X Session Management Protocol

X Consortium Standard

Mike Wexler

X Version 11, Release 7

Version 1.0

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE X CONSORTIUM BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Except as contained in this notice, the name of the X Consortium shall not be used in advertising or otherwise to promote the sale, use or other dealings in this Software without prior written authorization from the X Consortium.

X Window System is a trademark of The Open Group.

This document specifies a protocol that facilitates the management of groups of client applications by a session manager. The session manager can cause clients to save their state, to shut down, and to be restarted into a previously saved state. This protocol is layered on top of the X.Org ICE protocol.


Table of Contents

1. Acknowledgments
2. Definitions and Goals
3. Overview of the Protocol
4. Data Types
5. Protocol Setup and Message Format
6. Client Identification String
7. Protocol
8. Errors
9. State Diagrams
Client State Diagram
Session Manager State Diagram
10. Protocol Encoding
Types
Messages
11. Predefined Properties

Chapter 1. Acknowledgments

First I would like to thank the entire ICCCM and Intrinsics working groups for the comments and suggestions. I would like to make special thanks to the following people (in alphabetical order), Jordan Brown, Ellis Cohen, Donna Converse, Vania Joloboff, Stuart Marks, Ralph Mor and Bob Scheifler.

Chapter 2. Definitions and Goals

The purpose of the X Session Management Protocol (XSMP) is to provide a uniform mechanism for users to save and restore their sessions. A session is a group of clients, each of which has a particular state. The session is controlled by a network service called the session manager. The session manager issues commands to its clients on behalf of the user. These commands may cause clients to save their state or to terminate. It is expected that the client will save its state in such a way that the client can be restarted at a later time and resume its operation as if it had never been terminated. A client's state might include information about the file currently being edited, the current position of the insertion point within the file, or the start of an uncommitted transaction. The means by which clients are restarted is unspecified by this protocol.

For purposes of this protocol, a client of the session manager is defined as a connection to the session manager. A client is typically, though not necessarily, a process running an application program connected to an X Window System display. However, a client may be connected to more than one X display or not be connected to any X displays at all.

This protocol is layered on top of the X Consortium's ICE protocol and relies on the ICE protocol to handle connection management and authentication.

Chapter 3. Overview of the Protocol

Clients use XSMP to register themselves with the session manager (SM). When a client starts up, it should connect to the SM. The client should remain connected for as long as it runs. A client may resign from the session by issuing the proper protocol messages before disconnecting. Termination of the connection without notice will be taken as an indication that the client died unexpectedly.

Clients are expected to save their state in such a way as to allow multiple instantiations of themselves to be managed independently. A unique value called a client-ID is provided by the protocol for the purpose of disambiguating multiple instantiations of clients. Clients may use this ID, for example, as part of a filename in which to store the state for a particular instantiation. The client-ID should be saved as part of the command used to restart this client (the RestartCommand) so that the client will retain the same ID after it is restarted. Certain small pieces of state might also be stored in the RestartCommand. For example, an X11 client might place a '-twoWindow' option in its RestartCommand to indicate that it should start up in two window mode when it is restarted.

The client finds the network address of the SM in a system-dependent way. On POSIX systems an environment variable called SESSION_MANAGER will contain a list of network IDs. Each id will contain the transport name followed by a slash and the (transport-specific) address. A TCP/IP address would look like this:

tcp/hostname:portnumber

where the hostname is a fully qualified domain name. A Unix Domain address looks like this:

local/hostname:path

A DECnet address would look like this:

decnet/nodename::objname

If multiple network IDs are specified, they should be separated by commas.

Rationale

There was much discussion over whether the XSMP protocol should use X as the transport protocol or whether it should use its own independent transport. It was decided that it would use an independent protocol for several reasons. First, the Session Manager should be able to manage programs that do not maintain an X connection. Second, the X protocol is not appropriate to use as a general-purpose transport protocol. Third, a session might span multiple displays.

The protocol is connection based, because there is no other way for the SM to determine reliably when clients terminate.

