PyQt 5.4.2 bug example: QSGMaterial::createShader() result object is destroyed before use + application hangs at exit
| # PyQt 5.4.2 bug example: QSGMaterial::createShader() result object is destroyed | |
| # before use + application hangs at exit | |
| import textwrap | |
| import sys | |
| from PyQt5.QtQuick import ( | |
| QQuickItem, QSGMaterial, | |
| QSGMaterialShader, QSGMaterialType, | |
| QSGGeometry, QSGGeometryNode, QSGNode, QQuickView | |
| ) | |
| from PyQt5.QtQml import ( | |
| qmlRegisterType, QQmlEngine, QQmlComponent, QQmlImageProviderBase, | |
| QQmlProperty) | |
| from PyQt5.QtCore import pyqtProperty, pyqtSignal, QUrl, QTimer | |
| from PyQt5.QtWidgets import QApplication | |
| class MyMaterialShader(QSGMaterialShader): | |
| def __init__(self): | |
| super().__init__() | |
| self._matrix_uniform_id = None | |
| print("MyMaterialShader() created") | |
| def updateState(self, state, material, old_material): | |
| if state.isMatrixDirty(): | |
| self.program().setUniformValue( | |
| self._matrix_uniform_id, state.combinedMatrix()) | |
| if not isinstance(material, MyMaterial): | |
| return | |
| def attributeNames(self): | |
| return ["qt_VertexPosition", "qt_VertexTexCoord"] | |
| def initialize(self): | |
| self._matrix_uniform_id = self.program().uniformLocation("qt_Matrix") | |
| def vertexShader(self): | |
| return textwrap.dedent("""\ | |
| uniform highp mat4 qt_Matrix; | |
| attribute highp vec4 qt_VertexPosition; | |
| attribute highp vec2 qt_VertexTexCoord; | |
| varying highp vec2 qt_TexCoord; | |
| void main() | |
| { | |
| qt_TexCoord = qt_VertexTexCoord; | |
| gl_Position = qt_Matrix * qt_VertexPosition; | |
| } | |
| """) | |
| def fragmentShader(self): | |
| return textwrap.dedent("""\ | |
| varying highp vec2 qt_TexCoord; | |
| void main() | |
| { | |
| gl_FragColor = vec4(qt_TexCoord.x, qt_TexCoord.y, 1, 1); | |
| } | |
| """) | |
| def __del__(self): | |
| print("MyMaterialShader() destroyed") | |
| class MyMaterial(QSGMaterial): | |
| _type = QSGMaterialType() | |
| def __init__(self): | |
| super().__init__() | |
| def compare(self, other_material): | |
| if self is other_material: | |
| return 0 | |
| else: | |
| return -1 if id(self) < id(other_material) else 1 | |
| def createShader(self): | |
| shader = MyMaterialShader() | |
| # Problem #1: created in Python QSGMaterialShader object is being | |
| # destroyed when not referenced by Python. | |
| # QSGMaterialShader's are cached inside Qt and rarely destroyed, | |
| # so Qt fails with segfault when tries to use destroyed object. | |
| # Workaround: store Python QSGMaterialShader objects indefinitely. | |
| self._shader = shader # uncomment this for workaround | |
| return shader | |
| def type(self): | |
| return self._type | |
| class CustomShaderItem(QQuickItem): | |
| def __init__(self): | |
| super().__init__() | |
| self.setFlag(QQuickItem.ItemHasContents, True) | |
| def updatePaintNode(self, root_node, node_data): | |
| print("Root node:", root_node) | |
| if root_node is None: | |
| root_node = QSGGeometryNode() | |
| material = MyMaterial() | |
| root_node.setMaterial(material) | |
