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** Copyright (C) 2013 Digia Plc and/or its subsidiary(-ies).
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** This file is part of the Qt Solutions component.
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**     notice, this list of conditions and the following disclaimer in
**     the documentation and/or other materials provided with the
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**     from this software without specific prior written permission.
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#include <qt_windows.h>
#include "qtlockedfile.h"
#include <QFileInfo>

#define MUTEX_PREFIX "QtLockedFile mutex "
// Maximum number of concurrent read locks. Must not be greater than MAXIMUM_WAIT_OBJECTS
#define MAX_READERS MAXIMUM_WAIT_OBJECTS
#define QT_WA(unicode, ansi) unicode

Qt::HANDLE QtLockedFile::getMutexHandle(int idx, bool doCreate)
{
  if (mutexname.isEmpty())
  {
    QFileInfo fi(*this);
    mutexname = QString::fromLatin1(MUTEX_PREFIX) + fi.absoluteFilePath().toLower();
  }
  QString mname(mutexname);
  if (idx >= 0)
    mname += QString::number(idx);

  Qt::HANDLE mutex;
  if (doCreate)
  {
    QT_WA({ mutex = CreateMutexW(nullptr, FALSE, reinterpret_cast<LPCWSTR>(mname.utf16())); },
          { mutex = CreateMutexA(nullptr, FALSE, mname.toLocal8Bit().constData()); });
    if (!mutex)
    {
      qErrnoWarning("QtLockedFile::lock(): CreateMutex failed");
      return 0;
    }
  }
  else
  {
    QT_WA({ mutex = OpenMutexW(SYNCHRONIZE | MUTEX_MODIFY_STATE, FALSE, reinterpret_cast<LPCWSTR>(mname.utf16())); },
          { mutex = OpenMutexA(SYNCHRONIZE | MUTEX_MODIFY_STATE, FALSE, mname.toLocal8Bit().constData()); });
    if (!mutex)
    {
      if (GetLastError() != ERROR_FILE_NOT_FOUND)
        qErrnoWarning("QtLockedFile::lock(): OpenMutex failed");
      return 0;
    }
  }
  return mutex;
}

bool QtLockedFile::waitMutex(Qt::HANDLE mutex, bool doBlock)
{
  Q_ASSERT(mutex);
  DWORD res = WaitForSingleObject(mutex, doBlock ? INFINITE : 0);
  switch (res)
  {
    case WAIT_OBJECT_0:
    case WAIT_ABANDONED:
      return true;
      break;
    case WAIT_TIMEOUT:
      break;
    default:
      qErrnoWarning("QtLockedFile::lock(): WaitForSingleObject failed");
  }
  return false;
}

bool QtLockedFile::lock(LockMode mode, bool block)
{
  if (!isOpen())
  {
    qWarning("QtLockedFile::lock(): file is not opened");
    return false;
  }

  if (mode == NoLock)
    return unlock();

  if (mode == m_lock_mode)
    return true;

  if (m_lock_mode != NoLock)
    unlock();

  if (!wmutex && !(wmutex = getMutexHandle(-1, true)))
    return false;

  if (!waitMutex(wmutex, block))
    return false;

  if (mode == ReadLock)
  {
    int idx = 0;
    for (; idx < MAX_READERS; idx++)
    {
      rmutex = getMutexHandle(idx, false);
      if (!rmutex || waitMutex(rmutex, false))
        break;
      CloseHandle(rmutex);
    }
    bool ok = true;
    if (idx >= MAX_READERS)
    {
      qWarning("QtLockedFile::lock(): too many readers");
      rmutex = 0;
      ok = false;
    }
    else if (!rmutex)
    {
      rmutex = getMutexHandle(idx, true);
      if (!rmutex || !waitMutex(rmutex, false))
        ok = false;
    }
    if (!ok && rmutex)
    {
      CloseHandle(rmutex);
      rmutex = 0;
    }
    ReleaseMutex(wmutex);
    if (!ok)
      return false;
  }
  else
  {
    Q_ASSERT(rmutexes.isEmpty());
    for (int i = 0; i < MAX_READERS; i++)
    {
      Qt::HANDLE mutex = getMutexHandle(i, false);
      if (mutex)
        rmutexes.append(mutex);
    }
    if (rmutexes.size())
    {
      DWORD res = WaitForMultipleObjects(rmutexes.size(), rmutexes.constData(), TRUE, block ? INFINITE : 0);
      if (res != WAIT_OBJECT_0 && res != WAIT_ABANDONED)
      {
        if (res != WAIT_TIMEOUT)
          qErrnoWarning("QtLockedFile::lock(): WaitForMultipleObjects failed");
        m_lock_mode = WriteLock; // trick unlock() to clean up - semiyucky
        unlock();
        return false;
      }
    }
  }

  m_lock_mode = mode;
  return true;
}

bool QtLockedFile::unlock()
{
  if (!isOpen())
  {
    qWarning("QtLockedFile::unlock(): file is not opened");
    return false;
  }

  if (!isLocked())
    return true;

  if (m_lock_mode == ReadLock)
  {
    ReleaseMutex(rmutex);
    CloseHandle(rmutex);
    rmutex = 0;
  }
  else
  {
    foreach (Qt::HANDLE mutex, rmutexes)
    {
      ReleaseMutex(mutex);
      CloseHandle(mutex);
    }
    rmutexes.clear();
    ReleaseMutex(wmutex);
  }

  m_lock_mode = QtLockedFile::NoLock;
  return true;
}

QtLockedFile::~QtLockedFile()
{
  if (isOpen())
    unlock();
  if (wmutex)
    CloseHandle(wmutex);
}
