Handles (SourceMod Scripting)

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Handles are a special data type used in SourceMod Scripting. They represent a single internal and unique object. For example, there are "File" Handles for files, and "Menu" Handles for menus, but they are both encapsulated under the "Handle" tag.

Handles are more than "pointers" from C or C++ because they have a reference count. This means that the number of copies floating around in memory is tracked. The actual internal object is not destroyed until each copy is also destroyed.

Since SourcePawn does not have Garbage Collection, Handles are a special way of intelligently allowing plugins and SourceMod to manage their own memory.

For more information on using Handles in the SourceMod API, see Handle API (SourceMod).

Opening Handles

Opening a Handle is usually done implicitly by a native function. For example, OpenDirectory opens a new Handle which is used in other Directory natives. This associates a type with the Handle. Trying to use a Directory Handle with any other non-Directory native will cause an error (HandleError_Type), because Handles are type checked.

Handle hndl = OpenDirectory("addons/sourcemod/configs");

Closing Handles

Basic operation

Closing a Handle means seeing if the internal object can be removed from memory. For example, if a plugin creates an SQL connection, closing the Handle means closing and destroying the connection. This is almost always done using the delete operator and specifying the handle to close, e.g. delete hDir;

When to close

When a plugin unloads, all of its Handles are automatically destroyed. This does not mean, however, that closing Handles is optional. Consider the following code:

bool IsFileInFolder(const char[] path, const char[] file)
{
	char path[PLATFORM_MAX_PATH];
	FileType type;
 
	Handle dir = OpenDirectory(path);
	if (dir == null)
	{
		return false;
	}
 
	while (ReadDirEntry(dir, path, sizeof(path), type))
	{
		if (type == FileType_File && StrEqual(path, file))
		{
			return true;
		}
	}
 
	delete dir;
 
	return false;
}

This function searches a directory for a single file. If this function were to not close the handle with the delete operator, it would leak memory every time it was called, and eventually the script would fill up with a large number of lingering Handles that were left open.

So, when do you close Handles? There are generally two rules of thumb to go by:

  • If the native uses terminology such as "Opens a [...]" or "Creates a [...]" or gives explicit directions for closing.
  • If the Handle represents a temporary object or piece of information, and you will no longer be using it.

Most of the time, you will be closing Handles. Check the Handle Type documentation at the end of this page.

When you can't close

There are a few Handle types that cannot be closed. The major one is the Handle which identifies a plugin. Plugins cannot unload themselves, and thus destroying their own Handles is not allowed.

Furthermore, a script cannot close a Handle that is owned by another plugin. This is for protection against API mistakes and accidental errors. For example, if a Handle is shared between two plugins, one accidental free could invalidate a Handle unexpectedly. To allow the sharing of Handles, see Cloning Handles.

Reference counters

Closing Handles does not always destroy the internal data. This is the case when Handles are cloned. Each clone adds a reference count to the Handle, and closing each clone removes one reference count. The original object is only actually destroyed once the Handle has no more reference counters.

Cloning Handles

As briefly described earlier, there is a problem when scripts try to share Handles. Imagine this scenario:

  • Plugin 'A' creates a Handle.
  • Plugin 'B' received the Handle.
  • Plugin 'A' is unloaded, and the Handle is destroyed.
  • Plugin 'B' tries to use the Handle.

To prevent this, the CloneHandle native is provided. This function returns a new Handle that is a "copy" of the original. While their values won't be equal, they contain the same internal data. The data itself will not be destroyed until each copy and the original are closed with the delete operator. It does not matter what order they are freed in, however, each Handle can only be freed once.

There are two ways of cloning. A plugin can either clone a Handle itself, and become the owner, or it can explicitly set a new owner. The difference is one of API design. Example of the former:

DataBase g_hSQL;
/**
 * The other plugin calling this function must pass his ID in,
 * but doesn't have to call CloneHandle()
 */
public Database GetGlobalSQL(Handle otherPlugin)
{
   return view_as<DataBase>(CloneHandle(g_hSQL, otherPlugin));
}
 
/**
 * This code would appear in the other plugin
 */
DataBase sql = GetGlobalSQL(myself);
/* ... */
delete sql;

Example of the latter:

DataBase g_hSQL;
/**
 * The calling plugin must call CloneHandle() himself.
 */
public DataBase GetGlobalSQL()
{
   return g_hSQL;
}
 
/**
 * This code would appear in the other plugin
 */
DataBase sql = GetGlobalSQL();
if (sql != INVALID_HANDLE)
{
   sql = view_as<DataBase>(CloneHandle(sql));
}
delete sql;

Handle Types

The following is a list of some common Handle types provided by SourceMod and some documentation on each.

