Quelle BlockingResourceBase.cpp Sprache: C

/* -*- 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 "mozilla/BlockingResourceBase.h"

#ifdef DEBUG
#  include "prthread.h"

#  ifndef MOZ_CALLSTACK_DISABLED
#    include "CodeAddressService.h"
#    include "nsHashKeys.h"
#    include "mozilla/StackWalk.h"
#    include "nsTHashtable.h"
#  endif

#  include "mozilla/Attributes.h"
#  include "mozilla/CondVar.h"
#  include "mozilla/DeadlockDetector.h"
#  include "mozilla/RecursiveMutex.h"
#  include "mozilla/ReentrantMonitor.h"
#  include "mozilla/Mutex.h"
#  include "mozilla/RWLock.h"
#  include "mozilla/UniquePtr.h"

#  if defined(MOZILLA_INTERNAL_API)
#    include "mozilla/ProfilerThreadSleep.h"
#  endif  // MOZILLA_INTERNAL_API

#endif  // ifdef DEBUG

namespace mozilla {
//
// BlockingResourceBase implementation
//

// static members
const char* const BlockingResourceBase::kResourceTypeName[] = {
    // needs to be kept in sync with BlockingResourceType
    "Mutex", "ReentrantMonitor", "CondVar", "RecursiveMutex"};

#ifdef DEBUG

PRCallOnceType BlockingResourceBase::sCallOnce;
MOZ_THREAD_LOCAL(BlockingResourceBase*)
BlockingResourceBase::sResourceAcqnChainFront;
BlockingResourceBase::DDT* BlockingResourceBase::sDeadlockDetector;

void BlockingResourceBase::StackWalkCallback(uint32_t aFrameNumber, void* aPc,
                                             void* aSp, void* aClosure) {
#  ifndef MOZ_CALLSTACK_DISABLED
  AcquisitionState* state = (AcquisitionState*)aClosure;
  state->ref().AppendElement(aPc);
#  endif
}

void BlockingResourceBase::GetStackTrace(AcquisitionState& aState,
                                         const void* aFirstFramePC) {
#  ifndef MOZ_CALLSTACK_DISABLED
  // Clear the array...
  aState.reset();
  // ...and create a new one; this also puts the state to 'acquired' status
  // regardless of whether we obtain a stack trace or not.
  aState.emplace();

  MozStackWalk(StackWalkCallback, aFirstFramePC, kAcquisitionStateStackSize,
               aState.ptr());
#  endif
}

/**
* PrintCycle
* Append to |aOut| detailed information about the circular
* dependency in |aCycle|.  Returns true if it *appears* that this
* cycle may represent an imminent deadlock, but this is merely a
* heuristic; the value returned may be a false positive or false
* negative.
*
* *NOT* thread safe.  Calls |Print()|.
*
* FIXME bug 456272 hack alert: because we can't write call
* contexts into strings, all info is written to stderr, but only
* some info is written into |aOut|
*/
static bool PrintCycle(
    const BlockingResourceBase::DDT::ResourceAcquisitionArray& aCycle,
    nsACString& aOut) {
  NS_ASSERTION(aCycle.Length() > 1, "need > 1 element for cycle!");

  bool maybeImminent = true;

  fputs("=== Cyclical dependency starts at\n", stderr);
  aOut += "Cyclical dependency starts at\n";

  const BlockingResourceBase::DDT::ResourceAcquisitionArray::value_type res =
      aCycle.ElementAt(0);
  maybeImminent &= res->Print(aOut);

