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<!-- lifted from troff+ms+XMan by doclifter -->
<book id="synclib">

<bookinfo>
   <title>X Synchronization Extension Library</title>
   <subtitle>X Consortium Standard</subtitle>
   <releaseinfo>X Version 11, Release &fullrelvers;</releaseinfo>
   <releaseinfo>Version 3.0</releaseinfo>
   <authorgroup>
      <author>
        <firstname>Tim</firstname><surname>Glauert</surname>
        <affiliation>
          <orgname>Olivetti Research</orgname>
          <orgdiv>MultiWorks</orgdiv>
        </affiliation>
      </author>
      <author>
          <firstname>Dave</firstname>
          <surname>Carver</surname>
          <affiliation>
            <orgname>Digital Equipment Corporation</orgname>
            <orgdiv>MIT/Project Athena</orgdiv>
          </affiliation>
      </author>
      <author>
        <firstname>Jim</firstname>
        <surname>Gettys</surname>
        <affiliation>
          <orgname>Digital Equipment Corporation</orgname>
          <orgdiv>Cambridge Research Laboratory</orgdiv>
        </affiliation>
      </author>
      <author>
        <firstname>David</firstname>
        <othername>P.</othername>
        <surname>Wiggins</surname>
        <affiliation><orgname>X Consortium, Inc.</orgname></affiliation>
      </author>
   </authorgroup>
   <copyright><year>1991</year>
     <holder>Olivetti Research Limited, Cambridge England</holder>
     <holder>Digital Equipment Corporation, Maynard, Massachusetts</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, and the
X Consortium 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>
</legalnotice>

<legalnotice>
<para role="multiLicensing">Copyright &copy; 1991 X Consortium, Inc.</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 &ldquo;AS IS&rdquo;, 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>
<para>X Window System is a trademark of The OpenGroup.</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> and
<function>Alarm</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 <function>Await</function> request that waits until
one of a set of synchronization conditions, called TRIGGERs, becomes TRUE.
</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>
</sect1>
</chapter>

<chapter id="c_language_binding">
<title>C Language Binding</title>

<para>
The C routines provide direct access to the protocol and add no additional
semantics.
</para>
<para>
The include file for this extension is &lt;X11/extensions/sync.h&gt;.
Most of the names in the language binding are derived from the protocol
names by prepending XSync to the protocol name and changing the
capitalization.
</para>

<sect1 id="c_functions">
<title>C Functions</title>

<para>
Most of the following functions generate SYNC protocol requests.
</para>

<funcsynopsis id='xsyncqueryextension'>
<funcprototype>
  <funcdef>Status <function>XSyncQueryExtension</function></funcdef>
    <paramdef>Display <parameter> *dpy</parameter></paramdef>
    <paramdef>int <parameter> *event_base_return</parameter></paramdef>
    <paramdef>int <parameter> *error_base_return</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<para>
If dpy supports the SYNC extension,
<function>XSyncQueryExtension</function> returns True,
sets *event_base_return to the event number for the first SYNC event, and
sets *error_base_return to the error number for the first SYNC error. If dpy
does not support the SYNC extension, it returns False.
</para>

<funcsynopsis id='xsyncinitialize'>
<funcprototype>
  <funcdef>Status <function>XSyncInitialize</function></funcdef>
    <paramdef>Display <parameter> *dpy</parameter></paramdef>
    <paramdef>int <parameter> *major_version_return</parameter></paramdef>
    <paramdef>int <parameter> *minor_version_return</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<para>
<function>XSyncInitialize</function> sets *major_version_return and
*minor version return to the major/minor SYNC protocol version supported
by the server. If the XSync library is compatible with the version
returned by the server, this function returns <function>True</function>.
If dpy does not support the SYNC extension, or if there was an error
during communication with the server, or if the server and library protocol
versions are incompatible, this function returns <function>False</function>.
The only XSync function that may be called before this function is
XSyncQueryExtension. If a client violates this rule, the effects of all XSync
calls that it makes are undefined.
</para>