It should be noted that this protocol introduces another single point of failure into the system. Although it is possible for clients to continue running after the SM has exited, this will probably not be the case in normal practice. Normally the program that starts the SM will consider the session to be terminated when the SM exits (either normally or abnormally).

To get around this would require some sort of rendezvous server that would also introduce a single point of failure. In the absence of a generally available rendezvous server, XSMP is kept simple in the hopes of making simple reliable SMs.

Some clients may wish to manage the programs they start. For example, a mail program could start a text editor for editing the text of a mail message. A client that does this is a session manager itself; it should supply the clients it starts with the appropriate connection information (i.e., the SESSION_MANAGER environment variable) that specifies a connection to itself instead of to the top level session manager.

Each client has associated with it a list of properties. A property set by one client is not visible to any other client. These properties are used for the client to inform the SM of the client's current state. When a client initially connects to the SM, there are no properties set.

Chapter 4. Data Types

XSMP messages contain several types of data. Both the SM and the client always send messages in their native byte order. Thus, both sides may need to byte-swap the messages received. The need to do byte-swapping is determined at run-time by the ICE protocol.

If an invalid value is specified for a field of any of the enumerated types, a BadValue error message must be sent by the receiver of the message to the sender of the message.

Type NameDescription
BOOL

False or True

INTERACT_STYLENone Errors or Any
DIALOG_TYPEError or Normal
SAVE_TYPEGlobal Local or Both
CARD8a one-byte unsigned integer
CARD16a two-byte unsigned integer
CARD32a four-byte unsigned integer
ARRAY8a sequence of CARD8s
LISTofARRAY8a sequence of ARRAY8s
PROPERTYa property name (an ARRAY8), a type name, and a value of that type
LISTofPROPERTYa counted collection of ­PROPERTYs.

Chapter 5. Protocol Setup and Message Format

To start the XSMP protocol, the client sends the server an ICE ProtocolSetup message. All XSMP messages are in the standard ICE message format. The message's major opcode is assigned to XSMP by ICE at run-time. The different parties (client and SM) may be assigned different major opcodes for XSMP. Once assigned, all XSMP messages issued by this party will use the same major opcode. The message's minor opcode specifies which protocol message this message contains.

Chapter 6. Client Identification String

A client ID is a string of XPCS characters encoded in ISO Latin 1 (ISO 8859-1). No null characters are allowed in this string. The client ID string is used in the Register­Client and Register­ClientReply messages.

Client IDs consist of the pieces described below. The ID is formed by concatenating the pieces in sequence, without separator characters. All pieces are padded on the left with '0' characters so as to fill the specified length. Decimal numbers are encoded using the characters '0' through '9', and hexadecimal numbers using the characters '0' through '9' and 'A' through 'F'.

  • Version. This is currently the character '1'.

  • Address type and address. The address type will be one of


         '1'     a 4-byte IPv4 address encoded as 8 hexadecimal digits
         '2'     a 6-byte DECNET address encoded as 12 hexadecimal digits
         '6'     a 16-byte IPv6 address encoded as 32 hexadecimal digits

    The address is the one of the network addresses of the machine where the session manager (not the client) is running. For example, the IP address 198.112.45.11 would be encoded as the string "QC6702D0B".

  • Time stamp. A 13-digit decimal number specifying the number of milliseconds since 00:00:00 UTC, January 1, 1970.

  • Process-ID type and process-ID. The process-ID type will be one of


         '1' a POSIX process-ID encoded as a 10-digit decimal number.

    The process-ID is the process-ID of the session manager, not of a client.

  • Sequence number. This is a four-digit decimal number. It is incremented every time the session manager creates an ID. After reaching "Q9999" it wraps to "Q0000".

    Rationale

    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. The construction specified above will ensure that any client ID created by any user, session manager, and machine will be different from any other.

Chapter 7. Protocol

The protocol consists of a sequence of messages as described below. Each message type is specified by an ICE minor opcode. A given message type is sent either from a client to the session manager or from the session manager to a client; the appropriate direction is listed with each message's description. For each message type, the set of valid responses and possible error messages are listed. The ICE severity is given in parentheses following each error class.

