Add files using upload-large-folder tool

4a3b324 verified 2 months ago

48.2 kB

	<?xml version="1.0" encoding="UTF-8" ?>
	<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN"
	"http://www.oasis-open.org/docbook/xml/4.3/docbookx.dtd"
	[
	<!ENTITY % defs SYSTEM "defs.ent"> %defs;
	]>

	<!--translated from sync.tex, on 2010-06-29 10:52:00,
	by TeX4ht (http://www.cse.ohio-state.edu/~gurari/TeX4ht/) xhtml,docbook,html,refcaption -->


	<book id="sync">

	<bookinfo>
	<title>X Synchronization Extension Protocol</title>
	<subtitle>X Consortium Standard</subtitle>
	<authorgroup>
	<author>
	<firstname>Tim</firstname><surname>Glauert</surname>
	<affiliation>
	<orgname>Olivetti Research</orgname>
	<orgdiv>MultiWorks</orgdiv>
	</affiliation>
	</author>
	<othercredit>
	<firstname>Dave</firstname>
	<surname>Carver</surname>
	<affiliation>
	<orgname>Digital Equipment Corporation</orgname>
	<orgdiv>MIT/Project Athena</orgdiv>
	</affiliation>
	</othercredit>
	<othercredit>
	<firstname>Jim</firstname>
	<surname>Gettys</surname>
	<affiliation>
	<orgname>Digital Equipment Corporation</orgname>
	<orgdiv>Cambridge Research Laboratory</orgdiv>
	</affiliation>
	</othercredit>
	<othercredit>
	<firstname>David</firstname>
	<othername>P.</othername>
	<surname>Wiggins</surname>
	<affiliation><orgname>X Consortium, Inc.</orgname></affiliation>
	</othercredit>
	<othercredit>
	<firstname>James</firstname>
	<surname>Jones</surname>
	<affiliation><orgname>NVIDIA Corporation</orgname></affiliation>
	</othercredit>
	</authorgroup>
	<releaseinfo>X Version 11, Release &fullrelvers;</releaseinfo>
	<releaseinfo>Version 3.1</releaseinfo>
	<copyright><year>1991</year>
	<holder>Olivetti Research Limited, Cambridge England</holder>
	<holder>Digital Equipment Corporation, Maynard, Massachusetts</holder>
	<holder>X Consortium</holder>
	</copyright>
	<copyright><year>2010</year><holder>NVIDIA Corporation</holder></copyright>

	<legalnotice>
	<para>
	Permission to use, copy, modify, and distribute this documentation for any
	purpose and without fee is hereby granted, provided that the above
	copyright notice appear in all copies. Olivetti, Digital, MIT, the
	X Consortium, and NVIDIA make no representations about the suitability for
	any purpose of the information in this document. This documentation is
	provided as is without express or implied warranty.
	</para>

	<para>
	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:
	</para>

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

	<para>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.</para>

	<para>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.</para>
	</legalnotice>

	</bookinfo>

	<chapter id='Synchronization_Protocol'>
	<title>Synchronization Protocol</title>
	<para>
	The core X protocol makes no guarantees about the relative order of execution
	of requests for different clients. This means that any synchronization between
	clients must be done at the client level in an operating system-dependent and
	network-dependent manner. Even if there was an accepted standard for such
	synchronization, the use of a network introduces unpredictable delays between
	the synchronization of the clients and the delivery of the resulting requests
	to the X server.
	</para>

	<para>
	The core X protocol also makes no guarantees about the time at which requests
	are executed, which means that all clients with real-time constraints must
	implement their timing on the host computer. Any such timings are subject to
	error introduced by delays within the operating system and network and are
	inefficient because of the need for round-trip requests that keep the client
	and server synchronized.
	</para>

	<para>
	The synchronization extension provides primitives that allow synchronization
	between clients to take place entirely within the X server. This removes any
	error introduced by the network and makes it possible to synchronize clients
	on different hosts running different operating systems. This is important for
	multimedia applications, where audio, video, and graphics data streams are
	being synchronized. The extension also provides internal timers within the
	X server to which client requests can be synchronized. This allows simple
	animation applications to be implemented without any round-trip requests and
	makes best use of buffering within the client, network, and server.
	</para>

	<sect1 id='Description'>
	<title>Description</title>
	<para>
	The mechanism used by this extension for synchronization within the X
	server is to block the processing of requests from a client until a
	specific synchronization condition occurs. When the condition occurs, the
	client is released and processing of requests continues. Multiple clients
	may block on the same condition to give inter-client synchronization.
	Alternatively, a single client may block on a condition such as an animation
	frame marker.
	</para>

	<para>
	The extension adds <function>Counter</function>, <function>Alarm</function>,
	and <function>Fence</function> to the set of resources managed by the
	server. A counter has a 64-bit integer value that may be increased or
	decreased by client requests or by the server internally. A client can block
	by sending an Await request that waits until one of a set of synchronization
	conditions, called TRIGGERs, becomes TRUE. Alarms generate events when
	counter values go through a specified transition. A fence has two possible
	states: triggered and not triggered. Client requests can put the fence in
	either of these states. A client can block until one of a set of fences
	becomes triggered by sending an AwaitFence request. Fences are bound to a
	particular screen at creation time.
	</para>

