Chapter 4

Shell Widgets

If a shell widget is resized from the outside (typically by a window manager), the shell widget also resizes its managed child widget automatically. Similarly, if the shell's child widget needs to change size, it can make a geometry request to the shell, and the shell negotiates the size change with the outer environment. Clients should never attempt to change the size of their shells directly.

The five types of public shells are:

OverrideShell	Used for shell windows that completely bypass the window manager (for example, pop-up menu shells).
TransientShell	Used for shell windows that have the WM_TRANSIENT_FOR propertyset. The effect of this property is dependent upon the window manager being used.
TopLevelShell	Used for normal top-level windows (for example, any additional top level widgets an application needs).
ApplicationShell	Formerly used for the single main top-level window that the window manager identifies as an application instance and made obsolete by Session Shell.
SessionShell	Used for the single main top-level window that the window manager identifies as an application instance and that interacts with the session manager.

Widgets negotiate their size and position with their parent widget, that is, the widget that directly contains them. Widgets at the top of the hierarchy do not have parent widgets. Instead, they must deal with the outside world. To provide for this, each top-level widget is encapsulated in a special widget, called a shell widget.

Shell widgets, whose class is a subclass of the Composite class, encapsulate other widgets and can allow a widget to avoid the geometry clipping imposed by the parent-child window relationship. They also can provide a layer of communication with the window manager.

The eight different types of shells are

Shell	The base class for shell widgets; provides the fields needed for all types of shells. Shell is a direct subclass of compositeWidgetClass.
OverrideShell	A subclass of Shell; used for shell windows that completely bypass the window manager.
WMShell	A subclass of Shell, contains fields needed by the common window manager protocol .
VendorShell	A subclass of WMShell; contains fields used by vendor-specific window managers.
TransientShell	A subclass of VendorShell; used for shell windows that desire the WM_TRANSIENT_FOR property.
TopLevelShell	A subclass of VendorShell; used for normal top level windows.
ApplicationShell	A subolass of TopLevelShell; may be used for an application's additional root windows.
SessionShell	A subclass of ApplicationShell; used for an application's main root window.

Note that the classes Shell, WMShell, and VendorShell are internal and should not be instantiated or subclassed. Only OverrrideShell, TransientSell, TopLevelShell, ApplicationShell, and SessionShell are intended for public use.

4.1.1. ShellClassPart Definitions

Only the Shell class has additional class fields, which are all contained in the ShellClassExtensionRec. None of the other Shell classes have any additional class fields:

typedef struct ( XtPointer extension; } ShellClassPart, OverrideShellClassPart,

WMShellClassPart, VendorShellClassPart, TransientShellClassPart,
TopLevelShellClassPart, ApplicationShellClassPart, SessionShellClassPart;

The full Shell class record definitions are

typedef struct_ShellClassRec {
        CoreClassPart core_class;
        CompositeClassPart composite_class;
        ShellClassPart shell_class;
} ShellClassRec;

typedef struct {
        XtPointer next_extension;                 See Section 1.6.12
        XrmQuark record_type;                     See Section 1.6.12
        long version;                             See Section 1.6.12
        Cardinal record_size;                     See Section 1.6.12
        XtGeometryHandler root_geometry_manager;  See below
} ShellClassExtensionRec, *ShellClassExtension;

typedef struct_OverrideShellClassRec {
        CoreClassPart core_class;
        CompositeClassPart composite_class;
        ShellClassPart shell_class;
        OverrideShellClassPart override_shell_class;
} OverrideShellClassRec;

typedef struct_WMShellClassRec {
        CoreClassPart core_class;
        CompositeClassPart composite_class;
        ShellClassPart shell_class;
        WMShellClassPart wm_shell_class;
} WMShellClassRec;

typedef struct_VendorShellClassRec {
        CoreClassPart core_class;
        CompositeClassPart composite_class;
        ShellClassPart shell_class;
        WMShellClassPart wm_shell_class;
        VendorShellClassPart vendor_shell_class;
} VendorShellClassRec;