<funcsynopsis id='xsynclistsystemcounters'>
<funcprototype>
  <funcdef>XSyncSystemCounter *<function>XSyncListSystemCounters</function></funcdef>
    <paramdef>Display <parameter> *dpy</parameter></paramdef>
    <paramdef>int <parameter> *n_counters_return</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<para>
<function>XSyncListSystemCounters</function> returns a pointer to an array
of system counters supported by the display and sets *n_counters_return
to the number of counters in the array.  The array should be freed with
<function>XSyncFreeSystemCounterList</function>. If dpy does not support
the SYNC extension, or if there was an error during communication with
the server, or if the server does not support any system counters,
this function returns NULL.
</para>

<para>
XSyncSystemCounter has the following fields:
</para>

<literallayout remap='Ds'>
char *              name;        /* null-terminated name of system counter */
XSyncCounter        counter;     /* counter id of this system counter */
XSyncValue          resolution;  /* resolution of this system counter */
</literallayout>

<funcsynopsis id='xsyncfreesystemcounterlist'>
<funcprototype>
  <funcdef>void <function>XSyncFreeSystemCounterList</function></funcdef>
    <paramdef>XSyncSystemCounter <parameter> *list</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<para>
<function>XSyncFreeSystemCounterList</function> frees the memory
associated with the system counter list returned by
<function>XSyncListSystemCounters</function>.
</para>

<funcsynopsis id='xsynccreatecounter'>
<funcprototype>
  <funcdef>XSyncCounter <function>XSyncCreateCounter</function></funcdef>
    <paramdef>Display<parameter> *dpy</parameter></paramdef>
    <paramdef>XSyncValue<parameter> initial_value</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<para>
<function>XSyncCreateCounter</function> creates a counter on the dpy
with the given initial value and returns the counter ID. It returns
<function>None</function> if dpy does not support the SYNC extension.
</para>

<funcsynopsis id='xsyncsetcounter'>
<funcprototype>
  <funcdef>Status <function>XSyncSetCounter</function></funcdef>
    <paramdef>Display<parameter> *dpy</parameter></paramdef>
    <paramdef>XSyncCounter<parameter> counter</parameter></paramdef>
    <paramdef>XSyncValue<parameter> value</parameter></paramdef>
</funcprototype>
</funcsynopsis>


<para>
<function>XSyncSetCounter</function> sets counter to value. It returns
<function>False </function> if dpy does not
support the SYNC extension; otherwise, it returns <function>True</function>.
</para>

<funcsynopsis id='xsyncchangecounter'>
<funcprototype>
  <funcdef>Status <function>XSyncChangeCounter</function></funcdef>
    <paramdef>Display<parameter> *dpy</parameter></paramdef>
    <paramdef>XSyncCounter<parameter> counter</parameter></paramdef>
    <paramdef>XSyncValue<parameter> value</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<para>
<function>XSyncChangeCounter</function> adds value to counter. It returns
<function>False</function> if dpy does not support the SYNC extension;
otherwise, it returns
<function>True</function>.
</para>
<funcsynopsis id='xsyncdestroycounter'>
<funcprototype>
  <funcdef>Status <function>XSyncDestroyCounter</function></funcdef>
    <paramdef>Display<parameter> *dpy</parameter></paramdef>
    <paramdef>XSyncCounter<parameter> counter</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<para>
<function>XSyncDestroyCounter</function> destroys counter. It returns
<function>False</function> if dpy does not support the SYNC extension;
otherwise, it returns <function>True</function>.
</para>

<funcsynopsis id='xsyncquerycounter'>
<funcprototype>
  <funcdef>Status <function>XSyncQueryCounter</function></funcdef>
    <paramdef>Display<parameter> *dpy</parameter></paramdef>
    <paramdef>XSyncCounter<parameter> counter</parameter></paramdef>
    <paramdef>XSyncValue<parameter> *value_return</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<para>
<function>XSyncQueryCounter</function> sets *value_return to the current
value of counter. It returns <function>False</function> if there was an
error during communication with the server or if dpy does not support the
SYNC extension; otherwise, it returns <function>True</function>.
</para>

