xpcom/threads/BlockingResourceBase.h
author Henri Sivonen <hsivonen@hsivonen.fi>
Fri, 06 Jul 2018 10:44:43 +0300
changeset 489140 4ef0f163fdeb9afeddd87b37bfd987298c038542
parent 449929 f6ef04a022f3c5aa861e438298302a989308369e
child 508163 6f3709b3878117466168c40affa7bca0b60cf75b
permissions -rw-r--r--
Bug 1402247 - Use encoding_rs for XPCOM string encoding conversions. r=Nika,erahm,froydnj. Correctness improvements: * UTF errors are handled safely per spec instead of dangerously truncating strings. * There are fewer converter implementations. Performance improvements: * The old code did exact buffer length math, which meant doing UTF math twice on each input string (once for length calculation and another time for conversion). Exact length math is more complicated when handling errors properly, which the old code didn't do. The new code does UTF math on the string content only once (when converting) but risks allocating more than once. There are heuristics in place to lower the probability of reallocation in cases where the double math avoidance isn't enough of a saving to absorb an allocation and memcpy. * Previously, in UTF-16 <-> UTF-8 conversions, an ASCII prefix was optimized but a single non-ASCII code point pessimized the rest of the string. The new code tries to get back on the fast ASCII path. * UTF-16 to Latin1 conversion guarantees less about handling of out-of-range input to eliminate an operation from the inner loop on x86/x86_64. * When assigning to a pre-existing string, the new code tries to reuse the old buffer instead of first releasing the old buffer and then allocating a new one. * When reallocating from the new code, the memcpy covers only the data that is part of the logical length of the old string instead of memcpying the whole capacity. (For old callers old excess memcpy behavior is preserved due to bogus callers. See bug 1472113.) * UTF-8 strings in XPConnect that are in the Latin1 range are passed to SpiderMonkey as Latin1. New features: * Conversion between UTF-8 and Latin1 is added in order to enable faster future interop between Rust code (or otherwise UTF-8-using code) and text node and SpiderMonkey code that uses Latin1. MozReview-Commit-ID: JaJuExfILM9

/* -*- 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/. */


#ifndef mozilla_BlockingResourceBase_h
#define mozilla_BlockingResourceBase_h

#include "mozilla/Logging.h"

#include "nscore.h"
#include "nsDebug.h"
#include "nsError.h"
#include "nsISupportsImpl.h"

#ifdef DEBUG

// NB: Comment this out to enable callstack tracking.
#define MOZ_CALLSTACK_DISABLED

#include "prinit.h"

#include "nsString.h"

#ifndef MOZ_CALLSTACK_DISABLED
#include "nsTArray.h"
#endif

#include "nsXPCOM.h"
#endif

//
// This header is not meant to be included by client code.
//

namespace mozilla {

#ifdef DEBUG
template <class T> class DeadlockDetector;
#endif

/**
 * BlockingResourceBase
 * Base class of resources that might block clients trying to acquire them.
 * Does debugging and deadlock detection in DEBUG builds.
 **/
class BlockingResourceBase
{
public:
  // Needs to be kept in sync with kResourceTypeNames.
  enum BlockingResourceType { eMutex, eReentrantMonitor, eCondVar, eRecursiveMutex };

  /**
   * kResourceTypeName
   * Human-readable version of BlockingResourceType enum.
   */
  static const char* const kResourceTypeName[];


#ifdef DEBUG

  static size_t
  SizeOfDeadlockDetector(MallocSizeOf aMallocSizeOf);

  /**
   * Print
   * Write a description of this blocking resource to |aOut|.  If
   * the resource appears to be currently acquired, the current
   * acquisition context is printed and true is returned.
   * Otherwise, we print the context from |aFirstSeen|, the
   * first acquisition from which the code calling |Print()|
   * became interested in us, and return false.
   *
   * *NOT* thread safe.  Reads |mAcquisitionContext| without
   * synchronization, but this will not cause correctness
   * problems.
   *
   * 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|
   */
  bool Print(nsACString& aOut) const;

  size_t
  SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const
  {
    // NB: |mName| is not reported as it's expected to be a static string.
    //     If we switch to a nsString it should be added to the tally.
    //     |mChainPrev| is not reported because its memory is not owned.
    size_t n = aMallocSizeOf(this);
    return n;
  }

  // ``DDT'' = ``Deadlock Detector Type''
  typedef DeadlockDetector<BlockingResourceBase> DDT;

protected:
#ifdef MOZ_CALLSTACK_DISABLED
  typedef bool AcquisitionState;
#else
  typedef AutoTArray<void*, 24> AcquisitionState;
#endif

  /**
   * BlockingResourceBase
   * Initialize this blocking resource.  Also hooks the resource into
   * instrumentation code.
   *
   * Thread safe.
   *
   * @param aName A meaningful, unique name that can be used in
   *              error messages, et al.
   * @param aType The specific type of |this|, if any.
   **/
  BlockingResourceBase(const char* aName, BlockingResourceType aType);

  ~BlockingResourceBase();

  /**
   * CheckAcquire
   *
   * Thread safe.
   **/
  void CheckAcquire();

  /**
   * Acquire
   *
   * *NOT* thread safe.  Requires ownership of underlying resource.
   **/
  void Acquire(); //NS_NEEDS_RESOURCE(this)