RegisterClient [Client → SM]

  previous-ID: ARRAY8

  Valid Responses: RegisterClientReply

  Possible Errors: BadValue (CanContinue)
  

The client must send this message to the SM to register the client's existence. If a client is being restarted from a previous session, the previous-ID field must contain the client ID from the previous session. For new clients, previous-ID should be of zero length.

If previous-ID is not valid, the SM will send a BadValue error message to the client. At this point the SM reverts to the register state and waits for another RegisterClient The client should then send a RegisterClient with a null previous-ID field.

RegisterClientReply [Client ← SM]

  client-ID: ARRAY8
  

The client-ID specifies a unique identification for this client. If the client had specified an ID in the previous-ID field of the RegisterClient message, client-ID will be identical to the previously specified ID. If previous-ID was null, client-ID will be a unique ID freshly generated by the SM. The client-ID format is specified in section 6.

If the client didn't supply a previous-ID field to the Register­Client message, the SM must send a SaveYourself message with type = Local, shutdown = False, interact-style = None, and fast = False immediately after the RegisterClientReply The client should respond to this like any other Save­Yourself message.

SaveYourself [Client ← SM]

  type: SAVE_TYPE
  shutdown: BOOL
  interact-style: INTERACT_STYLE
  fast: BOOL

  Valid Responses:
    SetProperties
    DeleteProperties
    GetProperties
    SaveYourselfDone
    SaveYourselfPhase2Request
    InteractRequest
  

The SM sends this message to a client to ask it to save its state. The client writes a state file, if necessary, and, if necessary, uses SetProperties to inform the SM of how to restart it and how to discard the saved state. During this process it can, if allowed by interact-style, request permission to interact with the user by sending an InteractRequest message. After the state has been saved, or if it cannot be successfully saved, and the properties are appropriately set, the client sends a SaveYourselfDone message. If the client wants to save additional information after all the other clients have finished changing their own state, the client should send SaveYourselfPhase2Request instead of SaveYourselfDone The client must then freeze interaction with the user and wait until it receives a SaveComplete Die or a ShutdownCancelled message.

If interact-style is None the client must not interact with the user while saving state. If the interact-style is Errors the client may interact with the user only if an error condition arises. If interact-style is Any then the client may interact with the user for any purpose. This is done by sending an Interact­Request message. The SM will send an Interact message to each client that sent an Interact­Request The client must postpone all interaction until it gets the Interact message. When the client is done interacting it should send the SM an Interact­Done message. The Interact­Request message can be sent any time after a Save­Yourself and before a Save­Yourself­Done

Unusual circumstances may dictate multiple interactions. The client may initiate as many Interact­Request - Interact - InteractDone sequences as it needs before it sends SaveYourselfDone

When a client receives Save­Yourself and has not yet responded Save­Yourself­Done to a previous Save­Yourself it must send a Save­Yourself­Done and may then begin responding as appropriate to the newly received Save­Yourself

The type field specifies the type of information that should be saved: Global Local or Both The Local type indicates that the application must update the properties to reflect its current state, send a Save­Yourself­Done and continue. 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. The Global type indicates that the user wants the client to commit all of its data to permanent, globally-accessible storage. Both indicates that the client should do both of these. If Both is specified, the client should first commit the data to permanent storage before updating its SM properties.

Examples

If a word processor was sent a SaveYourself with a type of Local it could create a temporary file that included the current contents of the file, the location of the cursor, and other aspects of the current editing session. It would then update its Restart­Command property with enough information to find the temporary file, and its Discard­Command with enough information to remove it.

If a word processor was sent a SaveYourself with a type of Global it would simply save the currently edited file.

If a word processor was sent a SaveYourself with a type of Both it would first save the currently edited file. It would then create a temporary file with information such as the current position of the cursor and what file is being edited. It would then update its Restart­Command property with enough information to find the temporary file, and its Discard­Command with enough information to remove it.

