue"

This reverts commit c8c4a655.

Reason for revert: I fixed a bug in LazilyDeallocatedDeque here https://chromium-review.googlesource.com/c/chromium/src/+/1253982 which might be responsible for the crashes.  Lets re-enable LazilyDeallocatedDeque and see.

Original change's description:
> Revert "Second try at using LazilyDeallocatedDeque instead of circular_deque in TaskQueue"
> 
> This reverts commit 6410ee3d.
> 
> Reason for revert: This is causing some crashes.
> 
> Original change's description:
> > Second try at using LazilyDeallocatedDeque instead of circular_deque in TaskQueue
> > 
> > Previous patch: https://chromium-review.googlesource.com/c/chromium/src/+/1080792
> > 
> > Our usage pattern is unfortunate for existing queues such as
> > base::circular_deque.  We tend to fill up an empty queue and then drain all
> > those tasks until it's empty.  This means the queue yo-yos in size which
> > confuses the memory reclamation schemes of most queues.
> > 
> > As an optimisation we introduce a deque specialised for TaskQueueManager's
> > usage patterns. For performance (memory allocation isn't free) we don't
> > automatically reclaim memory when the queue becomes empty.  Instead we rely
> > on the surrounding code periodically calling MaybeShrinkQueue, ideally when
> > the queue is empty.
> > 
> > We keep track of the maximum recent queue size and rate limit
> > how often MaybeShrinkQueue actually shrinks the buffer to avoid unnecessary
> > churn.
> > 
> > This yields a nice win on our microbenchmark:
> > 
> > Patch: us/run for 10000 delayed tasks with N queues
> > 1 queue            4 queues           8 queues           32 queues
> > 33448.166666666664 33215.75496688742   33484.34           34018.37414965987
> > 33972.18243243243  33846.91891891892   34489.737931034484 34727.90277777778
> > 33367.90666666667  33167.54304635762   33392.96           33906.89864864865
> > 33392.13333333333  33107.17763157895   33340.18           33718.73825503356
> > 37921.01515151515  39379.06299212598   38851.27906976744  39366.03125
> > 38171.564885496184 37401.72388059701   37640.32330827068  37800.51127819549
> > 34691.2275862069   34359.61643835616   34993.468531468534 35366.795774647886
> > 35981.20863309353  35089.18881118881   38530.230769230766 39280.3515625
> > 39262.8671875      36411.384057971016  33576.10067114094  33939.69594594595
> > 37913.59848484849  38324.076335877864  38061.59848484849  39921.00793650794
> > Average 35812.1871 35430.24471         35636.02188        36204.63076
> > 
> > ToT: us/run for 10000 delayed tasks with N queues
> > 1 queue            4 queues           8 queues           32 queues
> > 40459.540322580644 40536.04838709677  38994.573643410855 38696.2
> > 39422.149606299216 39299.5            37888.18939393939  37874.74436090225
> > 38419.70229007633  38025.742424242424 37844.41353383459  38020.469696969696
> > 35052.72027972028  38147.80303030303  35504.89361702128  34138.02721088436
> > 37096.77777777778  34942.541666666664 37003.529411764706 37579.60447761194
> > 38818.67441860465  38233.068702290075 37978.628787878784 37867.57142857143
> > 38455.49618320611  37903.05303030303  38106.143939393936 38129.5
> > 40609.33064516129  37721.75187969925  34656.441379310345 34294.33561643836
> > 35273.704225352114 34646.324137931035 34335.643835616436 34311.82876712329
> > 35821.41428571429  35362.035211267605 37522.27611940299  35429.281690140844
> > Average 37942.951  37481.78685        36983.47337        36634.15632
> > 
> > Percentage improvement
> > 5.61570422	5.473437399	3.643388159	1.172472933
> > 
> > NB the reason the improvement goes down with the number of queues is because
> > we're saving malloc overhead in the queue, but a constant number of tasks are
> > posted across N queues.  This means the more queues we have in this test, the
> > less loaded the queues are individually.
> > 
> > Change-Id: I975d7f864dc55715fb9f949ef65321da93e4cef4
> > Reviewed-on: https://chromium-review.googlesource.com/1169043
> > Reviewed-by: Sami Kyöstilä <skyostil@chromium.org>
> > Commit-Queue: Alex Clarke <alexclarke@chromium.org>
> > Cr-Commit-Position: refs/heads/master@{#582586}
> 
> TBR=skyostil@chromium.org,alexclarke@chromium.org
> 
> # Not skipping CQ checks because original CL landed > 1 day ago.
> 
> Change-Id: Id8290646dba1dcea9fcf92d490b9ce4ac63ae702
> Reviewed-on: https://chromium-review.googlesource.com/1177561
> Reviewed-by: Alex Clarke <alexclarke@chromium.org>
> Reviewed-by: Sami Kyöstilä <skyostil@chromium.org>
> Commit-Queue: Alex Clarke <alexclarke@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#584314}