<funcsynopsis id='xsyncawait'>
<funcprototype>
  <funcdef>Status <function>XSyncAwait</function></funcdef>
    <paramdef>Display<parameter> *dpy</parameter></paramdef>
    <paramdef>XSyncWaitCondition<parameter> *wait_list</parameter></paramdef>
    <paramdef>int<parameter> n_conditions</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<para>
<function>XSyncAwait</function> awaits on the conditions in wait_list.
The n_conditions is the number of wait conditions in wait_list. It
returns <function>False</function> if dpy does not support the SYNC
extension; otherwise, it returns <function>True</function>. The await is
processed asynchronously by the server; this function always returns
immediately after issuing the request.
</para>
<para>
XSyncWaitCondition has the following fields:
</para>

<literallayout remap='Ds'>
XSyncCounter     trigger.counter;    /*counter to trigger on */
XSyncValueType   trigger.value_type; /*absolute/relative */
XSyncValue       trigger.wait_value; /*value to compare counter to */
XSyncTestType    trigger.test_type;  /*pos/neg comparison/transition */
XSyncValue       event_threshold;    /*send event if past threshold */
</literallayout>

<para>
<function>XSyncValueType</function> can be either
<function>XSyncAbsolute</function> or <function>XSyncRelative</function>.
</para>

<para>
<function>XSyncTestType</function> can be one of
<function>XSyncPositiveTransition</function>,
<function>XSyncNegativeTransition</function>,
<function>XSyncPositiveComparison</function>, or
<function>XSyncNegativeComparison</function>.
</para>

<funcsynopsis id='xsynccreatealarm'>
<funcprototype>
  <funcdef>XSyncAlarm <function>XSyncCreateAlarm</function></funcdef>
    <paramdef>Display<parameter> *dpy</parameter></paramdef>
    <paramdef>unsigned long<parameter> values_mask</parameter></paramdef>
    <paramdef>XSyncAlarmAttributes<parameter> *values`</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<para>
<function>XSyncCreateAlarm</function> creates an alarm and returns the
alarm ID. It returns None if the display does not support the SYNC
extension. The values_mask and values specify the alarm attributes.
</para>

<para>
<function>XSyncAlarmAttributes</function> has the following fields. The
attribute_mask column specifies the symbol that the caller should OR
into values_mask to indicate that the value for the corresponding
attribute was actually supplied. Default values are used for all
attributes that do not have their attribute_mask OR’ed into values_mask.
See the protocol description for <function>CreateAlarm</function> for the
defaults.
</para>

<literallayout remap='Ds'>
type                 field name           attribute_mask
XSyncCounter       trigger.counter;     XSyncCACounter
XSyncValueType     trigger.value_type;  XSyncCAValueType
XSyncValue         trigger.wait_value;  XSyncCAValue
XSyncTestType      trigger.test_type;   XSyncCATestType
XSyncValue         delta;               XSyncCADelta
Bool               events;              XSyncCAEvents
XSyncAlarmState    state;               client cannot set this
</literallayout>

<funcsynopsis id='xsyncdestroyalarm'>
<funcprototype>
  <funcdef>Status <function>XSyncDestroyAlarm</function></funcdef>
    <paramdef>Display<parameter> *dpy</parameter></paramdef>
    <paramdef>XSyncAlarm<parameter> alarm</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<para>
<function>XSyncDestroyAlarm</function> destroys alarm. It returns
<function>False</function> if dpy does not support
the SYNC extension; otherwise, it returns <function>True</function>.
</para>

<funcsynopsis id='xsyncqueryalarm'>
<funcprototype>
  <funcdef>Status <function>XSyncQueryAlarm</function></funcdef>
    <paramdef>Display<parameter> *dpy</parameter></paramdef>
    <paramdef>XSyncAlarm<parameter> alarm</parameter></paramdef>
    <paramdef>XSyncAlarmAttributes<parameter> *values_return</parameter></paramdef>
</funcprototype>
</funcsynopsis>


