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<a name="VipsThreadState"></a><div class="titlepage"></div>
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<h2><span class="refentrytitle"><a name="VipsThreadState.top_of_page"></a>VipsThreadState</span></h2>
<p>VipsThreadState — pools of worker threads</p>
</td>
<td valign="top" align="right"></td>
</tr></table></div>
<div class="refsect1">
<a name="VipsThreadState.stability-level"></a><h2>Stability Level</h2>
Stable, unless otherwise indicated
</div>
<div class="refsynopsisdiv">
<a name="VipsThreadState.synopsis"></a><h2>Synopsis</h2>
<pre class="synopsis">
#include <vips/vips.h>
<a class="link" href="VipsThreadState.html#VipsThreadState-struct" title="VipsThreadState">VipsThreadState</a>;
<a class="link" href="VipsThreadState.html#VipsThreadStateClass" title="VipsThreadStateClass">VipsThreadStateClass</a>;
<span class="returnvalue">void</span> * <a class="link" href="VipsThreadState.html#vips-thread-state-set" title="vips_thread_state_set ()">vips_thread_state_set</a> (<em class="parameter"><code><a class="link" href="libvips-VipsArgument.html#VipsObject"><span class="type">VipsObject</span></a> *object</code></em>,
<em class="parameter"><code><span class="type">void</span> *a</code></em>,
<em class="parameter"><code><span class="type">void</span> *b</code></em>);
<a class="link" href="VipsThreadState.html" title="VipsThreadState"><span class="returnvalue">VipsThreadState</span></a> * <a class="link" href="VipsThreadState.html#vips-thread-state-new" title="vips_thread_state_new ()">vips_thread_state_new</a> (<em class="parameter"><code><a class="link" href="VipsImage.html" title="VipsImage"><span class="type">VipsImage</span></a> *im</code></em>,
<em class="parameter"><code><span class="type">void</span> *a</code></em>);
<a class="link" href="VipsThreadState.html" title="VipsThreadState"><span class="returnvalue">VipsThreadState</span></a> * (<a class="link" href="VipsThreadState.html#VipsThreadStartFn" title="VipsThreadStartFn ()">*VipsThreadStartFn</a>) (<em class="parameter"><code><a class="link" href="VipsImage.html" title="VipsImage"><span class="type">VipsImage</span></a> *im</code></em>,
<em class="parameter"><code><span class="type">void</span> *a</code></em>);
<span class="returnvalue">int</span> (<a class="link" href="VipsThreadState.html#VipsThreadpoolAllocateFn" title="VipsThreadpoolAllocateFn ()">*VipsThreadpoolAllocateFn</a>) (<em class="parameter"><code><a class="link" href="VipsThreadState.html" title="VipsThreadState"><span class="type">VipsThreadState</span></a> *state</code></em>,
<em class="parameter"><code><span class="type">void</span> *a</code></em>,
<em class="parameter"><code><span class="type">gboolean</span> *stop</code></em>);
<span class="returnvalue">int</span> (<a class="link" href="VipsThreadState.html#VipsThreadpoolWorkFn" title="VipsThreadpoolWorkFn ()">*VipsThreadpoolWorkFn</a>) (<em class="parameter"><code><a class="link" href="VipsThreadState.html" title="VipsThreadState"><span class="type">VipsThreadState</span></a> *state</code></em>,
<em class="parameter"><code><span class="type">void</span> *a</code></em>);
<span class="returnvalue">int</span> (<a class="link" href="VipsThreadState.html#VipsThreadpoolProgressFn" title="VipsThreadpoolProgressFn ()">*VipsThreadpoolProgressFn</a>) (<em class="parameter"><code><span class="type">void</span> *a</code></em>);
<span class="returnvalue">int</span> <a class="link" href="VipsThreadState.html#vips-threadpool-run" title="vips_threadpool_run ()">vips_threadpool_run</a> (<em class="parameter"><code><a class="link" href="VipsImage.html" title="VipsImage"><span class="type">VipsImage</span></a> *im</code></em>,
<em class="parameter"><code><a class="link" href="VipsThreadState.html#VipsThreadStartFn" title="VipsThreadStartFn ()"><span class="type">VipsThreadStartFn</span></a> start</code></em>,