typedef struct_TransientShellClassRec {
        CoreClassPart core_class;
        CompositeClassPart composite_class;
        ShellClassPart shell_class;
        WMShellClassPart wm_shell_class;
        VendorShellClassPart vendor_shell_class;
        TransientShellClassPart transient_shell_class;
} TransientShellClassRec;

typedef struct_TopLevelShellClassRec {
        CoreClassPart core_class;
        CompositeClassPart composite_class ;
        ShellClassPart shell_class;
        WMShellClassPart wm_shell_class;
        VendorShellClassPart vendor_shell_class;
        TopLevelShellClassPart top_level_shell_class;
} TopLevelShellClassRec;

typedef struct _ApplicationShellClassRec {
        CoreClassPart core_class;
        CompositeClassPart composite_class;
        ShellClassPart shell_class;
        WMShellClassPart wm_shell_class;
        VendorShellClassPart vendor_shell_class;
        TopLevelShellClassPart top_level_shell_class;
        ApplicationShellClassPart application_shell_class;
} Application ShellClassRec ;

typedef struct_SessionShellClassRec {
        CoreClassPart core_class;
        CompositeClassPart composite class;
        ShellClassPart shell_class;
        WMShellClassPart wm_shell_class;
        VendorShellClassPart vendor_shell_class;
        TopLevelShellClassPart top_level_shell_class;
        ApplicationShellClassPart application_shell_class;
        Session S he llClassPart session_shell_class ;
} SessionShellClassRec;

The single occurrences of the class records and pointers for creating instances of shells are

extern ShellClassRec shellClassRec;
extern OverrideShellClassRec overrideShellClassRec;
extern WMShellClassRec wmShellClassRec;
extern VendorShellClassRec vendorShellClassRec;
extern TransientShellClassRec transientShellClassRec;
extern TopLevelShellClassRec topLevelShellClassRec;
extern ApplicationShellClassRec applicationShellClassRec;
extern SessionShellClassRec sessionShellClassRec;

extern WidgetClass shellWidgetClass;
extern WidgetClass overrideShellWidgetClass;
extern WidgetClass wmShellWidgetClass;
extern WidgetClass vendorShellWidgetClass;
extern WidgetClass transientShellWidgetClass;
extern WidgetClass topLevelShellWidgetClass;
extern WidgetClass applicationShellWidgetClass;
extern WidgetClass sessionShellWidgetClass;

The following opaque types and opaque variables are defined for generic operations on widgets whose class is a subclass of Shell.

The declarations for all Intrinsics-defined shells except VendorShell appear in Shell.h and ShellP.h. VendorShell has separate public and private .h files which are included by Shell.h and ShellP.h.

Shell.h uses incomplete structure definitions to ensure that the compiler catches attempts to access private data in any of the Shell instance or class data structures.

The symbolic constant for the ShellClassExtension version identifier is XtShellExtensionVersion (see Section 1.6.12).

The root_geometry_manager procedure acts as the parent geometry manager for geometry requests made by shell widgets. When a shell widget calls either XtMakeGeometryRequest or XtMakeResizeRequest, the root_geometry_manager procedure is invoked to negotiate the new geometry with the window manager. If the window manager permits the new geometry, the root_geometry_manager procedure should return XtGeometryYes; if the window manager denies the geometry request or it does not change the window geometry within some timeout interval (equal to wm timeout in the case of WMShell), the root_geometry_manager procedure should return XtGeometryNo. If the window manager makes some alternative geometry change, the root geometry procedure may either return XtGeometryNo and handle the new geometry as a resize, or may return XtGeometryAlmost in anticipation that the shell will accept the compromise. If the compromise is not accepted, the new size must then be handled as a resize. Subclasses of Shell that wish to provide their own root_geometry_manager procedures are strongly encouraged to use enveloping to invoke their superclass's root_geometry_manager procedure under most situations, as the window manager interaction may be very complex.

