sdk/1.0/docs/man/clEnqueueReadBuffer.xml

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<refentry>
    <refentryinfo>
        <keywordset>
            <keyword>         
                clEnqueueReadBuffer
            </keyword>
        </keywordset>
    </refentryinfo>

    <refmeta>
        <refentrytitle>       
            clEnqueueReadBuffer
        </refentrytitle>

        <refmiscinfo>
            <copyright>
                <year>2007-2009</year>
                <holder>The Khronos Group Inc. 
 Permission is hereby granted, free of charge, to any person obtaining a
copy of this software and/or associated documentation files (the
"Materials"), to deal in the Materials without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Materials, and to
permit persons to whom the Materials are furnished to do so, subject to
the condition that this copyright notice and permission notice shall be included
in all copies or substantial portions of the Materials.</holder>
            </copyright>
        </refmiscinfo>
        <manvolnum>2</manvolnum>
  
    </refmeta>


<!-- ================================ SYNOPSIS -->  

    <refnamediv id="clEnqueueReadBuffer">
        <refname>     
            clEnqueueReadBuffer
        </refname> 

        <refpurpose>          
            Enqueue commands to read from a buffer object to host memory.
        </refpurpose> 
    </refnamediv> 

    <refsynopsisdiv xmlns:xlink="http://www.w3.org/1999/xlink"><title></title>
        <funcsynopsis>
            <funcprototype>
                <funcdef>
                    <link xlink:href="scalarDataTypes.html">cl_int</link>
 <function>clEnqueueReadBuffer</function>
                </funcdef>

					<paramdef><link xlink:href="abstractDataTypes.html">cl_command_queue</link><parameter>command_queue</parameter></paramdef>
					<paramdef><link xlink:href="abstractDataTypes.html">cl_mem</link><parameter>buffer</parameter></paramdef>
					<paramdef><link xlink:href="enums.html#cl_bool">cl_bool</link><parameter>blocking_read</parameter></paramdef>
					<paramdef><link xlink:href="scalarDataTypes.html">size_t</link><parameter>offset</parameter></paramdef>
					<paramdef><link xlink:href="scalarDataTypes.html">size_t</link><parameter>cb</parameter></paramdef>
					<paramdef><link xlink:href="scalarDataTypes.html">void</link><parameter>*ptr</parameter></paramdef>
					<paramdef><link xlink:href="scalarDataTypes.html">cl_uint</link><parameter>num_events_in_wait_list</parameter></paramdef>
					<paramdef>const <link xlink:href="abstractDataTypes.html">cl_event</link><parameter>*event_wait_list</parameter></paramdef>
					<paramdef><link xlink:href="abstractDataTypes.html">cl_event</link><parameter>*event</parameter></paramdef>
                         
            </funcprototype>
        </funcsynopsis>     
    </refsynopsisdiv>


<!-- ================================ PARAMETERS --> 

    <refsect1 id="parameters">
        <title>Parameters</title>
        <variablelist>

            <varlistentry>
                <term><varname>command_queue</varname></term>
                <listitem>
                    <para> <!-- parameter description -->
                        Refers to the command-queue in which the read command will be
						queued. <varname>command_queue</varname> and <varname>buffer</varname> must be created with the same OpenCL context.
                    </para>
               </listitem>
            </varlistentry>
            <varlistentry>
                <term><varname>buffer</varname></term>
                <listitem>
                    <para>Refers to a valid buffer object.</para>
               </listitem>
            </varlistentry>
            <varlistentry>
                <term><varname>blocking_read</varname></term>
                <listitem>
                    <para> <!-- parameter description -->
                        Indicates if the read operations are <varname>blocking</varname> or non-blocking. If <varname>blocking_read</varname> is <constant>CL_TRUE</constant> i.e. the read command is blocking, <function>clEnqueueReadBuffer</function> does not return until the buffer data has been read and copied into memory pointed to by <varname>ptr</varname>.
					</para>
					<para>
						If <varname>blocking_read</varname> is <constant>CL_FALSE</constant> i.e. the read command is <varname>non-blocking</varname>, <function>clEnqueueReadBuffer</function>
						queues a <varname>non-blocking</varname> read command and returns. The contents of the buffer that <varname>ptr</varname> points to
						cannot be used until the read command has completed. The <varname>event</varname> argument returns an event
						object which can be used to query the execution status of the read command. When the read
						command has completed, the contents of the buffer that <varname>ptr</varname> points to can be used by the
						application.
					</para>
               </listitem>
            </varlistentry>
            <varlistentry>
                <term><varname>offset</varname></term>

                <listitem>
                    <para>The offset in bytes in the buffer object to read from.</para>
               </listitem>
            </varlistentry>
            <varlistentry>
                <term><varname>cb </varname></term>

                <listitem>
                    <para>The size in bytes of data being read.</para>
               </listitem>
            </varlistentry>

            <varlistentry>
                <term>
                    <varname>ptr </varname>
                </term>

                <listitem>
                    <para> <!-- parameter description -->
                        The pointer to buffer in host memory where data is to be read into.
                    </para>
               </listitem>
            </varlistentry>
			
			   <varlistentry>
                <term>
                    <varname> <!-- parameter name -->
						event_wait_list 
					</varname>
                </term>
                <term>
                    <varname> <!-- parameter name -->
						num_events_in_wait_list 
					</varname>
                </term>
				