<em class="parameter"><code><a class="link" href="VipsThreadState.html#VipsThreadpoolAllocateFn" title="VipsThreadpoolAllocateFn ()"><span class="type">VipsThreadpoolAllocateFn</span></a> allocate</code></em>,
<em class="parameter"><code><a class="link" href="VipsThreadState.html#VipsThreadpoolWorkFn" title="VipsThreadpoolWorkFn ()"><span class="type">VipsThreadpoolWorkFn</span></a> work</code></em>,
<em class="parameter"><code><a class="link" href="VipsThreadState.html#VipsThreadpoolProgressFn" title="VipsThreadpoolProgressFn ()"><span class="type">VipsThreadpoolProgressFn</span></a> progress</code></em>,
<em class="parameter"><code><span class="type">void</span> *a</code></em>);
<span class="returnvalue">void</span> <a class="link" href="VipsThreadState.html#vips-get-tile-size" title="vips_get_tile_size ()">vips_get_tile_size</a> (<em class="parameter"><code><a class="link" href="VipsImage.html" title="VipsImage"><span class="type">VipsImage</span></a> *im</code></em>,
<em class="parameter"><code><span class="type">int</span> *tile_width</code></em>,
<em class="parameter"><code><span class="type">int</span> *tile_height</code></em>,
<em class="parameter"><code><span class="type">int</span> *nlines</code></em>);
<span class="returnvalue">void</span> <a class="link" href="VipsThreadState.html#vips--print-renders" title="vips__print_renders ()">vips__print_renders</a> (<em class="parameter"><code><span class="type">void</span></code></em>);
<span class="returnvalue">void</span> <a class="link" href="VipsThreadState.html#vips-concurrency-set" title="vips_concurrency_set ()">vips_concurrency_set</a> (<em class="parameter"><code><span class="type">int</span> concurrency</code></em>);
<span class="returnvalue">int</span> <a class="link" href="VipsThreadState.html#vips-concurrency-get" title="vips_concurrency_get ()">vips_concurrency_get</a> (<em class="parameter"><code><span class="type">void</span></code></em>);
</pre>
</div>
<div class="refsect1">
<a name="VipsThreadState.object-hierarchy"></a><h2>Object Hierarchy</h2>
<pre class="synopsis">
GObject
+----<a class="link" href="libvips-VipsArgument.html#VipsObject">VipsObject</a>
+----VipsThreadState
</pre>
</div>
<div class="refsect1">
<a name="VipsThreadState.description"></a><h2>Description</h2>
<p>
<a class="link" href="VipsThreadState.html#vips-threadpool-run" title="vips_threadpool_run ()"><code class="function">vips_threadpool_run()</code></a> loops a set of threads over an image. Threads take it
in turns to allocate units of work (a unit might be a tile in an image),
then run in parallel to process those units. An optional progress function
can be used to give feedback.
</p>
</div>
<div class="refsect1">
<a name="VipsThreadState.details"></a><h2>Details</h2>
<div class="refsect2">
<a name="VipsThreadState-struct"></a><h3>VipsThreadState</h3>
<pre class="programlisting">typedef struct {
/* Image we run on.
*/
VipsImage *im;
/* This region is created and destroyed by the threadpool for the
* use of the worker.
*/
VipsRegion *reg;
/* Neither used nor set, do what you like with them.
*/
VipsRect pos;
int x, y;
/* Set in work to get the allocate to signal stop.
*/
gboolean stop;
/* The client data passed to the enclosing vips_threadpool_run().
*/
void *a;
} VipsThreadState;
</pre>
<p>
These per-thread values are carried around for your use by
<a class="link" href="VipsThreadState.html#vips-threadpool-run" title="vips_threadpool_run ()"><code class="function">vips_threadpool_run()</code></a>. They are private to each thread, so they are a
useful place
for <span class="type">VipsThreadpoolAllocate</span> and <span class="type">VipsThreadpoolWork</span> to communicate.
</p>
<p>
<em class="parameter"><code>reg</code></em> is created for you at the start of processing and freed at the end,
but you can do what you like with it.