Once the SM has send SaveYourself to a client, it can't send another SaveYourself to that client until the client either responds with a SaveYourselfDone or the SM sends a ShutdownCancelled

Advice to Implementors

If the client stores local any state in a file or similar "external" storage, it must create a distinct copy in response to each SaveYourself message. It must not simply refer to a previous copy, because the SM may discard that previous saved state using a DiscardCommand without knowing that it is needed for the new checkpoint.

The shutdown field specifies whether the system is being shut down.

Rationale

The interaction may be different depending on whether or not shutdown is set.

The client must save and then must prevent interaction until it receives a SaveComplete Die or a Shutdown­Cancelled because anything the user does after the save will be lost.

The fast field specifies whether or not the client should save its state as quickly as possible. For example, if the SM knows that power is about to fail, it should set the fast field to True.

SaveYourselfPhase2 [Client → SM]

  Valid Responses:
    SetProperties
    DeleteProperties
    GetProperties
    SaveYourselfDone
    InteractRequest
  

The SM sends this message to a client that has previously sent a SaveYourselfPhase2Request 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.

Rationale

Clients that manager other clients (window managers, workspace managers, etc) need to know when all clients they are managing are idle, so that the manager can save state related to each of the clients without being concerned with that state changing.

The client writes a state file, if necessary, and, if necessary, uses SetProperties to inform the SM of how to restart it and how to discard the saved state. During this process it can request permission to interact with the user by sending an InteractRequest message. This should only be done if an error occurs that requires user interaction to resolve. After the state has been saved, or if it cannot be successfully saved, and the properties are appropriately set, the client sends a SaveYourselfDone message.

SaveYourselfRequest [Client → SM]

  type: SAVE_TYPE
  shutdown: BOOL
  interact-style: INTERACT_STYLE
  fast: BOOL
  global: BOOL

  Valid Responses: SaveYourself
  

An application sends this to the SM to request a checkpoint. When the SM receives this request it may generate a SaveYourself message in response and it may leave the fields intact.

Example

A vendor of a UPS (Uninterruptible Power Supply) might include an SM 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 True then the resulting SaveYourself should be sent to all applications. If global is set to False then the resulting SaveYourself should be sent to the application that sent the Save­Yourself­Request

InteractRequest [Client → SM]

  dialog-type: DIALOG_TYPE

  Valid Responses: Interact ShutdownCancelled

  Possible Errors: BadState (CanContinue)
  

During a checkpoint or session-save operation, only one client at a time might be granted the privilege of interacting with the user. The InteractRequest message causes the SM to emit an Interact message at some later time if the shutdown is not cancelled by another client first.

The dialog-type field specifies either Errors indicating that the client wants to start an error dialog or Normal meaning the client wishes to start a non-error dialog.

Interact [Client ← SM]

  Valid Responses: InteractDone
  

This message grants the client the privilege of interacting with the user. When the client is done interacting with the user it must send an InteractDone message to the SM unless a shutdown cancel is received.

Advice to Implementors

If a client receives a ShutdownCancelled after receiving an Interact message, but before sending a InteractDone the client should abort the interaction and send a SaveYourselfDone

InteractDone [Client → SM]

  cancel-shutdown: BOOL

  Valid Responses: ShutdownCancelled
  

This message is used by a client to notify the SM that it is done interacting.

Setting the cancel-shutdown field to True indicates that the user has requested that the entire shutdown be cancelled. Cancel-shutdown may only be True if the corresponding SaveYourself message specified True for the shutdown field and Any or Errors for the interact-style field. Otherwise, cancel-shutdown must be False.

SaveYourselfDone [Client → SM]

  success: BOOL

  Valid Responses:
    SaveComplete
    Die
    ShutdownCancelled
  
  

This message is sent by a client to indicate that all of the properties representing its state have been updated. After sending SaveYourselfDone the client must wait for a SaveComplete ShutdownCancelled or Die message before changing its state. If the SaveYourself operation was successful, then the client should set the success field to True otherwise the client should set it to False.

Example

If a client tries to save its state and runs out of disk space, it should return False in the success field of the SaveYourselfDone message.