	<para>
	The <function>CreateCounter</function> request allows a client to create a
	<function>Counter</function> that can be changed by explicit
	<function>SetCounter</function> and <function>ChangeCounter</function>
	requests. These can be used to implement synchronization between different
	clients.
	</para>

	<para>
	There are some counters, called <function>System Counters</function>, that
	are changed by the server internally rather than by client requests. The
	effect of any change to a system counter is not visible until the server
	has finished processing the current request. In other words, system
	counters are apparently updated in the gaps between the execution of
	requests rather than during the actual execution of a request. The extension
	provides a system counter that advances with the server time as defined by
	the core protocol, and it may also provide counters that advance with the
	real-world time or that change each time the CRT screen is refreshed.
	Other extensions may provide their own extension-specific system counters.
	</para>

	<para>
	The extension provides an <function>Alarm</function> mechanism that allows
	clients to receive an event on a regular basis when a particular counter
	is changed.
	</para>

	<para>
	The <function>CreateFence</function> request allows a client to create a
	<function>Fence</function> that can be triggered and reset using
	<function>TriggerFence</function> and <function>ResetFence</function>
	requests, respectively. <function>CreateFence</function> takes a drawable
	argument that implies which screen the fence should be created on. The
	<function>TriggerFence</function> request changes the fence's state only
	after all previous rendering commands affecting objects owned by the given
	fence's screen have completed. Note that while fence objects are bound
	to a screen and the simple trigger operation provided by this extension
	operates at screen granularity, other extensions may add more fine-grained
	trigger operations based on any number of events. The screen binding
	merely establishes an upper bound for the scope of fence operations.
	</para>

	</sect1>
	<sect1 id='Types'>
	<title>Types</title>
	<para>
	Please refer to the X11 Protocol specification as this document uses
	syntactic conventions established there and references types defined there.
	</para>

	<para>The following new types are used by the extension.</para>

	<literallayout class="monospaced">
	INT64: 64-bit signed integer
	COUNTER: XID
	VALUETYPE: {Absolute,Relative};
	TESTTYPE: {PositiveTransition,NegativeTransition,
	PositiveComparison,NegativeComparison}
	TRIGGER: [
	counter:COUNTER,
	value-type:VALUETYPE,
	wait-value:INT64,
	test-type:TESTTYPE
	]
	WAITCONDITION: [
	trigger:TRIGGER,
	event-threshold:INT64
	]
	SYSTEMCOUNTER: [
	name:STRING8,
	counter:COUNTER,
	resolution:INT64
	]
	ALARM: XID
	ALARMSTATE: {Active,Inactive,Destroyed}
	FENCE: XID
	</literallayout>

	<para>
	The COUNTER type defines the client-side handle on a server
	<function>Counter</function>. The value of a counter is an INT64.
	</para>

	<para>
	The TRIGGER type defines a test on a counter that is either TRUE or FALSE. The
	value of the test is determined by the combination of a test value, the value
	of the counter, and the specified test-type.
	</para>

	<para>
	The test value for a trigger is calculated using the value-type and
	wait-value fields when the trigger is initialized. If the value-type field
	is not one of the named VALUETYPE constants, the request that initialized the
	trigger will return a <function>Value</function> error. If the value-type
	field is <function>Absolute</function>, the test value is given by the
	wait-value field. If the value-type field is <function>Relative</function>,
	the test value is obtained by adding the wait-value field to the value of the
	counter. If the resulting test value would lie outside the range for an
	INT64, the request that initialized the trigger will return a
	<function>Value</function> error. If counter is <function>None</function>
	and the value-type is <function>Relative</function>, the request that
	initialized the trigger will return a <function>Match</function> error. If
	counter is not None and does not name a valid counter, a Counter error is
	generated.
	</para>

	<para>
	If the test-type is <function>PositiveTransition</function>, the trigger is
	initialized to FALSE, and it will become TRUE when the counter changes from
	a value less than the test value to a value greater than or equal to the
	test value. If the test-type is <function>NegativeTransition</function>,
	the trigger is initialize to FALSE, and it will become TRUE when the counter
	changes from a value greater than the test value to a value less than or
	equal to the test value. If the test-type is
	<function>PositiveComparison</function>, the trigger is TRUE if the
	counter is greater than or equal to the test value and FALSE otherwise. If the
	test-type is <function>NegativeComparison</function>, the trigger is TRUE
	if the counter is less than or equal to the test value and FALSE otherwise.
	If the test-type is not one of the named TESTTYPE constants, the request that
	initialized the trigger will return a Value error. A trigger with a counter
	value of <function>None</function> and a valid test-type is always TRUE.
	</para>

	<para>
	The WAITCONDITION type is simply a trigger with an associated event-threshold.
	The event threshold is used by the <function>Await</function> request to
	decide whether or not to generate an event to the client after the trigger has
	become TRUE. By setting the event-threshold to an appropriate value, it is
	possible to detect the situation where an <function>Await</function> request
	was processed after the TRIGGER became TRUE, which usually indicates that
	the server is not processing requests as fast as the client expects.
	</para>