</p>
<div class="variablelist"><table border="0" class="variablelist">
<colgroup>
<col align="left" valign="top">
<col>
</colgroup>
<tbody>
<tr>
<td><p><span class="term"><a class="link" href="VipsImage.html" title="VipsImage"><span class="type">VipsImage</span></a> *<em class="structfield"><code><a name="VipsThreadState-struct.im"></a>im</code></em>;</span></p></td>
<td>the <a class="link" href="VipsImage.html" title="VipsImage"><span class="type">VipsImage</span></a> being operated upon</td>
</tr>
<tr>
<td><p><span class="term"><a class="link" href="VipsRegion.html" title="VipsRegion"><span class="type">VipsRegion</span></a> *<em class="structfield"><code><a name="VipsThreadState-struct.reg"></a>reg</code></em>;</span></p></td>
<td>a <span class="type">REGION</span>
</td>
</tr>
<tr>
<td><p><span class="term"><a class="link" href="libvips-rect.html#VipsRect" title="VipsRect"><span class="type">VipsRect</span></a> <em class="structfield"><code><a name="VipsThreadState-struct.pos"></a>pos</code></em>;</span></p></td>
<td>a <span class="type">Rect</span>
</td>
</tr>
<tr>
<td><p><span class="term"><span class="type">int</span> <em class="structfield"><code><a name="VipsThreadState-struct.x"></a>x</code></em>;</span></p></td>
<td>an int</td>
</tr>
<tr>
<td><p><span class="term"><span class="type">int</span> <em class="structfield"><code><a name="VipsThreadState-struct.y"></a>y</code></em>;</span></p></td>
<td>an int</td>
</tr>
<tr>
<td><p><span class="term"><span class="type">gboolean</span> <em class="structfield"><code><a name="VipsThreadState-struct.stop"></a>stop</code></em>;</span></p></td>
<td></td>
</tr>
<tr>
<td><p><span class="term"><span class="type">void</span> *<em class="structfield"><code><a name="VipsThreadState-struct.a"></a>a</code></em>;</span></p></td>
<td>client data</td>
</tr>
</tbody>
</table></div>
</div>
<hr>
<div class="refsect2">
<a name="VipsThreadStateClass"></a><h3>VipsThreadStateClass</h3>
<pre class="programlisting">typedef struct {
VipsObjectClass parent_class;
} VipsThreadStateClass;
</pre>
<p>
</p>
</div>
<hr>
<div class="refsect2">
<a name="vips-thread-state-set"></a><h3>vips_thread_state_set ()</h3>
<pre class="programlisting"><span class="returnvalue">void</span> * vips_thread_state_set (<em class="parameter"><code><a class="link" href="libvips-VipsArgument.html#VipsObject"><span class="type">VipsObject</span></a> *object</code></em>,
<em class="parameter"><code><span class="type">void</span> *a</code></em>,
<em class="parameter"><code><span class="type">void</span> *b</code></em>);</pre>
<p>
</p>
</div>
<hr>
<div class="refsect2">
<a name="vips-thread-state-new"></a><h3>vips_thread_state_new ()</h3>
<pre class="programlisting"><a class="link" href="VipsThreadState.html" title="VipsThreadState"><span class="returnvalue">VipsThreadState</span></a> * vips_thread_state_new (<em class="parameter"><code><a class="link" href="VipsImage.html" title="VipsImage"><span class="type">VipsImage</span></a> *im</code></em>,
<em class="parameter"><code><span class="type">void</span> *a</code></em>);</pre>
<p>
</p>
</div>
<hr>
<div class="refsect2">
<a name="VipsThreadStartFn"></a><h3>VipsThreadStartFn ()</h3>
<pre class="programlisting"><a class="link" href="VipsThreadState.html" title="VipsThreadState"><span class="returnvalue">VipsThreadState</span></a> * (*VipsThreadStartFn) (<em class="parameter"><code><a class="link" href="VipsImage.html" title="VipsImage"><span class="type">VipsImage</span></a> *im</code></em>,
<em class="parameter"><code><span class="type">void</span> *a</code></em>);</pre>
<p>
</p>
</div>
<hr>
<div class="refsect2">
<a name="VipsThreadpoolAllocateFn"></a><h3>VipsThreadpoolAllocateFn ()</h3>
<pre class="programlisting"><span class="returnvalue">int</span> (*VipsThreadpoolAllocateFn) (<em class="parameter"><code><a class="link" href="VipsThreadState.html" title="VipsThreadState"><span class="type">VipsThreadState</span></a> *state</code></em>,
<em class="parameter"><code><span class="type">void</span> *a</code></em>,
<em class="parameter"><code><span class="type">gboolean</span> *stop</code></em>);</pre>
<p>
This function is called to allocate a new work unit for the thread. It is
always single-threaded, so it can modify per-pool state (such as a
counter).
