Function lock_buffer

src/jrd/cch.cpp:4071–4219

static LockState lock_buffer(thread_db* tdbb, BufferDesc* bdb, const SSHORT wait,
	const SCHAR page_type)
{
/**************************************
 *
 *	l o c k _ b u f f e r
 *
 **************************************
 *
 * Functional description
 *	Get a lock on page for a buffer.  If the lock ever slipped
 *	below READ, indicate that the page must be read.
 *
 * input:
 *	wait: LCK_WAIT = 1	=> Wait as long a necessary to get the lock.
 *	      LCK_NO_WAIT = 0	=> If the lock can't be acquired immediately,
 *						give up and return -1.
 *	      <negative number>		=> Lock timeout interval in seconds.
 *
 * return: 0  => buffer locked, page is already in memory.
 *	   1  => buffer locked, page needs to be read from disk.
 *	   -1 => timeout on lock occurred, see input parameter 'wait'.
 *
 **************************************/
	SET_TDBB(tdbb);
	BufferControl* const bcb = bdb->bdb_bcb;
	fb_assert(!(bcb->bcb_flags & BCB_exclusive));

	const USHORT lock_type = (bdb->bdb_flags & (BDB_dirty | BDB_writer)) ? LCK_write : LCK_read;

	CCH_TRACE(("FE LOCK %d:%06d, %s", bdb->bdb_page.getPageSpaceID(), bdb->bdb_page.getPageNum(),
		(lock_type >= LCK_write) ? "EX" : "SH" ));

	Lock* const lock = bdb->bdb_lock;

	if (lock->lck_logical >= lock_type)
		return lsLockedHavePage;

	TEXT errmsg[MAX_ERRMSG_LEN + 1];

	ThreadStatusGuard tempStatus(tdbb);

	if (lock->lck_logical == LCK_none)
	{
		// Prevent header and TIP pages from generating blocking AST
		// overhead. The promise is that the lock will unconditionally
		// be released when the buffer use count indicates it is safe to do so.

		if (page_type == pag_header || page_type == pag_transactions)
		{
			fb_assert(lock->lck_ast == blocking_ast_bdb);
			fb_assert(lock->lck_object == bdb);
			lock->lck_ast = 0;
			lock->lck_object = NULL;
		}
		else {
			fb_assert(lock->lck_ast != NULL);
		}