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 (c969a93b0ca7)

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 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469
/* -*- 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 "CanvasDrawEventRecorder.h"

#include <string.h>

namespace mozilla {
namespace layers {

static const int32_t kCheckpointEventType = -1;
static const uint32_t kMaxSpinCount = 200;

static const TimeDuration kTimeout = TimeDuration::FromMilliseconds(100);
static const int32_t kTimeoutRetryCount = 50;

static const uint32_t kCacheLineSize = 64;
static const uint32_t kStreamSize = 64 * 1024;
static const uint32_t kShmemSize = kStreamSize + (2 * kCacheLineSize);

static_assert((static_cast<uint64_t>(UINT32_MAX) + 1) % kStreamSize == 0,
              "kStreamSize must be a power of two.");

bool CanvasEventRingBuffer::InitWriter(
    base::ProcessId aOtherPid, ipc::SharedMemoryBasic::Handle* aReadHandle,
    CrossProcessSemaphoreHandle* aReaderSem,
    CrossProcessSemaphoreHandle* aWriterSem,
    UniquePtr<WriterServices> aWriterServices) {
  mSharedMemory = MakeAndAddRef<ipc::SharedMemoryBasic>();
  if (NS_WARN_IF(!mSharedMemory->Create(kShmemSize)) ||
      NS_WARN_IF(!mSharedMemory->Map(kShmemSize))) {
    return false;
  }

  if (NS_WARN_IF(!mSharedMemory->ShareToProcess(aOtherPid, aReadHandle))) {
    return false;
  }

  mSharedMemory->CloseHandle();

  mBuf = static_cast<char*>(mSharedMemory->memory());
  mBufPos = mBuf;
  mAvailable = kStreamSize;

  static_assert(sizeof(ReadFooter) <= kCacheLineSize,
                "ReadFooter must fit in kCacheLineSize.");
  mRead = reinterpret_cast<ReadFooter*>(mBuf + kStreamSize);
  mRead->count = 0;
  mRead->returnCount = 0;
  mRead->state = State::Processing;

  static_assert(sizeof(WriteFooter) <= kCacheLineSize,
                "WriteFooter must fit in kCacheLineSize.");
  mWrite = reinterpret_cast<WriteFooter*>(mBuf + kStreamSize + kCacheLineSize);
  mWrite->count = 0;
  mWrite->returnCount = 0;
  mWrite->requiredDifference = 0;
  mWrite->state = State::Processing;

  mReaderSemaphore.reset(
      CrossProcessSemaphore::Create("SharedMemoryStreamParent", 0));
  *aReaderSem = mReaderSemaphore->ShareToProcess(aOtherPid);
  mReaderSemaphore->CloseHandle();
  mWriterSemaphore.reset(
      CrossProcessSemaphore::Create("SharedMemoryStreamChild", 0));
  *aWriterSem = mWriterSemaphore->ShareToProcess(aOtherPid);
  mWriterSemaphore->CloseHandle();

  mWriterServices = std::move(aWriterServices);

  mGood = true;
  return true;
}

bool CanvasEventRingBuffer::InitReader(
    const ipc::SharedMemoryBasic::Handle& aReadHandle,
    const CrossProcessSemaphoreHandle& aReaderSem,
    const CrossProcessSemaphoreHandle& aWriterSem,
    UniquePtr<ReaderServices> aReaderServices) {
  mSharedMemory = MakeAndAddRef<ipc::SharedMemoryBasic>();
  if (NS_WARN_IF(!mSharedMemory->SetHandle(
          aReadHandle, ipc::SharedMemory::RightsReadWrite)) ||
      NS_WARN_IF(!mSharedMemory->Map(kShmemSize))) {
    return false;
  }

  mSharedMemory->CloseHandle();

  mBuf = static_cast<char*>(mSharedMemory->memory());
  mRead = reinterpret_cast<ReadFooter*>(mBuf + kStreamSize);
  mWrite = reinterpret_cast<WriteFooter*>(mBuf + kStreamSize + kCacheLineSize);
  mReaderSemaphore.reset(CrossProcessSemaphore::Create(aReaderSem));
  mReaderSemaphore->CloseHandle();
  mWriterSemaphore.reset(CrossProcessSemaphore::Create(aWriterSem));
  mWriterSemaphore->CloseHandle();