<para>
<function>XSyncQueryAlarm</function> sets *values_return to the alarm’s
attributes. It returns <function>False</function> if there was an error
during communication with the server or if dpy does not support the
SYNC extension; otherwise, it returns <function>True</function>.
</para>

<funcsynopsis id='xsyncchangealarm'>
<funcprototype>
  <funcdef>Status <function>XSyncChangeAlarm</function></funcdef>
    <paramdef>Display<parameter> *dpy</parameter></paramdef>
    <paramdef>XSyncAlarm<parameter> alarm</parameter></paramdef>
    <paramdef>unsigned long<parameter> values_mask</parameter></paramdef>
    <paramdef>XSyncAlarmAttributes<parameter> *values</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<para>
<function>XSyncChangeAlarm</function> changes alarm’s attributes. The
attributes to change are specified as in
<function>XSyncCreateAlarm</function>. It returns
<function>False</function> if dpy does not support
the SYNC extension; otherwise, it returns <function>True</function>.
</para>

<funcsynopsis id='xsyncsetpriority'>
<funcprototype>
  <funcdef>Status <function>XSyncSetPriority</function></funcdef>
    <paramdef>Display<parameter> *dpy</parameter></paramdef>
    <paramdef>XID<parameter> client_resource_id</parameter></paramdef>
    <paramdef>int<parameter> priority</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<para>
<function>XSyncSetPriority</function> sets the priority of the client
owning client_resource_id to priority. If client_resource_id is None, it
sets the caller’s priority. It returns
<function>False</function> if dpy does not support the SYNC extension;
otherwise, it returns <function>True</function>.
</para>

<funcsynopsis id='xsyncgetpriority'>
<funcprototype>
  <funcdef>Status <function>XSyncGetPriority</function></funcdef>
    <paramdef>Display<parameter> *dpy</parameter></paramdef>
    <paramdef>XID<parameter> client_resource_id</parameter></paramdef>
    <paramdef>int<parameter> *return_priority</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<para>
<function>XSyncGetPriority</function> sets *return_priority to the
priority of the client owning client_resource_id. If client_resource_id
is None, it sets *return_priority to the caller’s priority. It returns
<function>False</function> if there was an error during communication
with the server or if dpy does not support the SYNC extension; otherwise, it
returns <function>True</function>.
</para>

</sect1>

<sect1 id="c_macros_functions">
<title>C Macros/Functions</title>

<para>
The following procedures manipulate 64-bit values. They are defined both as
macros and as functions. By default, the macro form is used. To use the
function form, #undef the macro name to uncover the function.
</para>

<funcsynopsis id='xsyncinttovalue'>
<funcprototype>
  <funcdef>void <function>XSyncIntToValue</function></funcdef>
    <paramdef>XSyncValue<parameter> *pv</parameter></paramdef>
    <paramdef>int<parameter> i</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<para>
Converts i to an <function>XSyncValue</function> and stores it in *pv.
Performs sign extension (*pv will have the same sign as i.)
</para>

<funcsynopsis id='xsyncintstovalue'>
<funcprototype>
  <funcdef>void <function>XSyncIntsToValue</function></funcdef>
    <paramdef>XSyncValue<parameter> *pv</parameter></paramdef>
    <paramdef>unsigned int<parameter> low</parameter></paramdef>
    <paramdef>int<parameter> high</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<para>
Stores low in the low 32 bits of *pv and high in the high 32 bits of *pv.
</para>


<funcsynopsis id='xsyncvaluegreaterthan'>
<funcprototype>
  <funcdef>Bool <function>XSyncValueGreaterThan</function></funcdef>
    <paramdef>XSyncValue<parameter> a</parameter></paramdef>
    <paramdef>XSyncValue<parameter> b</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<para>
Returns <function>True</function> if a is greater than b, else returns
<function>False</function>.
</para>

