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.

Mercurial (4a108e94d3e2)

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 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483
/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* 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/. */

#ifndef PROFILER_PSEUDO_STACK_H_
#define PROFILER_PSEUDO_STACK_H_

#include "mozilla/ArrayUtils.h"
#include <stdint.h>
#include "js/ProfilingStack.h"
#include <stdlib.h>
#include "mozilla/Atomics.h"
#include "nsISupportsImpl.h"

/* we duplicate this code here to avoid header dependencies
 * which make it more difficult to include in other places */
#if defined(_M_X64) || defined(__x86_64__)
#define V8_HOST_ARCH_X64 1
#elif defined(_M_IX86) || defined(__i386__) || defined(__i386)
#define V8_HOST_ARCH_IA32 1
#elif defined(__ARMEL__)
#define V8_HOST_ARCH_ARM 1
#else
#warning Please add support for your architecture in chromium_types.h
#endif

// STORE_SEQUENCER: Because signals can interrupt our profile modification
//                  we need to make stores are not re-ordered by the compiler
//                  or hardware to make sure the profile is consistent at
//                  every point the signal can fire.
#ifdef V8_HOST_ARCH_ARM
// TODO Is there something cheaper that will prevent
//      memory stores from being reordered

typedef void (*LinuxKernelMemoryBarrierFunc)(void);
LinuxKernelMemoryBarrierFunc pLinuxKernelMemoryBarrier __attribute__((weak)) =
    (LinuxKernelMemoryBarrierFunc) 0xffff0fa0;

# define STORE_SEQUENCER() pLinuxKernelMemoryBarrier()
#elif defined(V8_HOST_ARCH_IA32) || defined(V8_HOST_ARCH_X64)
# if defined(_MSC_VER)
#  include <intrin.h>
#  define STORE_SEQUENCER() _ReadWriteBarrier();
# elif defined(__INTEL_COMPILER)
#  define STORE_SEQUENCER() __memory_barrier();
# elif __GNUC__
#  define STORE_SEQUENCER() asm volatile("" ::: "memory");
# else
#  error "Memory clobber not supported for your compiler."
# endif
#else
# error "Memory clobber not supported for your platform."
#endif

// We can't include <algorithm> because it causes issues on OS X, so we use
// our own min function.
static inline uint32_t sMin(uint32_t l, uint32_t r) {
  return l < r ? l : r;
}

// A stack entry exists to allow the JS engine to inform SPS of the current
// backtrace, but also to instrument particular points in C++ in case stack
// walking is not available on the platform we are running on.
//
// Each entry has a descriptive string, a relevant stack address, and some extra
// information the JS engine might want to inform SPS of. This class inherits
// from the JS engine's version of the entry to ensure that the size and layout
// of the two representations are consistent.
class StackEntry : public js::ProfileEntry
{
};

class ProfilerMarkerPayload;
template<typename T>
class ProfilerLinkedList;
class JSStreamWriter;
class JSCustomArray;
class ThreadProfile;
class ProfilerMarker {
  friend class ProfilerLinkedList<ProfilerMarker>;
public:
  explicit ProfilerMarker(const char* aMarkerName,
         ProfilerMarkerPayload* aPayload = nullptr,
         float aTime = 0);

  ~ProfilerMarker();

  const char* GetMarkerName() const {
    return mMarkerName;
  }

  void
  StreamJSObject(JSStreamWriter& b) const;

  void SetGeneration(int aGenID);

  bool HasExpired(int aGenID) const {
    return mGenID + 2 <= aGenID;
  }

  float GetTime();

private:
  char* mMarkerName;
  ProfilerMarkerPayload* mPayload;
  ProfilerMarker* mNext;
  float mTime;
  int mGenID;
};

// Foward declaration
typedef struct _UnwinderThreadBuffer UnwinderThreadBuffer;

/**
 * This struct is used to add a mNext field to UnwinderThreadBuffer objects for
 * use with ProfilerLinkedList. It is done this way so that UnwinderThreadBuffer
 * may continue to be opaque with respect to code outside of UnwinderThread2.cpp
 */
struct LinkedUWTBuffer
{
  LinkedUWTBuffer()
    :mNext(nullptr)
  {}
  virtual ~LinkedUWTBuffer() {}
  virtual UnwinderThreadBuffer* GetBuffer() = 0;
  LinkedUWTBuffer*  mNext;
};

template<typename T>
class ProfilerLinkedList {
public:
  ProfilerLinkedList()
    : mHead(nullptr)
    , mTail(nullptr)
  {}

  void insert(T* elem)
  {
    if (!mTail) {
      mHead = elem;
      mTail = elem;
    } else {
      mTail->mNext = elem;
      mTail = elem;
    }
    elem->mNext = nullptr;
  }

  T* popHead()
  {
    if (!mHead) {
      MOZ_ASSERT(false);
      return nullptr;
    }

