X Session Management Library

To open a connection with a session manager, use SmcOpenConnection

The network_ids_list argument is a null-terminated string containing a list of network IDs for the session manager, separated by commas. If network_ids_list is NULL, the value of the SESSION_MANAGER environment variable will be used. Each network ID has the following format:

An attempt will be made to use the first network ID. If that fails, an attempt will be made using the second network ID, and so on.

After the connection is established, SmcOpenConnection registers the client with the session manager. If the client is being restarted from a previous session, previous_id should contain a null terminated string representing the client ID from the previous session. If the client is first joining the session, previous_id should be set to NULL. If previous_id is specified but is determined to be invalid by the session manager, SMlib will re-register the client with previous_id set to NULL.

If SmcOpenConnection succeeds, it returns an opaque connection pointer of type SmcConn and the client_id_ret argument contains the client ID to be used for this session. The client_id_ret should be freed with a call to free when no longer needed. On failure, SmcOpenConnection returns NULL, and the reason for failure is returned in error_string_ret.

Note that SMlib uses the ICE protocol to establish a connection with the session manager. If an ICE connection already exists between the client and session manager, it might be possible for the same ICE connection to be used for session management.

The context argument indicates how willing the client is to share the ICE connection with other protocols. If context is NULL, then the caller is always willing to share the connection. If context is not NULL, then the caller is not willing to use a previously opened ICE connection that has a different non-NULL context associated with it.

As previously discussed (section 3, “Understanding SMlib's Dependence on ICE”), the client will have to keep track of when ICE connections are created or destroyed (using IceAddConnectionWatch and IceRemoveConnectionWatch and will have to call IceProcessMessages each time a select shows that there is data to read on an ICE connection. For further information, see the “Inter-Client Exchange Library” standard.

The callbacks argument contains a set of callbacks used to respond to session manager events. The mask argument specifies which callbacks are set. All of the callbacks specified in this version of SMlib are mandatory. The mask argument is necessary in order to maintain backwards compatibility in future versions of the library.

The following values may be ORed together to obtain a mask value:

For each callback, the client can register a pointer to client data. When SMlib invokes the callback, it will pass the client data pointer.

typedef struct {

	struct {
		SmcSaveYourselfProc callback;
		SmPointer client_data;
	} save_yourself;

	struct {
		SmcDieProc callback;
		SmPointer client_data;
	} die;

	struct {
		SmcSaveCompleteProc callback;
		SmPointer client_data;
	} save_complete;

	struct {
		SmcShutdownCancelledProc callback;
		SmPointer client_data;
	} shutdown_cancelled;

} SmcCallbacks;

To close a connection with a session manager, use SmcCloseConnection

The reason_msgs argument will most likely be NULL if resignation is expected by the client. Otherwise, it contains a list of null-terminated Compound Text strings representing the reason for termination. The session manager should display these reason messages to the user.

Note that SMlib used the ICE protocol to establish a connection with the session manager, and various protocols other than session management may be active on the ICE connection. When SmcCloseConnection is called, the ICE connection will be closed only if all protocols have been shutdown on the connection. Check the ICElib standard for IceAddConnectionWatch and IceRemoveConnectionWatch to learn how to set up a callback to be invoked each time an ICE connection is opened or closed. Typically this callback adds/removes the ICE file descriptor from the list of active descriptors to call select on (or calls XtAppAddInput or XtRemoveInput).

SmcCloseConnection returns one of the following values:

To modify callbacks set up in SmcOpenConnection use SmcModifyCallbacks

When specifying a value for the mask argument, the following values may be ORed together:

To set session management properties for this client, use SmcSetProperties

The properties are specified as an array of property pointers. Previously set property values may be over-written using the SmcSetProperties function. Note that the session manager is not expected to restore property values when the session is restarted. Because of this, clients should not try to use the session manager as a database for storing application specific state.

For a description of session management properties and the SmProp structure, see section 7, “Session Management Properties.”

To delete properties previously set by the client, use SmcDeleteProperties

To get properties previously stored by the client, use SmcGetProperties

The return value of SmcGetProperties is zero for failure and a positive value for success.