</p>
<p>
<em class="parameter"><code>a</code></em>, <em class="parameter"><code>b</code></em>, <em class="parameter"><code>c</code></em> are the values supplied to the call to
<a class="link" href="VipsThreadState.html#vips-threadpool-run" title="vips_threadpool_run ()"><code class="function">vips_threadpool_run()</code></a>.
</p>
<p>
It should set <em class="parameter"><code>stop</code></em> to <code class="literal">TRUE</code> to indicate that no work could be allocated
because the job is done.
</p>
<p>
See also: <a class="link" href="VipsThreadState.html#vips-threadpool-run" title="vips_threadpool_run ()"><code class="function">vips_threadpool_run()</code></a>.
</p>
<div class="variablelist"><table border="0" class="variablelist">
<colgroup>
<col align="left" valign="top">
<col>
</colgroup>
<tbody>
<tr>
<td><p><span class="term"><em class="parameter"><code>state</code></em> :</span></p></td>
<td>per-thread state</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>a</code></em> :</span></p></td>
<td>client data</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>stop</code></em> :</span></p></td>
<td>set this to signal end of computation</td>
</tr>
<tr>
<td><p><span class="term"><span class="emphasis"><em>Returns</em></span> :</span></p></td>
<td>0 on success, or -1 on error</td>
</tr>
</tbody>
</table></div>
</div>
<hr>
<div class="refsect2">
<a name="VipsThreadpoolWorkFn"></a><h3>VipsThreadpoolWorkFn ()</h3>
<pre class="programlisting"><span class="returnvalue">int</span> (*VipsThreadpoolWorkFn) (<em class="parameter"><code><a class="link" href="VipsThreadState.html" title="VipsThreadState"><span class="type">VipsThreadState</span></a> *state</code></em>,
<em class="parameter"><code><span class="type">void</span> *a</code></em>);</pre>
<p>
This function is called to process a work unit. Many copies of this can run
at once, so it should not write to the per-pool state. It can write to
per-thread state.
</p>
<p>
<em class="parameter"><code>a</code></em>, <em class="parameter"><code>b</code></em>, <em class="parameter"><code>c</code></em> are the values supplied to the call to
<a class="link" href="VipsThreadState.html#vips-threadpool-run" title="vips_threadpool_run ()"><code class="function">vips_threadpool_run()</code></a>.
</p>
<p>
See also: <a class="link" href="VipsThreadState.html#vips-threadpool-run" title="vips_threadpool_run ()"><code class="function">vips_threadpool_run()</code></a>.
</p>
<div class="variablelist"><table border="0" class="variablelist">
<colgroup>
<col align="left" valign="top">
<col>
</colgroup>
<tbody>
<tr>
<td><p><span class="term"><em class="parameter"><code>state</code></em> :</span></p></td>
<td>per-thread state</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>a</code></em> :</span></p></td>
<td>client data</td>
</tr>
<tr>
<td><p><span class="term"><span class="emphasis"><em>Returns</em></span> :</span></p></td>
<td>0 on success, or -1 on error</td>
</tr>
</tbody>
</table></div>
</div>
<hr>
<div class="refsect2">
<a name="VipsThreadpoolProgressFn"></a><h3>VipsThreadpoolProgressFn ()</h3>
<pre class="programlisting"><span class="returnvalue">int</span> (*VipsThreadpoolProgressFn) (<em class="parameter"><code><span class="type">void</span> *a</code></em>);</pre>
<p>
This function is called by the main thread once for every work unit
processed. It can be used to give the user progress feedback.
</p>
<p>
See also: <a class="link" href="VipsThreadState.html#vips-threadpool-run" title="vips_threadpool_run ()"><code class="function">vips_threadpool_run()</code></a>.
