// reads a resource or a reservation data item
protected virtual bool Read <I, R>(Transaction context, StorageContext storageContext, StorageIndex <I> index, I rID, bool lockPage, out R data)
{
// look for the resource in the index
IndexItem <I> address = index.GetResourceAddress(rID);
if (null == address)
{
data = default(R);
return(false);
}
if (lockPage)
{
// Aquire a lock on the logical page address to ensure that the page is not
// being written while we read the data
this.LockPage(context, MyLM.LockMode.Read, address.Page);
}
// find the physical page
int fileAddress = storageContext.PageTable.GetPhysicalPage(address.Page);
// get the page
StoragePage page = new StoragePage();
this.aReadPageData(page, fileAddress);
// read the data
data = (R)page.ReadRecord(address.Record);
return(true);
}
// writes a resource or reservation data item
protected virtual bool Write <I, R>(Transaction context, StorageContext storageContext, StorageIndex <I> index, I rID, R data)
{
// look for the resource in the index
IndexItem <I> address = index.GetResourceAddress(rID);
if (null == address &&
null == data)
{
// nothing to do:
// user probably wanted to delete an non-existing item
return(true);
}
else if (null == address &&
null != data)
{
address = new IndexItem <I>
{
Page = storageContext.PageTable.GetLastLogicalPage(),
Record = -1
};
}
// Aquire a lock on the logical page address to ensure that we have access to the page
this.LockPage(context, MyLM.LockMode.Write, address.Page);
// find the physical page
int fileAddress = storageContext.PageTable.GetPhysicalPage(address.Page);
// get the page
StoragePage page = new StoragePage();
if (0 <= fileAddress)
{
this.aReadPageData(page, fileAddress);
}
// write the record
while (true)
{
try
{
if (0 > address.Record)
{
address.Record = page.AddRecord(data);
}
else
{
page.WriteRecord(address.Record, data);
}
}
catch (StoragePage.InsuffcientSpaceException)
{
// did not fit on last page so allocate a new page
page = new StoragePage();
address.Page = -1;
fileAddress = -1;
continue;
}
break;
}
// write the page
fileAddress = this.aWritePageData(page, storageContext, fileAddress);
// update the page table
if (0 > address.Page)
{
address.Page = storageContext.PageTable.SetLogicalPage(fileAddress);
}
else
{
storageContext.PageTable.UpdatePage(address.Page, fileAddress);
}
// update the index
if (null == data)
{
// handle deletes
address = null;
}
index.SetResourceAddress(rID, address);
return(true);
}