SaveYourselfPhase2Request [Client → SM]

  Valid Responses:
    ShutdownCancelled
    SaveYourselfPhase2
  
  

This message is sent by a client to indicate that it needs to be informed when all the other clients are quiescent, so it can continue its state.

Die [Client ← SM]

  Valid Responses: ConnectionClosed
  

When the SM wants a client to die it sends a Die message. Before the client dies it responds by sending a ConnectionClosed message and may then close its connection to the SM at any time.

SaveComplete [Client → SM]

  Valid Responses:
  

When the SM is done with a checkpoint, it will send each of the clients a SaveComplete message. The client is then free to change its state.

ShutdownCancelled [Client ← SM]
  

The shutdown currently in process has been aborted. The client can now continue as if the shutdown had never happened. If the client has not sent SaveYourselfDone yet, the client can either abort the save and send SaveYourselfDone with the success field set to False or it can continue with the save and send a SaveYourselfDone with the success field set to reflect the outcome of the save.

ConnectionClosed [Client → SM]

  reason: LISTofARRAY8
  

Specifies that the client has decided to terminate. It should be immediately followed by closing the connection.

The reason field specifies why the client is resigning from the session. It is encoded as an array of Compound Text strings. If the resignation is expected by the user, there will typically be zero ARRAY8s here. But if the client encountered an unexpected fatal error, the error message (which might otherwise be printed on stderr on a POSIX system) should be forwarded to the SM here, one ARRAY8 per line of the message. It is the responsibility of the SM to display this reason to the user.

After sending this message, the client must not send any additional XSMP messages to the SM.

Advice to Implementors

If additional messages are received, they should be discarded.

Rationale

The reason for sending the ConnectionClosed message before actually closing the connections is that some transport protocols will not provide immediate notification of connection closure.

SetProperties [Client → SM]

  properties: LISTofPROPERTY
  

Sets the specified properties to the specified values. Existing properties not specified in the Set­Properties message are unaffected. Some properties have predefined semantics. See section 11, “Predefined Properties.”

The protocol specification recommends that property names used for properties not defined by the standard should begin with an underscore. To prevent conflicts among organizations, additional prefixes should be chosen (for example, _KPC_FAST_SAVE_OPTION). The organizational prefixes should be registered with the X Registry. The XSMP reserves all property names not beginning with an underscore for future use.

DeleteProperties [Client → SM]

  property-names: LISTofARRAY8
  

Removes the named properties.

GetProperties [Client → SM]

  Valid Responses: GetPropertiesReply
  

Requests that the SM respond with the values of all the properties for this client.

GetPropertiesReply [Client ← SM]

  values: LISTofPROPERTY
  

This message is sent in reply to a GetProperties message and includes the values of all the properties.

Chapter 8. Errors

When the receiver of a message detects an error condition, the receiver sends an ICE error message to the sender. There are only two types of errors that are used by the XSMP: BadValue and BadState These are both defined in the ICE protocol.

Any message received out-of-sequence will generate a BadState error message.

Chapter 9. State Diagrams

These state diagrams are designed to cover all actions of both the client and the SM.

Client State Diagram


start:
     ICE protocol setup complete → register


register:
     send RegisterClient → collect-id


collect-id:
     receive RegisterClientReply → idle


shutdown-cancelled:
     send SaveYourselfDone → idle


idle: [Undoes any freeze of interaction with user.]
     receive Die → die
     receive SaveYourself → freeze-interaction
     send GetProperties → idle
     receive GetPropertiesReply → idle
     send SetProperties → idle
     send DeleteProperties → idle
     send ConnectionClosed → connection-closed
     send SaveYourselfRequest → idle


die:
     send ConnectionClosed → connection-closed


freeze-interaction:
     freeze interaction with user → save-yourself


save-yourself:
     receive ShutdownCancelled → shutdown-cancelled
     send SetProperties → save-yourself
     send DeleteProperties → save-yourself
     send GetProperties → save-yourself
     receive GetPropertiesReply → save-yourself
     send InteractRequest → interact-request
     send SaveYourselfPhase2Request → waiting-for-phase2

