Chapter 4. Shell Widgets

Table of Contents

Shell widgets hold an application's top-level widgets to allow them to communicate with the window manager and session manager. Shells have been designed to be as nearly invisible as possible. Clients have to create them, but they should never have to worry about their sizes.

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 property set. 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 SessionShell.
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.

Shell Widget Definitions

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 subclass 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, TransientShell, TopLevelShell, ApplicationShell, and SessionShell are intended for public use.

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 the section called “Class Extension Records”
XrmQuark record_type; See the section called “Class Extension Records”
long version; See the section called “Class Extension Records”
Cardinal record_size; See the section called “Class Extension Records”
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;
} ApplicationShellClassRec;

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;
SessionShellClassPart 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.

Types	Variables
ShellWidget	shellWidgetClass
OverrideShellWidget	overrideShellWidgetClass
WMShellWidget	wmShellWidgetClass
VendorShellWidget	vendorShellWidgetClass
TransientShellWidget	transientShellWidgetClass
TopLevelShellWidget	topLevelShellWidgetClass
ApplicationShellWidget	applicationShellWidgetClass
SessionShellWidget	sessionShellWidgetClass
ShellWidgetClass
OverrideShellWidgetClass
WMShellWidgetClass
VendorShellWidgetClass
TransientShellWidgetClass
TopLevelShellWidgetClass
ApplicationShellWidgetClass
SessionShellWidgetClass

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 the section called “Class Extension Records”).

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 does not change the window geometry within some timeout interval (equal to wm_timeout in the case of WMShells), the root_geometry_manager procedure should return XtGeometryNo. If the window manager makes some alternative geometry change, the root_geometry_manager procedure may return either XtGeometryNo and handle the new geometry as a resize or 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.

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;
XtCallbackList popup_callback;
XtCallbackList popdown_callback;
Visual * visual;
} ShellPart;

typedef struct {
int empty;
} OverrideShellPart;

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;

The full shell widget instance record definitions are:

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;

Shell Resources

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

Name	Class	Representation
XtNallowShellResize	XtCAllowShellResize	XtRBoolean
XtNcreatePopupChildProc	XtCCreatePopupChildProc	XtRFunction
XtNgeometry	XtCGeometry	XtRString
XtNoverrideRedirect	XtCOverrideRedirect	XtRBoolean
XtNpopdownCallback	XtCCallback	XtRCallback
XtNpopupCallback	XtCCallback	XtRCallback
XtNsaveUnder	XtCSaveUnder	XtRBoolean
XtNvisual	XtCVisual	XtRVisual

OverrideShell declares no additional resources beyond those defined by Shell.

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

Name	Class	Representation
XtNbaseHeight	XtCBaseHeight	XtRInt
XtNbaseWidth	XtCBaseWidth	XtRInt
XtNclientLeader	XtCClientLeader	XtRWidget
XtNheightInc	XtCHeightInc	XtRInt
XtNiconMask	XtCIconMask	XtRBitmap
XtNiconPixmap	XtCIconPixmap	XtRBitmap
XtNiconWindow	XtCIconWindow	XtRWindow
XtNiconX	XtCIconX	XtRInt
XtNiconY	XtCIconY	XtRInt
XtNinitialState	XtCInitialState	XtRInitialState
XtNinput	XtCInput	XtRBool
XtNmaxAspectX	XtCMaxAspectX	XtRInt
XtNmaxAspectY	XtCMaxAspectY	XtRInt
XtNmaxHeight	XtCMaxHeight	XtRInt
XtNmaxWidth	XtCMaxWidth	XtRInt
XtNminAspectX	XtCMinAspectX	XtRInt
XtNminAspectY	XtCMinAspectY	XtRInt
XtNminHeight	XtCMinHeight	XtRInt
XtNminWidth	XtCMinWidth	XtRInt
XtNtitle	XtCTitle	XtRString
XtNtitleEncoding	XtCTitleEncoding	XtRAtom
XtNtransient	XtCTransient	XtRBoolean
XtNwaitforwm, XtNwaitForWm	XtCWaitforwm, XtCWaitForWm	XtRBoolean
XtNwidthInc	XtCWidthInc	XtRInt
XtNwindowRole	XtCWindowRole	XtRString
XtNwinGravity	XtCWinGravity	XtRGravity
XtNwindowGroup	XtCWindowGroup	XtRWindow
XtNwmTimeout	XtCWmTimeout	XtRInt
XtNurgency	XtCUrgency	XtRBoolean
_

The class resource list for VendorShell is implementation-defined.

The resource names, classes, and representation types that are specified in the transient\%ShellClassRec resource list are:

Name	Class	Representation
XtNtransientFor	XtCTransientFor	XtRWidget

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

Name	Class	Representation
XtNiconName	XtCIconName	XtRString
XtNiconNameEncoding	XtCIconNameEncoding	XtRAtom
XtNiconic	XtCIconic	XtRBoolean

The resource names, classes, and representation types that are specified in the application\%ShellClassRec resource list are:

