Function LockBuffer

src/backend/storage/buffer/bufmgr.c:4289–4308

* Acquire or release the content_lock for the buffer. */

 * Acquire or release the content_lock for the buffer.
 */
void
LockBuffer(Buffer buffer, int mode)
{
	BufferDesc *buf;

	Assert(BufferIsPinned(buffer));
	if (BufferIsLocal(buffer))
		return;					/* local buffers need no lock */

	buf = GetBufferDescriptor(buffer - 1);

	if (mode == BUFFER_LOCK_UNLOCK)
		ReleaseContentLock(buf);
	else if (mode == BUFFER_LOCK_SHARE)
		AcquireContentLock(buf, LW_SHARED);
	else if (mode == BUFFER_LOCK_EXCLUSIVE)
		AcquireContentLock(buf, LW_EXCLUSIVE);
	else
		elog(ERROR, "unrecognized buffer lock mode: %d", mode);
}

/*
 * Acquire the content_lock for the buffer, but only if we don't have to wait.