  BlockingResourceBase::DDT::ResourceAcquisitionArray::index_type i;
  BlockingResourceBase::DDT::ResourceAcquisitionArray::size_type len =
      aCycle.Length();
  const BlockingResourceBase::DDT::ResourceAcquisitionArray::value_type* it =
      1 + aCycle.Elements();
  for (i = 1; i < len - 1; ++i, ++it) {
    fputs("\n--- Next dependency:\n", stderr);
    aOut += "\nNext dependency:\n";

    maybeImminent &= (*it)->Print(aOut);
  }

  fputs("\n=== Cycle completed at\n", stderr);
  aOut += "Cycle completed at\n";
  (*it)->Print(aOut);

  return maybeImminent;
}

bool BlockingResourceBase::Print(nsACString& aOut) const {
  fprintf(stderr, "--- %s : %s", kResourceTypeName[mType], mName);
  aOut += BlockingResourceBase::kResourceTypeName[mType];
  aOut += " : ";
  aOut += mName;

  bool acquired = IsAcquired();

  if (acquired) {
    fputs(" (currently acquired)\n", stderr);
    aOut += " (currently acquired)\n";
  }

  fputs(" calling context\n", stderr);
#  ifdef MOZ_CALLSTACK_DISABLED
  fputs(" [stack trace unavailable]\n", stderr);
#  else
  const AcquisitionState& state = acquired ? mAcquired : mFirstSeen;

  CodeAddressService<> addressService;

  for (uint32_t i = 0; i < state.ref().Length(); i++) {
    const size_t kMaxLength = 1024;
    char buffer[kMaxLength];
    addressService.GetLocation(i + 1, state.ref()[i], buffer, kMaxLength);
    const char* fmt = " %s\n";
    aOut.AppendLiteral(" ");
    aOut.Append(buffer);
    aOut.AppendLiteral("\n");
    fprintf(stderr, fmt, buffer);
  }

#  endif

  return acquired;
}

BlockingResourceBase::BlockingResourceBase(
    const char* aName, BlockingResourceBase::BlockingResourceType aType)
    : mName(aName),
      mType(aType)
#  ifdef MOZ_CALLSTACK_DISABLED
      ,
      mAcquired(false)
#  else
      ,
      mAcquired()
#  endif
{
  MOZ_ASSERT(mName, "Name must be nonnull");
  // PR_CallOnce guaranatees that InitStatics is called in a
  // thread-safe way
  if (PR_SUCCESS != PR_CallOnce(&sCallOnce, InitStatics)) {
    MOZ_CRASH("can't initialize blocking resource static members");
  }

  mChainPrev = 0;
  sDeadlockDetector->Add(this);
}

BlockingResourceBase::~BlockingResourceBase() {
  // we don't check for really obviously bad things like freeing
  // Mutexes while they're still locked.  it is assumed that the
  // base class, or its underlying primitive, will check for such
  // stupid mistakes.
  mChainPrev = 0;  // racy only for stupidly buggy client code
  if (sDeadlockDetector) {
    sDeadlockDetector->Remove(this);
  }
}

void BlockingResourceBase::AssertSafeToProcessEventLoop() {
  for (BlockingResourceBase* res = ResourceChainFront(); res != nullptr;
       res = res->mChainPrev) {
    // It's more OK to hold reentrant/recursive types across nested event loops,
    // as it should hopefully not lead to deadlocks, so allow them for now.
    if (res->mType == eReentrantMonitor || res->mType == eRecursiveMutex) {
      continue;
    }

    // Allow specifically named mutexes to be held across a nested event loop,
    // in order to get this check landed.
    nsDependentCString name(res->mName);
    if (name != "GraphRunner::mMonitor"_ns ||            // Bug 1928770
        name != "SourceSurfaceSkia::mChangeMutex"_ns) {  // Bug 1928772
      continue;
    }

    // This is a potential deadlock, as ProcessNextEvent could process any
    // runnable on the current thread, including one which could attempt to
    // acquire the mutex.
    fputs(
        "###!!! ERROR: Potential deadlock detected:\n"
        "=== Holding blocking resource across call to ProcessNextEvent\n",
        stderr);
    nsAutoCString out(
        "Potential deadlock detected:\n"
        "Holding blocking resource across call to ProcessNextEvent\n");
    res->Print(out);
    NS_ERROR(out.get());
    MOZ_CRASH_UNSAFE_PRINTF("Holding '%s' across call to ProcessNextEvent",
                            res->mName);
  }
}

size_t BlockingResourceBase::SizeOfDeadlockDetector(
    MallocSizeOf aMallocSizeOf) {
  return sDeadlockDetector
             ? sDeadlockDetector->SizeOfIncludingThis(aMallocSizeOf)
             : 0;
}