    T* head = mHead;

    mHead = head->mNext;
    if (!mHead) {
      mTail = nullptr;
    }

    return head;
  }

  const T* peek() {
    return mHead;
  }

private:
  T* mHead;
  T* mTail;
};

typedef ProfilerLinkedList<ProfilerMarker> ProfilerMarkerLinkedList;
typedef ProfilerLinkedList<LinkedUWTBuffer> UWTBufferLinkedList;

template<typename T>
class ProfilerSignalSafeLinkedList {
public:
  ProfilerSignalSafeLinkedList()
    : mSignalLock(false)
  {}

  ~ProfilerSignalSafeLinkedList()
  {
    if (mSignalLock) {
      // Some thread is modifying the list. We should only be released on that
      // thread.
      abort();
    }

    while (mList.peek()) {
      delete mList.popHead();
    }
  }

  // Insert an item into the list.
  // Must only be called from the owning thread.
  // Must not be called while the list from accessList() is being accessed.
  // In the profiler, we ensure that by interrupting the profiled thread
  // (which is the one that owns this list and calls insert() on it) until
  // we're done reading the list from the signal handler.
  void insert(T* aElement) {
    MOZ_ASSERT(aElement);

    mSignalLock = true;
    STORE_SEQUENCER();

    mList.insert(aElement);

    STORE_SEQUENCER();
    mSignalLock = false;
  }

  // Called within signal, from any thread, possibly while insert() is in the
  // middle of modifying the list (on the owning thread). Will return null if
  // that is the case.
  // Function must be reentrant.
  ProfilerLinkedList<T>* accessList()
  {
    if (mSignalLock) {
      return nullptr;
    }
    return &mList;
  }

private:
  ProfilerLinkedList<T> mList;

  // If this is set, then it's not safe to read the list because its contents
  // are being changed.
  volatile bool mSignalLock;
};

// Stub eventMarker function for js-engine event generation.
void ProfilerJSEventMarker(const char *event);

// the PseudoStack members are read by signal
// handlers, so the mutation of them needs to be signal-safe.
struct PseudoStack
{
public:
  // Create a new PseudoStack and acquire a reference to it.
  static PseudoStack *create()
  {
    return new PseudoStack();
  }

  // This is called on every profiler restart. Put things that should happen at that time here.
  void reinitializeOnResume() {
    // This is needed to cause an initial sample to be taken from sleeping threads. Otherwise sleeping
    // threads would not have any samples to copy forward while sleeping.
    mSleepId++;
  }

  void addLinkedUWTBuffer(LinkedUWTBuffer* aBuff)
  {
    mPendingUWTBuffers.insert(aBuff);
  }

  UWTBufferLinkedList* getLinkedUWTBuffers()
  {
    return mPendingUWTBuffers.accessList();
  }

  void addMarker(const char *aMarkerStr, ProfilerMarkerPayload *aPayload, float aTime)
  {
    ProfilerMarker* marker = new ProfilerMarker(aMarkerStr, aPayload, aTime);
    mPendingMarkers.insert(marker);
  }

  // called within signal. Function must be reentrant
  ProfilerMarkerLinkedList* getPendingMarkers()
  {
    // The profiled thread is interrupted, so we can access the list safely.
    // Unless the profiled thread was in the middle of changing the list when
    // we interrupted it - in that case, accessList() will return null.
    return mPendingMarkers.accessList();
  }

  void push(const char *aName, js::ProfileEntry::Category aCategory, uint32_t line)
  {
    push(aName, aCategory, nullptr, false, line);
  }

  void push(const char *aName, js::ProfileEntry::Category aCategory,
    void *aStackAddress, bool aCopy, uint32_t line)
  {
    if (size_t(mStackPointer) >= mozilla::ArrayLength(mStack)) {
      mStackPointer++;
      return;
    }

    // In order to ensure this object is kept alive while it is
    // active, we acquire a reference at the outermost push.  This is
    // released by the corresponding pop.
    if (mStackPointer == 0) {
      ref();
    }

    volatile StackEntry &entry = mStack[mStackPointer];

    // Make sure we increment the pointer after the name has
    // been written such that mStack is always consistent.
    entry.setLabel(aName);
    entry.setCppFrame(aStackAddress, line);
    MOZ_ASSERT(entry.flags() == js::ProfileEntry::IS_CPP_ENTRY);

    uint32_t uint_category = static_cast<uint32_t>(aCategory);
    MOZ_ASSERT(
      uint_category >= static_cast<uint32_t>(js::ProfileEntry::Category::FIRST) &&
      uint_category <= static_cast<uint32_t>(js::ProfileEntry::Category::LAST));

    entry.setFlag(uint_category);

    // Track if mLabel needs a copy.
    if (aCopy)
      entry.setFlag(js::ProfileEntry::FRAME_LABEL_COPY);
    else
      entry.unsetFlag(js::ProfileEntry::FRAME_LABEL_COPY);

    // Prevent the optimizer from re-ordering these instructions
    STORE_SEQUENCER();
    mStackPointer++;
  }