Note that the library does not block until the properties reply comes back. Rather, a callback of type SmcPropReplyProc is invoked when the data is ready.

To free each property, use SmFreeProperty (see section 8, “Freeing Data”). To free the actual array of pointers, use free

After receiving a “Save Yourself” message with an interact_style of SmInteractStyleErrors or SmInteractStyleAny the client may choose to interact with the user. Because only one client can interact with the user at a time, the client must call SmcInteractRequest and wait for an “Interact” message from the session manager.

The return value of SmcInteractRequest is zero for failure and a positive value for success.

The dialog_type argument specifies either SmDialogError indicating that the client wants to start an error dialog, or SmDialogNormal meaning that the client wishes to start a nonerror dialog.

Note that if a shutdown is in progress, the user may have the option of cancelling the shutdown. If the shutdown is cancelled, the clients that have not interacted yet with the user will receive a “Shutdown Cancelled” message instead of the “Interact” message.

The SmcInteractProc callback will be invoked when the “Interact” message arrives from the session manager.

After interacting with the user (in response to an “Interact” message), you should call SmcInteractDone

The cancel_shutdown argument may only be True if the corresponding “Save Yourself” specified True for shutdown and SmInteractStyleErrors or SmInteractStyleAny for the interact_style.

To request a checkpoint from the session manager, use SmcRequestSaveYourself

The save_type, shutdown, interact_style, and fast arguments are discussed in more detail in section 5.1.1, “The Save Yourself Callback.”

If global is set to True then the resulting “Save Yourself” should be sent to all clients in the session. For example, a vendor of a Uninterruptible Power Supply (UPS) might include a Session Management client that would monitor the status of the UPS and generate a fast shutdown if the power is about to be lost.

If global is set to False then the “Save Yourself” should only be sent to the client that requested it.

In response to a “Save Yourself”, the client may request to be informed when all the other clients are quiescent so that it can save their state. To do so, use SmcRequestSaveYourselfPhase2

The return value of SmcRequestSaveYourselfPhase2 is zero for failure and a positive value for success.

This request is needed by clients that manage other clients (for example, window managers, workspace managers, and so on). The manager must make sure that all of the clients that are being managed are in an idle state so that their state can be saved.

After saving state in response to a “Save Yourself” message, you should call SmcSaveYourselfDone

Before calling SmcSaveYourselfDone the client must have set each required property at least once since the client registered with the session manager.

SmcProtocolVersion returns the major version of the session management protocol associated with this session.

SmcProtocolRevision returns the minor version of the session management protocol associated with this session.

SmcVendor returns a string that provides some identification of the owner of the session manager. The string should be freed with a call to free

SmcRelease returns a string that provides the release number of the session manager. The string should be freed with a call to free

SmcClientID returns a null-terminated string for the client ID associated with this connection. This information was also returned in SmcOpenConnection (it is provided here for convenience). Call free on this pointer when the client ID is no longer needed.

SmcGetIceConnection returns the ICE connection object associated with this session management connection object. The ICE connection object can be used to get some additional information about the connection. Some of the more useful functions which can be used on the IceConn are IceConnectionNumber, IceConnectionString, IceLastSentSequenceNumber, IceLastReceivedSequenceNumber, and IcePing. For further information, see the “Inter-Client Exchange Library” standard.

If the client receives an unexpected protocol error from the session manager, an error handler is invoked by SMlib. A default error handler exists that simply prints the error message to stderr and exits if the severity of the error is fatal. The client can change this error handler by calling the SmcSetErrorHandler function.

The error handler. You should pass NULL to restore the default handler.

SmcSetErrorHandler returns the previous error handler.

The SmcErrorHandler has the following type:

Note that this error handler is invoked for protocol related errors. To install an error handler to be invoked when an IO error occurs, use IceSetIOErrorHandler For further information, see the “Inter-Client Exchange Library” standard.

SmsInitialize is the first SMlib function that should be called by a session manager. It provides information about the session manager and registers a callback that will be invoked each time a new client connects to the session manager.