| root_node.setFlag(QSGNode.OwnsMaterial) | |
| x = 0 | |
| y = 0 | |
| width = 100 | |
| height = 100 | |
| geometry = QSGGeometry( | |
| QSGGeometry.defaultAttributes_TexturedPoint2D(), | |
| 5) | |
| geometry.setDrawingMode(QSGGeometry.GL_TRIANGLE_STRIP) | |
| root_node.setGeometry(geometry) | |
| root_node.setFlag(QSGNode.OwnsGeometry) | |
| vertices = geometry.vertexDataAsTexturedPoint2D() | |
| vertices[0].set(x, y, 0, 0) | |
| vertices[1].set(x + width, y, 1, 0) | |
| vertices[2].set(x + width, y + height, 1, 1) | |
| vertices[3].set(x, y + height, 0, 1) | |
| vertices[4].set(x, y, 0, 0) | |
| root_node.markDirty(QSGNode.DirtyGeometry) | |
| root_node.markDirty(QSGNode.DirtyMaterial) | |
| # According to documentation, lifetime of QSGNode is managed by Qt, | |
| # so we cannot safely store it in Python. | |
| # Transfer ownership to C++ to workaround this issue. | |
| import sip | |
| sip.transferto(root_node, root_node) | |
| return root_node | |
| def main(): | |
| app = QApplication(sys.argv) | |
| qml_engine = QQmlEngine() | |
| view = QQuickView(qml_engine, None) | |
| scene_uri = QUrl.fromLocalFile("MaterialTest.qml") | |
| view.setSource(scene_uri) | |
| assert not view.errors() | |
| shader_item = CustomShaderItem() | |
| shader_item.setProperty("parent", view.rootObject()) | |
| view.show() | |
| exit_code = app.exec_() | |
| #print("Destroying QQuickView") | |
| #del view | |
| #print("QQuickView destroyed") | |
| # Problem #2: destroying QQuickView that used Python-created QSGGeometryNode | |
| # leads to deadlock. | |
| # | |
| # As I see, when QQuickView is being destroyed it waits until render thread | |
| # clean ups all resources, which causes QSGGeometryNode to be destroyed, | |
| # which asks to lock GIL, which is still locked by main thread. | |
| # | |
| # Here is stack traces at the moment of deadlock: | |
| # | |
| # (gdb) info threads | |
| # Id Target Id Frame | |
| # 4 Thread 0x7f705ca83700 (LWP 23802) "QXcbEventReader" 0x00007f706b51c12d in poll () at ../sysdeps/unix/syscall-template.S:81 | |
| # 3 Thread 0x7f7057df9700 (LWP 23803) "QQmlThread" 0x00007f706b51c12d in poll () at ../sysdeps/unix/syscall-template.S:81 | |
| # 2 Thread 0x7f7055aa7700 (LWP 23804) "QSGRenderThread" pthread_cond_timedwait@@GLIBC_2.3.2 () at ../nptl/sysdeps/unix/sysv/linux/x86_64/pthread_cond_timedwait.S:238 | |
| # * 1 Thread 0x7f706bf21780 (LWP 23801) "python" pthread_cond_wait@@GLIBC_2.3.2 () at ../nptl/sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185 | |
| # (gdb) bt | |
| # #0 pthread_cond_wait@@GLIBC_2.3.2 () at ../nptl/sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185 | |
| # #1 0x00007f706505e482 in QWaitConditionPrivate::wait (this=0x2cffb00, time=18446744073709551615) at thread/qwaitcondition_unix.cpp:136 | |
| # #2 0x00007f706505e255 in QWaitCondition::wait (this=0x2cff538, mutex=0x2cff530, time=18446744073709551615) at thread/qwaitcondition_unix.cpp:208 | |
| # #3 0x00007f70664b4527 in QSGThreadedRenderLoop::releaseResources (this=0x2a09600, w=0x27dcb80, inDestructor=true) at scenegraph/qsgthreadedrenderloop.cpp:1059 | |