  // Pop the stack.  If the stack is empty and all other references to
  // this PseudoStack have been dropped, then the PseudoStack is
  // deleted and "false" is returned.  Otherwise "true" is returned.
  bool popAndMaybeDelete()
  {
    mStackPointer--;
    if (mStackPointer == 0) {
      // Release our self-owned reference count.  See 'push'.
      deref();
      return false;
    } else {
      return true;
    }
  }
  bool isEmpty()
  {
    return mStackPointer == 0;
  }
  uint32_t stackSize() const
  {
    return sMin(mStackPointer, mozilla::sig_safe_t(mozilla::ArrayLength(mStack)));
  }

  void sampleRuntime(JSRuntime *runtime) {
    mRuntime = runtime;
    if (!runtime) {
      // JS shut down
      return;
    }

    static_assert(sizeof(mStack[0]) == sizeof(js::ProfileEntry),
                  "mStack must be binary compatible with js::ProfileEntry.");
    js::SetRuntimeProfilingStack(runtime,
                                 (js::ProfileEntry*) mStack,
                                 (uint32_t*) &mStackPointer,
                                 uint32_t(mozilla::ArrayLength(mStack)));
    if (mStartJSSampling)
      enableJSSampling();
  }
  void enableJSSampling() {
    if (mRuntime) {
      js::EnableRuntimeProfilingStack(mRuntime, true);
      js::RegisterRuntimeProfilingEventMarker(mRuntime, &ProfilerJSEventMarker);
      mStartJSSampling = false;
    } else {
      mStartJSSampling = true;
    }
  }
  void jsOperationCallback() {
    if (mStartJSSampling)
      enableJSSampling();
  }
  void disableJSSampling() {
    mStartJSSampling = false;
    if (mRuntime)
      js::EnableRuntimeProfilingStack(mRuntime, false);
  }

  // Keep a list of active checkpoints
  StackEntry volatile mStack[1024];
 private:

  // A PseudoStack can only be created via the "create" method.
  PseudoStack()
    : mStackPointer(0)
    , mSleepId(0)
    , mSleepIdObserved(0)
    , mSleeping(false)
    , mRefCnt(1)
    , mRuntime(nullptr)
    , mStartJSSampling(false)
    , mPrivacyMode(false)
  { }

  // A PseudoStack can only be deleted via deref.
  ~PseudoStack() {
    if (mStackPointer != 0) {
      // We're releasing the pseudostack while it's still in use.
      // The label macros keep a non ref counted reference to the
      // stack to avoid a TLS. If these are not all cleared we will
      // get a use-after-free so better to crash now.
      abort();
    }
  }

  // No copying.
  PseudoStack(const PseudoStack&) = delete;
  void operator=(const PseudoStack&) = delete;

  // Keep a list of pending markers that must be moved
  // to the circular buffer
  ProfilerSignalSafeLinkedList<ProfilerMarker> mPendingMarkers;
  // List of LinkedUWTBuffers that must be processed on the next tick
  ProfilerSignalSafeLinkedList<LinkedUWTBuffer> mPendingUWTBuffers;
  // This may exceed the length of mStack, so instead use the stackSize() method
  // to determine the number of valid samples in mStack
  mozilla::sig_safe_t mStackPointer;
  // Incremented at every sleep/wake up of the thread
  int mSleepId;
  // Previous id observed. If this is not the same as mSleepId, this thread is not sleeping in the same place any more
  mozilla::Atomic<int> mSleepIdObserved;
  // Keeps tack of whether the thread is sleeping or not (1 when sleeping 0 when awake)
  mozilla::Atomic<int> mSleeping;
  // This class is reference counted because it must be kept alive by
  // the ThreadInfo, by the reference from tlsPseudoStack, and by the
  // current thread when callbacks are in progress.
  mozilla::Atomic<int> mRefCnt;

 public:
  // The runtime which is being sampled
  JSRuntime *mRuntime;
  // Start JS Profiling when possible
  bool mStartJSSampling;
  bool mPrivacyMode;

  enum SleepState {NOT_SLEEPING, SLEEPING_FIRST, SLEEPING_AGAIN};

  // The first time this is called per sleep cycle we return SLEEPING_FIRST
  // and any other subsequent call within the same sleep cycle we return SLEEPING_AGAIN
  SleepState observeSleeping() {
    if (mSleeping != 0) {
      if (mSleepIdObserved == mSleepId) {
        return SLEEPING_AGAIN;
      } else {
        mSleepIdObserved = mSleepId;
        return SLEEPING_FIRST;
      }
    } else {
      return NOT_SLEEPING;
    }
  }


  // Call this whenever the current thread sleeps or wakes up
  // Calling setSleeping with the same value twice in a row is an error
  void setSleeping(int sleeping) {
    MOZ_ASSERT(mSleeping != sleeping);
    mSleepId++;
    mSleeping = sleeping;
  }

  void ref() {
    ++mRefCnt;
  }

  void deref() {
    int newValue = --mRefCnt;
    if (newValue == 0) {
      delete this;
    }
  }
};

#endif