                <listitem>
                    <para> <!-- parameter description -->
						<varname>event_wait_list</varname> and <varname>num_events_in_wait_list</varname> specify events that need to complete before this particular command can be executed. If <varname>event_wait_list</varname> is NULL, then this particular command
does not wait on any event to complete. If <varname>event_wait_list</varname> is NULL, <varname>num_events_in_wait_list</varname> must be 0. If <varname>event_wait_list</varname> is not NULL, the list of events pointed to by <varname>event_wait_list</varname> must be valid and <varname>num_events_in_wait_list</varname> must be greater than 0. The events specified in <varname>event_wait_list</varname> act as synchronization points. The context associated with events in <varname>event_wait_list</varname> and <varname>command_queue</varname> must be the same.
                    </para>
               </listitem>
            </varlistentry>	
 		    <varlistentry>
                <term>
                    <varname> <!-- parameter name -->
						event 
					</varname>
                </term>

                <listitem>
                    <para> <!-- parameter description -->
						Returns an event object that identifies this particular read command and can be used
to query or queue a wait for this particular command to complete. <varname>event</varname> can be NULL in which
						case it will not be possible for the application to query the status of this command or queue a
						wait for this command to complete.
                    </para>
               </listitem>
            </varlistentry>				

        

 
            <!-- END PARAMETER TABLE  -->          





        </variablelist>
    </refsect1>

    
<!-- ================================ NOTES  -->        
 

    <refsect1 id="notes"><title>Notes</title>
			<para>
				Calling <function>clEnqueueReadBuffer</function> to read a region of the buffer object with the <varname>ptr</varname> argument value
				set to <varname>host_ptr</varname> + <varname>offset</varname>, where <varname>host_ptr</varname> is a pointer to the memory region specified when the
				buffer object being read is created with <constant>CL_MEM_USE_HOST_PTR</constant>, must meet the following
				requirements in order to avoid undefined behavior:
			</para>
        <itemizedlist mark="disc">
            <listitem>All commands that use this buffer object have finished execution before the read
						command begins execution</listitem>.
			<listitem>The buffer object is not mapped</listitem>.
			<listitem>The buffer object is not used by any command-queue until the read command has
						finished execution</listitem>.

		</itemizedlist>
	</refsect1>
    

<!-- ================================ ERRORS  -->       


    <refsect1 id="errors"><title>Errors</title>
        <para>
			<function>clEnqueueReadBuffer</function> returns <errorname>CL_SUCCESS</errorname> if the function is
			executed successfully. Otherwise, it returns one of the following errors:
        </para>
        <itemizedlist mark="disc">
            <listitem>
				<errorname>CL_INVALID_COMMAND_QUEUE</errorname> if <varname>command_queue</varname> is not a valid command-queue.
			</listitem>
			<listitem>
				<errorname>CL_INVALID_CONTEXT</errorname> if the context associated with <varname>command_queue</varname> and <varname>buffer</varname> are not the same or if the context associated with <varname>command_queue</varname> and events in			
				<varname>event_wait_list</varname> are not the same.
			</listitem>
			<listitem>			
				<errorname>CL_INVALID_MEM_OBJECT</errorname> if <varname>buffer</varname> is not a valid buffer object.
			</listitem>
			<listitem>
				<errorname>CL_INVALID_VALUE</errorname> if the region being read specified by (<varname>offset</varname>, <varname>cb</varname>) is out of bounds or if <varname>ptr</varname> is a NULL value.
			</listitem>
			<listitem>
				<errorname>CL_INVALID_EVENT_WAIT_LIST</errorname> if <varname>event_wait_list</varname> is NULL and
				<varname>num_events_in_wait_list</varname> greater than 0, or <varname>event_wait_list</varname> is not NULL and <varname>num_events_in_wait_list</varname> is 0, or if event objects in <varname>event_wait_list</varname> are not valid events.
			</listitem>
			<listitem>
				<errorname>CL_MEM_OBJECT_ALLOCATION_FAILURE</errorname> if there is a failure to allocate memory for
				data store associated with <varname>buffer</varname>.
			</listitem>
			<listitem>
				<errorname>CL_OUT_OF_HOST_MEMORY</errorname> if there is a failure to allocate resources required by the
				OpenCL implementation on the host.	
			</listitem>

        </itemizedlist>
    </refsect1>
    

<!-- ================================ EXAMPLE  -->  
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<!-- ================================ SPECIFICATION  -->        
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    <refsect1 id="specification"><title>Specification</title>
        <para>
            <imageobject>
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            </imageobject>
			
				      
            <olink uri="clEnqueueReadBuffer">OpenCL Specification</olink>
        </para>
    </refsect1>     


<!-- ================================ ALSO SEE  -->     
   

    <refsect1 id="seealso"><title>Also see</title>
        <para>
            <citerefentry><refentrytitle>clEnqueueCopyBuffer</refentrytitle></citerefentry>, 
			<citerefentry><refentrytitle>clEnqueueWriteBuffer</refentrytitle></citerefentry>
        </para>
    </refsect1>

<!-- ================================ COPYRIGHT  -->  
<!-- Content included from copyright.inc.xsl -->

    <refsect3 id="Copyright"><title></title>
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                <imagedata fileref="KhronosLogo.jpg" format="jpg" />
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		<para />
    </refsect3>

</refentry>