| # #4 0x00007f70664b2ed8 in QSGThreadedRenderLoop::windowDestroyed (this=0x2a09600, window=0x2768670) at scenegraph/qsgthreadedrenderloop.cpp:825 | |
| # #5 0x00007f70664ad512 in QSGRenderLoop::cleanup () at scenegraph/qsgrenderloop.cpp:94 | |
| # #6 0x00007f70652d2c9e in qt_call_post_routines () at kernel/qcoreapplication.cpp:294 | |
| # #7 0x00007f705fdc6734 in QApplication::~QApplication (this=0x26c6ed0, __in_chrg=<optimized out>) at kernel/qapplication.cpp:808 | |
| # #8 0x00007f70607e5758 in sipQApplication::~sipQApplication (this=0x26c6ed0, __in_chrg=<optimized out>) at sipQtWidgetspart0.cpp:301912 | |
| # #9 0x00007f70607e5788 in sipQApplication::~sipQApplication (this=0x26c6ed0, __in_chrg=<optimized out>) at sipQtWidgetspart0.cpp:301915 | |
| # #10 0x00007f70607e8f21 in release_QApplication (sipCppV=0x26c6ed0) at sipQtWidgetspart0.cpp:303524 | |
| # #11 0x00007f70607e8fba in dealloc_QApplication (sipSelf=0x7f705fc42168) at sipQtWidgetspart0.cpp:303538 | |
| # #12 0x00007f7061cae346 in ?? () from /home/bob/work/proplan/env/lib/python3.4/site-packages/sip.so | |
| # #13 0x00007f7061caf5e9 in ?? () from /home/bob/work/proplan/env/lib/python3.4/site-packages/sip.so | |
| # #14 0x0000000000598732 in subtype_dealloc.lto_priv () at ../Objects/typeobject.c:1201 | |
| # #15 0x00000000004c88c7 in frame_dealloc.lto_priv () at ../Objects/frameobject.c:429 | |
| # #16 0x0000000000503dfb in fast_function (nk=<optimized out>, na=<optimized out>, n=0, pp_stack=0x7ffd401cf350, func=<optimized out>) at ../Python/ceval.c:4336 | |
| # #17 call_function (oparg=<optimized out>, pp_stack=0x7ffd401cf350) at ../Python/ceval.c:4262 | |
| # #18 PyEval_EvalFrameEx () at ../Python/ceval.c:2838 | |
| # #19 0x00000000005a9cb5 in PyEval_EvalCodeEx () at ../Python/ceval.c:3588 | |
| # Python Exception <class 'RuntimeError'> Type does not have a target.: | |
| # Python Exception <class 'RuntimeError'> Type does not have a target.: | |
| # #20 0x00000000005e7105 in PyEval_EvalCode (locals=, globals=, co=<code at remote 0x7f706bdf5420>) at ../Python/ceval.c:775 | |
| # #21 run_mod () at ../Python/pythonrun.c:2180 | |
| # #22 0x00000000005e71c9 in PyRun_FileExFlags () at ../Python/pythonrun.c:2133 | |
| # #23 0x00000000005e79aa in PyRun_SimpleFileExFlags () at ../Python/pythonrun.c:1606 | |
| # #24 0x00000000005fb69d in run_file (p_cf=<optimized out>, filename=<optimized out>, fp=<optimized out>) at ../Modules/main.c:319 | |
| # #25 Py_Main () at ../Modules/main.c:751 | |
| # #26 0x00000000004c2e7f in main () at ../Modules/python.c:69 | |
| # #27 0x00007f706b450ec5 in __libc_start_main (main=0x4c2da0 <main>, argc=2, argv=0x7ffd401cf7c8, init=<optimized out>, fini=<optimized out>, rtld_fini=<optimized out>, stack_end=0x7ffd401cf7b8) | |
| # at libc-start.c:287 | |
| # #28 0x00000000005b8db9 in _start () | |
| # (gdb) thread 2 | |
| # [Switching to thread 2 (Thread 0x7f7055aa7700 (LWP 23804))] | |
| # #0 pthread_cond_timedwait@@GLIBC_2.3.2 () at ../nptl/sysdeps/unix/sysv/linux/x86_64/pthread_cond_timedwait.S:238 | |
| # 238 ../nptl/sysdeps/unix/sysv/linux/x86_64/pthread_cond_timedwait.S: No such file or directory. | |
| # (gdb) bt | |