  mReaderServices = std::move(aReaderServices);

  mGood = true;
  return true;
}

bool CanvasEventRingBuffer::WaitForAndRecalculateAvailableSpace() {
  uint32_t bufPos = mOurCount % kStreamSize;
  uint32_t maxToWrite = kStreamSize - bufPos;
  mAvailable = std::min(maxToWrite, WaitForBytesToWrite());
  if (!mAvailable) {
    mGood = false;
    mBufPos = nullptr;
    return false;
  }

  mBufPos = mBuf + bufPos;
  return true;
}

void CanvasEventRingBuffer::write(const char* const aData, const size_t aSize) {
  const char* curDestPtr = aData;
  size_t remainingToWrite = aSize;
  if (remainingToWrite > mAvailable) {
    if (!WaitForAndRecalculateAvailableSpace()) {
      return;
    }
  }

  if (remainingToWrite <= mAvailable) {
    memcpy(mBufPos, curDestPtr, remainingToWrite);
    UpdateWriteTotalsBy(remainingToWrite);
    return;
  }

  do {
    memcpy(mBufPos, curDestPtr, mAvailable);
    IncrementWriteCountBy(mAvailable);
    curDestPtr += mAvailable;
    remainingToWrite -= mAvailable;
    if (!WaitForAndRecalculateAvailableSpace()) {
      return;
    }
  } while (remainingToWrite > mAvailable);

  memcpy(mBufPos, curDestPtr, remainingToWrite);
  UpdateWriteTotalsBy(remainingToWrite);
}

void CanvasEventRingBuffer::IncrementWriteCountBy(uint32_t aCount) {
  mOurCount += aCount;
  mWrite->count = mOurCount;
  if (mRead->state != State::Processing) {
    CheckAndSignalReader();
  }
}

void CanvasEventRingBuffer::UpdateWriteTotalsBy(uint32_t aCount) {
  IncrementWriteCountBy(aCount);
  mBufPos += aCount;
  mAvailable -= aCount;
}

bool CanvasEventRingBuffer::WaitForAndRecalculateAvailableData() {
  uint32_t bufPos = mOurCount % kStreamSize;
  uint32_t maxToRead = kStreamSize - bufPos;
  mAvailable = std::min(maxToRead, WaitForBytesToRead());
  if (!mAvailable) {
    mGood = false;
    mBufPos = nullptr;
    return false;
  }

  mBufPos = mBuf + bufPos;
  return true;
}

void CanvasEventRingBuffer::read(char* const aOut, const size_t aSize) {
  char* curSrcPtr = aOut;
  size_t remainingToRead = aSize;
  if (remainingToRead > mAvailable) {
    if (!WaitForAndRecalculateAvailableData()) {
      return;
    }
  }

  if (remainingToRead <= mAvailable) {
    memcpy(curSrcPtr, mBufPos, remainingToRead);
    UpdateReadTotalsBy(remainingToRead);
    return;
  }

  do {
    memcpy(curSrcPtr, mBufPos, mAvailable);
    IncrementReadCountBy(mAvailable);
    curSrcPtr += mAvailable;
    remainingToRead -= mAvailable;
    if (!WaitForAndRecalculateAvailableData()) {
      return;
    }
  } while (remainingToRead > mAvailable);

  memcpy(curSrcPtr, mBufPos, remainingToRead);
  UpdateReadTotalsBy(remainingToRead);
}

void CanvasEventRingBuffer::IncrementReadCountBy(uint32_t aCount) {
  mOurCount += aCount;
  mRead->count = mOurCount;
  if (mWrite->state != State::Processing) {
    CheckAndSignalWriter();
  }
}

void CanvasEventRingBuffer::UpdateReadTotalsBy(uint32_t aCount) {
  IncrementReadCountBy(aCount);
  mBufPos += aCount;
  mAvailable -= aCount;
}

