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

