public RC Fetch(Pid id, bool createFlag, out PgHdr pageOut)
{
Debug.Assert(id > 0);
// If the pluggable cache (sqlite3_pcache*) has not been allocated, allocate it now.
if (Cache == null && createFlag)
{
var p = _pcache.Create(SizePage, SizeExtra + 0, Purgeable);
p.Cachesize(get_CacheSize());
Cache = p;
}
ICachePage page = null;
var create = (createFlag ? 1 : 0) * (1 + ((!Purgeable || Dirty == null) ? 1 : 0));
if (Cache != null)
{
page = Cache.Fetch(id, create > 0);
}
if (page == null && create == 1)
{
// Find a dirty page to write-out and recycle. First try to find a page that does not require a journal-sync (one with PGHDR_NEED_SYNC
// cleared), but if that is not possible settle for any other unreferenced dirty page.
#if EXPENSIVE_ASSERT
CheckSynced(this);
#endif
PgHdr pg;
for (pg = Synced; pg != null && (pg.Refs != 0 || (pg.Flags & PgHdr.PGHDR.NEED_SYNC) != 0); pg = pg.DirtyPrev)
{
;
}
Synced = pg;
if (pg == null)
{
for (pg = DirtyTail; pg != null && pg.Refs != 0; pg = pg.DirtyPrev)
{
;
}
}
if (pg != null)
{
#if LOG_CACHE_SPILL
SysEx.Log(RC.FULL, "spill page %d making room for %d - cache used: %d/%d", pg.ID, id, _pcache->Pagecount(Cache), NumberOfCachePages(this));
#endif
var rc = Stress(StressArg, pg);
if (rc != RC.OK && rc != RC.BUSY)
{
pageOut = null;
return(rc);
}
}
page = Cache.Fetch(id, true);
}
PgHdr pgHdr = null;
if (page != null)
{
//pgHdr = page.Extra;
if (page.Data == null)
{
//page.Page = page;
page.Data = C._alloc(SizePage);
//page.Extra = this;
page.Cache = this;
page.ID = id;
}
Debug.Assert(page.Cache == Cache);
Debug.Assert(page.ID == id);
//Debug.Assert(page.Data == page.Buffer);
//Debug.Assert(page.Extra == this);
if (page.Refs == 0)
{
Refs++;
}
page.Refs++;
if (id == 1)
{
Page1 = pgHdr;
}
}
pageOut = pgHdr;
return(pgHdr == null && create != 0 ? RC.NOMEM : RC.OK);
}