void CanvasEventRingBuffer::CheckAndSignalReader() {
  do {
    switch (mRead->state) {
      case State::Processing:
        return;
      case State::AboutToWait:
        // The reader is making a decision about whether to wait. So, we must
        // wait until it has decided to avoid races.
        continue;
      case State::Waiting:
        if (mRead->count != mOurCount) {
          // We have to use compareExchange here because the reader can change
          // from Waiting to Stopped.
          if (mRead->state.compareExchange(State::Waiting, State::Processing)) {
            mReaderSemaphore->Signal();
            return;
          }

          MOZ_ASSERT(mRead->state == State::Stopped);
          continue;
        }
        return;
      case State::Stopped:
        if (mRead->count != mOurCount) {
          mRead->state = State::Processing;
          mWriterServices->ResumeReader();
        }
        return;
      default:
        MOZ_ASSERT_UNREACHABLE("Invalid waiting state.");
        return;
    }
  } while (true);
}

bool CanvasEventRingBuffer::HasDataToRead() {
  return (mWrite->count != mOurCount);
}

bool CanvasEventRingBuffer::StopIfEmpty() {
  // Double-check that the writer isn't waiting.
  CheckAndSignalWriter();
  mRead->state = State::AboutToWait;
  if (HasDataToRead()) {
    mRead->state = State::Processing;
    return false;
  }

  mRead->state = State::Stopped;
  return true;
}

bool CanvasEventRingBuffer::WaitForDataToRead(TimeDuration aTimeout,
                                              int32_t aRetryCount) {
  uint32_t spinCount = kMaxSpinCount;
  do {
    if (HasDataToRead()) {
      return true;
    }
  } while (--spinCount != 0);

  // Double-check that the writer isn't waiting.
  CheckAndSignalWriter();
  mRead->state = State::AboutToWait;
  if (HasDataToRead()) {
    mRead->state = State::Processing;
    return true;
  }

  mRead->state = State::Waiting;
  do {
    if (mReaderSemaphore->Wait(Some(aTimeout))) {
      MOZ_RELEASE_ASSERT(HasDataToRead());
      return true;
    }

    if (mReaderServices->WriterClosed()) {
      // Something has gone wrong on the writing side, just return false so
      // that we can hopefully recover.
      return false;
    }
  } while (aRetryCount-- > 0);

  // We have to use compareExchange here because the writer can change our
  // state if we are waiting. signaled
  if (!mRead->state.compareExchange(State::Waiting, State::Stopped)) {
    MOZ_RELEASE_ASSERT(HasDataToRead());
    MOZ_RELEASE_ASSERT(mRead->state == State::Processing);
    // The writer has just signaled us, so consume it before returning
    MOZ_ALWAYS_TRUE(mReaderSemaphore->Wait());
    return true;
  }

  return false;
}

int32_t CanvasEventRingBuffer::ReadNextEvent() {
  int32_t nextEvent;
  ReadElement(*this, nextEvent);
  while (nextEvent == kCheckpointEventType) {
    ReadElement(*this, nextEvent);
  }

  return nextEvent;
}

uint32_t CanvasEventRingBuffer::CreateCheckpoint() {
  WriteElement(*this, kCheckpointEventType);
  return mOurCount;
}

bool CanvasEventRingBuffer::WaitForCheckpoint(uint32_t aCheckpoint) {
  return WaitForReadCount(aCheckpoint, kTimeout, kTimeoutRetryCount);
}

void CanvasEventRingBuffer::CheckAndSignalWriter() {
  do {
    switch (mWrite->state) {
      case State::Processing:
        return;
      case State::AboutToWait:
        // The writer is making a decision about whether to wait. So, we must
        // wait until it has decided to avoid races.
        continue;
      case State::Waiting:
        if (mWrite->count - mOurCount <= mWrite->requiredDifference) {
          mWrite->state = State::Processing;
          mWriterSemaphore->Signal();
        }
        return;
      default:
        MOZ_ASSERT_UNREACHABLE("Invalid waiting state.");
        return;
    }
  } while (true);
}

bool CanvasEventRingBuffer::WaitForReadCount(uint32_t aReadCount,
                                             TimeDuration aTimeout,
                                             int32_t aRetryCount) {
  uint32_t requiredDifference = mOurCount - aReadCount;
  uint32_t spinCount = kMaxSpinCount;
  do {
    if (mOurCount - mRead->count <= requiredDifference) {
      return true;
    }
  } while (--spinCount != 0);

