internal void WriteByteArrayTo(IJournalledResource data, long position, byte[] buf, int off, int len)
{
if (PARANOID_CHECKS)
{
lock (write_lock) {
if (write_lock_count == 0)
{
Console.Out.WriteLine("Write without a Lock!");
Console.Out.WriteLine(new ApplicationException().StackTrace);
}
}
}
long page_number = position / page_size;
int start_offset = (int)(position % page_size);
int to_write = System.Math.Min(len, page_size - start_offset);
BMPage page = FetchPage(data, page_number);
lock (page) {
try {
page.Initialize();
page.Write(start_offset, buf, off, to_write);
} finally {
page.Dispose();
}
}
len -= to_write;
while (len > 0)
{
off += to_write;
position += to_write;
++page_number;
to_write = System.Math.Min(len, page_size);
page = FetchPage(data, page_number);
lock (page) {
try {
page.Initialize();
page.Write(0, buf, off, to_write);
} finally {
page.Dispose();
}
}
len -= to_write;
}
}
internal void WriteByteTo(IJournalledResource data,
long position, int b)
{
if (PARANOID_CHECKS)
{
lock (write_lock) {
if (write_lock_count == 0)
{
Console.Out.WriteLine("Write without a Lock!");
Console.Out.WriteLine(new ApplicationException().StackTrace);
}
}
}
long page_number = position / page_size;
BMPage page = FetchPage(data, page_number);
lock (page) {
try {
page.Initialize();
page.Write((int)(position % page_size), (byte)b);
} finally {
page.Dispose();
}
}
}
internal int ReadByteArrayFrom(IJournalledResource data, long position, byte[] buf, int off, int len)
{
int orig_len = len;
long page_number = position / page_size;
int start_offset = (int)(position % page_size);
int to_read = System.Math.Min(len, page_size - start_offset);
BMPage page = FetchPage(data, page_number);
lock (page) {
try {
page.Initialize();
page.Read(start_offset, buf, off, to_read);
} finally {
page.Dispose();
}
}
len -= to_read;
while (len > 0)
{
off += to_read;
position += to_read;
++page_number;
to_read = System.Math.Min(len, page_size);
page = FetchPage(data, page_number);
lock (page) {
try {
page.Initialize();
page.Read(0, buf, off, to_read);
} finally {
page.Dispose();
}
}
len -= to_read;
}
return(orig_len);
}
// ------
// Buffered access methods. These are all thread safe methods. When a page
// is accessed the page is synchronized so no 2 or more operations can
// Read/Write from the page at the same time. An operation can Read/Write to
// different pages at the same time, however, and this requires thread safety
// at a lower level (in the IJournalledResource implementation).
// ------
internal int ReadByteFrom(IJournalledResource data, long position)
{
long page_number = position / page_size;
int v;
BMPage page = FetchPage(data, page_number);
lock (page) {
try {
page.Initialize();
v = ((int)page.Read((int)(position % page_size))) & 0x0FF;
} finally {
page.Dispose();
}
}
return(v);
}
/// <summary>
/// Called when a new page is created.
/// </summary>
/// <param name="page"></param>
private void PageCreated(BMPage page)
{
// lock (T_lock) {
if (PARANOID_CHECKS)
{
int i = page_list.IndexOf(page);
if (i != -1)
{
BMPage f = (BMPage)page_list[i];
if (f == page)
{
throw new ApplicationException("Same page added multiple times.");
}
if (f != null)
{
throw new ApplicationException("Duplicate pages.");
}
}
}
page.t = current_T;
++current_T;
++current_page_count;
page_list.Add(page);
// Below is the page purge algorithm. If the maximum number of pages
// has been created we sort the page list weighting each page by time
// since last accessed and total number of accesses and clear the bottom
// 20% of this list.
// Check if we should purge old pages and purge some if we do...
if (current_page_count > max_pages)
{
// Purge 20% of the cache
// Sort the pages by the current formula,
// ( 1 / page_access_count ) * (current_t - page_t)
// Further, if the page has written data then we multiply by 0.75.
// This scales down page writes so they have a better chance of
// surviving in the cache than page writes.
Object[] pages = page_list.ToArray();
Array.Sort(pages, PageCacheComparer);
int purge_size = System.Math.Max((int)(pages.Length * 0.20f), 2);
for (int i = 0; i < purge_size; ++i)
{
BMPage dpage = (BMPage)pages[pages.Length - (i + 1)];
lock (dpage) {
dpage.Dispose();
}
}
// Remove all the elements from page_list and set it with the sorted
// list (minus the elements we removed).
page_list.Clear();
for (int i = 0; i < pages.Length - purge_size; ++i)
{
page_list.Add(pages[i]);
}
current_page_count -= purge_size;
}
// }
}