Name	Class	Representation
XtNargc	XtCArgc	XtRInt
XtNargv	XtCArgv	XtRStringArray

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

Name	Class	Representation
XtNcancelCallback	XtCCallback	XtRCallback
XtNcloneCommand	XtCCloneCommand	XtRCommandArgArray
XtNconnection	XtCConnection	XtRSmcConn
XtNcurrentDirectory	XtCCurrentDirectory	XtRDirectoryString
XtNdieCallback	XtCCallback	XtRCallback
XtNdiscardCommand	XtCDiscardCommand	XtRCommandArgArray
XtNenvironment	XtCEnvironment	XtREnvironmentArray
XtNerrorCallback	XtCCallback	XtRCallback
XtNinteractCallback	XtCCallback	XtRCallback
XtNjoinSession	XtCJoinSession	XtRBoolean
XtNprogramPath	XtCProgramPath	XtRString
XtNresignCommand	XtCResignCommand	XtRCommandArgArray
XtNrestartCommand	XtCRestartCommand	XtRCommandArgArray
XtNrestartStyle	XtCRestartStyle	XtRRestartStyle
XtNsaveCallback	XtCCallback	XtRCallback
XtNsaveCompleteCallback	XtCCallback	XtRCallback
XtNsessionID	XtCSessionID	XtRString
XtNshutdownCommand	XtCShutdownCommand	XtRCommandArgArray

ShellPart Default Values

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:

Field	Default Value
geometry	NULL
create_popup_child_proc	NULL
grab_kind	(none)
spring_loaded	(none)
popped_up	`False`
allow_shell_resize	`False`
client_specified	(internal)
save_under	`True` for OverrideShell and TransientShell, False otherwise
override_redirect	`True` for OverrideShell, `False` otherwise
popup_callback	NULL
popdown_callback	NULL
visual	`CopyFromParent`

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 the section called “Parsing the Window Geometry” 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 pop-up 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 the section called “Window Attributes” in Xlib — C Language X Interface and the section called “Pop-up Windows” and the section called “Redirection of Operations” 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:

Field	Default Value
title	Icon name, if specified, otherwise the application's name
wm_timeout	Five seconds, in units of milliseconds
wait_for_wm	`True`
transient	`True` for TransientShell, `False` otherwise
urgency	`False`
client_leader	NULL
window_role	NULL
min_width	`XtUnspecifiedShellInt`
min_height	`XtUnspecifiedShellInt`
max_width	`XtUnspecifiedShellInt`
max_height	`XtUnspecifiedShellInt`
width_inc	`XtUnspecifiedShellInt`
height_inc	`XtUnspecifiedShellInt`
min_aspect_x	`XtUnspecifiedShellInt`
min_aspect_y	`XtUnspecifiedShellInt`
max_aspect_x	`XtUnspecifiedShellInt`
max_aspect_y	`XtUnspecifiedShellInt`
input	`False`
initial_state	Normal
icon_pixmap	None
icon_window	None
icon_x	`XtUnspecifiedShellInt`
icon_y	`XtUnspecifiedShellInt`
icon_mask	None
window_group	`XtUnspecifiedWindow`
base_width	`XtUnspecifiedShellInt`
base_height	`XtUnspecifiedShellInt`
win_gravity	`XtUnspecifiedShellInt`
title_encoding	See text

The title and title_encoding fields are stored in the WM_NAME property 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 wait_for_wm to False (later events may reset this value). When wait_for_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 nondefault 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:

Field	Replacement
base_width, base_height	0
width_inc, height_inc	1
max_width, max_height	32767
min_width, min_height	1
min_aspect_x, min_aspect_y	-1
max_aspect_x, max_aspect_y	-1
icon_x, icon_y	-1
win_gravity	Value returned by `XWMGeometry` if called, else `NorthWestGravity`

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, 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:

Field	Replacement
transient_for	NULL

The realize and set_values procedures of TransientShell store the WM_TRANSIENT_FOR property on the shell window if transient is True. If transient_for 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 the following additional resources:

Field	Default Value
icon_name	Shell widget's name
iconic	False
icon_name_encoding	See text

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 XStdICCTextStyle. 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:

Field	Default Value
argc	0
argv	NULL

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

Field	Default Value
cancel_callbacks	NULL
clone_command	See text
connection	NULL
current_dir	NULL
die_callbacks	NULL
discard_command	NULL
environment	NULL
error_callbacks	NULL
interact_callbacks	NULL
join_session	True
program_path	NULL
resign_command	NULL
restart_command	See text
restart_style	SmRestartIfRunning
save_callbacks	NULL
save_complete_callbacks	NULL
session_id	NULL
shutdown_command	NULL

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 that 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. See the section called “Joining a Session” and the section called “Resigning from a Session” for more information on the functionality of this resource.

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_command. Whether or not restart_command 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 the section called “Predefined Resource Converters”.

The resource type EnvironmentArray is a NULL-terminated 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.

Session Participation

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.

Joining a Session

When a Session shell is created, if connection is NULL, and if join_session is True, and if argv or restart_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 ensure 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.

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 performed 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 operation. (See the section called “Resigning from a Session”.) The phase is used by manager clients, such as a window manager, to distinguish between the first and second phase of a save operation. 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 noninitial value, and when the field is applicable, subsequent tokens passed to the application during the current save operation will always contain the noninitial 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 that 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 that has a deferred outcome, use XtSessionGetToken.

XtCheckpointToken XtSessionGetToken(Widget widget);

widget

Specifies the Session shell widget which manages session participation.

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 the section called “Interacting with the User during a Checkpoint” and the section called “Completing a Save”). To return a token, use XtSessionReturnToken.

void XtSessionReturnToken(XtCheckpointToken token);

void XtSessionReturnToken(XtCheckpointToken token);

token

Specifies a token that was received as the call_data by a procedure on the interact callback list or a token that was received by a call to XtSessionGetToken.

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.

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 that 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.

Interacting with the User during a Checkpoint

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.

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.

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.

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 that watches for protocol messages. The call_data for these callbacks is NULL.

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 that 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 that exit in response to user actions and that 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 that 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.