After the SmsInitialize function is called, the session manager should call the IceListenForConnections function to listen for new connections. Afterwards, each time a client connects, the session manager should call IceAcceptConnection

See section 9, “Authentication of Clients,” for more details on authentication (including host based authentication). Also see the “Inter-Client Exchange Library” standard for further details on listening for and accepting ICE connections.

Each time a new client connects to the session manager, the SmsNewClientProc callback is invoked. The session manager obtains a new opaque connection object that it should use for all future interaction with the client. At this time, the session manager must also register a set of callbacks to respond to the different messages that the client might send.

If a failure occurs, the SmsNewClientProc should return a zero status as well as allocate and return a failure reason string in failure_reason_ret. SMlib will be responsible for freeing this memory.

The session manager must register a set of callbacks to respond to client events. The mask_ret argument specifies which callbacks are set. All of the callbacks specified in this version of SMlib are mandatory. The mask_ret argument is necessary in order to maintain backwards compatibility in future versions of the library.

The following values may be ORed together to obtain a mask value:

For each callback, the session manager can register a pointer to manager data specific to that callback. This pointer will be passed to the callback when it is invoked by SMlib.

typedef struct {
	struct {
		SmsRegisterClientProc callback;
		SmPointer manager_data;
	} register_client;

	struct {
		SmsInteractRequestProc callback;
		SmPointer manager_data;
	} interact_request;

	struct {
		SmsInteractDoneProc callback;
		SmPointer manager_data;
	} interact_done;

	struct {
		SmsSaveYourselfRequestProc callback;
		SmPointer manager_data;
	} save_yourself_request;

	struct {
		SmsSaveYourselfPhase2RequestProc callback;
		SmPointer manager_data;
	} save_yourself_phase2_request;

	struct {
		SmsSaveYourselfDoneProc callback;
		SmPointer manager_data;
	} save_yourself_done;

	struct {
		SmsCloseConnectionProc callback;
		SmPointer manager_data;
	} close_connection;

	struct {
		SmsSetPropertiesProc callback;
		SmPointer manager_data;
	} set_properties;

	struct {
		SmsDeletePropertiesProc callback;
		SmPointer manager_data;
	} delete_properties;

	struct {
		SmsGetPropertiesProc callback;
		SmPointer manager_data;
	} get_properties;

} SmsCallbacks;

To register a client (in response to a SmsRegisterClientProc callback), use SmsRegisterClientReply.

The return value of SmsRegisterClientReply is zero for failure and a positive value for success. Failure will occur if SMlib can not allocate memory to hold a copy of the client ID for it's own internal needs.

If a non-NULL previous_id was specified when the client registered itself, client_id should be identical to previous_id.

Otherwise, client_id should be a unique ID freshly generated by the session manager. In addition, the session manager should send a “Save Yourself” message with type = Local, shutdown = False, interact-style = None, and fast = False immediately after registering the client.

Note that once a client ID has been assigned to the client, the client keeps this ID indefinitely. If the client is terminated and restarted, it will be reassigned the same ID. It is desirable to be able to pass client IDs around from machine to machine, from user to user, and from session manager to session manager, while retaining the identity of the client. This, combined with the indefinite persistence of client IDs, means that client IDs need to be globally unique.

You should call the SmsGenerateClientID function to generate a globally unique client ID.

NULL will be returned if the ID could not be generated. Otherwise, the return value of the function is the client ID. It should be freed with a call to free when no longer needed.

To send a “Save Yourself” to a client, use SmsSaveYourself.

The session manager sends a “Save Yourself” message to a client either to checkpoint it or just before termination so that it can save its state. The client responds with zero or more “Set Properties” messages to update the properties indicating how to restart the client. When all the properties have been set, the client sends a “Save Yourself Done” message.

If interact_style is SmInteractStyleNone the client must not interact with the user while saving state. If interact_style is SmInteractStyleErrors the client may interact with the user only if an error condition arises. If interact_style is SmInteractStyleAny then the client may interact with the user for any purpose. The client must send an “Interact Request” message and wait for an “Interact” message from the session manager before it can interact with the user. When the client is done interacting with the user, it should send an “Interact Done” message. The “Interact Request” message can be sent any time after a “Save Yourself” and before a “Save Yourself Done.”