  /**
   * Release
   * Remove this resource from the current thread's acquisition chain.
   * The resource does not have to be at the front of the chain, although
   * it is confusing to release resources in a different order than they
   * are acquired.  This generates a warning.
   *
   * *NOT* thread safe.  Requires ownership of underlying resource.
   **/
  void Release();             //NS_NEEDS_RESOURCE(this)

  /**
   * ResourceChainFront
   *
   * Thread safe.
   *
   * @return the front of the resource acquisition chain, i.e., the last
   *         resource acquired.
   */
  static BlockingResourceBase* ResourceChainFront()
  {
    return
      (BlockingResourceBase*)PR_GetThreadPrivate(sResourceAcqnChainFrontTPI);
  }

  /**
   * ResourceChainPrev
   *
   * *NOT* thread safe.  Requires ownership of underlying resource.
   */
  static BlockingResourceBase* ResourceChainPrev(
      const BlockingResourceBase* aResource)
  {
    return aResource->mChainPrev;
  } //NS_NEEDS_RESOURCE(this)

  /**
   * ResourceChainAppend
   * Set |this| to the front of the resource acquisition chain, and link
   * |this| to |aPrev|.
   *
   * *NOT* thread safe.  Requires ownership of underlying resource.
   */
  void ResourceChainAppend(BlockingResourceBase* aPrev)
  {
    mChainPrev = aPrev;
    PR_SetThreadPrivate(sResourceAcqnChainFrontTPI, this);
  } //NS_NEEDS_RESOURCE(this)

  /**
   * ResourceChainRemove
   * Remove |this| from the front of the resource acquisition chain.
   *
   * *NOT* thread safe.  Requires ownership of underlying resource.
   */
  void ResourceChainRemove()
  {
    NS_ASSERTION(this == ResourceChainFront(), "not at chain front");
    PR_SetThreadPrivate(sResourceAcqnChainFrontTPI, mChainPrev);
  } //NS_NEEDS_RESOURCE(this)

  /**
   * GetAcquisitionState
   * Return whether or not this resource was acquired.
   *
   * *NOT* thread safe.  Requires ownership of underlying resource.
   */
  AcquisitionState GetAcquisitionState()
  {
    return mAcquired;
  }

  /**
   * SetAcquisitionState
   * Set whether or not this resource was acquired.
   *
   * *NOT* thread safe.  Requires ownership of underlying resource.
   */
  void SetAcquisitionState(const AcquisitionState& aAcquisitionState)
  {
    mAcquired = aAcquisitionState;
  }

  /**
   * ClearAcquisitionState
   * Indicate this resource is not acquired.
   *
   * *NOT* thread safe.  Requires ownership of underlying resource.
   */
  void ClearAcquisitionState()
  {
#ifdef MOZ_CALLSTACK_DISABLED
    mAcquired = false;
#else
    mAcquired.Clear();
#endif
  }

  /**
   * IsAcquired
   * Indicates if this resource is acquired.
   *
   * *NOT* thread safe.  Requires ownership of underlying resource.
   */
  bool IsAcquired() const
  {
#ifdef MOZ_CALLSTACK_DISABLED
    return mAcquired;
#else
    return !mAcquired.IsEmpty();
#endif
  }

  /**
   * mChainPrev
   * A series of resource acquisitions creates a chain of orders.  This
   * chain is implemented as a linked list; |mChainPrev| points to the
   * resource most recently Acquire()'d before this one.
   **/
  BlockingResourceBase* mChainPrev;

private:
  /**
   * mName
   * A descriptive name for this resource.  Used in error
   * messages etc.
   */
  const char* mName;

  /**
   * mType
   * The more specific type of this resource.  Used to implement
   * special semantics (e.g., reentrancy of monitors).
   **/
  BlockingResourceType mType;

  /**
   * mAcquired
   * Indicates if this resource is currently acquired.
   */
  AcquisitionState mAcquired;

#ifndef MOZ_CALLSTACK_DISABLED
  /**
   * mFirstSeen
   * Inidicates where this resource was first acquired.
   */
  AcquisitionState mFirstSeen;
#endif

  /**
   * sCallOnce
   * Ensures static members are initialized only once, and in a
   * thread-safe way.
   */
  static PRCallOnceType sCallOnce;

  /**
   * sResourceAcqnChainFrontTPI
   * Thread-private index to the front of each thread's resource
   * acquisition chain.
   */
  static unsigned sResourceAcqnChainFrontTPI;

  /**
   * sDeadlockDetector
   * Does as named.
   */
  static DDT* sDeadlockDetector;

  /**
   * InitStatics
   * Inititialize static members of BlockingResourceBase that can't
   * be statically initialized.
   *
   * *NOT* thread safe.
   */
  static PRStatus InitStatics();

  /**
   * Shutdown
   * Free static members.
   *
   * *NOT* thread safe.
   */
  static void Shutdown();

  static void StackWalkCallback(uint32_t aFrameNumber, void* aPc,
                                void* aSp, void* aClosure);
  static void GetStackTrace(AcquisitionState& aState);

#  ifdef MOZILLA_INTERNAL_API
  // so it can call BlockingResourceBase::Shutdown()
  friend void LogTerm();
#  endif  // ifdef MOZILLA_INTERNAL_API

#else  // non-DEBUG implementation

  BlockingResourceBase(const char* aName, BlockingResourceType aType) {}

  ~BlockingResourceBase() {}

#endif
};


} // namespace mozilla


#endif // mozilla_BlockingResourceBase_h