	<para>
	The SYSTEMCOUNTER type provides the client with information about a
	<function>System</function>Counter. The name field is the textual name of
	the counter that identifies the counter to the client. The counter field
	is the client-side handle that should be used in requests that require a
	counter. The resolution field gives the approximate step size of the system
	counter. This is a hint to the client
	that the extension may not be able to resolve two wait conditions with test
	values that differ by less than this step size. A microsecond clock, for
	example, may advance in steps of 64 microseconds, so a counter based on this
	clock would have a resolution of 64.
	</para>

	<para>
	The only system counter that is guaranteed to be present is called SERVERTIME,
	which counts milliseconds from some arbitrary starting point. The least
	significant 32 bits of this counter track the value of Time used by the
	server in Events and Requests. Other system counters may be provided by
	different implementations of the extension. The X Consortium will maintain a
	registry of system counter names to avoid collisions in the name space.
	</para>

	<para>
	An ALARM is the client-side handle on an <function>Alarm</function> resource.
	</para>

	<para>
	The FENCE type defines the client-side handle on a server
	<function>Fence</function>. A fence can only be in one of two states,
	represented by a BOOL. If the value is TRUE, the fence is in the triggered
	state. Otherwise, the fence is in the not triggered state.
	</para>

	</sect1>

	<sect1 id='Errors'>
	<title>Errors</title>

	<variablelist>
	<varlistentry>
	<term>Counter</term>
	<listitem>
	<para>
	This error is generated if the value for a COUNTER argument in a request
	does not name a defined COUNTER.
	</para>
	</listitem>
	</varlistentry>
	<varlistentry>
	<term>Alarm</term>
	<listitem>
	<para>
	This error is generated if the value for an ALARM argument in a request
	does not name a defined ALARM.
	</para>
	</listitem>
	</varlistentry>
	<varlistentry>
	<term>Fence</term>
	<listitem>
	<para>
	This error is generated if the value for a FENCE argument in a request
	does not name a defined FENCE.
	</para>
	</listitem>
	</varlistentry>
	</variablelist>

	</sect1>
	<sect1 id='Requests'>
	<title>Requests</title>

	<variablelist>
	<varlistentry>
	<term>Initialize</term>
	<listitem>
	<literallayout class="monospaced">
	version-major,version-minor: CARD8
	=>
	version-major,version-minor: CARD8
	</literallayout>