BitBuffers

Type: bf_read or bf_write
Closeable: Only if explicitly stated
Cloneable: Only if it can also be closed
API: Core
Found in: bitbuffer.inc

There are four types of BitBuffer Handles. They are separated into bf_write (writable buffer) and bf_read (readable buffer). These are directly abstracted from their Half-Life 2 counterpart. Internally, there are separate Handle types for each; certain functions will use BitBuffer handles that cannot be freed.

ConVars

Type: ConVar
Closeable: No
Cloneable: No
API: Core
Found in: convars.inc

ConVar Handles are primarily used for getting and setting a console variable's value. They cannot be cloned nor deleted since they exist until SourceMod is shut down.

DataPacks

Type: DataPack
Closeable: Yes
Cloneable: Yes
API: Core
Found in: datapack.inc

DataPack Handles are used to pack data into a sequential stream, for unpacking later. They are unidirectional, meaning that reading and writing affects the same position in the stream.

The DataPack type is exposed for Extensions to use.

Directories

Type: Directory
Closeable: Yes
Cloneable: Yes
API: Core
Found in: files.inc

Directory Handles are used for opening and enumerating the contents of a directory (folder) on the filesystem.

Database Drivers

Type: DBDriver
Closeable: Yes
Cloneable: No
API: Core
Found in: dbi.inc

DBDriver Handles contain information about a database driver. They are static and cannot be closed.

Database Queries

Type: IQuery
Closeable: Yes
Cloneable: No
API: Core
Found in: dbi.inc
Type: IPreparedQuery
Closeable: Yes
Cloneable: No
API: Core
Found in: dbi.inc

Database Queries wrap an IQuery pointer for database queries. Closing a query frees its resources, including any prepared statement information and any result sets.

Databases

Type: IDatabase
Closeable: Yes
Cloneable: Yes
API: Core
Found in: dbi.inc

Database Handles wrap an IDatabase pointer for database connections. Closing these disconnects the database and frees any related resources.

Events

Type: Event
Closeable: No
Cloneable: No
API: Core
Found in: events.inc

Event Handles are used for getting and setting data in Half-Life 2 game events as well as for firing them. They can only be closed using CancelCreatedEvent() if the event was not fired for some reason.

Files

Type: File
Closeable: Yes
Cloneable: Yes
API: Core
Found in: files.inc

File Handles are used for opening, reading from, writing to, and creating to files on the file system.

Forwards

Type: Forward
Closeable: Yes
Cloneable: Only if explicitly stated
API: Core
Found in: functions.inc

Forward Handles are primarily used when calling functions inside a forward container. There are two types of forwards: global and private. Only private forwards can be cloned.

KeyValues

Type: KeyValues
Closeable: Yes
Cloneable: No
API: Core
Found in: keyvalues.inc

KeyValues Handles abstract the Valve data type KeyValues, which are tree-based, recursive key to value mapping structures, often used to enumerate properties or configuration file directives.

Plugins

Type: Plugin
Closeable: No
Cloneable: No
API: Core
Found in: sourcemod.inc

Plugin Handles are used for the unique identification of a Plugin. They are owned by Core and cannot be cloned or closed by any other plugin or extension. However, plugins can use Handles for certain natives which enumerate or retrieve information on plugins.

Plugin Handles should not be cached globally, as plugins can become unloaded, and the Handle will be invalid.

Plugin Iterators

Type: PluginIter
Closeable: Yes
Cloneable: No
API: Core
Found in: sourcemod.inc

Plugin Iterators allow you to walk over a list of plugins. They are intended for temporary use only.

Protobuf

Type: protobuf
Closeable: No
Cloneable: No
API: Core
Found in: protobuf.inc

Protobuf Handles are currently used for usermessages in supported games. They directly reference protobuf Messages, which can be a usermessage or a Message field inside of a usermessage. They are owned and managed by Core and cannot be cloned or closed by a plugin.

SMC Parsers

Type: SMC Parser
Closeable: Yes
Cloneable: No
API: Core
Found in: textparse.inc

SMC Parsers are Handles which contain a set of functions for hooking parse events in an SMC file. Since they directly reference functions in a plugin, they cannot be cloned.

Timers

Type: Timer
Closeable: Yes
Cloneable: No
API: Core
Found in: timers.inc

Timers are temporary Handles which are automatically closed on any of the following events:

  • The timer ends (via Plugin_Stop or being a one-time timer that is finished)
  • The timer is killed via KillTimer
  • The timer is closed via delete hHandle;
  • The timer's parent plugin unloads