If save_type is SmSaveLocal the client must update the properties to reflect its current state. Specifically, it should save enough information to restore the state as seen by the user of this client. It should not affect the state as seen by other users. If save_type is SmSaveGlobal the user wants the client to commit all of its data to permanent, globally accessible storage. If save_type is SmSaveBoth the client should do both of these (it should first commit the data to permanent storage before updating its properties).

The shutdown argument specifies whether the session is being shut down. The interaction is different depending on whether or not shutdown is set. If not shutting down, then the client can save and resume normal operation. If shutting down, the client must save and then must prevent interaction until it receives either a “Die” or a “Shutdown Cancelled,” because anything the user does after the save will be lost.

The fast argument specifies that the client should save its state as quickly as possible. For example, if the session manager knows that power is about to fail, it should set fast to True.

In order to send a “Save Yourself Phase 2” message to a client, use SmsSaveYourselfPhase2

The session manager sends this message to a client that has previously sent a “Save Yourself Phase 2 Request” message. This message informs the client that all other clients are in a fixed state and this client can save state that is associated with other clients.

To send an “Interact” message to a client, use SmsInteract.

The “Interact” message grants the client the privilege of interacting with the user. When the client is done interacting with the user, it must send an “Interact Done” message to the session manager.

To send a “Save Complete” message to a client, use SmsSaveComplete.

The session manager sends this message when it is done with a checkpoint. The client is then free to change its state.

To send a “Die” message to a client, use SmsDie.

Before the session manager terminates, it should wait for a “Connection Closed” message from each client that it sent a “Die” message to, timing out appropriately.

To cancel a shutdown, use SmsShutdownCancelled.

The client can now continue as if the shutdown had never happened. If the client has not sent a “Save Yourself Done” message yet, it can either abort the save and send a “Save Yourself Done” with the success argument set to False or it can continue with the save and send a “Save Yourself Done” with the success argument set to reflect the outcome of the save.

In response to a “Get Properties” message, the session manager should call SmsReturnProperties.

The properties are returned as an array of property pointers. For a description of session management properties and the SmProp structure, see section 7, “Session Management Properties.”

To check that a client is still alive, you should use the IcePing function provided by the ICE library. To do so, the ICE connection must be obtained using the SmsGetIceConnection (see section 6.12, “Using Sms Informational Functions”).

When the Ping reply is ready (if ever), the IcePingReplyProc callback will be invoked. A session manager should have some sort of timeout period, after which it assumes the client has unexpectedly died.

When the session manager receives a “Connection Closed” message or otherwise detects that the client aborted the connection, it should call the SmsCleanUp function in order to free up the connection object.

SmsProtocolVersion returns the major version of the session management protocol associated with this session.

SmsProtocolRevision returns the minor version of the session management protocol associated with this session.

SmsClientID returns a null-terminated string for the client ID associated with this connection. You should call free on this pointer when the client ID is no longer needed.

To obtain the host name of a client, use SmsClientHostName. This host name will be needed to restart the client.

The string returned is of the form protocol/hostname, where protocol is one of {tcp, decnet, local}. You should call free on the string returned when it is no longer needed.

SmsGetIceConnection returns the ICE connection object associated with this session management connection object. The ICE connection object can be used to get some additional information about the connection. Some of the more useful functions which can be used on the IceConn are IceConnectionNumber and IceLastSequenceNumber. For further information, see the “Inter-Client Exchange Library” standard.

If the session manager receives an unexpected protocol error from a client, an error handler is invoked by SMlib. A default error handler exists which simply prints the error message (it does not exit). The session manager can change this error handler by calling SmsSetErrorHandler.

The error handler. You should pass NULL to restore the default handler.

SmsSetErrorHandler returns the previous error handler. The SmsErrorHandler has the following type:

Note that this error handler is invoked for protocol related errors. To install an error handler to be invoked when an IO error occurs, use IceSetIOErrorHandler. For further information, see the “Inter-Client Exchange Library” standard.