</p>
<div class="variablelist"><table border="0" class="variablelist">
<colgroup>
<col align="left" valign="top">
<col>
</colgroup>
<tbody>
<tr>
<td><p><span class="term"><em class="parameter"><code>a</code></em> :</span></p></td>
<td>client data</td>
</tr>
<tr>
<td><p><span class="term"><span class="emphasis"><em>Returns</em></span> :</span></p></td>
<td>0 on success, or -1 on error</td>
</tr>
</tbody>
</table></div>
</div>
<hr>
<div class="refsect2">
<a name="vips-threadpool-run"></a><h3>vips_threadpool_run ()</h3>
<pre class="programlisting"><span class="returnvalue">int</span> vips_threadpool_run (<em class="parameter"><code><a class="link" href="VipsImage.html" title="VipsImage"><span class="type">VipsImage</span></a> *im</code></em>,
<em class="parameter"><code><a class="link" href="VipsThreadState.html#VipsThreadStartFn" title="VipsThreadStartFn ()"><span class="type">VipsThreadStartFn</span></a> start</code></em>,
<em class="parameter"><code><a class="link" href="VipsThreadState.html#VipsThreadpoolAllocateFn" title="VipsThreadpoolAllocateFn ()"><span class="type">VipsThreadpoolAllocateFn</span></a> allocate</code></em>,
<em class="parameter"><code><a class="link" href="VipsThreadState.html#VipsThreadpoolWorkFn" title="VipsThreadpoolWorkFn ()"><span class="type">VipsThreadpoolWorkFn</span></a> work</code></em>,
<em class="parameter"><code><a class="link" href="VipsThreadState.html#VipsThreadpoolProgressFn" title="VipsThreadpoolProgressFn ()"><span class="type">VipsThreadpoolProgressFn</span></a> progress</code></em>,
<em class="parameter"><code><span class="type">void</span> *a</code></em>);</pre>
<p>
This function runs a set of threads over an image. Each thread first calls
<em class="parameter"><code>start</code></em> to create new per-thread state, then runs
<em class="parameter"><code>allocate</code></em> to set up a new work unit (perhaps the next tile in an image, for
example), then <em class="parameter"><code>work</code></em> to process that work unit. After each unit is
processed, <em class="parameter"><code>progress</code></em> is called, so that the operation can give
progress feedback. <em class="parameter"><code>progress</code></em> may be <code class="literal">NULL</code>.
</p>
<p>
The object returned by <em class="parameter"><code>start</code></em> must be an instance of a subclass of
<a class="link" href="VipsThreadState.html" title="VipsThreadState"><span class="type">VipsThreadState</span></a>. Use this to communicate between <em class="parameter"><code>allocate</code></em> and <em class="parameter"><code>work</code></em>.
</p>
<p>
<em class="parameter"><code>allocate</code></em> and <em class="parameter"><code>start</code></em> are always single-threaded (so they can write to the
per-pool state), whereas <em class="parameter"><code>work</code></em> can be executed concurrently. <em class="parameter"><code>progress</code></em> is
always called by
the main thread (ie. the thread which called <a class="link" href="VipsThreadState.html#vips-threadpool-run" title="vips_threadpool_run ()"><code class="function">vips_threadpool_run()</code></a>).
</p>
<p>
See also: <a class="link" href="VipsThreadState.html#vips-concurrency-set" title="vips_concurrency_set ()"><code class="function">vips_concurrency_set()</code></a>.
</p>
<div class="variablelist"><table border="0" class="variablelist">
<colgroup>
<col align="left" valign="top">
<col>
</colgroup>
<tbody>
<tr>
<td><p><span class="term"><em class="parameter"><code>im</code></em> :</span></p></td>
<td>image to loop over</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>start</code></em> :</span></p></td>
<td>allocate per-thread state</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>allocate</code></em> :</span></p></td>
<td>allocate a work unit</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>work</code></em> :</span></p></td>
<td>process a work unit</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>progress</code></em> :</span></p></td>
<td>give progress feedback about a work unit, or <code class="literal">NULL</code>
</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>a</code></em> :</span></p></td>
<td>client data</td>
</tr>
<tr>
<td><p><span class="term"><span class="emphasis"><em>Returns</em></span> :</span></p></td>
<td>0 on success, or -1 on error.</td>
</tr>
</tbody>
</table></div>
</div>
<hr>
<div class="refsect2">
<a name="vips-get-tile-size"></a><h3>vips_get_tile_size ()</h3>
<pre class="programlisting"><span class="returnvalue">void</span> vips_get_tile_size (<em class="parameter"><code><a class="link" href="VipsImage.html" title="VipsImage"><span class="type">VipsImage</span></a> *im</code></em>,
<em class="parameter"><code><span class="type">int</span> *tile_width</code></em>,
<em class="parameter"><code><span class="type">int</span> *tile_height</code></em>,
<em class="parameter"><code><span class="type">int</span> *nlines</code></em>);</pre>
<p>
Pick a tile size and a buffer height for this image and the current
value of <a class="link" href="VipsThreadState.html#vips-concurrency-get" title="vips_concurrency_get ()"><code class="function">vips_concurrency_get()</code></a>. The buffer height
will always be a multiple of tile_height.