save-yourself:
     if shutdown mode:
          send SaveYourselfDone → save-yourself-done
     otherwise:
          send SaveYourselfDone → idle


waiting-for-phase2:
     receive ShutdownCancelled → shutdown-cancelled
     receive SaveYourselfPhase2 → phase2


phase2:
     receive ShutdownCancelled → shutdown-cancelled
     send SetProperties → save-yourself
     send DeleteProperties → save-yourself
     send GetProperties → save-yourself
     receive GetPropertiesReply → save-yourself
     send InteractRequest → interact-request (errors only)
     if shutdown mode:
          send SaveYourselfDone → save-yourself-done
     otherwise:
          send SaveYourselfDone → idle


interact-request:
     receive Interact → interact
     receive ShutdownCancelled → shutdown-cancelled


interact:
     send InteractDone → save-yourself
     receive ShutdownCancelled → shutdown-cancelled


save-yourself-done: (changing state is forbidden)
     receive SaveComplete → idle
     receive Die → die
     receive ShutdownCancelled → idle


connection-closed:
     client stops participating in session 

Session Manager State Diagram


start:
     receive ProtocolSetup → protocol-setup


protocol-setup:
     send ProtocolSetupReply → register


register:
     receive RegisterClient → acknowledge-register


acknowledge-register:
     send RegisterClientReply → idle


idle:
     receive SetProperties → idle
     receive DeleteProperties → idle
     receive ConnectionClosed → start
     receive GetProperties → get-properties
     receive SaveYourselfRequest → save-yourself
     send SaveYourself → saving-yourself


save-yourself:
     send SaveYourself → saving-yourself


get-properties:
     send GetPropertiesReply → idle


saving-get-properties:
     send GetPropertiesReply → saving-yourself


saving-yourself:
     receive InteractRequest → saving-yourself
     send Interact → saving-yourself
     send ShutdownCancelled → idle
     receive InteractDone → saving-yourself
     receive SetProperties → saving-yourself
      receive DeleteProperties → saving-yourself
     receive GetProperties → saving-get-properties
     receive SaveYourselfPhase2Request → start-phase2
     receive SaveYourselfDone → save-yourself-done


start-phase2:
     If all clients have sent either SaveYourselfPhase2Request or SaveYourselfDone:
          send SaveYourselfPhase2 → phase2
     else
          → saving-yourself


phase2:
     receive InteractRequest → saving-yourself
     send Interact → saving-yourself
     send ShutdownCancelled → idle
     receive InteractDone → saving-yourself
     receive SetProperties → saving-yourself
      receive DeleteProperties → saving-yourself
     receive GetProperties → saving-get-properties
     receive SaveYourselfDone → save-yourself-done


save-yourself-done:
     If all clients are saved:
          If shutting down:
               send Die → die
          otherwise
               send SaveComplete → idle

     If some clients are not saved:
     → saving-yourself


die:
     SM stops accepting connections

Chapter 10. Protocol Encoding

Table of Contents

Types
Messages

Types

BOOL
 0False 
 1True 
INTERACT_STYLE
 0None 
 1Errors 
 2Any 
DIALOG_TYPE
 0Error 
 1Normal 
SAVE_TYPE
 0Global 
 1Local 
 2Both 
ARRAY8
 4CARD32length
 nListofCARD8, the arrayp = pad (4 + n, 8)
 2Both 
LISTofARRAY8
 4CARD32count
 4 unused
 aARRAY8first array
 bARRAY8second array
 .  
 .  
 .  
 qARRAY8last array
PROPERTY
 aARRAY8name
 bARRAY8type (XPCS encoded in Latin-1, case sensitive)
 cLISTofARRAY8values
LISTofPROPERTY
 4CARD32count
 4 unused
 aPROPERTYfirst property
 bPROPERTYsecond property
 .  
 .  
 .  
 qPROPERTYlast property

Messages

XSMP is a sub-protocol of ICE. The major opcode is assigned at run-time by ICE and is represented here by '?'.

