DXR is a code search and navigation tool aimed at making sense of large projects. It supports full-text and regex searches as well as structural queries.

Header

Mercurial (803daa1cbd9b)

VCS Links

Line Code
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "JobScheduler.h"
#include "Logging.h"

namespace mozilla {
namespace gfx {

JobScheduler* JobScheduler::sSingleton = nullptr;

bool JobScheduler::Init(uint32_t aNumThreads, uint32_t aNumQueues) {
  MOZ_ASSERT(!sSingleton);
  MOZ_ASSERT(aNumThreads >= aNumQueues);

  sSingleton = new JobScheduler();
  sSingleton->mNextQueue = 0;

  for (uint32_t i = 0; i < aNumQueues; ++i) {
    sSingleton->mDrawingQueues.push_back(new MultiThreadedJobQueue());
  }

  for (uint32_t i = 0; i < aNumThreads; ++i) {
    sSingleton->mWorkerThreads.push_back(
        WorkerThread::Create(sSingleton->mDrawingQueues[i % aNumQueues]));
  }
  return true;
}

void JobScheduler::ShutDown() {
  MOZ_ASSERT(IsEnabled());
  if (!IsEnabled()) {
    return;
  }

  for (auto queue : sSingleton->mDrawingQueues) {
    queue->ShutDown();
    delete queue;
  }

  for (WorkerThread* thread : sSingleton->mWorkerThreads) {
    // this will block until the thread is joined.
    delete thread;
  }

  sSingleton->mWorkerThreads.clear();
  delete sSingleton;
  sSingleton = nullptr;
}

JobStatus JobScheduler::ProcessJob(Job* aJob) {
  MOZ_ASSERT(aJob);
  auto status = aJob->Run();
  if (status == JobStatus::Error || status == JobStatus::Complete) {
    delete aJob;
  }
  return status;
}

void JobScheduler::SubmitJob(Job* aJob) {
  MOZ_ASSERT(aJob);
  RefPtr<SyncObject> start = aJob->GetStartSync();
  if (start && start->Register(aJob)) {
    // The Job buffer starts with a non-signaled sync object, it
    // is now registered in the list of task buffers waiting on the
    // sync object, so we should not place it in the queue.
    return;
  }

  GetQueueForJob(aJob)->SubmitJob(aJob);
}

void JobScheduler::Join(SyncObject* aCompletion) {
  RefPtr<EventObject> waitForCompletion = new EventObject();
  JobScheduler::SubmitJob(new SetEventJob(waitForCompletion, aCompletion));
  waitForCompletion->Wait();
}

MultiThreadedJobQueue* JobScheduler::GetQueueForJob(Job* aJob) {
  return aJob->IsPinnedToAThread() ? aJob->GetWorkerThread()->GetJobQueue()
                                   : GetDrawingQueue();
}

Job::Job(SyncObject* aStart, SyncObject* aCompletion, WorkerThread* aThread)
    : mNextWaitingJob(nullptr),
      mStartSync(aStart),
      mCompletionSync(aCompletion),
      mPinToThread(aThread) {
  if (mStartSync) {
    mStartSync->AddSubsequent(this);
  }
  if (mCompletionSync) {
    mCompletionSync->AddPrerequisite(this);
  }
}

Job::~Job() {
  if (mCompletionSync) {
    // printf(" -- Job %p dtor completion %p\n", this, mCompletionSync);
    mCompletionSync->Signal();
    mCompletionSync = nullptr;
  }
}

JobStatus SetEventJob::Run() {
  mEvent->Set();
  return JobStatus::Complete;
}

SetEventJob::SetEventJob(EventObject* aEvent, SyncObject* aStart,
                         SyncObject* aCompletion, WorkerThread* aWorker)
    : Job(aStart, aCompletion, aWorker), mEvent(aEvent) {}

SetEventJob::~SetEventJob() {}

SyncObject::SyncObject(uint32_t aNumPrerequisites)
    : mSignals(aNumPrerequisites),
      mFirstWaitingJob(nullptr)
#ifdef DEBUG
      ,
      mNumPrerequisites(aNumPrerequisites),
      mAddedPrerequisites(0)
#endif
{
}

