public override void Read(long pageNumber, byte[] buffer, int offset)
{
lock (journalMap) {
if (!dataOpen)
{
throw new IOException("Assertion failed: Data file is not open.");
}
}
// The list of all journal entries on this page number
var allJournalEntries = new List <JournalEntry>(4);
try {
// The map index.
lock (journalMap) {
int i = ((int)(pageNumber & 0x0FFFFFFF) % journalMap.Length);
var entry = journalMap[i];
JournalEntry prev = null;
while (entry != null)
{
bool deletedHash = false;
JournalFile file = entry.File;
// Note that once we have a reference the journal file can not be
// deleted.
file.Reference();
// If the file is closed (or deleted)
if (file.IsDeleted)
{
deletedHash = true;
// Deleted so remove the reference to the journal
file.Dereference();
// Remove the journal entry from the chain.
if (prev == null)
{
journalMap[i] = entry.Next;
}
else
{
prev.Next = entry.Next;
}
}
// Else if not closed then is this entry the page number?
else if (entry.PageNumber == pageNumber)
{
allJournalEntries.Add(entry);
}
else
{
// Not the page we are looking for so remove the reference to the
// file.
file.Dereference();
}
// Only move prev is we have NOT deleted a hash entry
if (!deletedHash)
{
prev = entry;
}
entry = entry.Next;
}
}
// Read any data from the underlying file
if (thereIsBackingData)
{
long pagePosition = pageNumber * JournaledSystem.PageSize;
// First Read the page from the underlying store.
Data.Read(pagePosition, buffer, offset, JournaledSystem.PageSize);
}
else
{
// Clear the buffer
for (int i = offset; i < (JournaledSystem.PageSize + offset); ++i)
{
buffer[i] = 0;
}
}
// Rebuild from the journal file(s)
int sz = allJournalEntries.Count;
for (int i = 0; i < sz; ++i)
{
var entry = allJournalEntries[i];
var file = entry.File;
long position = entry.Position;
lock (file) {
file.BuildPage(pageNumber, position, buffer, offset);
}
}
} finally {
// Make sure we remove the reference for all the journal files.
int sz = allJournalEntries.Count;
for (int i = 0; i < sz; ++i)
{
var entry = allJournalEntries[i];
JournalFile file = entry.File;
file.Dereference();
}
}
}
public override void Write(long pageNumber, byte[] buffer, int offset, int count)
{
lock (journalMap) {
if (!dataOpen)
{
throw new IOException("Assertion failed: Data file is not open.");
}
// Make this modification input the log
var journal = JournaledSystem.LogPageModification(Name, pageNumber, buffer, offset, count);
// This adds the modification to the END of the hash list. This means
// when we reconstruct the page the journals will always be input the
// correct order - from oldest to newest.
// The map index.
int i = ((int)(pageNumber & 0x0FFFFFFF) % journalMap.Length);
var entry = journalMap[i];
// Make sure this entry is added to the END
if (entry == null)
{
// Add at the head if no first entry
journalMap[i] = journal;
journal.Next = null;
}
else
{
// Otherwise search to the end
// The number of journal entries input the linked list
int journalEntryCount = 0;
while (entry.Next != null)
{
entry = entry.Next;
++journalEntryCount;
}
// and add to the end
entry.Next = journal;
journal.Next = null;
// If there are over 35 journal entries, scan and remove all entries
// on journals that have persisted
if (journalEntryCount > 35)
{
entry = journalMap[i];
JournalEntry prev = null;
while (entry != null)
{
bool deletedHash = false;
JournalFile file = entry.File;
// Note that once we have a reference the journal file can not be
// deleted.
file.Reference();
// If the file is closed (or deleted)
if (file.IsDeleted)
{
deletedHash = true;
// Deleted so remove the reference to the journal
file.Dereference();
// Remove the journal entry from the chain.
if (prev == null)
{
journalMap[i] = entry.Next;
}
else
{
prev.Next = entry.Next;
}
}
// Remove the reference
file.Dereference();
// Only move prev is we have NOT deleted a hash entry
if (!deletedHash)
{
prev = entry;
}
entry = entry.Next;
}
}
}
}
}