If no ShellClassPart extension record is declared with record_type equal to NULLQUARK, then XtInheritRootGeometryManager is assumed.

4.1.2. ShellPart Definition

The various shell widgets have the following additional instance fields defined in their widget records:

typedef struct {
        String geometry;
        XtCreatePopupChildProc create_popup_child_proc;
        XtGrabKind grab_kind;
        Boolean spring_loaded;
        Boolean popped_up;
        Boolean allow_shell_resize;
        Boolean client_specified;
        Boolean save_under;
        Boolean override_redirect;
        XtCallbackListpopup_callback;
        XtCallbackListpopdown_callback;
        Visual* visual;
} ShellPart;

typedef struct {
        String title;
        int wm_timeout;
        Boolean wait_for_wm;
        Boolean transient;
        Boolean urgency;
        Widget client_leader;
        String window_role;
        struct_OldXSizeHints {
               long flags;
               int x, y;
               int width, height;
               int min_width, min_height;
               int max_width, max_height;
               int width_inc, height_inc;
               struct {
                       int x;
                       int y;
               } min_aspect, max_aspect;
        } size_hints;
        XWMHints wm_hints;
        int base_width, base_height, win_gravity;
        Atom title_encoding;
} WMShellPart;

typedef struct {
        int vendor_specific;
} VendorShellPart;

typedef struct {
        Widget transient_for;
} TransientShellPart;

typedef struct {
        String icon_name;
        Boolean iconic;
        Atom icon_name_encoding;
} TopLevelShellPart;

typedef struct {
        char *class;
        XrmClass xrm_class;
        int argc;
        char **argv;
} ApplicationShellPart;

typedef struct {
        SmcConn connection;
        String session_id;
        String * restart_command;
        String * clone_command;
        String * discard_command;
        String * resign_command;
        String * shutdown_command;
        String * environment;
        String current_dir;
        String program_path;
        unsigned char restart_style;
        Boolean join_session;
        XtCallbackList save_callbacks;
        XtCallbackList interact_callbacks;
        XtCallbackList cancel_callbacks;
        XtCallbackList save_complete_callbacks;
        XtCallbackList die_callbacks;
        XtCallbackList error_callbacks;
} SessionShellPart ;

typedef struct {
        CorePart core;
        CompositePart composite;
        ShellPart shell;
} ShellRec, *ShellWidget;

typedef struct {
        CorePart core;
        CompositePart composite;
        ShellPart shell;
        OverrideShellPart override;
} OverrideShellRec, *OverrideShellWidget;

typedef struct {
        CorePart core;
        CompositePart composite;
        ShellPart shell;
        WMShellPart wm;
} WMShellRec, *WMShellWidget;

typedef struct {
        CorePart core;
        CompositePart composite;
        ShellPart shell;
        WMShellPart wm;
        VendorShellPart vendor;
} VendorShellRec, *VendorShellWidget;

typedef struct {
        CorePart core;
        CompositePart composite;
        ShellPart shell;
        WMShellPart wm;
        VendorShellPart vendor;
        TransientShellPart transient;
} TransientShellRec, *TransientShellWidget;

typedef struct {
        CorePart core;
        CompositePart composite;
        ShellPart shell;
        WMShellPart wm;
        VendorShellPart vendor;
        TopLevelShellPart topLevel;
} TopLevelShellRec, *TopLevelShellWidget;

typedef struct {
        CorePart core;
        CompositePart composite;
        ShellPart shell;
        WMShellPart wm;
        VendorShellPart vendor;
        TopLevelShellPart topLevel;
        ApplicationShellPart application;
} ApplicationShellRec, *ApplicationShellWidget;

typedef struct {
        CorePart core;
        CompositePart composite;
        ShellPart shell;
        WMShellPart wm;
        VendorShellPart vendor;
        TopLevelShellPart topLevel;
        ApplicationShellPart application;
        SessionShellPart session;
} SessionShellRec, *SessionShellWidget;

4.1.3. Shell Resources

The resource names, classes, and representation types specified in the shellClassRec resource list are

OverrideShell declares no additional resources beyond those defined by Shell.