SyncObject::~SyncObject() { MOZ_ASSERT(mFirstWaitingJob == nullptr); }

bool SyncObject::Register(Job* aJob) {
  MOZ_ASSERT(aJob);

  // For now, ensure that when we schedule the first subsequent, we have already
  // created all of the prerequisites. This is an arbitrary restriction because
  // we specify the number of prerequisites in the constructor, but in the
  // typical scenario, if the assertion FreezePrerequisite blows up here it
  // probably means we got the initial nmber of prerequisites wrong. We can
  // decide to remove this restriction if needed.
  FreezePrerequisites();

  int32_t signals = mSignals;

  if (signals > 0) {
    AddWaitingJob(aJob);
    // Since Register and Signal can be called concurrently, it can happen that
    // reading mSignals in Register happens before decrementing mSignals in
    // Signal, but SubmitWaitingJobs happens before AddWaitingJob. This ordering
    // means the SyncObject ends up in the signaled state with a task sitting in
    // the waiting list. To prevent that we check mSignals a second time and
    // submit again if signals reached zero in the mean time. We do this instead
    // of holding a mutex around mSignals+mJobs to reduce lock contention.
    int32_t signals2 = mSignals;
    if (signals2 == 0) {
      SubmitWaitingJobs();
    }
    return true;
  }

  return false;
}

void SyncObject::Signal() {
  int32_t signals = --mSignals;
  MOZ_ASSERT(signals >= 0);

  if (signals == 0) {
    SubmitWaitingJobs();
  }
}

void SyncObject::AddWaitingJob(Job* aJob) {
  // Push (using atomics) the task into the list of waiting tasks.
  for (;;) {
    Job* first = mFirstWaitingJob;
    aJob->mNextWaitingJob = first;
    if (mFirstWaitingJob.compareExchange(first, aJob)) {
      break;
    }
  }
}

void SyncObject::SubmitWaitingJobs() {
  // Scheduling the tasks can cause code that modifies <this>'s reference
  // count to run concurrently, and cause the caller of this function to
  // be owned by another thread. We need to make sure the reference count
  // does not reach 0 on another thread before the end of this method, so
  // hold a strong ref to prevent that!
  RefPtr<SyncObject> kungFuDeathGrip(this);

  // First atomically swap mFirstWaitingJob and waitingJobs...
  Job* waitingJobs = nullptr;
  for (;;) {
    waitingJobs = mFirstWaitingJob;
    if (mFirstWaitingJob.compareExchange(waitingJobs, nullptr)) {
      break;
    }
  }

  // ... and submit all of the waiting tasks in waitingJob now that they belong
  // to this thread.
  while (waitingJobs) {
    Job* next = waitingJobs->mNextWaitingJob;
    waitingJobs->mNextWaitingJob = nullptr;
    JobScheduler::GetQueueForJob(waitingJobs)->SubmitJob(waitingJobs);
    waitingJobs = next;
  }
}

bool SyncObject::IsSignaled() { return mSignals == 0; }

void SyncObject::FreezePrerequisites() {
  MOZ_ASSERT(mAddedPrerequisites == mNumPrerequisites);
}

void SyncObject::AddPrerequisite(Job* aJob) {
  MOZ_ASSERT(++mAddedPrerequisites <= mNumPrerequisites);
}

void SyncObject::AddSubsequent(Job* aJob) {}

WorkerThread::WorkerThread(MultiThreadedJobQueue* aJobQueue)
    : mQueue(aJobQueue) {
  aJobQueue->RegisterThread();
}

void WorkerThread::Run() {
  SetName("gfx worker");

  for (;;) {
    Job* commands = nullptr;
    if (!mQueue->WaitForJob(commands)) {
      mQueue->UnregisterThread();
      return;
    }

    JobStatus status = JobScheduler::ProcessJob(commands);

    if (status == JobStatus::Error) {
      // Don't try to handle errors for now, but that's open to discussions.
      // I expect errors to be mostly OOM issues.
      gfxDevCrash(LogReason::JobStatusError)
          << "Invalid job status " << (int)status;
    }
  }
}

}  // namespace gfx
}  // namespace mozilla