	<para>
	This request must be executed before any other requests for this extension. If a
	client violates this rule, the results of all SYNC requests that it issues are
	undefined. The request takes the version number of the extension that the
	client wishes to use and returns the actual version number being implemented
	by the extension for this client. The extension may return different
	version numbers to a client depending of the version number supplied by
	that client. This request should be executed only once for each client
	connection.
	</para>
	<para>
	Given two different versions of the SYNC protocol, v1 and v2, v1 is
	compatible with v2 if and only if v1.version_major = v2.version_major
	and v1.version_minor <= v2.version_minor. Compatible means that the
	functionality is fully supported in an identical fashion in the two versions.
	</para>
	<para>
	This document describes major version 3, minor version 1 of the SYNC protocol.
	</para>
	</listitem>
	</varlistentry>
	<varlistentry>
	<term>ListSystemCounters</term>
	<listitem>
	<literallayout class="monospaced">
	=>
	system-counters: LISTofSYSTEMCOUNTER
	Errors: Alloc
	</literallayout>
	<para>
	This request returns a list of all the system counters that are available at
	the time the request is executed, which includes the system counters
	that are maintained by other extensions. The list returned by this
	request may change as counters are created and destroyed by other extensions.
	</para>
	</listitem>
	</varlistentry>
	<varlistentry>
	<term>CreateCounter</term>
	<listitem>
	<literallayout class="monospaced">
	id: COUNTER
	initial-value: INT64
	Errors: IDChoice,Alloc
	</literallayout>
	<para>
	This request creates a counter and assigns the specified id to it. The counter
	value is initialized to the specified initial-value and there are no clients
	waiting on the counter.
	</para>
	</listitem>
	</varlistentry>
	<varlistentry>
	<term>DestroyCounter</term>
	<listitem>
	<literallayout class="monospaced">
	counter: COUNTER
	Errors: Counter,Access
	</literallayout>
	<para>
	This request destroys the given counter and sets the counter fields for all
	triggers that specify this counter to <function>None</function>. All clients
	waiting on the counter are released and a <function>CounterNotify</function>
	event with the destroyed field set to TRUE is sent to each waiting client,
	regardless of the event-threshold. All alarms specifying the counter become
	<function>Inactive</function> and an <function>AlarmNotify</function>
	event with a state field of <function>Inactive</function> is generated. A
	counter is destroyed automatically when the connection to the creating client
	is closed down if the close-down mode is Destroy. An
	<function>Access</function> error is generated if counter is a system
	counter. A <function>Counter</function> error is generated if counter does
	not name a valid counter.
	</para>
	</listitem>
	</varlistentry>
	<varlistentry>
	<term>QueryCounter</term>
	<listitem>
	<literallayout class="monospaced">
	counter: COUNTER
	=>
	value: INT64
	Errors: <function>Counter</function>
	</literallayout>
	<para>
	This request returns the current value of the given counter or a generates
	Counter error if counter does not name a valid counter.
	</para>
	</listitem>
	</varlistentry>
	<varlistentry>
	<term>Await</term>
	<listitem>
	<literallayout class="monospaced">
	wait-list: LISTofWAITCONDITION
	Errors: Counter,Alloc,Value
	</literallayout>
	<para>
	When this request is executed, the triggers in the wait-list are initialized
	using the wait-value and value-type fields, as described in the definition of
	TRIGGER above. The processing of further requests for the client is blocked
	until one or more of the triggers becomes TRUE. This may happen immediately,
	as a result of the initialization, or at some later time, as a result of
	a subsequent <function>SetCounter</function>,
	<function>ChangeCounter</function> or
	<function>DestroyCounter</function> request.
	</para>
	<para>
	A Value error is generated if wait-list is empty.
	</para>
	<para>
	When the client becomes unblocked, each trigger is checked to determine
	whether a <function>CounterNotify</function> event should be generated.
	The difference between the counter and the test value is calculated by
	subtracting the test value from the value of the counter. If the test-type
	is <function>PositiveTransition</function> or
	<function>PositiveComparison</function>, a
	<function>CounterNotify</function> event is generated if the difference is
	at least event-threshold. If the test-type is
	<function>NegativeTransition</function> or
	<function>NegativeComparison</function>, a
	<function>CounterNotify</function> event is generated if the difference
	is at most event-threshold. If the difference lies outside the range for an
	INT64, an event is not generated.
	</para>
	<para>
	This threshold check is made for each trigger in the list and a
	<function>CounterNotify</function> event is generated for every trigger for
	which the check succeeds. The check for
	<function>CounterNotify</function> events is performed even if one of the
	triggers is TRUE when the request is first executed. Note that a
	<function>CounterNotify</function> event may be generated for a trigger
	that is FALSE if there are multiple triggers in the request. A
	<function>CounterNotify</function> event with the destroyed flag set to
	TRUE is always generated if the counter for one of the triggers is
	destroyed.
	</para>
	</listitem>
	</varlistentry>
	<varlistentry>
	<term>ChangeCounter</term>
	<listitem>
	<literallayout class="monospaced">
	counter: COUNTER
	amount: INT64
	Errors: <function>Counter,Access,Value</function>
	</literallayout>
	<para>
	This request changes the given counter by adding amount to the current
	counter value. If the change to this counter satisfies a trigger for which a client
	is waiting, that client is unblocked and one or more
	<function>CounterNotify</function> events may be generated. If the change to
	the counter satisfies the trigger for an alarm, an
	<function>AlarmNotify</function> event is generated and the
	alarm is updated. An <function>Access</function> error is generated if
	counter is a system counter. A <function>Counter</function> error is
	generated if counter does not name a valid counter. If the resulting value
