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<th>Priority</th>
<td>medium
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<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Line drawing not thread-safe"
href="https://bugs.freedesktop.org/show_bug.cgi?id=74355">74355</a>
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<th>Assignee</th>
<td>chris@chris-wilson.co.uk
</td>
</tr>
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<th>Summary</th>
<td>Line drawing not thread-safe
</td>
</tr>
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<th>QA Contact</th>
<td>cairo-bugs@cairographics.org
</td>
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<th>Severity</th>
<td>major
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr>
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<th>OS</th>
<td>Windows (All)
</td>
</tr>
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<th>Reporter</th>
<td>hguijtra@xs4all.nl
</td>
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<th>Hardware</th>
<td>x86-64 (AMD64)
</td>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Version</th>
<td>1.10.2
</td>
</tr>
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<th>Component</th>
<td>image backend
</td>
</tr>
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<th>Product</th>
<td>cairo
</td>
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<p>
<div>
<pre>I'm drawing graphs with lots (millions) of tiny line pieces. To speed up this
process I used multiple threads to draw the line pieces. This greatly improves
performance, but typically causes a crash within a few minutes.
I've tried to do this in two ways:
1. share a single cairo_surface_t between the threads, and have each thread
draw using its own cairo_t. This crashes, but maybe I'm hoping for too much
(although an image surface is essentially just a big array of bytes that should
be writable from multiple threads).
2. create a cairo_surface_t and cairo_t for each thread, and merge the results
after drawing has completed. This crashes in pixman. The only Cairo calls that
happen on a per-thread basis are cairo_set_line_cap, cairo_set_source_rgba,
cairo_set_line_width, cairo_set_dash, cairo_move_to, cairo_line_to, and
cairo_stroke.
Because I'm using the Gnome binary DLLs from
<a href="http://www.gtk.org/download/win32.php">http://www.gtk.org/download/win32.php</a> I cannot provide a meaningful stacktrace.
I have tried compiling a later version of Cairo but although I managed to
compile it, the resulting DLL is utterly unstable on Windows. However, I do
believe this might have something to do with the problem described at
<a href="http://lists.freedesktop.org/archives/cairo/2011-July/022123.html">http://lists.freedesktop.org/archives/cairo/2011-July/022123.html</a>.</pre>
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</p>
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