The resource names, classes, and representation types specified in the wmShellClassRec resource list are

The class resource list for VendorShell is implementation-defined.

The resource names, classes, and representation types that are specified in the transientShellClassRec resource list are

The resource names, classes, and representation types that are specified in the topLevelShell
ClassRec resource list are

The resource names, classes, and representation types that are specified in the applicationShellClassRec resource list are

The resource names, classes, and representation types that are specified in the sessionShellClassRec resource list are

The default values for fields common to all classes of public shells (filled in by the Shell resource lists and the Shell initialize procedures) are

The geometry field specifies the size and position and is usually given only on a command line or in a defaults file. If the geometry field is non-NULL when a widget of class WMShell is realized, the geometry specification is parsed using XWMGeometry with a default geometry string constructed from the values of x, y, width, height, width_inc, and height_inc and the size and position flags in the window manager size hints are set. If the geometry specifies an x or y position, then USPosition is set. If the geometry specifies a width or height, then USSize is set. Any fields in the geometry specification override the corresponding values in the Core x, y,width, and height fields. If geometry is NULL or contains only a partial specification, then the Core x, y, width, and height fields are used and PPosition and PSize are set as appropriate. The geometry string is not copied by any of the Intrinsics Shell classes; a client specifying the string in an arglist or varargs list must ensure that the value remains valid until the shell widget is realized. For further information on the geometry string, see Section 10.3 in Xlib - C Language X Interface.

The create_popup_child_ proc procedure is called by the XtPopup procedure and may remain NULL. The grab_kind, spring_loaded, and popped_up fields maintain widget state information as described under XtPopup, XtMenuPopup, XtPopdown, and XtMenuPopdown. The allow_shell_resize field controls whether the widget contained by the shell is allowed to try to resize itself. If allow_shell_resize is False, any geometry requests made by the child will always return XtGeometryNo without interacting with the window manager. Setting save_ under True instructs the server to attempt to save the contents of windows obscured by the shell when it is mapped and to restore those contents automatically when the shell is unmapped. It is useful for popup menus. Setting override_redirect True determines whether the window manager can intercede when the shell window is mapped. For further information on override_redirect, see Section 3.2 in Xlib - C Language X Interface and Sections 4.1.10 and 4.2.2 in the Inter-Client Communication Conventions Manual. The pop-up and pop-down callbacks are called during XtPopup and XtPopdown. The default value of the visual resource is the symbolic value CopyFromParent. The Intrinsics do not need to query the parent's visual type when the default value is used; if a client using XtGetValues to examine the visual type receives the value CopyFromParent, it must then use XGetWindowAttributes if it needs the actual visual type.

The default values for Shell fields in WMShell and its subclasses are

The title and title_encoding fields are stored in the WM_NAMEproperty on the shell's window by the WMShell realize procedure. If the title_encoding field is None, the title string is assumed to be in the encoding of the current locale and the encoding of the WM_NAME property is set to XStdICCTextStyle. If a language procedure has not been set the default value of title encoding is XA_STRING, otherwise the default value is None. The wm_timeout field specifies, in milliseconds, the amount of time a shell is to wait for confirmation of a geometry request to the window manager. If none comes back within that time, the shell assumes the window manager is not functioning properly and sets waitfor_wm to False (later events may reset this value). When waitfor_wm is False, the shell does not wait for a response but relies on asynchronous notification. If transient is True, the WM_TRANSIENT_FOR property will be stored on the shell window with a value as specified below. The interpretation of this property is specific to the window manager under which the application is run; see the Inter-Client Communication Conventions Manual for more details.

