gecko-dev/storage/SQLiteMutex.h

/* -*- 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_