	for the counter would be outside the range for an INT64, a
	<function>Value</function> error is generated and the counter is not changed.
	</para>
	<para>
	It should be noted that all the clients whose triggers are satisfied by this
	change are unblocked, so this request cannot be used to implement mutual
	exclusion.
	</para>
	</listitem>
	</varlistentry>
	<varlistentry>
	<term>SetCounter</term>
	<listitem>
	<literallayout class="monospaced">
	counter: COUNTER
	value: INT64
	Errors: <function>Counter,Access</function>
	</literallayout>
	<para>
	This request sets the value of the given counter to value. The effect is
	equivalent to executing the appropriate ChangeCounter request to change
	the counter value to value. An Access error is generated if counter names a
	system counter. A Counter error is generated if counter does not name a valid
	counter.
	</para>
	</listitem>
	</varlistentry>
	<varlistentry>
	<term>CreateAlarm</term>
	<listitem>
	<literallayout class="monospaced">
	id: ALARM
	values-mask: CARD32
	values-list: LISTofVALUE
	left">Errors: IDChoice,Counter,Match,Value,Alloc
	</literallayout>
	<para>
	This request creates an alarm and assigns the identifier id to it. The
	values-mask and values-list specify the attributes that are to be explicitly
	initialized. The attributes for an Alarm and their defaults are:
	</para>
	<informaltable frame="none">
	<?dbfo keep-together="always" ?>
	<tgroup cols='4' align='left' colsep='0' rowsep='0'>
	<colspec colname='c1' colwidth="1.0*" colsep='1'/>
	<colspec colname='c2' colwidth="1.0*" colsep='1'/>
	<colspec colname='c3' colwidth="1.0*"/>
	<colspec colname='c4' colwidth="1.3*"/>
	<thead>
	<row rowsep='1'>
	<entry>Attribute</entry>
	<entry>Type</entry>
	<entry namest='c3' nameend='c4'>Default</entry>
	</row>
	</thead>
	<tbody>
	<row>
	<entry>trigger</entry>
	<entry>TRIGGER</entry>
	<entry>counter</entry>
	<entry>None</entry>
	</row>
	<row>
	<entry></entry>
	<entry></entry>
	<entry>value-type</entry>
	<entry>Absolute</entry>
	</row>
	<row>
	<entry></entry>
	<entry></entry>
	<entry>value</entry>
	<entry>0</entry>
	</row>
	<row>
	<entry></entry>
	<entry></entry>
	<entry>test-type</entry>
	<entry>PositiveComparison</entry>
	</row>
	<row>
	<entry>delta</entry>
	<entry>INT64</entry>
	<entry>1</entry>
	</row>
	<row>
	<entry>events</entry>
	<entry>BOOL</entry>
	<entry>TRUE</entry>
	</row>
	</tbody>
	</tgroup>
	</informaltable>
	<para>
	The trigger is initialized as described in the definition of TRIGGER, with an
	error being generated if necessary.
	</para>
	<para>
	If the counter is <function>None</function>, the state of the alarm is set
	to <function>Inactive</function>, else it is set to Active.
	</para>
	<para>
	Whenever the trigger becomes TRUE, either as a result of this request or as the
	result of a <function>SetCounter</function>,
	<function>ChangeCounter</function>, <function>DestroyCounter</function>, or
	<function>ChangeAlarm</function> request, an
	<function>AlarmNotify</function> event is generated and the alarm is
	updated. The alarm is updated by repeatedly adding delta to the value of the
	trigger and reinitializing it until it becomes FALSE. If this update would
	cause value to fall outside the range for an INT64, or if the counter
	value is <function>None</function>, or if the delta is 0 and test-type
	is <function>PositiveComparison</function> or
	<function>NegativeComparison</function>, no change is made to value and
	the alarm state is changed to <function>Inactive</function> before the
	event is generated. No further events are generated by an
	<function>Inactive</function> alarm until a <function>ChangeAlarm</function>
	or <function>DestroyAlarm </function> request is executed.
	</para>
	<para>
	If the test-type is <function>PositiveComparison</function> or
	<function>PositiveTransition and</function> delta is less than zero, or
	if the test-type is <function>NegativeComparison</function> or
	<function>NegativeTransition</function> and delta is greater than zero,
	a <function>Match</function> error is generated.
	</para>
	<para>
	The events value enables or disables delivery of
	<function>AlarmNotify</function> events
	to the requesting client. The alarm keeps a separate event flag for
	each client so that other clients may select to receive events from this
	alarm.
	</para>
	<para>
	An <function>AlarmNotify</function> event is always generated at some time
	after the execution of a <function>CreateAlarm</function> request. This
	will happen immediately if the trigger is TRUE, or it will happen later
	when the trigger becomes TRUE or the Alarm is destroyed.
	</para>
	</listitem>
	</varlistentry>
	<varlistentry>
	<term>ChangeAlarm</term>
	<listitem>
	<literallayout class="monospaced">
	id: ALARM
	values-mask: CARD32
	values-list: LISTofVALUE
	Errors: Alarm,Counter,Value,Match
	</literallayout>
	<para>
	This request changes the parameters of an Alarm. All of the parameters
	specified for the <function>CreateAlarm</function> request may be changed
	using this request. The trigger is reinitialized and an
	<function>AlarmNotify</function> event is generated if appropriate, as
	explained in the description of the <function>CreateAlarm</function> request.
	</para>
	<para>
	Changes to the events flag affect the event delivery to the requesting
	client only and may be used by a client to select or deselect event delivery
	from an alarm created by another client.
	</para>
	<para>
	The order in which attributes are verified and altered is server-dependent.
	If an error is generated, a subset of the attributes may have been altered.
	</para>
	</listitem>
	</varlistentry>
	<varlistentry>
	<term>DestroyAlarm</term>
	<listitem>
	<literallayout class="monospaced">
	alarm: ALARM
	Errors: Alarm
	</literallayout>
	<para>
	This request destroys an alarm. An alarm is automatically destroyed when the
	creating client is closed down if the close-down mode is
	<function>Destroy</function>. When an alarm is destroyed, an
	<function>AlarmNotify</function> event is generated with a state value of
	<function>Destroyed</function>.
	</para>
	</listitem>
	</varlistentry>
	<varlistentry>
	<term>QueryAlarm</term>
	<listitem>
	<literallayout class="monospaced">
	alarm: ALARM
	=>
	trigger: TRIGGER
	delta: INT64
	events: ALARMEVENTMASK
	state: ALARMSTATE
	Errors: <function>Alarm</function>
	</literallayout>
	<para>This request retrieves the current parameters for an Alarm.</para>