The realize and set_values procedures of WMShell store the WM_CLIENT_LEADER property on the shell window. When client_leader is not NULL and the client leader widget is realized, the property will be created with the value of the window of the client leader widget. When client_leader is NULL and the shell widget has a NULL parent, the widget's window is used as the value of the property. When client_leader is NULL and the shell widget has a non-NULL parent, a search is made for the closest shell ancestor with a non-NULL client_leader, and if none is found the shell ancestor with a NULL parent is the result. If the resulting widget is realized, the property is created with the value of the widget's window.

When the value of window_role is not NULL, the realize and set_values procedures store the WM_WINDOW_ROLE property on the shell's window with the value of the resource.

All other resources specify fields in the window manager hints and the window manager size hints. The realize and set values procedures of WMShell set the corresponding flag bits in the hints if any of the fields contain non-default values. In addition, if a flag bit is set that refers to a field with the value XtUnspecifiedShellInt, the value of the field is modified as follows:

If the shell widget has a non-NULL parent, then the realize and set_values procedures replace the value XtUnspecifiedWindow in the window_group field with the window id of the root widget of the widget tree if the root widget is realized. The symbolic constant XtUnspecifiedWindowGroup may be used to indicate that the window_group hint flag bit is not to be set. If transient is True and the shell's class is not a subclass of TransientShell and window_group is not XtUnspecifiedWindowGroup the WMShell realize and set_values procedures then store the WM TRANSIENT FOR property with the value of window_group.

Transient shells have the following additional resource:

The realize and set_values procedures of TransientShell store the WM_TRANSIENT_FOR property on the shell window if transient is True. If transientfor is non-NULL and the widget specified by transient_for is realized, then its window is used as the value of the WM_TRANSIENT_FOR property; otherwise, the value of window_group is used.

TopLevel shells have the following additional resources:

The icon_name and icon_name_encoding fields are stored in the WM_ICON_NAME property on the shell's window by the TopLevelShell realize procedure. If the icon name encoding field is None, the icon_name string is assumed to be in the encoding of the current locale and the encoding of the WM_ICON_NAME property is set to XStdlCCTextStyle. If a language procedure has not been set the default value of icon_name_encoding is XA_STRING, otherwise the default value is None. The iconic field may be used by a client to request that the window manager iconify or deiconify the shell; the TopLevelShell set_values procedure will send the appropriate WM_CHANGE_STATE message (as specified by the Inter-Client Communication Conventions Manual) if this resource is changed from False to True, and will call XtPopup specifying grab kind as XtGrabNone if iconic is changed from True to False. The XtNiconic resource is also an alternative way to set the XtNinitialState resource to indicate that a shell should be initially displayed as an icon; the TopLevelShell initialize procedure will set initial_state to IconicState if iconic is True.

Application shells have the following additional resources:

The argc and argv fields are used to initialize the standard property WM_COMMAND. See the Inter-Client Communication Conventions Manual for more information.

The default values for the SessionShell instance fields, which are filled in from the resource lists and by the initialize procedure, are

The connection field contains the session connection object, or NULL if a session connection is not being managed by this widget.

The session_id is an identification assigned to the session participant by the session manager. The session id will be passed to the session manager as the client identifier of the previous session. When a connection is established with the session manager, the client id assigned by the session manager is stored in the session id field. When not NULL, the session_id of the Session shell widget which is at the root of the widget tree of the client leader widget will be used to create the SM_CLIENT_ID property on the client leader's window.

If join_ session is False, the widget will not attempt to establish a connection to the session manager at shell creation time.

The restart command, clone_command, discard command, resign_command, shutdown_command, environment, current_dir, program_path, and restart_style fields contain standard session properties.

When a session connection is established or newly managed by the shell, the shell initialize and set_values methods check the values of the restart_ command, clone_command, and program path resources. At that time, if restart command is NULL, the value of the argv resource will be copied to restart_comrnand. Whether or not restart_comrnand was NULL, if "-xtsessionID" "<session id>" does not already appear in the restart command, it will be added by the initialize and set_values methods at the beginning of the command arguments; if the "-xtsessionID" argument already appears with an incorrect session id in the following argument, that argument will be replaced with the current session id.

