Method cache_reader

src/jrd/cch.cpp:2865–3014

#ifdef CACHE_READER
void BufferControl::cache_reader(BufferControl* bcb)
{
/**************************************
 *
 *	c a c h e _ r e a d e r
 *
 **************************************
 *
 * Functional description
 *	Prefetch pages into cache for sequential scans.
 *	Use asynchronous I/O to keep two prefetch requests
 *	busy at a time.
 *
 **************************************/
	Database* dbb = bcb->bcb_database;
	Database::SyncGuard dsGuard(dbb);

	FbLocalStatus status_vector;

	// Establish a thread context.
	ThreadContextHolder tdbb(status_vector);

	// Dummy attachment needed for lock owner identification.
	tdbb->setDatabase(dbb);
	Jrd::Attachment* const attachment = Attachment::create(dbb, nullptr);
	tdbb->setAttachment(attachment);
	attachment->att_filename = dbb->dbb_filename;
	Jrd::ContextPoolHolder context(tdbb, bcb->bcb_bufferpool);

	// This try block is specifically to protect the LCK_init call: if
	// LCK_init fails we won't be able to accomplish anything anyway, so
	// return, unlike the other try blocks further down the page.

	BufferControl* bcb = NULL;

	try {

		LCK_init(tdbb, LCK_OWNER_attachment);
		TRA_init(attachment);
		bcb = dbb->dbb_bcb;
		bcb->bcb_flags |= BCB_cache_reader;
		dbb->dbb_reader_init.post();	// Notify our creator that we have started
	}
	catch (const Firebird::Exception& ex)
	{
		ex.stuffException(status_vector);
		iscDbLogStatus(dbb->dbb_filename.c_str(), status_vector);
		return 0;
	}

	try {

	// Set up dual prefetch control blocks to keep multiple prefetch
	// requests active at a time. Also helps to prevent the cache reader
	// from becoming dedicated or locked into a single request's prefetch demands.

	prf prefetch1, prefetch2;
	prefetch_init(&prefetch1, tdbb);