TBR=skyostil@chromium.org,alexclarke@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Change-Id: Ia3931cc50bc18fda4df3f385927498728c7a2e8f
Reviewed-on: https://chromium-review.googlesource.com/1254301Reviewed-by: Alex Clarke <alexclarke@chromium.org>
Reviewed-by: Sami Kyöstilä <skyostil@chromium.org>
Commit-Queue: Alex Clarke <alexclarke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#595772}

base/task/sequence_manager/task_queue_impl.cc

@@ -332,6 +332,10 @@ void TaskQueueImpl::ReloadEmptyImmediateQueue(TaskDeque* queue) {
   AutoLock immediate_incoming_queue_lock(immediate_incoming_queue_lock_);
   queue->swap(immediate_incoming_queue());
 
+  // Since |immediate_incoming_queue| is empty, now is a good time to consider
+  // reducing it's capacity if we're wasting memory.
+  immediate_incoming_queue().MaybeShrinkQueue();
+
   // Activate delayed fence if necessary. This is ideologically similar to
   // ActivateDelayedFenceIfNeeded, but due to immediate tasks being posted
   // from any thread we can't generate an enqueue order for the fence there,
@@ -509,6 +513,13 @@ void TaskQueueImpl::AsValueInto(TimeTicks now,
   state->SetInteger("delayed_work_queue_size",
                     main_thread_only().delayed_work_queue->Size());
 
+  state->SetInteger("immediate_incoming_queue_capacity",
+                    immediate_incoming_queue().capacity());
+  state->SetInteger("immediate_work_queue_capacity",
+                    immediate_work_queue()->Capacity());
+  state->SetInteger("delayed_work_queue_capacity",
+                    delayed_work_queue()->Capacity());
+
   if (!main_thread_only().delayed_incoming_queue.empty()) {
     TimeDelta delay_to_next_task =
         (main_thread_only().delayed_incoming_queue.top().delayed_run_time -
@@ -870,6 +881,9 @@ void TaskQueueImpl::SweepCanceledDelayedTasks(TimeTicks now) {
 
   main_thread_only().delayed_incoming_queue = std::move(remaining_tasks);
 
+  // Also consider shrinking the work queue if it's wasting memory.
+  main_thread_only().delayed_work_queue->MaybeShrinkQueue();
+
   LazyNow lazy_now(now);
   UpdateDelayedWakeUp(&lazy_now);
 }

base/task/sequence_manager/task_queue_impl.h

@@ -12,7 +12,6 @@
 #include <set>
 
 #include "base/callback.h"
-#include "base/containers/circular_deque.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "base/message_loop/message_loop.h"
@@ -381,7 +380,7 @@ class BASE_EXPORT TaskQueueImpl {
   // empty.
   void PushOntoImmediateIncomingQueueLocked(Task task);
 
-  using TaskDeque = circular_deque<Task>;
+  using TaskDeque = LazilyDeallocatedDeque<Task>;
 