After this, the shell initialize and set_values procedures check the clone command. If clone command is NULL, restart command will be copied to clone command, except the "-xtsessionID" and following argument will not be copied.

Finally, the shell initialize and set_values procedures check the program_path. If program_path is NULL, the first element of restart_command is copied to program_path.

The possible values of restart_ style are SmRestartIfRunning, SmRestartAnyway, SmRestartImmediately, and SmRestartNever. A resource converter is registered for this resource; for the strings that it recognizes see section 9.6.1.

The resource type EnvironmentArray is an array of pointers to strings; each string has the format "name=value". The '=' character may not appear in the name, and the string is terminated by a null character.

Applications can participate in a user's session, exchanging messages with the session manager as described in the X Session Management Protocol and the X Session Management Library.

When a widget of sessionShellWidgetClass or a subclass is created, the widget provides support for the application as a session participant, and continues to provide support until the widget is destroyed.

4.2.1. Joining a Session

When a Session shell is created, if connection is NULL, and if join_session is True, and if argv or rrestart_ command is not NULL, and if in POSIX environments the SESSION_MANAGER environment variable is defined, the shell will attempt to establish a new connection with the session manager.

To transfer management of an existing session connection from an application to the shell at widget creation time, pass the existing session connection ID as the connection resource value when creating the Session shell, and if the other creation-time conditions on session participation are met, the widget will maintain the connection with the session manager. The application must insure that only one Session shell manages the connection.

In the Session shell set_values procedure, if join_session changes from False to True and connection is NULL and when in POSIX environments the SESSION_MANAGER environment variable is defined, the shell will attempt to open a connection to the session manager. If connection changes from NULL to non-NULL, the Session shell will take over management of that session connection and will set join session to True . If join session changes from False to True and connection is not NULL, the Session shell will take over management of the session connection.

When a successful connection has been established, connection contains the session connection ID for the session participant. When the shell begins to manage the connection, it will call XtAppAddInput to register the handler which watches for protocol messages from the session manager. When the attempt to connect fails, a warning message is issued and connection is set to NULL.

While the connection is being managed, if a SaveYourself, SaveYourselfPhase2, Interact, ShutdownCancelled, SaveComplete, or Die message is received from the session manager, the Session shell will call out to application callback procedures registered on the respective callback list of the Session shell, and will send SaveYourselfPhase2Request, InteractRequest, InteractDone, SaveYourselfDone, and ConnectionClosed messages as appropriate. Initially, all of the client's session properties are undefined. When any of the session property resource values are defined or change, the Session shell initialize and set_values procedures will update the client's session property value by a SetProperties or a DeleteProperties message, as appropriate. The session ProcessID and UserID properties are always set by the shell when it is possible to determine the value of these properties.

4.2.2. Saving Application State

The session manager instigates an application checkpoint by sending a SaveYourself request. Applications are responsible for saving their state in response to the request.

When the SaveYourself request arrives, the procedures registered on the Session shell's save callback list are called. If the application does not register any save callback procedures on the save callback list, the shell will report to the session manager that the application failed to save its state. Each procedure on the save callback list receives a token in the call data parameter.

The checkpoint token in the call_ data parameter is of type XtCheckpointToken.

typedef struct {
        int save_type;
        int interact_style;
        Boolean shutdown;
        Boolean fast;
        Boolean cancel_shutdown
        int phase;
        int interact_dialog type; /*return*/
        Boolean request_cancel; /* return */
        Boolean request_next_phase; /* return */
        Boolean save_success; /* return */
} XtCheckpointTokenRec, *XtCheckpointToken;

The save_ type, interact_style, shutdown, and fast fields of the token contain the parameters of the SaveYourself message. The possible values of save_ type are SmSaveLocal, SmSaveGlobal, and SmSaveBoth; these indicate the type of information to be saved. The possible values of interact style are SmInteractStyleNone, SmInteractStyleErrors, and SmInteractStyleAny; these indicate whether user interaction would be permitted and if so, what kind of interaction. If shutdown is True, the checkpoint is being perforrned in preparation for the end of the session. If fast is ,True, the client should perform the checkpoint as quickly as possible. If cancel_ shutdown is True, a ShutdownCancelled message has been received for the current save operadon. The phase is used by manager clients, such as a window manager, to distinguish between the first and second phase of a save operadon. The phase will be either 1 or 2. The remaining fields in the checkpoint token structure are provided for the application to communicate with the shell.