To start the XSMP protocol, the client sends the server an ICE ProtocolSetup message. The protocol-name field should be specified as "XSMP", the major version of the protocol is 1, the minor version is 0. These values may change if the protocol is revised. The minor version number will be incremented if the change is compatible, otherwise the major version number will be incremented.

In ProtocolReply message sent by the session manager, the XSMP protocol defines the vendor parameter as product identification of the session manager, and defines the release parameter as the software release identification of the session manager. The session manager should supply this information in the ICE ProtocolReply message.

RegisterClient
 1?XSMP
 11opcode
 2 unused
 4a/8length of remaining data in 8-byte units
 aARRAY8previous-ID
RegisterClientReply
 1?XSMP
 12opcode
 2 unused
 4a/8length of remaining data in 8-byte units
 aARRAY8client-ID
SaveYourself
 1?XSMP
 13opcode
 2 unused
 41length of remaining data in 8-byte units
 1SAVE_TYPEtype
 1BOOLshutdown
 1INTERACT_STYLEinteract-style
 1BOOLfast
 4 unused
SaveYourselfRequest
 1?XSMP
 14opcode
 2 unused
 41length of remainning data in 8-byte units
 1SAVE_TYPEtype
 1BOOLshutdown
 1INTERACT_STYLEinteract-style
 1BOOLfast
 3 unused
InteractRequest
 1?XSMP
 15opcode
 1DIALOG_TYPEdialog type
 1 unused
 40length of remaining data in 8-byte units
Interact
 1?XSMP
 16opcode
 2 unused
 40length of remaining data in 8-byte units
InteractDone
 1?XSMP
 17opcode
 1BOOLcancel-shutdown
 1 unused
InteractDone
 1?XSMP
 17opcode
 1BOOLcancel-shutdown
 1 unused
 40length of remaining data in 8-byte units
SaveYourselfDone
 1?XSMP
 18opcode
 1BOOLsuccess
 1 unused
 40length of remaining data in 8-byte units
Die
 1?XSMP
 19opcode
 1 unused
 40length of remaining data in 8-byte units
ShutdownCancelled
 1?XSMP
 110opcode
 2 unused
 40length of remaining data in 8-byte units
ConnectionClosed
 1?XSMP
 111opcode
 2 unused
 4a/8length of remaining data in 8-byte units
 aLISTofARRAY8reason
SetProperties
 1?XSMP
 112opcode
 2 unused
 4a/8length of remaining data in 8-byte units
 aLISTofPROPERTYproperties
DeleteProperties
 1?XSMP
 113opcode
 2 unused
 4a/8length of remaining data in 8-byte units
 aLISTofPROPERTYproperties
GetProperties
 1?XSMP
 114opcode
 2 unused
 40length of remaining data in 8-byte units
GetPropertiesReply
 1?XSMP
 115opcode
 2 unused
 4a/8length of remaining data in 8-byte units
 aLISTofPROPERTYproperties
SaveYourselfPhase2Request
 1?XSMP
 116opcode
 2 unused
 40length of remaining data in 8-byte units
SaveYourselfPhase2
 1?XSMP
 117opcode
 2 unused
 40length of remaining data in 8-byte units
SaveComplete
 1?XSMP
 118opcode
 2 unused
 40length of remaining data in 8-byte units

Chapter 11. Predefined Properties

All property values are stored in a LISTofARRAY8. If the type of the property is CARD8, the value is stored as a LISTofARRAY8 with one ARRAY8 that is one byte long. That single byte contains the CARD8. If the type of the property is ARRAY8, the value is stored in the first element of a single element LISTofARRAY8.

The required properties must be set each time a client connects with the SM. The properties must be set after the client sends RegisterClient and before the client sends SaveYourselfDone Otherwise, the behavior of the session manager is not defined.

Clients may set, get, and delete nonstandard properties. The lifetime of stored properties does not extend into subsequent sessions.

