private void AvoidDirtyRead()
{
// if disk are exclusive don't need check dirty read
if (_disk.IsExclusive)
{
return;
}
_log.Write(Logger.CACHE, "checking disk to avoid dirty read");
// empty cache? just exit
if (_cache.CleanUsed == 0)
{
return;
}
// get ChangeID from cache
var header = _cache.GetPage(0) as HeaderPage;
var changeID = header == null ? 0 : header.ChangeID;
// and get header from disk
var disk = BasePage.ReadPage(_disk.ReadPage(0)) as HeaderPage;
// if header change, clear cache and add new header to cache
if (disk.ChangeID != changeID)
{
_log.Write(Logger.CACHE, "file changed from another process, cleaning all cache pages");
_cache.ClearPages();
_cache.AddPage(disk);
}
}
/// <summary>
/// Get a page from cache or from disk (get from cache or from disk)
/// </summary>
public T GetPage <T>(uint pageID)
where T : BasePage
{
lock (_disk)
{
var page = _cache.GetPage(pageID);
// is not on cache? load from disk
if (page == null)
{
var buffer = _disk.ReadPage(pageID);
// if datafile are encrypted, decrypt buffer (header are not encrypted)
if (_crypto != null && pageID > 0)
{
buffer = _crypto.Decrypt(buffer);
}
page = BasePage.ReadPage(buffer);
_cache.AddPage(page);
}
return((T)page);
}
}
/// <summary>
/// Get a page from cache or from disk (and put on cache)
/// </summary>
public T GetPage <T>(uint pageID)
where T : BasePage, new()
{
var page = _cache.GetPage <T>(pageID);
if (page == null)
{
page = _disk.ReadPage <T>(pageID);
_cache.AddPage(page);
}
return(page);
}
/// <summary>
/// Get a page from cache or from disk (and put on cache)
/// </summary>
public T GetPage <T>(uint pageID, bool setDirty = false)
where T : BasePage
{
var page = _cache.GetPage(pageID);
// is not on cache? load from disk
if (page == null)
{
var buffer = _disk.ReadPage(pageID);
page = BasePage.ReadPage(buffer);
_cache.AddPage(page);
}
#if DEBUG
// if page is empty, convert to T
if (page.PageType == PageType.Empty && typeof(T) != typeof(BasePage))
{
throw new Exception("Pager.GetPage<T>() never shuld happend");
}
#endif
// set page as dirty if passing by param
if (setDirty)
{
this.SetDirty((T)page);
}
return((T)page);
}
/// <summary>
/// Test if cache still valid (if datafile was changed by another process reset cache)
/// Returns true if file was changed
/// [Thread Safe]
/// </summary>
private bool DetectDatabaseChanges()
{
// if disk are exclusive don't need check dirty read
if (_disk.IsExclusive)
{
return(false);
}
// empty cache? just exit
if (_cache.CleanUsed == 0)
{
return(false);
}
_log.Write(Logger.CACHE, "checking disk to detect database changes from another process");
// get ChangeID from cache
var header = _cache.GetPage(0) as HeaderPage;
var changeID = header == null ? 0 : header.ChangeID;
// and get header from disk
var disk = BasePage.ReadPage(_disk.ReadPage(0)) as HeaderPage;
// if disk header are in recovery mode, throw exception to datafile re-open and recovery pages
if (disk.Recovery)
{
_log.Write(Logger.ERROR, "datafile in recovery mode, need re-open database");
throw LiteException.NeedRecover();
}
// if header change, clear cache and add new header to cache
if (disk.ChangeID != changeID)
{
_log.Write(Logger.CACHE, "file changed from another process, cleaning all cache pages");
_cache.ClearPages();
_cache.AddPage(disk);
return(true);
}
return(false);
}