<funcsynopsis id='xsyncvaluelessthan'>
<funcprototype>
  <funcdef>Bool <function>XSyncValueLessThan</function></funcdef>
    <paramdef>XSyncValue<parameter> a</parameter></paramdef>
    <paramdef>XSyncValue<parameter> b</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<para>
Returns <function>True</function> if a is less than b, else returns
<function>False</function>.
</para>


<funcsynopsis id='xsyncvaluegreaterorequal'>
<funcprototype>
  <funcdef>Bool <function>XSyncValueGreaterOrEqual</function></funcdef>
    <paramdef>XSyncValue<parameter> a</parameter></paramdef>
    <paramdef>XSyncValue<parameter> b</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<para>
Returns <function>True</function> if a is greater than or equal to b,
else returns <function>False</function>.
</para>

<funcsynopsis id='xsyncvaluelessorequal'>
<funcprototype>
  <funcdef>Bool <function>XSyncValueLessOrEqual</function></funcdef>
    <paramdef>XSyncValue<parameter> a</parameter></paramdef>
    <paramdef>XSyncValue<parameter> b</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<para>
Returns <function>True</function> if a is less than or equal to b,
else returns <function>False</function>.
</para>

<funcsynopsis id='xsyncvalueequal'>
<funcprototype>
  <funcdef>Bool <function>XSyncValueEqual</function></funcdef>
    <paramdef>XSyncValue<parameter> a</parameter></paramdef>
    <paramdef>XSyncValue<parameter> b</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<para>
Returns <function>True</function> if a is equal to b,
else returns <function>False</function>.
</para>

<funcsynopsis id='xsyncvalueisnegative'>
<funcprototype>
  <funcdef>Bool <function>XSyncValueIsNegative</function></funcdef>
    <paramdef>XSyncValue<parameter> v</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<para>
Returns <function>True</function> if v is negative,
else returns <function>False</function>.
</para>

<funcsynopsis id='xsyncvalueiszero'>
<funcprototype>
  <funcdef>Bool <function>XSyncValueIsZero</function></funcdef>
    <paramdef>XSyncValue<parameter> v</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<para>
Returns <function>True</function> if v is zero,
else returns <function>False</function>.
</para>

<funcsynopsis id='xsyncvalueispositive'>
<funcprototype>
  <funcdef>Bool <function>XSyncValueIsPositive</function></funcdef>
    <paramdef>XSyncValue<parameter> v</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<para>
Returns <function>True</function> if v is positive,
else returns <function>False</function>.
</para>

<funcsynopsis id='xsyncvaluelow32'>
<funcprototype>
  <funcdef>unsigned int <function>XSyncValueLow32</function></funcdef>
    <paramdef>XSyncValue<parameter> v</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<para>
Returns the low 32 bits of v.
</para>

<funcsynopsis id='xsyncvaluehigh32'>
<funcprototype>
  <funcdef>unsigned int <function>XSyncValueHigh32</function></funcdef>
    <paramdef>XSyncValue<parameter> v</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<para>
Returns the high 32 bits of v.
</para>

<funcsynopsis id='xsyncvalueadd'>
<funcprototype>
  <funcdef>void <function>XSyncValueAdd</function></funcdef>
    <paramdef>XSyncValue<parameter> *presult</parameter></paramdef>
    <paramdef>XSyncValue<parameter> a</parameter></paramdef>
    <paramdef>XSyncValue<parameter> b</parameter></paramdef>
    <paramdef>Bool<parameter> *poverflow</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<para>
Adds a to b and stores the result in *presult. If the result could not
fit in 64 bits, *poverﬂow is set to <function>True</function>, else it is
set to <function>False</function>.
</para>

<funcsynopsis id='xsyncvaluesubtract'>
<funcprototype>
  <funcdef>void <function>XSyncValueSubtract</function></funcdef>
    <paramdef>XSyncValue<parameter> *presult</parameter></paramdef>
    <paramdef>XSyncValue<parameter> a</parameter></paramdef>
    <paramdef>XSyncValue<parameter> b</parameter></paramdef>
    <paramdef>Bool<parameter> *poverflow</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<para>
Subtracts b from a and stores the result in *presult. If the result could not
fit in 64 bits, *poverﬂow is set to <function>True</function>, else it is
set to <function>False</function>.
</para>