   // Extracts all the tasks from the immediate incoming queue and swaps it with
   // |queue| which must be empty.

base/task/sequence_manager/work_queue.cc

@@ -67,7 +67,7 @@ void WorkQueue::Push(TaskQueueImpl::Task task) {
 #endif
 
   // Make sure the |enqueue_order()| is monotonically increasing.
-  DCHECK(was_empty || tasks_.rbegin()->enqueue_order() < task.enqueue_order());
+  DCHECK(was_empty || tasks_.back().enqueue_order() < task.enqueue_order());
 
   // Amoritized O(1).
   tasks_.push_back(std::move(task));
@@ -133,10 +133,17 @@ TaskQueueImpl::Task WorkQueue::TakeTaskFromWorkQueue() {
   TaskQueueImpl::Task pending_task = std::move(tasks_.front());
   tasks_.pop_front();
   // NB immediate tasks have a different pipeline to delayed ones.
-  if (queue_type_ == QueueType::kImmediate && tasks_.empty()) {
-    // Short-circuit the queue reload so that OnPopQueue does the right thing.
+  if (tasks_.empty()) {
+    // NB delayed tasks are inserted via Push, no don't need to reload those.
+    if (queue_type_ == QueueType::kImmediate) {
+      // Short-circuit the queue reload so that OnPopQueue does the right
+      // thing.
       task_queue_->ReloadEmptyImmediateQueue(&tasks_);
     }
+    // Since the queue is empty, now is a good time to consider reducing it's
+    // capacity if we're wasting memory.
+    tasks_.MaybeShrinkQueue();
+  }
 
   // OnPopQueue calls GetFrontTaskEnqueueOrder which checks BlockedByFence() so
   // we don't need to here.
@@ -154,11 +161,17 @@ bool WorkQueue::RemoveAllCanceledTasksFromFront() {
     task_removed = true;
   }
   if (task_removed) {
-    // NB immediate tasks have a different pipeline to delayed ones.
-    if (queue_type_ == QueueType::kImmediate && tasks_.empty()) {
-      // Short-circuit the queue reload so that OnPopQueue does the right thing.
+    if (tasks_.empty()) {
+      // NB delayed tasks are inserted via Push, no don't need to reload those.
+      if (queue_type_ == QueueType::kImmediate) {
+        // Short-circuit the queue reload so that OnPopQueue does the right
+        // thing.
         task_queue_->ReloadEmptyImmediateQueue(&tasks_);
       }
+      // Since the queue is empty, now is a good time to consider reducing it's
+      // capacity if we're wasting memory.
+      tasks_.MaybeShrinkQueue();
+    }
     work_queue_sets_->OnPopQueue(this);
     task_queue_->TraceQueueSize();
   }
@@ -231,6 +244,10 @@ void WorkQueue::PopTaskForTesting() {
   tasks_.pop_front();
 }
 
+void WorkQueue::MaybeShrinkQueue() {
+  tasks_.MaybeShrinkQueue();
+}
+
 }  // namespace internal
 }  // namespace sequence_manager
 }  // namespace base

base/task/sequence_manager/work_queue.h

@@ -77,6 +77,8 @@ class BASE_EXPORT WorkQueue {
 
   size_t Size() const { return tasks_.size(); }
 
+  size_t Capacity() const { return tasks_.capacity(); }
+
   // Pulls a task off the |tasks_| and informs the WorkQueueSets.  If the
   // task removed had an enqueue order >= the current fence then WorkQueue
   // pretends to be empty as far as the WorkQueueSets is concerned.
@@ -130,6 +132,9 @@ class BASE_EXPORT WorkQueue {
   // Test support function. This should not be used in production code.
   void PopTaskForTesting();
 
+  // Shrinks |tasks_| if it's wasting memory.
+  void MaybeShrinkQueue();
+
  private:
   bool InsertFenceImpl(EnqueueOrder fence);