PRStatus BlockingResourceBase::InitStatics() {
  MOZ_ASSERT(sResourceAcqnChainFront.init());
  sDeadlockDetector = new DDT();
  if (!sDeadlockDetector) {
    MOZ_CRASH("can't allocate deadlock detector");
  }
  return PR_SUCCESS;
}

void BlockingResourceBase::Shutdown() {
  delete sDeadlockDetector;
  sDeadlockDetector = 0;
}

MOZ_NEVER_INLINE void BlockingResourceBase::CheckAcquire() {
  if (mType == eCondVar) {
    MOZ_ASSERT_UNREACHABLE(
        "FIXME bug 456272: annots. to allow CheckAcquire()ing condvars");
    return;
  }

  BlockingResourceBase* chainFront = ResourceChainFront();
  mozilla::UniquePtr<DDT::ResourceAcquisitionArray> cycle(
      sDeadlockDetector->CheckAcquisition(chainFront ? chainFront : 0, this));
  if (!cycle) {
    return;
  }

#  ifndef MOZ_CALLSTACK_DISABLED
  // Update the current stack before printing.
  GetStackTrace(mAcquired, CallerPC());
#  endif

  fputs("###!!! ERROR: Potential deadlock detected:\n", stderr);
  nsAutoCString out("Potential deadlock detected:\n");
  bool maybeImminent = PrintCycle(*cycle, out);

  if (maybeImminent) {
    fputs("\n###!!! Deadlock may happen NOW!\n\n", stderr);
    out.AppendLiteral("\n###!!! Deadlock may happen NOW!\n\n");
  } else {
    fputs("\nDeadlock may happen for some other execution\n\n", stderr);
    out.AppendLiteral("\nDeadlock may happen for some other execution\n\n");
  }

  // Only error out if we think a deadlock is imminent.
  if (maybeImminent) {
    NS_ERROR(out.get());
  } else {
    NS_WARNING(out.get());
  }
}

MOZ_NEVER_INLINE void BlockingResourceBase::Acquire() {
  if (mType == eCondVar) {
    MOZ_ASSERT_UNREACHABLE(
        "FIXME bug 456272: annots. to allow Acquire()ing condvars");
    return;
  }
  NS_ASSERTION(!IsAcquired(), "reacquiring already acquired resource");

  ResourceChainAppend(ResourceChainFront());

#  ifdef MOZ_CALLSTACK_DISABLED
  mAcquired = true;
#  else
  // Take a stack snapshot.
  GetStackTrace(mAcquired, CallerPC());
  MOZ_ASSERT(IsAcquired());

  if (!mFirstSeen) {
    mFirstSeen = mAcquired.map(
        [](AcquisitionState::ValueType& state) { return state.Clone(); });
  }
#  endif
}

void BlockingResourceBase::Release() {
  if (mType == eCondVar) {
    MOZ_ASSERT_UNREACHABLE(
        "FIXME bug 456272: annots. to allow Release()ing condvars");
    return;
  }

  BlockingResourceBase* chainFront = ResourceChainFront();
  NS_ASSERTION(chainFront && IsAcquired(),
               "Release()ing something that hasn't been Acquire()ed");

  if (chainFront == this) {
    ResourceChainRemove();
  } else {
    // remove this resource from wherever it lives in the chain
    // we walk backwards in order of acquisition:
    //  (1)  ...node<-prev<-curr...
    //              /     /
    //  (2)  ...prev<-curr...
    BlockingResourceBase* curr = chainFront;
    BlockingResourceBase* prev = nullptr;
    while (curr && (prev = curr->mChainPrev) && (prev != this)) {
      curr = prev;
    }
    if (prev == this) {
      curr->mChainPrev = prev->mChainPrev;
    }
  }