<funcsynopsis id='xsyncmaxvalue'>
<funcprototype>
  <funcdef>void <function>XSyncMaxValue</function></funcdef>
    <paramdef>XSyncValue<parameter> *pv</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<para>
Sets *pv to the maximum value expressible in 64 bits.
</para>

<funcsynopsis id='xsyncminvalue'>
<funcprototype>
  <funcdef>void <function>XSyncMinValue</function></funcdef>
    <paramdef>XSyncValue<parameter> *pv</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<para>
Sets *pv to the minimum value expressible in 64 bits.
</para>

</sect1>

<sect1 id="events">
<title>Events</title>

<para>
Let <emphasis remap='I'>event_base</emphasis> be the value event base return as defined in the function
<function>XSyncQueryExtension</function>.
</para>

<para>
An <function>XSyncCounterNotifyEvent</function>’s type field has the value
event_base + <function>XSyncCounterNotify</function>. The fields of this
structure are:
</para>

<literallayout remap='Ds'>
int              type;          /* event base + XSyncCounterNotify */
unsigned long    serial;        /* number of last request processed by server */
Bool             send event;    /* true if this came from a SendEvent request */
Display *        display;       /* Display the event was read from */
XSyncCounter     counter;       /* counter involved in await */
XSyncValue       wait_value;    /* value being waited for */
XSyncValue       counter_value; /* counter value when this event was sent */
Time             time;          /* milliseconds */
int              count;         /* how many more events to come */
Bool             destroyed;     /* True if counter was destroyed */
</literallayout>

<para>
An <function>XSyncAlarmNotifyEvent</function>’s type field has the value
event_base + <function>XSyncAlarmNotify</function>. The fields of
this structure are:
</para>

<literallayout remap='Ds'>
int             type;         /* event_base + XSyncAlarmNotify */
unsigned long   serial;       /* number of last request processed by server */
Bool            send_event;   /* true if this came from a SendEvent request */
Display *       display;      /*Display the event was read from */
XSyncAlarm      alarm;        /* alarm that triggered */
XSyncValue      counter_value /* value that triggered the alarm */
XSyncValue      alarm_value   /* test value of trigger in alarm */
Time            time;         /* milliseconds */
XSyncAlarmState state;        /* new state of alarm */
</literallayout>

</sect1>

<sect1 id="errors">
<title>Errors</title>
<para>
Let <emphasis remap='I'>error_base</emphasis> be the value
<emphasis remap='I'>error_base_return</emphasis> as defined in the function
<function>XSyncQueryExtension</function>.
</para>

<para>
An <function>XSyncAlarmError</function>’s error_code field has
<function>XSyncBadAlarm</function>. The fields of this structure are:
</para>

<literallayout remap='Ds'>
int                type
Display *          display;      /* Display the event was read from */
XSyncCounter       counter;      /* resource id */
unsigned long      serial;       /* serial number of failed request */
unsigned char      error_code;   /* error_base + XSyncBadAlarm */
unsigned char      request_code; /* Major op-code of failed request */
unsigned char      minor_code;   /* Minor op-code of failed request */
</literallayout>

<para>
An <function>XSyncCounterError</function>’s error code field has the value
error_base + <function>XSyncBadCounter</function>. The fields of this
structure are:
</para>
<literallayout remap='Ds'>
int                type
Display *          display;      /* Display the event was read from */
XSyncCounter       counter;      /* resource id */
unsigned long      serial;       /* serial number of failed request */
unsigned char      error_code;   /* error_base + XSyncBadCounter */
unsigned char      request_code; /* Major op-code of failed request */
unsigned char      minor_code;   /* Minor op-code of failed request */
</literallayout>

</sect1>
</chapter>
</book>