  // Double-check that the reader isn't waiting.
  CheckAndSignalReader();
  mWrite->state = State::AboutToWait;
  if (mOurCount - mRead->count <= requiredDifference) {
    mWrite->state = State::Processing;
    return true;
  }

  mWrite->requiredDifference = requiredDifference;
  mWrite->state = State::Waiting;

  do {
    if (mWriterSemaphore->Wait(Some(aTimeout))) {
      MOZ_ASSERT(mOurCount - mRead->count <= requiredDifference);
      return true;
    }

    if (mWriterServices->ReaderClosed()) {
      // Something has gone wrong on the reading side, just return false so
      // that we can hopefully recover.
      return false;
    }
  } while (aRetryCount-- > 0);

  return false;
}

uint32_t CanvasEventRingBuffer::WaitForBytesToWrite() {
  uint32_t streamFullReadCount = mOurCount - kStreamSize;
  if (!WaitForReadCount(streamFullReadCount + 1, kTimeout,
                        kTimeoutRetryCount)) {
    mGood = false;
    return 0;
  }

  return mRead->count - streamFullReadCount;
}

uint32_t CanvasEventRingBuffer::WaitForBytesToRead() {
  if (!WaitForDataToRead(kTimeout, kTimeoutRetryCount)) {
    return 0;
  }

  return mWrite->count - mOurCount;
}

void CanvasEventRingBuffer::ReturnWrite(const char* aData, size_t aSize) {
  uint32_t writeCount = mRead->returnCount;
  uint32_t bufPos = writeCount % kStreamSize;
  uint32_t bufRemaining = kStreamSize - bufPos;
  uint32_t availableToWrite =
      std::min(bufRemaining, (mWrite->returnCount + kStreamSize - writeCount));
  while (availableToWrite < aSize) {
    if (availableToWrite) {
      memcpy(mBuf + bufPos, aData, availableToWrite);
      writeCount += availableToWrite;
      mRead->returnCount = writeCount;
      bufPos = writeCount % kStreamSize;
      bufRemaining = kStreamSize - bufPos;
      aData += availableToWrite;
      aSize -= availableToWrite;
    }

    availableToWrite = std::min(
        bufRemaining, (mWrite->returnCount + kStreamSize - writeCount));
  }

  memcpy(mBuf + bufPos, aData, aSize);
  writeCount += aSize;
  mRead->returnCount = writeCount;
}

void CanvasEventRingBuffer::ReturnRead(char* aOut, size_t aSize) {
  uint32_t readCount = mWrite->returnCount;
  uint32_t bufPos = readCount % kStreamSize;
  uint32_t bufRemaining = kStreamSize - bufPos;
  uint32_t availableToRead =
      std::min(bufRemaining, (mRead->returnCount - readCount));
  while (availableToRead < aSize) {
    if (availableToRead) {
      memcpy(aOut, mBuf + bufPos, availableToRead);
      readCount += availableToRead;
      mWrite->returnCount = readCount;
      bufPos = readCount % kStreamSize;
      bufRemaining = kStreamSize - bufPos;
      aOut += availableToRead;
      aSize -= availableToRead;
    } else {
      // Double-check that the reader isn't waiting.
      CheckAndSignalReader();
    }

    availableToRead = std::min(bufRemaining, (mRead->returnCount - readCount));
  }

  memcpy(aOut, mBuf + bufPos, aSize);
  readCount += aSize;
  mWrite->returnCount = readCount;
}

}  // namespace layers
}  // namespace mozilla