XC-MISC Extension

X Consortium Standard

Bob Scheifler

   X Consortium

David P. Wiggins

   X Consortium

   X Version 11, Release 7.7

   Version 1.1

   Copyright © 1994 X Consortium

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     __________________________________________________________

   Table of Contents

   1. Overview
   2. Requests
   3. Events and Errors
   4. Encoding

Chapter 1. Overview

   When an X client connects to an X server, it receives a fixed
   range of resource IDs to use to identify the client's resources
   inside the X server. Xlib hands these out sequentially as
   needed. When it overruns the end of the range, an IDChoice
   protocol error results. Long running clients, or clients that
   use resource IDs at a rapid rate, may encounter this
   circumstance. When it happens, there are usually many resource
   IDs available, but Xlib doesn't know about them.

   One approach to solving this problem would be to have Xlib
   notice when a resource is freed and recycle its ID for future
   use. This strategy runs into difficulties because sometimes
   freeing one resource causes others to be freed (for example,
   when a window is destroyed, so are its children). To do a
   complete job, Xlib would have to maintain a large amount of
   state that currently resides only in the server (the entire
   window tree in the above example). Even if a less comprehensive
   strategy was adopted, such as recycling only those IDs that
   Xlib can identify without maintaining additional state, the
   additional bookkeeping at resource creation and destruction
   time would likely introduce unacceptable overhead.

   To avoid the problems listed above, the server's complete
   knowledge of all resource IDs in use by a client is leveraged.
   This extension provides two ways for Xlib to query the server
   for available resource IDs. Xlib can use these extension
   requests behind the scenes when it has exhausted its current
   pool of resource IDs.

Chapter 2. Requests

   XCMiscGetVersion
     * client_major_version: CARD16
     * client_minor_version: CARD16

   =>
     * client_major_version: CARD16
     * client_minor_version: CARD16

   If supplied, the client_major_version and client_minor_version
   indicate what version of the protocol the client wants the
   server to implement. The server version numbers returned
   indicate the protocol this extension actually supports. This
   might not equal the version sent by the client. An
   implementation can (but need not) support more than one version
   simultaneously. The server_major_version and the
   server_minor_version are a mechanism to support future
   revisions of the XC-MISC protocol which may be necessary. In
   general, the major version would increment for incompatible
   changes, and the minor version would increment for small,
   upward-compatible changes. Servers that support the protocol
   defined in this document will return a server_major_version of
   one (1), and a server_minor_version of one (1).

   XCMiscGetXIDRange

   =>
     * start_id: XID
     * count: CARD32

   This request returns a range of available resource IDs for the
   client issuing the request. start_id is the first ID in the
   range. count is the number of IDs in the range. The returned
   range may or may not be the largest possible range.

   XCMiscGetXIDList
     * count: CARD32

   =>
     * ids: LISTofXID

   This request returns the a list of individual resource IDs in
   ids. count is the number of resource IDs requested. The number
   returned may be smaller than the number requested.

Chapter 3. Events and Errors

   No new events or errors are defined by this extension.

Chapter 4. Encoding

   Please refer to the X11 Protocol Encoding document as this
   document uses conventions established there.

   The name of this extension is "XC-MISC".
XCMiscGetVersion
     1     CARD8          opcode
     1     0                      XC-MISC opcode
     2     2                      request length
     2     CARD16         client_major_version
     2     CARD16         client_minor_version

 =>
     1     1          Reply
     1                unused
     2     CARD16     sequence number
     4     0          length
     2     CARD16     server_major_version
     2     CARD16     server_minor_version
     20               unused

XCMiscGetXIDRange
     1     CARD8        opcode
     1     1                   XC-MISC opcode
     2     1                   request length

 =>
     1     1          Reply
     1                unused
     2     CARD16     sequence number
     4     0          length
     4     XID        start_id
     4     CARD32     count
     16               unused

XCMiscGetXIDList
     1     CARD8          opcode
     1     2                      XC-MISC opcode
     2     2                      request length
     4     CARD32         count

 =>
     1     1          Reply
     1                unused
     2     CARD16     sequence number
     4     CARD32     length
     4     CARD32     number of XIDs in ids
     20               unused
     4n    LISTofXID  ids
