gecko-dev/xpcom/glue/BlockingResourceBase.h

/* -*- 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 "prlog.h"

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

#ifdef DEBUG
#include "prinit.h"
#include "prthread.h"

#include "nsStringGlue.h"

#include "mozilla/DeadlockDetector.h"
#include "nsXPCOM.h"
#endif

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

namespace mozilla {


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

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


#ifdef DEBUG

private:
  // forward declaration for the following typedef
  struct DeadlockDetectorEntry;

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

  /**
   * DeadlockDetectorEntry
   * We free BlockingResources, but we never free entries in the
   * deadlock detector.  This struct outlives its BlockingResource
   * and preserves all the state needed to print subsequent
   * error messages.
   *
   * These objects are owned by the deadlock detector.
   */
  struct DeadlockDetectorEntry
  {
    DeadlockDetectorEntry(const char* aName,
                          BlockingResourceType aType)
      : mName(aName)
      , mType(aType)
      , mAcquisitionContext(CallStack::kNone)
    {
      NS_ABORT_IF_FALSE(mName, "Name must be nonnull");
    }

    /**
     * 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.  |Print()| can
     * be forced to print the context from |aFirstSeen| regardless
     * by passing |aPrintFirstSeenCx=true|.
     *
     * *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(const DDT::ResourceAcquisition& aFirstSeen,
               nsACString& aOut,
               bool aPrintFirstSeenCx = false) const;

    /**
     * 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;
    /**
     * mAcquisitionContext
     * The calling context from which this resource was acquired, or
     * |CallStack::kNone| if it is currently free (or freed).
     */
    CallStack mAcquisitionContext;
  };

protected:
  /**
   * 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.
   *
   * @param aCallContext the client's calling context from which the
   *        original acquisition request was made.
   **/
  void CheckAcquire(const CallStack& aCallContext);

  /**
   * Acquire
   *
   * *NOT* thread safe.  Requires ownership of underlying resource.
   *
   * @param aCallContext the client's calling context from which the
   *        original acquisition request was made.
   **/
  void Acquire(const CallStack& aCallContext); //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)

  /**
   * 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 DDT::ResourceAcquisitionArray* aCycle,
                         nsACString& aOut);

  /**
   * 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)

  /**
   * GetAcquisitionContext
   * Return the calling context from which this resource was acquired,
   * or CallStack::kNone if it's currently free.
   *
   * *NOT* thread safe.  Requires ownership of underlying resource.
   */
  CallStack GetAcquisitionContext()
  {
    return mDDEntry->mAcquisitionContext;
  }

  /**
   * SetAcquisitionContext
   * Set the calling context from which this resource was acquired.
   *
   * *NOT* thread safe.  Requires ownership of underlying resource.
   */
  void SetAcquisitionContext(CallStack aAcquisitionContext)
  {
    mDDEntry->mAcquisitionContext = aAcquisitionContext;
  }

  /**
   * 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:
  /**
   * mDDEntry
   * The key for this BlockingResourceBase in the deadlock detector.
   */
  DeadlockDetectorEntry* mDDEntry;

  /**
   * 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()
  {
    PR_NewThreadPrivateIndex(&sResourceAcqnChainFrontTPI, 0);
    sDeadlockDetector = new DDT();
    if (!sDeadlockDetector) {
      NS_RUNTIMEABORT("can't allocate deadlock detector");
    }
    return PR_SUCCESS;
  }

  /**
   * Shutdown
   * Free static members.
   *
   * *NOT* thread safe.
   */
  static void Shutdown()
  {
    delete sDeadlockDetector;
    sDeadlockDetector = 0;
  }

#  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