  ClearAcquisitionState();
}

//
// Debug implementation of (OffTheBooks)Mutex
void OffTheBooksMutex::Lock() {
  CheckAcquire();
  this->lock();
  mOwningThread = PR_GetCurrentThread();
  Acquire();
}

bool OffTheBooksMutex::TryLock() {
  bool locked = this->tryLock();
  if (locked) {
    mOwningThread = PR_GetCurrentThread();
    Acquire();
  }
  return locked;
}

void OffTheBooksMutex::Unlock() {
  Release();
  mOwningThread = nullptr;
  this->unlock();
}

void OffTheBooksMutex::AssertCurrentThreadOwns() const {
  MOZ_ASSERT(IsAcquired() && mOwningThread == PR_GetCurrentThread());
}

//
// Debug implementation of RWLock
//

bool RWLock::TryReadLock() {
  bool locked = this->detail::RWLockImpl::tryReadLock();
  MOZ_ASSERT_IF(locked, mOwningThread == nullptr);
  return locked;
}

void RWLock::ReadLock() {
  // All we want to ensure here is that we're not attempting to acquire the
  // read lock while this thread is holding the write lock.
  CheckAcquire();
  this->detail::RWLockImpl::readLock();
  MOZ_ASSERT(mOwningThread == nullptr);
}

void RWLock::ReadUnlock() {
  MOZ_ASSERT(mOwningThread == nullptr);
  this->detail::RWLockImpl::readUnlock();
}

bool RWLock::TryWriteLock() {
  bool locked = this->detail::RWLockImpl::tryWriteLock();
  if (locked) {
    mOwningThread = PR_GetCurrentThread();
    Acquire();
  }
  return locked;
}

void RWLock::WriteLock() {
  CheckAcquire();
  this->detail::RWLockImpl::writeLock();
  mOwningThread = PR_GetCurrentThread();
  Acquire();
}

void RWLock::WriteUnlock() {
  Release();
  mOwningThread = nullptr;
  this->detail::RWLockImpl::writeUnlock();
}

//
// Debug implementation of ReentrantMonitor
void ReentrantMonitor::Enter() {
  BlockingResourceBase* chainFront = ResourceChainFront();

  // the code below implements monitor reentrancy semantics

  if (this == chainFront) {
    // immediately re-entered the monitor: acceptable
    PR_EnterMonitor(mReentrantMonitor);
    ++mEntryCount;
    return;
  }

  // this is sort of a hack around not recording the thread that
  // owns this monitor
  if (chainFront) {
    for (BlockingResourceBase* br = ResourceChainPrev(chainFront); br;
         br = ResourceChainPrev(br)) {
      if (br == this) {
        NS_WARNING(
            "Re-entering ReentrantMonitor after acquiring other resources.");

        // show the caller why this is potentially bad
        CheckAcquire();

        PR_EnterMonitor(mReentrantMonitor);
        ++mEntryCount;
        return;
      }
    }
  }

  CheckAcquire();
  PR_EnterMonitor(mReentrantMonitor);
  NS_ASSERTION(mEntryCount == 0, "ReentrantMonitor isn't free!");
  Acquire();  // protected by mReentrantMonitor
  mEntryCount = 1;
}

void ReentrantMonitor::Exit() {
  if (--mEntryCount == 0) {
    Release();  // protected by mReentrantMonitor
  }
  PRStatus status = PR_ExitMonitor(mReentrantMonitor);
  NS_ASSERTION(PR_SUCCESS == status, "bad ReentrantMonitor::Exit()");
}

nsresult ReentrantMonitor::Wait(PRIntervalTime aInterval) {
  AssertCurrentThreadIn();

