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core(parallel): plugins support by alalek · Pull Request #19470 · opencv/opencv · GitHub
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I have a problem with OpenMP backend built as a plugin (Ubuntu 18): With gdb: |
mshabunin
reviewed
Feb 12, 2021
| @@ -0,0 +1,60 @@ | |||
| function(ocv_create_builtin_core_parallel_plugin name target) | |||
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This file and plugin_standalone.cmake are similar to videoio/cmake/plugin*.cmake. Can they be unified somehow? Maybe moved to the root cmake/ directory?
alalek
commented
Feb 12, 2021
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@mshabunin Thanks!
Added task to find workaround for cases with unloading crashes
| message(STATUS "OpenMP detection requires CMake 3.9+") # OpenMP::OpenMP_CXX target | ||
| endif() | ||
|
|
||
| find_package(OpenMP) |
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libraryRelease unload /build/lib/libopencv_core_parallel_openmp.so
Segmentation fault
LD_DEBUG=libs dump is:
[ PASSED ] 1 test.
[ INFO:0] global /home/alalek/projects/opencv/dev/modules/core/src/utils/plugin_loader.impl.hpp (50) libraryRelease unload /home/alalek/projects/opencv/build/opencv/lib/libopencv_core_parallel_openmp.so
232271:
232271: calling fini: /home/alalek/projects/opencv/build/opencv/lib/libopencv_core_parallel_openmp.so [0]
232271:
232271:
232271: calling fini: /lib64/libgomp.so.1 [0]
232271:
Segmentation fault (core dumped)
libgomp.so.1 is de-initialized (finit call), but its worker threads are still alive (gdb shows that).
So,
- this is a bug of
libgomp.so.1(no idea why worker threads are not terminated during unload stage) - we should not force OpenMP thread pool termination from OpenCV side, because application can use OpenMP directly
- some workaround is required (probably don't unload parallel plugins)
The similar issue can be observed with TBB
Issue is sporadic with TBB (not 100% reproducible).
GDB:
[ RUN ] Core_Rand.parallel_for_stable_results
[New Thread 0x7fffd46b7640 (LWP 232758)]
[New Thread 0x7fffa8ffa640 (LWP 232760)]
[New Thread 0x7fffb07f8640 (LWP 232759)]
[ OK ] Core_Rand.parallel_for_stable_results (174 ms)
...
[ INFO:0] global /home/alalek/projects/opencv/dev/modules/core/src/utils/plugin_loader.impl.hpp (50) libraryRelease unload /home/alalek/projects/opencv/build/opencv/lib/libopencv_core_parallel_onetbb.so
Thread 34 "opencv_test_cor" received signal SIGSEGV, Segmentation fault.
(gdb) info threads
...
33 Thread 0x7fffd46b7640 (LWP 232758) "opencv_test_cor" 0x00007ffff47ba55d in syscall () from /lib64/libc.so.6
* 34 Thread 0x7fffa8ffa640 (LWP 232760) "opencv_test_cor" 0x00007fffe749ba32 in ?? ()
35 Thread 0x7fffb07f8640 (LWP 232759) "opencv_test_cor" 0x00007ffff47ba55d in syscall () from /lib64/libc.so.6
(232760 is created during the test run)
LD_DEBUG dump:
[ INFO:0] global /home/alalek/projects/opencv/dev/modules/core/src/utils/plugin_loader.impl.hpp (50) libraryRelease unload /home/alalek/projects/opencv/build/opencv/lib/libopencv_core_parallel_onetbb.so
232863:
232863: calling fini: /home/alalek/projects/opencv/build/opencv/lib/libopencv_core_parallel_onetbb.so [0]
232863:
232863:
232863: calling fini: /lib64/libtbb.so.2 [0]
232863:
232863:
232863: calling fini: /lib64/libirml.so.1 [0]
232863:
Segmentation fault (core dumped)
TODO: Will try to check some workarounds.
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Added code to prevent automatic unloading of parallel backend library (including underlying libraries).
There is no huge impact, because plugins are kept loaded until opencv_core unloading anyway.
alalek
commented
Feb 15, 2021
Comment on lines
+3
to
+16
| # FIXIT: stop using PARENT_SCOPE in dependencies | ||
| if(PROJECT_NAME STREQUAL "OpenCV") | ||
| macro(add_backend backend_id cond_var) | ||
| if(${cond_var}) | ||
| include("${CMAKE_CURRENT_LIST_DIR}/detect_${backend_id}.cmake") | ||
| endif() | ||
| endmacro() | ||
| else() | ||
| function(add_backend backend_id cond_var) | ||
| if(${cond_var}) | ||
| include("${CMAKE_CURRENT_LIST_DIR}/detect_${backend_id}.cmake") | ||
| endif() | ||
| endfunction() | ||
| endif() |
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There is inconsistency in scope of dependencies.
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Perhaps we could switch to target checks instead of HAVE_ variables. Additional information can be stored in custom target properties.
mshabunin
approved these changes
Feb 16, 2021
This was referenced Feb 19, 2021
This was referenced Mar 13, 2021
Merged
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relates #19365
Usage examples are on GitHub PR page.
Hardening option:
Control environment variables:
OPENCV_PARALLEL_PRIORITY_TBB=0- disableOPENCV_PARALLEL_PRIORITY_LIST=TBB- preferred backends namesOPENCV_PARALLEL_BACKEND=TBB- forced backend nameTasks:
setParallelForBackend(const std::string& backendName, ...))ParallelForAPIHAVE_OPENMP(create define from CMake)OPENCV_PLUGIN_MODULE_PREFIXplugin_standalone.cmakevideoio/misc/build_plugins.sh