| # #0 pthread_cond_timedwait@@GLIBC_2.3.2 () at ../nptl/sysdeps/unix/sysv/linux/x86_64/pthread_cond_timedwait.S:238 | |
| # #1 0x00000000004ff96c in PyCOND_TIMEDWAIT (cond=<optimized out>, mut=<optimized out>, us=5000) at ../Python/condvar.h:103 | |
| # #2 take_gil.lto_priv () at ../Python/ceval_gil.h:224 | |
| # #3 0x00000000004ffb43 in PyEval_RestoreThread () at ../Python/ceval.c:448 | |
| # #4 0x00000000005e7c67 in PyGILState_Ensure () at ../Python/pystate.c:793 | |
| # #5 0x00007f7061cb6307 in ?? () from /home/bob/work/proplan/env/lib/python3.4/site-packages/sip.so | |
| # #6 0x00007f7066888341 in sipQSGGeometryNode::~sipQSGGeometryNode (this=0x7f70480e6580, __in_chrg=<optimized out>) at sipQtQuickpart0.cpp:7733 | |
| # #7 0x00007f706688837c in sipQSGGeometryNode::~sipQSGGeometryNode (this=0x7f70480e6580, __in_chrg=<optimized out>) at sipQtQuickpart0.cpp:7734 | |
| # #8 0x00007f706646a178 in QSGNode::destroy (this=0x7f70480e6210) at scenegraph/coreapi/qsgnode.cpp:389 | |
| # #9 0x00007f706646a01d in QSGNode::~QSGNode (this=0x7f70480e6210, __in_chrg=<optimized out>) at scenegraph/coreapi/qsgnode.cpp:320 | |
| # #10 0x00007f706646a05c in QSGNode::~QSGNode (this=0x7f70480e6210, __in_chrg=<optimized out>) at scenegraph/coreapi/qsgnode.cpp:321 | |
| # #11 0x00007f706646a178 in QSGNode::destroy (this=0x7f70480e6080) at scenegraph/coreapi/qsgnode.cpp:389 | |
| # #12 0x00007f706646a01d in QSGNode::~QSGNode (this=0x7f70480e6080, __in_chrg=<optimized out>) at scenegraph/coreapi/qsgnode.cpp:320 | |
| # #13 0x00007f706646b49e in QSGTransformNode::~QSGTransformNode (this=0x7f70480e6080, __in_chrg=<optimized out>) at scenegraph/coreapi/qsgnode.cpp:1156 | |
| # #14 0x00007f706646b4ce in QSGTransformNode::~QSGTransformNode (this=0x7f70480e6080, __in_chrg=<optimized out>) at scenegraph/coreapi/qsgnode.cpp:1158 | |
| # #15 0x00007f70664efcb7 in QQuickWindowPrivate::cleanupNodesOnShutdown (item=0x273d390) at items/qquickwindow.cpp:2588 | |
| # #16 0x00007f70664effc4 in QQuickWindowPrivate::cleanupNodesOnShutdown (item=0x2d31f90) at items/qquickwindow.cpp:2616 | |
| # #17 0x00007f70664effc4 in QQuickWindowPrivate::cleanupNodesOnShutdown (item=0x2a052d0) at items/qquickwindow.cpp:2616 | |
| # #18 0x00007f70664f002b in QQuickWindowPrivate::cleanupNodesOnShutdown (this=0x2a057b0) at items/qquickwindow.cpp:2624 | |
| # #19 0x00007f70664b0df5 in QSGRenderThread::invalidateOpenGL (this=0x2cff4f0, window=0x2768670, inDestructor=true, fallback=0x2cff590) at scenegraph/qsgthreadedrenderloop.cpp:465 | |
| # #20 0x00007f70664b0520 in QSGRenderThread::event (this=0x2cff4f0, e=0x2cfd3f0) at scenegraph/qsgthreadedrenderloop.cpp:390 | |
| # #21 0x00007f70664b2078 in QSGRenderThread::processEventsAndWaitForMore (this=0x2cff4f0) at scenegraph/qsgthreadedrenderloop.cpp:644 | |
| # #22 0x00007f70664b23f3 in QSGRenderThread::run (this=0x2cff4f0) at scenegraph/qsgthreadedrenderloop.cpp:672 | |
| # #23 0x00007f706505cd9b in QThreadPrivate::start (arg=0x2cff4f0) at thread/qthread_unix.cpp:337 | |
| # #24 0x00007f706b7fc182 in start_thread (arg=0x7f7055aa7700) at pthread_create.c:312 | |
| # #25 0x00007f706b52947d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:111 | |