NameTypePosix TypeRequired?
CloneCommandOS-specificLISTofARRAY8Yes
CurrentDirectoryOS-specificARRAY8No
DiscardCommandOS-specificLISTofARRAY8No*
EnvironmentOS-specificLISTofARRAY8No
ProcessIDOS-specificARRAY8No
ProgramOS-specificARRAY8Yes
RestartCommandOS-specificLISTofARRAY8Yes
ResignCommandOS-specificLISTofARRAY8No
RestartStyleHintCARD8CARD8No
ShutdownCommandOS-specificLISTofARRAY8No
UserIDARRAY8ARRAY8Yes

* Required if any state is stored in an external repository (e.g., state file).

CloneCommand

This is like the RestartCommand except it restarts a copy of the application. The only difference is that the application doesn't supply its client id at register time. On POSIX systems the type should be a LISTofARRAY8.

CurrentDirectory

On POSIX-based systems specifies the value of the current directory that needs to be set up prior to starting the program and should be of type ARRAY8.

DiscardCommand

The discard command contains a command that when delivered to the host that the client is running on (determined from the connection), will cause it to discard any information about the current state. If this command is not specified, the SM will assume that all of the client's state is encoded in the Restart­Command On POSIX systems the type should be LISTofARRAY8.

Environment

On POSIX based systems, this will be of type LISTofARRAY8 where the ARRAY8s alternate between environment variable name and environment variable value.

ProcessID

This specifies an OS-specific identifier for the process. On POSIX systems this should of type ARRAY8 and contain the return value of getpid() turned into a Latin-1 (decimal) string.

Program

The name of the program that is running. On POSIX systems this should be the first parameter passed to execve and should be of type ARRAY8.

RestartCommand

The restart command contains a command that when delivered to the host that the client is running on (determined from the connection), will cause the client to restart in its current state. On POSIX-based systems this is of type LISTofARRAY8 and each of the elements in the array represents an element in the argv array. This restart command should ensure that the client restarts with the specified client-ID.

ResignCommand

A client that sets the RestartStyleHint to RestartAnyway uses this property to specify a command that undoes the effect of the client and removes any saved state.

Example

A user runs xmodmap. xmodmap registers with the SM, sets Restart­Style­Hint to Restart­Anyway and then terminates. In order to allow the SM (at the user's request) to undo this, xmodmap would register a Resign­Command that undoes the effects of the xmodmap.

RestartStyleHint

If the RestartStyleHint property is present, it will contain the style of restarting the client prefers. If this flag isn't specified, RestartIfRunning is assumed. The possible values are as follows:

NameValue
RestartIfRunning0
RestartAnyway1
RestartImmediately2
RestartNever3

The RestartIfRunning style is used in the usual case. The client should be restarted in the next session if it is connected to the session manager at the end of the current session.

The RestartAnyway style is used to tell the SM that the application should be restarted in the next session even if it exits before the current session is terminated. It should be noted that this is only a hint and the SM will follow the policies specified by its users in determining what applications to restart.

Rationale

This can be specified by a client which supports (as MS-Windows clients do) a means for the user to indicate while exiting that restarting is desired. It can also be used for clients that spawn other clients and then go away, but which want to be restarted.

A client that uses RestartAnyway should also set the ResignCommand and ShutdownCommand properties to commands that undo the state of the client after it exits.

The RestartImmediately style is like RestartAnyway but in addition, the client is meant to run continuously. If the client exits, the SM should try to restart it in the current session.

Advice to Implementors

It would be wise to sanity-check the frequency which which RestartImmediately clients are restarted, to avoid a sick client being restarted continuously.

The RestartNever style specifies that the client does not wish to be restarted in the next session.

Advice to Implementors

This should be used rarely, if at all. It will cause the client to be silently left out of sessions when they are restarted and will probably be confusing to users.

ShutdownCommand

This command is executed at shutdown time to clean up after a client that is no longer running but retained its state by setting RestartStyleHint to RestartAnyway The command must not remove any saved state as the client is still part of the session.

Example

A client is run at start up time that turns on a camera. This client then exits. At session shutdown, the user wants the camera turned off. This client would set the Restart­Style­Hint to Restart­Anyway and would register a Shutdown­Command that would turn off the camera.

UserID

Specifies the user's ID. On POSIX-based systems this will contain the the user's name (the pw_name field of struct passwd).