  // save monitor state and reset it to empty
  int32_t savedEntryCount = mEntryCount;
  AcquisitionState savedAcquisitionState = TakeAcquisitionState();
  BlockingResourceBase* savedChainPrev = mChainPrev;
  mEntryCount = 0;
  mChainPrev = 0;

  nsresult rv;
  {
#  if defined(MOZILLA_INTERNAL_API)
    AUTO_PROFILER_THREAD_SLEEP;
#  endif
    // give up the monitor until we're back from Wait()
    rv = PR_Wait(mReentrantMonitor, aInterval) == PR_SUCCESS ? NS_OK
                                                             : NS_ERROR_FAILURE;
  }

  // restore saved state
  mEntryCount = savedEntryCount;
  SetAcquisitionState(std::move(savedAcquisitionState));
  mChainPrev = savedChainPrev;

  return rv;
}

//
// Debug implementation of RecursiveMutex
void RecursiveMutex::Lock() {
  BlockingResourceBase* chainFront = ResourceChainFront();

  // the code below implements mutex reentrancy semantics

  if (this == chainFront) {
    // immediately re-entered the mutex: acceptable
    LockInternal();
    ++mEntryCount;
    return;
  }

  // this is sort of a hack around not recording the thread that
  // owns this monitor
  if (chainFront) {
    for (BlockingResourceBase* br = ResourceChainPrev(chainFront); br;
         br = ResourceChainPrev(br)) {
      if (br == this) {
        NS_WARNING(
            "Re-entering RecursiveMutex after acquiring other resources.");

        // show the caller why this is potentially bad
        CheckAcquire();

        LockInternal();
        ++mEntryCount;
        return;
      }
    }
  }

  CheckAcquire();
  LockInternal();
  NS_ASSERTION(mEntryCount == 0, "RecursiveMutex isn't free!");
  Acquire();  // protected by us
  mOwningThread = PR_GetCurrentThread();
  mEntryCount = 1;
}

void RecursiveMutex::Unlock() {
  if (--mEntryCount == 0) {
    Release();  // protected by us
    mOwningThread = nullptr;
  }
  UnlockInternal();
}

void RecursiveMutex::AssertCurrentThreadIn() const {
  MOZ_ASSERT(IsAcquired() && mOwningThread == PR_GetCurrentThread());
}

//
// Debug implementation of CondVar
void OffTheBooksCondVar::Wait() {
  // Forward to the timed version of OffTheBooksCondVar::Wait to avoid code
  // duplication.
  CVStatus status = Wait(TimeDuration::Forever());
  MOZ_ASSERT(status == CVStatus::NoTimeout);
}

CVStatus OffTheBooksCondVar::Wait(TimeDuration aDuration) {
  AssertCurrentThreadOwnsMutex();

  // save mutex state and reset to empty
  AcquisitionState savedAcquisitionState = mLock->TakeAcquisitionState();
  BlockingResourceBase* savedChainPrev = mLock->mChainPrev;
  PRThread* savedOwningThread = mLock->mOwningThread;
  mLock->mChainPrev = 0;
  mLock->mOwningThread = nullptr;

  // give up mutex until we're back from Wait()
  CVStatus status;
  {
#  if defined(MOZILLA_INTERNAL_API)
    AUTO_PROFILER_THREAD_SLEEP;
#  endif
    status = mImpl.wait_for(*mLock, aDuration);
  }

  // restore saved state
  mLock->SetAcquisitionState(std::move(savedAcquisitionState));
  mLock->mChainPrev = savedChainPrev;
  mLock->mOwningThread = savedOwningThread;

  return status;
}

#endif  // ifdef DEBUG

}  // namespace mozilla

quality94%

¤ Dauer der Verarbeitung: 0.3 Sekunden (vorverarbeitet) ¤

Wurzel

Suchen

Beweissystem der NASA

Beweissystem Isabelle

NIST Cobol Testsuite

Cephes Mathematical Library

Wiener Entwicklungsmethode

Haftungshinweis

Die Informationen auf dieser Webseite wurden nach bestem Wissen sorgfältig zusammengestellt. Es wird jedoch weder Vollständigkeit, noch Richtigkeit, noch Qualität der bereit gestellten Informationen zugesichert.

Bemerkung:

Die farbliche Syntaxdarstellung ist noch experimentell.