	</listitem>
	</varlistentry>
	<varlistentry>
	<term>SetPriority</term>
	<listitem>
	<literallayout class="monospaced">
	client-resource: XID
	priority: INT32
	Errors: <function>Match</function>
	</literallayout>
	<para>
	This request changes the scheduling priority of the client that created
	client-resource. If client-resource is <function>None</function>, then
	the priority for the client making the request is changed. A
	<function>Match</function> error is generated if client-resource is not
	<function>None</function> and does not name an existing resource in the
	server. For any two priority values, A and B, A is higher priority if
	and only if A is greater than B.
	</para>
	<para>
	The priority of a client is set to 0 when the initial client connection is
	made.
	</para>
	<para>
	The effect of different client priorities depends on the particular
	implementation of the extension, and in some cases it may have no effect at
	all. However, the intention is that higher priority clients will have
	their requests executed before those of lower priority clients.
	</para>
	<para>
	For most animation applications, it is desirable that animation clients be
	given priority over nonrealtime clients. This improves the smoothness of the
	animation on a loaded server. Because a server is free to implement very strict
	priorities, processing requests for the highest priority client to the
	exclusion of all others, it is important that a client that may potentially
	monopolize the whole server, such as an animation that produces continuous
	output as fast as it can with no rate control, is run at low rather than high
	priority.
	</para>
	</listitem>
	</varlistentry>
	<varlistentry>
	<term>GetPriority</term>
	<listitem>
	<literallayout class="monospaced">
	client-resource: XID
	=>
	priority: INT32
	Errors: <function>Match</function>
	</literallayout>
	<para>
	This request returns the scheduling priority of the client that created
	client-resource. If client-resource is <function>None</function>, then the
	priority for the client making the request is returned. A
	<function>Match</function> error is generated if client-resource is
	not <function>None</function> and does not name an existing resource in the
	server.
	</para>
	</listitem>
	</varlistentry>
	<varlistentry>
	<term>CreateFence</term>
	<listitem>
	<literallayout class="monospaced">
	drawable: DRAWABLE
	id: FENCE
	initially-triggered: BOOL
	Errors: <function>IDChoice</function>,<function>Alloc</function>
	</literallayout>
	<para>
	This request creates a fence on the screen associated with drawable and
	assigns the specified id to it. The fence is in the triggered state iff
	initially-triggered is TRUE. There are no clients waiting on the fence.
	</para>
	</listitem>
	</varlistentry>
	<varlistentry>
	<term>TriggerFence</term>
	<listitem>
	<literallayout class="monospaced">
	fence: FENCE
	Errors: <function>Fence</function>
	</literallayout>
	<para>
	This request puts the given fence in the triggered state after all rendering
	from previous requests that affects resources owned by the fence's screen has
	completed. This includes requests from other clients if those requests have
	been dispatched. This request has no visible effects if the fence was already
	in the triggered state. A <function>Fence</function> error is generated if
	fence does not name a valid fence.
	</para>
	<para>
	Note that the given fence's state is not necessarily directly modified by this
	request. The state change need only be queued to occur after the required
	rendering has completed. Clients should take care to not assume the fence will
	be in the triggered state in subsequent requests, such as those that operate
	on the given fence immediately. <function>AwaitFence</function> should first
	be issued if subsequent requests require the fence to be in the triggered
	state.
	</para>
	</listitem>
	</varlistentry>
	<varlistentry>
	<term>ResetFence</term>
	<listitem>
	<literallayout class="monospaced">
	fence: FENCE
	Errors: <function>Fence</function>,<function>Match</function>
	</literallayout>
	<para>
	This request immediately puts the given fence in the not triggered state.
	A <function>Match</function> error is generated if the fence is not in the
	triggered state. A <function>Fence</function> error is generated if fence
	does not name a valid fence.
	</para>
	<para>
	See the warnings above regarding <function>TriggerFence</function>'s delayed
	effect. In particular, a <function>TriggerFence</function> request
	immediately followed by a <function>ResetFence</function> request is likely
	to result in a <function>Match</function> error. An
	<function>AwaitFence</function> request should be issued between the two.
	</para>
	</listitem>
	</varlistentry>
	<varlistentry>
	<term>DestroyFence</term>
	<listitem>
	<literallayout class="monospaced">
	fence: FENCE
	Errors: <function>Fence</function>
	</literallayout>
	<para>
	This request destroys the given fence. All clients waiting on this fence are
	released. A fence is destroyed automatically when the connection to the client
	that created the fence is closed if the close-down mode is
	<function>DestroyAll</function>. A <function>Fence</function> error is
	generated if fence does not name a valid fence.
	</para>
	</listitem>
	</varlistentry>
	<varlistentry>
	<term>QueryFence</term>
	<listitem>
	<literallayout class="monospaced">
	fence: FENCE
	=>
	triggered: BOOL
	Errors: <function>Fence</function>
	</literallayout>
	<para>
	This request returns TRUE if the given fence is triggered, or FALSE if it
	is not triggered. A <function>Fence</function> error is generated if
	fence does not name a valid fence.
	</para>
	</listitem>
	</varlistentry>
	<varlistentry>
	<term>AwaitFence</term>
	<listitem>
	<literallayout class="monospaced">
	fence-list: LISTofFENCE
	Errors: <function>Fence</function>,<function>Alloc</function>
	</literallayout>
	<para>
	When this request is executed, the processing of further requests for the
	client is blocked until one or more of the fences in fence-list reaches the
	triggered state. If any of the fences are already in the triggered state,
	request processing resumes immediately. A <function>Fence</function> error
	is generated if any member of fence-list does not name a valid fence.
	</para>
	</listitem>
	</varlistentry>
	</variablelist>
	</sect1>