Upon entry to the first application save callback procedure, the return fields in the token have the following initial values: interact_ dialog_type is SmDialogNormal; request_cancel is False; request_next_phase is False; and save_success is True. When a token is returned with any of the four return fields containing a non-Initial value, and when the field is applicable, subsequent tokens passed to the application during the current save operation will always contain the non-initial value.

The purpose of the token's save_ success field is to indicate the outcome of the entire operation to the session manager and ultimately, to the user. Returning False indicates some portion of the application state could not be successfully saved. If any token is returned to the shell with save_ success False, tokens subsequently received by the application for the current save operation will show save success as False. When the shell sends the final status of the checkpoint to the session manager, it will indicate failure to save application state if any token was returned with save success False.

Session participants which manage and save the state of other clients should structure their save or interact callbacks to set request next_phase to True when phase is 1, which will cause the shell to send the SaveYourselfPhase2Request when the first phase is complete. When the SaveYourselfPhase2 message is received, the shell will invoke the save callbacks a second time with phase equal to 2. Manager clients should save the state of other clients when the callbacks are invoked the second time and phase equal to 2.

The application may request additional tokens while a checkpoint is under way, and these additional tokens must be returned by an explicit call.

To request an additional token for a save callback response which has a deferred outcome, use XtSessionGetToken .

XtCheckpointToken XtSessionGetToken(widget)

Widget widget;

The XtSessionGetToken function will return NULL if no checkpoint operation is currently under way.

To indicate the completion of checkpoint processing including user interaction, the application must signal the Session shell by returning all tokens. (See Sections 4.2.2.2 and 4.2.2.4). To return a token use XtSessionReturnToken.

void XtSessionReturnToken(token)

XtCheckpointToken token;

Tokens passed as call_data to save callbacks are implicitly returned when the save callback procedure returns. A save callback procedure should not call XtSessionReturnToken on the token passed in its call data.

4.2.2.1. Requesting Interaction

When the token interact style allows user interaction, the application may interact with the user during the checkpoint, but must wait for permission to interact. Applications request permission to interact with the user during the checkpointing operation by registering a procedure on the Session shell's interact callback list. When all save callback procedures have returned, and each time a token which was granted by a call to XtSessionGetToken is returned, the Session shell examines the interact callback list. If interaction is permitted and the interact callback list is not empty, the shell will send an InteractRequest to the session manager when an interact request is not already outstanding for the application.

The type of interaction dialog that will be requested is specified by the interact_dialog_type field in the checkpoint token. The possible values for interact_ dialog_type are SmDialogError and SmDialogNormal. If a token is returned with interact_ dialog_type containing SmDialogError, the interact request and any subsequent interact requests will be for an error dialog; otherwise, the request will be for a normal dialog with the user.

When a token is returned with save success False or interact_dialog_type SmDialogError, tokens subsequently passed to callbacks during the same active SaveYourself response will reflect these changed values, indicating that an error condition has occurred during the checkpoint.

The request cancel field is a return value for interact callbacks only. Upon return from a procedure on the save callback list, the value of the token's request cancel field is not examined by the shell. This is also true of tokens received through a call to XtSessionGetToken.

4.2.2.2. Interacting with the User

When the session manager grants the application's request for user interaction, the Session shell receives an Interact message. The procedures registered on the interact callback list are executed, but not as if executing a typical callback list. These procedures are individually executed in sequence, with a checkpoint token functioning as the sequencing mechanism. Each step in the sequence begins by removing a procedure from the interact callback list and executing it with a token passed in the call data. The interact callback will typically pop up a dialog box and return. When the user interaction and associated application checkpointing has completed, the application must return the token by calling XtSessionReturnToken. Returning the token completes the current step, and triggers the next step in the sequence.