</p>
<div class="variablelist"><table border="0" class="variablelist">
<colgroup>
<col align="left" valign="top">
<col>
</colgroup>
<tbody>
<tr>
<td><p><span class="term"><em class="parameter"><code>im</code></em> :</span></p></td>
<td>image to guess for</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>tile_width</code></em> :</span></p></td>
<td>return selected tile width</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>tile_height</code></em> :</span></p></td>
<td>return selected tile height</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>nlines</code></em> :</span></p></td>
<td>return buffer height in scanlines</td>
</tr>
</tbody>
</table></div>
</div>
<hr>
<div class="refsect2">
<a name="vips--print-renders"></a><h3>vips__print_renders ()</h3>
<pre class="programlisting"><span class="returnvalue">void</span> vips__print_renders (<em class="parameter"><code><span class="type">void</span></code></em>);</pre>
<p>
</p>
</div>
<hr>
<div class="refsect2">
<a name="vips-concurrency-set"></a><h3>vips_concurrency_set ()</h3>
<pre class="programlisting"><span class="returnvalue">void</span> vips_concurrency_set (<em class="parameter"><code><span class="type">int</span> concurrency</code></em>);</pre>
<p>
Sets the number of worker threads that vips should use when running a
<span class="type">VipsThreadPool</span>.
</p>
<p>
The special value 0 means "default". In this case, the number of threads is
set by the environmnt variable IM_CONCURRENCY, or if that is not set, the
number of threads availble on the hist machine.
</p>
<p>
See also: <a class="link" href="VipsThreadState.html#vips-concurrency-get" title="vips_concurrency_get ()"><code class="function">vips_concurrency_get()</code></a>.
</p>
<div class="variablelist"><table border="0" class="variablelist">
<colgroup>
<col align="left" valign="top">
<col>
</colgroup>
<tbody><tr>
<td><p><span class="term"><em class="parameter"><code>concurrency</code></em> :</span></p></td>
<td>number of threads to run</td>
</tr></tbody>
</table></div>
</div>
<hr>
<div class="refsect2">
<a name="vips-concurrency-get"></a><h3>vips_concurrency_get ()</h3>
<pre class="programlisting"><span class="returnvalue">int</span> vips_concurrency_get (<em class="parameter"><code><span class="type">void</span></code></em>);</pre>
<p>
Returns the number of worker threads that vips should use when running a
<span class="type">VipsThreadPool</span>.
</p>
<p>
vips gets this values from these sources in turn:
</p>
<p>
If <a class="link" href="VipsThreadState.html#vips-concurrency-set" title="vips_concurrency_set ()"><code class="function">vips_concurrency_set()</code></a> has been called, this value is used. The special
value 0 means "default". You can also use the command-line argument
"--vips-concurrency" to set this value.
</p>
<p>
If <a class="link" href="VipsThreadState.html#vips-concurrency-set" title="vips_concurrency_set ()"><code class="function">vips_concurrency_set()</code></a> has not been called and no command-line argument
was used, vips uses the value of the environment variable IM_CONCURRENCY,
</p>
<p>
If IM_CONCURRENCY has not been set, vips find the number of hardware
threads that the host machine can run in parallel and uses that value.
</p>
<p>
The final value is clipped to the range 1 - 1024.
</p>
<p>
See also: <a class="link" href="VipsThreadState.html#vips-concurrency-get" title="vips_concurrency_get ()"><code class="function">vips_concurrency_get()</code></a>.
</p>
<div class="variablelist"><table border="0" class="variablelist">
<colgroup>
<col align="left" valign="top">
<col>
</colgroup>
<tbody><tr>
<td><p><span class="term"><span class="emphasis"><em>Returns</em></span> :</span></p></td>
<td>number of worker threads to use.</td>
</tr></tbody>
</table></div>
</div>
</div>
<div class="refsect1">
<a name="VipsThreadState.see-also"></a><h2>See Also</h2>
<a class="link" href="libvips-generate.html" title="generate">generate</a>
</div>
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