	<sect1 id='Events'>
	<title>Events</title>

	<variablelist>
	<varlistentry>
	<term>CounterNotify</term>
	<listitem>
	<literallayout class="monospaced">
	counter: COUNTER
	wait-value: INT64
	counter-value: INT64
	time: TIME
	count: CARD16
	destroyed: BOOL
	</literallayout>
	<para>
	<function>CounterNotify</function> events may be generated when a client
	becomes unblocked after an <function>Await</function> request has been
	processed. The wait-value is the value being waited for, and counter-value
	is the actual value of the counter at the time the event was generated.
	The destroyed flag is TRUE if this request was generated as the result of
	the destruction of the counter and FALSE otherwise. The time is the server
	time at which the event was generated.
	</para>
	<para>
	When a client is unblocked, all the <function>CounterNotify</function>
	events for the Await request are generated contiguously. If count is 0,
	there are no more events to follow for this request. If count is n,
	there are at least n more events to follow.
	</para>
	</listitem>
	</varlistentry>
	<varlistentry>
	<term>AlarmNotify</term>
	<listitem>
	<literallayout class="monospaced">
	alarm: ALARM
	counter-value: INT64
	alarm-value: INT64
	state: ALARMSTATE
	time: TIME
	</literallayout>
	<para>
	An <function>AlarmNotify</function> event is generated when an alarm is
	triggered. alarm-value is the test value of the trigger in the alarm when
	it was triggered, counter-value is the value of the counter that triggered
	the alarm, and time is the server time at which the event was generated.
	The state is the new state of the alarm. If state is
	<function>Inactive</function>, no more events will be generated by this
	alarm until a <function>ChangeAlarm</function> request is executed, the alarm
	is destroyed, or the counter for the alarm is destroyed.
	</para>
	</listitem>
	</varlistentry>
	</variablelist>
	</sect1>
	</chapter>

	<chapter id='Encoding'>
	<title>Encoding</title>
	<para>
	Please refer to the X11 Protocol Encoding document as this section uses
	syntactic conventions established there and references types defined there.
	</para>
	<para>The name of this extension is "SYNC".</para>

	<sect1 id='Encoding_New_Types'>
	<title>Encoding New Types</title>
	<para>
	The following new types are used by the extension.
	</para>

	<literallayout class="monospaced">
	ALARM: CARD32
	ALARMSTATE:
	0 Active
	1 Inactive
	2 Destroyed
	COUNTER: CARD32
	INT64: 64-bit signed integer
	SYSTEMCOUNTER:
	4 COUNTER counter
	8 INT64 resolution
	2 n length of name in bytes
	n STRING8 name
	p pad,p=pad(n+2)
	TESTTYPE:
	0 PositiveTransition
	1 NegativeTransition
	2 PositiveComparison
	3 NegativeComparison
	TRIGGER:
	4 COUNTER counter
	4 VALUETYPE wait-type
	8 INT64 wait-value
	4 TESTTYPE test-type VALUETYPE:
	0 Absolute
	1 Relative
	WAITCONDITION:
	20 TRIGGER trigger
	8 INT64 event threshold
	FENCE: CARD32
	</literallayout>

	<para>
	An INT64 is encoded in 8 bytes with the most significant 4 bytes
	first followed by the least significant 4 bytes. Within these 4-byte
	groups, the byte ordering determined during connection setup is used.
	</para>
	</sect1>

	<sect1 id='Encoding_Errors'>
	<title>Encoding Errors</title>
	<literallayout class="monospaced">
	<function>Counter</function>
	1 0 Error
	1 Base + 0 code
	2 CARD16 sequence number
	4 CARD32 bad counter
	2 CARD16 minor opcode
	1 CARD8 major opcode
	21 unused
	<function>Alarm</function>
	1 0 Error
	1 Base + 1 code
	2 CARD16 sequence number
	4 CARD32 bad alarm
	2 CARD16 minor opcode
	1 CARD8 major opcode
	21 unused
	<function>Fence</function>
	1 0 Error
	1 Base + 2 code
	2 CARD16 sequence number
	4 CARD32 bad fence
	2 CARD16 minor opcode
	1 CARD8 major opcode
	21 unused
	</literallayout>

	</sect1>

	<sect1 id='Encoding_Requests'>
	<title>Encoding Requests</title>

	<literallayout class="monospaced">
	<function>Initialize</function>
	1 CARD8 major opcode
	1 0 minor opcode
	2 2 request length
	1 CARD8 major version
	1 CARD8 minor version
	2 unused
	=>
	1 1 Reply
	1 unused
	2 CARD16 sequence number
	4 0 reply length
	1 CARD8 major version
	1 CARD8 minor version
	2 unused
	20 unused

	<function>ListSystemCounters</function>
	1 CARD8 major opcode
	1 1 minor opcode
	2 1 request length
	=>
	1 1 Reply
	1 unused
	2 CARD16 sequence number
	4 0 reply length
	4 INT32 list length
	20 unused
	4n list of SYSTEMCOUNTER system counters