During interaction the client may request cancellation of a shutdown. When a token passed as call data to an interact procedure is returned, if shutdown is True and cancel_shutdown is False, request_cancel indicates whether the application requests that the pending shutdown be cancelled. If request_cancel is True, the field will also be True in any tokens subsequently granted during the checkpoint operation. When a token is returned requesting cancellation of the session shutdown, pending interact procedures will still be called by the Session shell. When all interact procedures have been removed from the interact callback list, executed, and the final interact token returned to the shell, an InteractDone message is sent to the session manager, indicating whether a pending session shutdown is requested to be cancelled.

4.2.2.3. Responding to a Shutdown Cancellation

Callbacks registered on the cancel callback list are invoked when the Session shell processes a ShutdownCancelled message from the session manager. This may occur during the processing of save callbacks, while waiting for interact permission, during user interaction, or after the save operation is complete and the application is expecting a SaveComplete or a Die message. The call_data for these callbacks is NULL.

When the shell notices that a pending shutdown has been cancelled, the token cancel_shutdown field will be True in tokens subsequently given to the application.

Receiving notice of a shutdown cancellation does not cancel the pending execution of save callbacks or interact callbacks. After the cancel callbacks execute, if interact_ style is not SmInteractStyleNone and the interact list is not empty, the procedures on the interact callback list will be executed and passed a token with interact style SmInteractStyleNone. The application should not interact with the user, and the Session shell will not send an InteractDone message.

4.2.2.4. Completing a Save

When there is no user interaction, the shell regards the application as having finished saving state when all callback procedures on the save callback list have returned, and any additional tokens passed out by XtSessionGetToken have been returned by corresponding calls to XtSessionReturnToken. If the save operation involved user interaction, the above completion conditions apply, and in addition, all requests for interaction have been granted or cancelled, and all tokens passed to interact callbacks have been returned through calls to XtSessionReturnToken. If the save operation involved a manager client that requested the second phase, the above conditions apply to both the first and second phase of the save operation.

When the application has finished saving state, the Session shell will report the result to the session manager by sending the SaveYourselfDone message. If the session is continuing, the shell will receive the SaveComplete message when all applications have completed saving state. This message indicates that applications may again allow changes to their state. The shell will execute the save_complete callbacks. The call_data for these callbacks is NULL.

4.2.3. Responding to a Shutdown

Callbacks registered on the die callback list are invoked when the session manager sends a Die message. The callbacks on this list should do whatever is appropriate to quit the application. Before executing procedures on the die callback list, the Session shell will close the connection to the session manager and will remove the handler which watches for protocol messages. The call data for these callbacks is NULL.

4.2.4. Resigning from a Session

When the Session shell widget is destroyed, the destroy method will close the connection to the session manager by sending a ConnectionClosed protocol message, and will remove the input callback which was watching for session protocol messages.

When XtSetValues is used to set join session to False, the set_values method of the Session shell will close the connection to the session manager if one exists by sending a ConnectionClosed message, and connection will be set to NULL.

Applications which exit in response to user actions and which do not wait for phase 2 destroy to complete on the Session shell should set join_session to False before exiting.

When XtSetValues is used to set connection to NULL, the Session shell will stop managing the connection, if one exists. However that session connection will not be closed.

Applications which wish to ensure continuation of a session connection beyond the destruction of the shell, should first retrieve the connection resource value, then set the connection resource to NULL, and then they may safely destroy the widget without losing control of the session connection.

The error callback list will be called if an unrecoverable communications error occurs while the shell is managing the connection. The shell will close the connection, set connection to NULL,

remove the input callback, and call the procedures registered on the error callback list. The call data for these callbacks is NULL.