Running pthread-show-text with the following patch shows that all threads are sharing the same cairo_font_face_t. However cairo_font_face_t are not thread safe. diff --git a/test/pthread-show-text.c b/test/pthread-show-text.c index 0f076cb61..4069fd756 100644 --- a/test/pthread-show-text.c +++ b/test/pthread-show-text.c @@ -67,6 +67,7 @@ draw_thread (void *arg) CAIRO_FONT_SLANT_NORMAL, CAIRO_FONT_WEIGHT_NORMAL); cairo_set_font_size (cr, NUM_ITERATIONS); + printf("font: %p\n", cairo_get_font_face(cr)); cairo_font_extents (cr, &extents); cairo_move_to (cr, 1, HEIGHT - extents.descent - 1); Additionally running with thread sanitizer gives: TESTING pthread-show-text pthread-show-text.image.rgb24 [0x1]: font: 0x7b1400002850 font: 0x7b1400002850 font: 0x7b1400002850 font: 0x7b1400002850 font: 0x7b1400002850 font: 0x7b1400002850 font: 0x7b1400002850 font: 0x7b1400002850 ================== WARNING: ThreadSanitizer: data race (pid=356) Write of size 4 at 0x7b54000114b8 by thread T3 (mutexes: write M109): #0 _cairo_scaled_font_freeze_cache /home/jrmuizel/src/cairo/src/cairo-scaled-font.c:796:31 (libcairo.so.2+0x12b597) #1 INT_cairo_scaled_font_text_to_glyphs /home/jrmuizel/src/cairo/src/cairo-scaled-font.c:2034:5 (libcairo.so.2+0x12ea6c) #2 cairo_show_text /home/jrmuizel/src/cairo/src/cairo.c:3552:14 (libcairo.so.2+0x193244) #3 draw_thread /home/jrmuizel/src/cairo/test/pthread-show-text.c:85:2 (cairo-test-suite+0x54e428) Previous read of size 4 at 0x7b54000114b8 by thread T8: #0 INT_cairo_scaled_font_destroy /home/jrmuizel/src/cairo/src/cairo-scaled-font.c:1326:5 (libcairo.so.2+0x129cdd) #1 _cairo_gstate_unset_scaled_font /home/jrmuizel/src/cairo/src/cairo-gstate.c:1709:2 (libcairo.so.2+0x6a144) #2 _cairo_gstate_set_font_size /home/jrmuizel/src/cairo/src/cairo-gstate.c:1719:5 (libcairo.so.2+0x6efa7) #3 _cairo_default_context_set_font_size /home/jrmuizel/src/cairo/src/cairo-default-context.c:1224:12 (libcairo.so.2+0x5ce8f) #4 INT_cairo_set_font_size /home/jrmuizel/src/cairo/src/cairo.c:3164:14 (libcairo.so.2+0x1922c0) #5 draw_thread /home/jrmuizel/src/cairo/test/pthread-show-text.c:81:2 (cairo-test-suite+0x54e3aa) Location is heap block of size 536 at 0x7b5400011300 allocated by thread T1: #0 malloc <null> (cairo-test-suite+0x431d7b) #1 _cairo_ft_font_face_scaled_font_create /home/jrmuizel/src/cairo/src/cairo-ft-font.c:2016:19 (libcairo.so.2+0x24b48f) #2 INT_cairo_scaled_font_create /home/jrmuizel/src/cairo/src/cairo-scaled-font.c:1144:14 (libcairo.so.2+0x12d19b) #3 _cairo_gstate_ensure_scaled_font /home/jrmuizel/src/cairo/src/cairo-gstate.c:1915:19 (libcairo.so.2+0x6f5ca) #4 _cairo_gstate_get_scaled_font /home/jrmuizel/src/cairo/src/cairo-gstate.c:1787:14 (libcairo.so.2+0x6f3c4) #5 _cairo_default_context_get_scaled_font /home/jrmuizel/src/cairo/src/cairo-default-context.c:1300:14 (libcairo.so.2+0x5d31f) #6 INT_cairo_get_scaled_font /home/jrmuizel/src/cairo/src/cairo.c:3348:12 (libcairo.so.2+0x192823) #7 cairo_show_text /home/jrmuizel/src/cairo/src/cairo.c:3529:19 (libcairo.so.2+0x193003) #8 draw_thread /home/jrmuizel/src/cairo/test/pthread-show-text.c:85:2 (cairo-test-suite+0x54e428) Mutex M109 (0x7b5400011478) created at: #0 pthread_mutex_lock <null> (cairo-test-suite+0x438fa5) #1 _cairo_scaled_font_freeze_cache /home/jrmuizel/src/cairo/src/cairo-scaled-font.c:795:5 (libcairo.so.2+0x12b57a) #2 INT_cairo_scaled_font_text_to_glyphs /home/jrmuizel/src/cairo/src/cairo-scaled-font.c:2034:5 (libcairo.so.2+0x12ea6c) #3 cairo_show_text /home/jrmuizel/src/cairo/src/cairo.c:3552:14 (libcairo.so.2+0x193244) #4 draw_thread /home/jrmuizel/src/cairo/test/pthread-show-text.c:85:2 (cairo-test-suite+0x54e428) Thread T3 (tid=361, running) created by main thread at: #0 pthread_create <null> (cairo-test-suite+0x4326f6) #1 draw /home/jrmuizel/src/cairo/test/pthread-show-text.c:107:13 (cairo-test-suite+0x54e06a) #2 cairo_test_for_target /home/jrmuizel/src/cairo/test/cairo-test.c:933:14 (cairo-test-suite+0x4c6dd4) #3 _cairo_test_context_run_for_target /home/jrmuizel/src/cairo/test/cairo-test.c:1536:15 (cairo-test-suite+0x4c45c0) #4 _cairo_test_runner_draw /home/jrmuizel/src/cairo/test/cairo-test-runner.c:247:12 (cairo-test-suite+0x4cceb4) #5 main /home/jrmuizel/src/cairo/test/cairo-test-runner.c:937:13 (cairo-test-suite+0x4ca5e8) Thread T8 (tid=366, running) created by main thread at: #0 pthread_create <null> (cairo-test-suite+0x4326f6) #1 draw /home/jrmuizel/src/cairo/test/pthread-show-text.c:107:13 (cairo-test-suite+0x54e06a) #2 cairo_test_for_target /home/jrmuizel/src/cairo/test/cairo-test.c:933:14 (cairo-test-suite+0x4c6dd4) #3 _cairo_test_context_run_for_target /home/jrmuizel/src/cairo/test/cairo-test.c:1536:15 (cairo-test-suite+0x4c45c0) #4 _cairo_test_runner_draw /home/jrmuizel/src/cairo/test/cairo-test-runner.c:247:12 (cairo-test-suite+0x4cceb4) #5 main /home/jrmuizel/src/cairo/test/cairo-test-runner.c:937:13 (cairo-test-suite+0x4ca5e8) Thread T1 (tid=358, running) created by main thread at: #0 pthread_create <null> (cairo-test-suite+0x4326f6) #1 draw /home/jrmuizel/src/cairo/test/pthread-show-text.c:107:13 (cairo-test-suite+0x54e06a) #2 cairo_test_for_target /home/jrmuizel/src/cairo/test/cairo-test.c:933:14 (cairo-test-suite+0x4c6dd4) #3 _cairo_test_context_run_for_target /home/jrmuizel/src/cairo/test/cairo-test.c:1536:15 (cairo-test-suite+0x4c45c0) #4 _cairo_test_runner_draw /home/jrmuizel/src/cairo/test/cairo-test-runner.c:247:12 (cairo-test-suite+0x4cceb4) #5 main /home/jrmuizel/src/cairo/test/cairo-test-runner.c:937:13 (cairo-test-suite+0x4ca5e8) SUMMARY: ThreadSanitizer: data race /home/jrmuizel/src/cairo/src/cairo-scaled-font.c:796:31 in _cairo_scaled_font_freeze_cache ================== pthread-show-text.image.rgb24 [0x1]: FAIL ThreadSanitizer: reported 1 warnings pthread-show-text: UNTESTED
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