X Version 11, Release 7.7
Copyright © 1994 X Consortium
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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.
If supplied, the
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).
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
This request returns the a list of individual resource IDs in
count is the number of resource IDs requested.
The number returned may be smaller than the number requested.
Please refer to the X11 Protocol Encoding document as this document uses conventions established there.
The name of this extension is “XC-MISC”.
XCMiscGetVersion1 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
XCMiscGetXIDRange1 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
XCMiscGetXIDList1 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