	<function>CreateCounter</function>
	1 CARD8 major opcode
	1 2 minor opcode
	2 4 request length
	4 COUNTER id
	8 INT64 initial value

	<function>DestroyCounter</function>
	1 CARD8 major opcode
	1 6 minor opcode<footnote><para>A previous version of this document gave an incorrect minor opcode</para></footnote>
	2 2 request length
	4 COUNTER counter
	=>
	1 1 Reply
	1 unused
	2 CARD16 sequence number
	4 0 reply length
	8 INT64 counter value
	16 unused

	Await
	1 CARD8 major opcode
	1 7 minor opcode<footnote><para>A previous version of this document gave an incorrect minor opcode.</para></footnote>
	2 1 + 7*n request length
	28n LISTofWAITCONDITION wait conditions

	ChangeCounter
	1 CARD8 major opcode
	1 4 minor opcode<footnote><para>A previous version of this document gave an incorrect minor opcode.</para></footnote>
	2 4 request length
	4 COUNTER counter
	8 INT64 amount

	SetCounter
	1 CARD8 major opcode
	1 3 minor opcode<footnote><para>A previous version of this document gave an incorrect minor opcode.</para></footnote>
	2 4 request length
	4 COUNTER counter
	8 INT64 value

	CreateAlarm
	1 CARD8 major opcode
	1 8 minor opcode
	2 3+n request length
	4 ALARM id
	4 BITMASK values mask

	#x00000001 counter
	#x00000002 value-type
	#x00000004 value
	#x00000008 test-type
	#x00000010 delta
	#x00000020 events

	4n LISTofVALUE values

	VALUES
	4 COUNTER counter
	4 VALUETYPE value-type
	8 INT64 value
	4 TESTTYPE test-type
	8 INT64 delta
	4 BOOL events

	ChangeAlarm
	1 CARD8 major opcode
	1 9 minor opcode
	2 3+n request length
	4 ALARM id
	4 BITMASK values mask
	encodings as for <function>CreateAlarm</function>
	4n LISTofVALUE values
	encodings as for <function>CreateAlarm</function>

	DestroyAlarm
	1 CARD8 major opcode
	1 11 minor opcode<footnote><para>A previous version of this document gave an incorrect minor opcode.</para></footnote>
	2 2 request length
	4 ALARM alarm

	QueryAlarm
	1 CARD8 major opcode
	1 10 minor opcode<footnote><para>A previous version of this document gave an incorrect minor opcode.</para></footnote>
	2 2 request length
	4 ALARM alarm
	=>
	1 1 Reply
	1 unused
	2 CARD16 sequence number
	4 2 reply length
	20 TRIGGER trigger
	8 INT64 delta
	1 BOOL events
	1 ALARMSTATE state
	2 unused

	SetPriority
	1 CARD8 major opcode
	1 12 minor opcode
	2 3 request length
	4 CARD32 id
	4 INT32 priority

	GetPriority
	1 CARD8 major opcode
	1 13 minor opcode
	2 1 request length
	4 CARD32 id
	=>
	1 1 Reply
	1 unused
	2 CARD16 sequence number
	4 0 reply length
	4 INT32 priority
	20 unused

	CreateFence
	1 CARD8 major opcode
	1 14 minor opcode
	2 4 request length
	4 DRAWABLE drawable
	4 FENCE id
	1 BOOL initially triggered
	3 unused

	TriggerFence
	1 CARD8 major opcode
	1 15 minor opcode
	2 2 request length
	4 FENCE id

	ResetFence
	1 CARD8 major opcode
	1 16 minor opcode
	2 2 request length
	4 FENCE id

	DestroyFence
	1 CARD8 major opcode
	1 17 minor opcode
	2 2 request length
	4 FENCE id

	QueryFence
	1 CARD8 major opcode
	1 18 minor opcode
	2 2 request length
	4 FENCE id
	=>
	1 1 Reply
	1 unused
	2 CARD16 sequence number
	4 0 reply length
	1 BOOL triggered
	23 unused

	AwaitFence
	1 CARD8 major opcode
	1 19 minor opcode
	2 1 + n request length
	4*n LISTofFENCE wait conditions

	</literallayout>

	</sect1>

	<sect1 id='Encoding_Events'>
	<title>Encoding Events</title>

	<literallayout class="monospaced">
	<function>CounterNotify</function>
	1 Base + 0 code
	1 0 kind
	2 CARD16 sequence number
	4 COUNTER counter
	8 INT64 wait value
	8 INT64 counter value
	4 TIME timestamp
	2 CARD16 count
	1 BOOL destroyed
	1 unused

	<function>AlarmNotify</function>
	1 Base + 1 code
	1 1 kind
	2 CARD16 sequence number
	4 ALARM alarm
	8 INT64 counter value
	8 INT64 alarm value
	4 TIME timestamp
	1 ALARMSTATE state
	3 unused
	</literallayout>
	</sect1>
	</chapter>
	</book>