storage/SQLiteMutex.h
author Marco Bonardo <mbonardo@mozilla.com>
Fri, 16 Jun 2017 17:43:23 +0200
changeset 365017 eacdba5020640bc50ba6690e9e3eb57ee7a8f2c8
parent 288573 ec1879bdc5dc04d4a810c5177be94eb9b3218b9b
child 448947 6f3709b3878117466168c40affa7bca0b60cf75b
permissions -rw-r--r--
Bug 1371945 - Avoid a possible thread-safety problem with unfinalized statements. r=asuth Avoids a thread-safety race condition on shutdown where we could try to finalize a statement twice. Allows the async thread to be referenced until ShutdownAsyncThread, so async finalizers can make use of it. Removes the no more useful mAsyncExecutionThreadIsAlive. Nullifies the sqlite3_mutex pointer when the connection is closed, since it would be a dangling pointer. Use a ScopeExit to ensure the connection and the mutex pointers are always nullified on failure. Makes asyncClose bailout early if a Close method was already invoked before. Makes AsyncInitDatabase not use AsyncClose to just shutdown the async thread. Fixes various unfinalized statements in consumers code. Makes mConnectionClosed better follow mDBConn status. Replaces some mutex locking isClosed() calls with lockless isConnectionReadyOnThisThread. MozReview-Commit-ID: 6sftFehsQTt

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
 * vim: sw=2 ts=2 et lcs=trail\:.,tab\:>~ :
 * 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_storage_SQLiteMutex_h_
#define mozilla_storage_SQLiteMutex_h_

#include "mozilla/BlockingResourceBase.h"
#include "sqlite3.h"

namespace mozilla {
namespace storage {

/**
 * Wrapper class for sqlite3_mutexes.  To be used whenever we want to use a
 * sqlite3_mutex.
 *
 * @warning Never EVER wrap the same sqlite3_mutex with a different SQLiteMutex.
 *          If you do this, you void the deadlock detector's warranty!
 */
class SQLiteMutex : private BlockingResourceBase
{
public:
  /**
   * Constructs a wrapper for a sqlite3_mutex that has deadlock detecting.
   *
   * @param aName
   *        A name which can be used to reference this mutex.
   */
  explicit SQLiteMutex(const char *aName)
  : BlockingResourceBase(aName, eMutex)
  , mMutex(nullptr)
  {
  }

  /**
   * Sets the mutex that we are wrapping.  We generally do not have access to
   * our mutex at class construction, so we have to set it once we get access to
   * it.
   *
   * @param aMutex
   *        The sqlite3_mutex that we are going to wrap.
   */
  void initWithMutex(sqlite3_mutex *aMutex)
  {
    NS_ASSERTION(aMutex, "You must pass in a valid mutex!");
    NS_ASSERTION(!mMutex, "A mutex has already been set for this!");
    mMutex = aMutex;
  }

  /**
   * After a connection has been successfully closed, its mutex is a dangling
   * pointer, and as such it should be destroyed.
   */
  void destroy() {
    mMutex = NULL;
  }

#if !defined(DEBUG) || defined(MOZ_SYSTEM_SQLITE)
  /**
   * Acquires the mutex.
   */
  void lock()
  {
    ::sqlite3_mutex_enter(mMutex);
  }

  /**
   * Releases the mutex.
   */
  void unlock()
  {
    ::sqlite3_mutex_leave(mMutex);
  }

  /**
   * Asserts that the current thread owns the mutex.
   */
  void assertCurrentThreadOwns()
  {
  }

  /**
   * Asserts that the current thread does not own the mutex.
   */
  void assertNotCurrentThreadOwns()
  {
  }

#else
  void lock()
  {
    MOZ_ASSERT(mMutex, "No mutex associated with this wrapper!");

    // While SQLite Mutexes may be recursive, in our own code we do not want to
    // treat them as such.

    CheckAcquire();
    ::sqlite3_mutex_enter(mMutex);
    Acquire(); // Call is protected by us holding the mutex.
  }

  void unlock()
  {
    MOZ_ASSERT(mMutex, "No mutex associated with this wrapper!");

    // While SQLite Mutexes may be recursive, in our own code we do not want to
    // treat them as such.
    Release(); // Call is protected by us holding the mutex.
    ::sqlite3_mutex_leave(mMutex);
  }

  void assertCurrentThreadOwns()
  {
    MOZ_ASSERT(mMutex, "No mutex associated with this wrapper!");
    MOZ_ASSERT(sqlite3_mutex_held(mMutex),
               "Mutex is not held, but we expect it to be!");
  }

  void assertNotCurrentThreadOwns()
  {
    MOZ_ASSERT(mMutex, "No mutex associated with this wrapper!");
    MOZ_ASSERT(sqlite3_mutex_notheld(mMutex),
               "Mutex is held, but we expect it to not be!");
  }
#endif // ifndef DEBUG

private:
  sqlite3_mutex *mMutex;
};

/**
 * Automatically acquires the mutex when it enters scope, and releases it when
 * it leaves scope.
 */
class MOZ_STACK_CLASS SQLiteMutexAutoLock
{
public:
  explicit SQLiteMutexAutoLock(SQLiteMutex &aMutex)
  : mMutex(aMutex)
  {
    mMutex.lock();
  }

  ~SQLiteMutexAutoLock()
  {
    mMutex.unlock();
  }

private:
  SQLiteMutex &mMutex;
};

/**
 * Automatically releases the mutex when it enters scope, and acquires it when
 * it leaves scope.
 */
class MOZ_STACK_CLASS SQLiteMutexAutoUnlock
{
public:
  explicit SQLiteMutexAutoUnlock(SQLiteMutex &aMutex)
  : mMutex(aMutex)
  {
    mMutex.unlock();
  }

  ~SQLiteMutexAutoUnlock()
  {
    mMutex.lock();
  }

private:
  SQLiteMutex &mMutex;
};

} // namespace storage
} // namespace mozilla

#endif // mozilla_storage_SQLiteMutex_h_