| # (gdb) thread 3 | |
| # [Switching to thread 3 (Thread 0x7f7057df9700 (LWP 23803))] | |
| # #0 0x00007f706b51c12d in poll () at ../sysdeps/unix/syscall-template.S:81 | |
| # 81 ../sysdeps/unix/syscall-template.S: No such file or directory. | |
| # (gdb) bt | |
| # #0 0x00007f706b51c12d in poll () at ../sysdeps/unix/syscall-template.S:81 | |
| # #1 0x00007f7063bc0fe4 in g_main_context_poll (priority=2147483647, n_fds=1, fds=0x7f70500013e0, timeout=-1, context=0x7f70500009b0) at /build/buildd/glib2.0-2.40.2/./glib/gmain.c:4028 | |
| # #2 g_main_context_iterate (context=context@entry=0x7f70500009b0, block=block@entry=1, dispatch=dispatch@entry=1, self=<optimized out>) at /build/buildd/glib2.0-2.40.2/./glib/gmain.c:3729 | |
| # #3 0x00007f7063bc10ec in g_main_context_iteration (context=0x7f70500009b0, may_block=1) at /build/buildd/glib2.0-2.40.2/./glib/gmain.c:3795 | |
| # #4 0x00007f706534d149 in QEventDispatcherGlib::processEvents (this=0x7f70500008e0, flags=...) at kernel/qeventdispatcher_glib.cpp:418 | |
| # #5 0x00007f70652d0f1e in QEventLoop::processEvents (this=0x7f7057df8e10, flags=...) at kernel/qeventloop.cpp:128 | |
| # #6 0x00007f70652d11df in QEventLoop::exec (this=0x7f7057df8e10, flags=...) at kernel/qeventloop.cpp:204 | |
| # #7 0x00007f70650558e0 in QThread::exec (this=0x2732370) at thread/qthread.cpp:503 | |
| # #8 0x00007f706598c5c5 in QQmlThreadPrivate::run (this=0x2732370) at qml/ftw/qqmlthread.cpp:141 | |
| # #9 0x00007f706505cd9b in QThreadPrivate::start (arg=0x2732370) at thread/qthread_unix.cpp:337 | |
| # #10 0x00007f706b7fc182 in start_thread (arg=0x7f7057df9700) at pthread_create.c:312 | |
| # #11 0x00007f706b52947d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:111 | |
| # (gdb) thread 4 | |
| # [Switching to thread 4 (Thread 0x7f705ca83700 (LWP 23802))] | |
| # #0 0x00007f706b51c12d in poll () at ../sysdeps/unix/syscall-template.S:81 | |
| # 81 in ../sysdeps/unix/syscall-template.S | |
| # (gdb) bt | |
| # #0 0x00007f706b51c12d in poll () at ../sysdeps/unix/syscall-template.S:81 | |
| # #1 0x00007f7067770b72 in poll (__timeout=-1, __nfds=1, __fds=0x7f705ca82d00) at /usr/include/x86_64-linux-gnu/bits/poll2.h:46 | |
| # #2 _xcb_conn_wait (c=c@entry=0x28a2c60, cond=cond@entry=0x28a2ca0, vector=vector@entry=0x0, count=count@entry=0x0) at ../../src/xcb_conn.c:447 | |
| # #3 0x00007f706777264f in xcb_wait_for_event (c=0x28a2c60) at ../../src/xcb_in.c:622 | |
| # #4 0x00007f705fb3df81 in QXcbEventReader::run (this=0x28b0b90) at qxcbconnection.cpp:1105 | |
| # #5 0x00007f706505cd9b in QThreadPrivate::start (arg=0x28b0b90) at thread/qthread_unix.cpp:337 | |
| # #6 0x00007f706b7fc182 in start_thread (arg=0x7f705ca83700) at pthread_create.c:312 | |
| # #7 0x00007f706b52947d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:111 | |
| # | |
| # (This issue is not reproduces in Windows, since Qt 5.4 still uses single | |
| # threaded rendering there.) | |
| return exit_code | |
| if __name__ == "__main__": | |
| exit_code = main() | |
| sys.exit(exit_code) |
| import QtQuick 2.0 | |
| Item { | |
| } |
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