Function CacheRegisterSyscacheCallback

src/backend/utils/cache/inval.c:1530–1561

* CacheRegisterSyscacheCallback * Register the specified function to be called for all future * invalidation events in the specified cache. The cache ID and the * hash value of the tuple being invalidated will be passed to the * function. * * NOTE: Hash value zero will be passed if a cache reset request is received. * In this case the called routines should flush all cached state. * Y

 * flush all cached state anyway.
 */
void
CacheRegisterSyscacheCallback(int cacheid,
							  SyscacheCallbackFunction func,
							  Datum arg)
{
	if (cacheid < 0 || cacheid >= SysCacheSize)
		elog(FATAL, "invalid cache ID: %d", cacheid);
	if (syscache_callback_count >= MAX_SYSCACHE_CALLBACKS)
		elog(FATAL, "out of syscache_callback_list slots");

	if (syscache_callback_links[cacheid] == 0)
	{
		/* first callback for this cache */
		syscache_callback_links[cacheid] = syscache_callback_count + 1;
	}
	else
	{
		/* add to end of chain, so that older callbacks are called first */
		int			i = syscache_callback_links[cacheid] - 1;

		while (syscache_callback_list[i].link > 0)
			i = syscache_callback_list[i].link - 1;
		syscache_callback_list[i].link = syscache_callback_count + 1;
	}

	syscache_callback_list[syscache_callback_count].id = cacheid;
	syscache_callback_list[syscache_callback_count].link = 0;
	syscache_callback_list[syscache_callback_count].function = func;
	syscache_callback_list[syscache_callback_count].arg = arg;

	++syscache_callback_count;
}

/*
 * CacheRegisterRelcacheCallback