void Shrink(Delegate_deleteFile procDeleteFile)
{
List <string> keys = new List <string>();
List <PageItem> items = new List <PageItem>();
foreach (string key in _pageTable.Keys)
{
PageItem item = _pageTable[key];
if (item.State == "OK")
{
keys.Add(key);
}
}
if (keys.Count > 0)
{
foreach (string key in keys)
{
_pageTable.Remove(key);
}
foreach (PageItem item in items)
{
if (procDeleteFile != null)
{
procDeleteFile(item.FilePath);
}
else
{
item.Delete();
}
}
}
}
// 清除和指定路径相关的 PageItem 元素
public void ClearByRecPath(string strRecPath,
Delegate_deleteFile procDeleteFile)
{
var pairs = new List <KeyValuePair <string, PageItem> >();
_lock.EnterReadLock();
try
{
DateTime now = DateTime.Now;
foreach (var pair in _pageTable)
{
PageItem item = pair.Value;
if (item.RecordPath == strRecPath ||
item.RecordPath.StartsWith(strRecPath + "_"))
{
pairs.Add(pair);
}
}
}
finally
{
_lock.ExitReadLock();
}
if (pairs.Count > 0)
{
_lock.EnterWriteLock();
try
{
foreach (var pair in pairs)
{
_pageTable.Remove(pair.Key);
}
}
finally
{
_lock.ExitWriteLock();
}
foreach (var pair in pairs)
{
if (procDeleteFile != null)
{
procDeleteFile(pair.Value.FilePath);
}
else
{
pair.Value.Delete();
}
}
}
}
// 清除已经失效的 PageItem
// parameters:
// delta 闲置多少时间以上才清理
public void Clean(bool bLock,
TimeSpan delta,
Delegate_deleteFile procDeleteFile,
CancellationToken token)
{
List <string> keys = new List <string>();
List <PageItem> items = new List <PageItem>();
if (bLock)
{
_lock.EnterReadLock();
}
try
{
DateTime now = DateTime.Now;
foreach (string key in _pageTable.Keys)
{
token.ThrowIfCancellationRequested();
PageItem item = _pageTable[key];
if (item.State == "OK" &&
now - item.LastUse > delta)
{
keys.Add(key);
items.Add(item);
}
}
}
finally
{
if (bLock)
{
_lock.ExitReadLock();
}
}
if (keys.Count > 0)
{
if (bLock)
{
_lock.EnterWriteLock();
}
try
{
foreach (string key in keys)
{
token.ThrowIfCancellationRequested();
_pageTable.Remove(key);
}
}
finally
{
if (bLock)
{
_lock.ExitWriteLock();
}
}
foreach (PageItem item in items)
{
token.ThrowIfCancellationRequested();
if (procDeleteFile != null)
{
procDeleteFile(item.FilePath);
}
else
{
item.Delete();
}
}
}
}
// 准备一个 PageItem 对象。如果在 _pageTable 中已经存在了，则直接利用它；如果没有，则新创建一个
// 但要处理好一个文件，新创建好的 PageItem 对象，其物理文件还没有来得及创建，如果这段时间又有另一个线程并发获得使用了这个对象，则会发生冲突。解决办法是，规定只返回准备好物理文件的 PageItem 对象。这样可能会出现两个线程都同时在创建相似属性的 PageItem 对象的可能
public PageItem GetPage(string object_recpath,
int page_no,
int dpi,
string format,
Delegate_prepareFile procPrepareFile,
Delegate_deleteFile procDeleteFile,
CancellationToken token)
{
string key = PageItem.MakeKey(object_recpath, page_no, dpi, format);
PageItem item = null;
bool bNew = false; // 是否新创建了 PageItem 对象
bool bFreely = false; // 是否为独立的 Page Item 对象。独立的 PageItem 对象不被集合管理
_lock.EnterWriteLock();
try
{
if (_pageTable.TryGetValue(key, out item) == true &&
item.State == "OK")
{
return(item);
}
if (item == null)
{
if (_pageTable.Count >= MAX_ITEMS)
{
// 紧急清理一次
Clean(false, TimeSpan.FromMilliseconds(0), procDeleteFile, token);
}
item = new PageItem
{
RecordPath = object_recpath,
Page = page_no,
DPI = dpi,
Format = format,
State = "Lock"
};
if (this._pageTable.Count < MAX_ITEMS)
{
_pageTable.Add(key, item);
}
else
{
bFreely = true;
}
bNew = true;
}
else
{
// 等待状态变成 OK
bNew = false;
}
}
finally
{
_lock.ExitWriteLock();
}
if (bNew == true)
{
try
{
// 创建物理文件
var ret = procPrepareFile();
item.FilePath = ret.Item1;
item.TotalPage = ret.Item2;
if (bFreely)
{
item.State = "Freely";
}
else
{
item.State = "OK";
}
// Thread.Sleep(10000);
}
catch
{
_lock.EnterWriteLock();
try
{
_pageTable.Remove(key);
}
finally
{
_lock.ExitWriteLock();
}
throw;
}
}
else
{
TimeSpan timeout = TimeSpan.FromSeconds(10);
DateTime start = DateTime.Now;
// 等待状态变为 OK
while (true)
{
Thread.Sleep(100);
if (item.State == "OK")
{
break;
}
// TODO: 超时要抛出异常
if (DateTime.Now - start >= timeout)
{
throw new TimeoutException("PageItem 对象被其它请求占用。请稍后重试");
}
}
}
return(item);
}
