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https://github.com/IfcOpenShell/IfcOpenShell.git
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Dion Moult
19bff92a47
Loading a federated project (.ifcfed) with several models segfaults
non-deterministically on a fresh start. The viewer's SceneLoader spawns
one background std::thread per model in startDataSourceLoad() to
construct an ifcopenshell::file; with cached sidecars all models reach
that point near-simultaneously, so multiple threads parse different IFC
files at once. Parsing touches the process-wide schema singleton, which
was not thread-safe in two places.
Race 1 — concurrent schema population
-------------------------------------
schema_registry::get() lazily runs the schema's get_() function (e.g.
Ifc4::get_schema() -> IFC4_populate_schema()) and mutates entries_ with
no lock. Two threads calling schema_by_name("IFC4") at once both run
IFC4_populate_schema() concurrently, which fills global arrays
(IFC4_types[], strings[]). One thread reads a slot the other is still
writing.
Core-dump evidence (gdb thread apply all bt):
Thread 1 SIGSEGV in IFC4_populate_schema Ifc4-schema.cpp:1989
<- Ifc4::get_schema
<- schema_registry::get schema.cpp:241
<- schema_by_name("IFC4")
<- ifcopenshell::file::file (NWCH-PIR-SS...ifc)
<- SceneLoader::startDataSourceLoad lambda SceneLoader.cpp:315
Thread 3 also in IFC4_populate_schema (entity ctor for
"IfcMaterialProfileSetUsageTapering")
<- Ifc4::get_schema
<- schema_registry::get schema.cpp:241
<- ifcopenshell::file::file (NWCH-PIR-PT...ifc)
<- SceneLoader::startDataSourceLoad lambda
Two threads inside IFC4_populate_schema() at the same time is the race.
Fix: guard schema_registry's bind()/get()/names()/clear() with a
recursive_mutex (recursive because get() re-enters bind() via
load_schema_plugin(), and a freshly populated schema registers itself
through register_schema()). get() is serialized, so only the first
thread populates the schema; the rest block briefly and then observe
the finished result. Returned schema pointers are stable for the
process lifetime, so holding the lock only across get() is sufficient.
Race 2 — lazy all_attributes_ cache filled during parsing
---------------------------------------------------------
entity::all_attributes() lazily fills a `mutable` optional cache on the
shared schema entity the first time it is accessed — and that first
access happens during parsing (parse_context::construct), not during
schema population. With race 1 fixed, two parser threads still raced
here: both saw the cache empty, both did all_attributes_.emplace() and
std::copy() into it, corrupting the vector.
Core-dump evidence after the race-1 fix:
Thread 1 SIGSEGV in attribute::type_of_attribute (this=0xe130...55c)
<- std::transform(first=0x4, last=0xb0d1...) <-- garbage
iterators into a corrupt std::vector
<- parse_context::construct over
decl->as_entity()->all_attributes() file.cpp:249
<- instance_streamer::read_instance
<- ifcopenshell::file::file (NWCH-PIR-PT...ifc)
<- SceneLoader::startDataSourceLoad lambda
The begin pointer 0x4 is a half-written vector being read mid-resize by
another thread.
Fix: force every entity's all_attributes_ cache in the
schema_definition constructor, while construction is still
single-threaded. The schema is then genuinely immutable after
construction, so concurrent parsing needs no hot-path lock.
Both crashes reproduce reliably on a fresh start at native speed but
vanish under gdb (which serializes thread scheduling) — the classic
signature of a data race. With both fixes the federated load completes
cleanly.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
IfcOpenShell
IfcOpenShell is an open source (LGPL) software library for working with Industry Foundation Classes (IFC). Complete parsing support is provided for IFC2x3 TC1, IFC4 Add2 TC1, IFC4x1, IFC4x2, and IFC4x3 Add2. Extensive geometric support is implemented for the IFC releases IFC2x3 TC1 and IFC4 Add2 TC1. Extending with support for arbitrary IFC schemas is possible at compile-time when using C++ and at run-time when using Python.
In addition to a C++ and Python API, IfcOpenShell comes with an ecosystem of tools, notably including IfcConvert (an application to convert IFC models to other formats), Bonsai (an add-on to Blender providing a graphical IFC authoring platform), and many other libraries, CLI apps, and more. Support is also provided for auxiliary standards such as BCF and IDS.
For more information, see:
Development is sponsored through your generous donations!
Contents
| Name | Description | License | Service |
|---|---|---|---|
| bcf | Library to read and write BCF-XML and query OpenCDE BCF-API modules | LGPL-3.0-or-later |   |
| bonsai | Add-on to Blender providing a graphical native IFC authoring platform | GPL-3.0-or-later |    |
| bsdd | Library to query the bSDD API | LGPL-3.0-or-later |  |
| ifc2ca | Utility to convert IFC structural analysis models to Code_Aster | LGPL-3.0-or-later | |
| ifc4d | Convert to and from IFC and project management software | LGPL-3.0-or-later |  |
| ifc5d | Report and optimise cost information from IFC | LGPL-3.0-or-later |  |
| ifcbimtester | Wrapper for Gherkin based unit testing for IFC models | LGPL-3.0-or-later | |
| ifcblender | Historic Blender IFC import add-on | LGPL-3.0-or-later* | |
| ifccityjson | Convert CityJSON to IFC | LGPL-3.0-or-later |  |
| ifcclash | Clash detection library and CLI app | LGPL-3.0-or-later |  |
| ifcconvert | CLI app to convert IFC to many other formats | LGPL-3.0-or-later* |   |
| ifccsv | Library and CLI app to export and import schedules from IFC | LGPL-3.0-or-later |  |
| ifcdiff | Compare changes between IFC models | LGPL-3.0-or-later |  |
| ifcedit | CLI wrapper for ifcopenshell.api IFC model mutation functions | LGPL-3.0-or-later |  |
| ifcfm | Extract IFC data for FM handover requirements | LGPL-3.0-or-later |  |
| ifcmax | Historic extension for IFC support in 3DS Max | LGPL-3.0-or-later* | |
| ifcmcp | MCP server for querying and editing IFC building models | LGPL-3.0-or-later |  |
| ifcopenshell-python | Python library for IFC manipulation | LGPL-3.0-or-later* |         |
| ifcpatch | Utility to run pre-packaged scripts to manipulate IFCs | LGPL-3.0-or-later |  |
| ifcquery | CLI tool for querying and inspecting IFC building models | LGPL-3.0-or-later |  |
| ifcsverchok | Blender Add-on for visual node programming with IFC | GPL-3.0-or-later |  |
| ifctester | Library, CLI and webapp for IDS model auditing | LGPL-3.0-or-later |  |
The IfcOpenShell C++ codebase is split into multiple interal libraries:
| Name | Description | License |
|---|---|---|
| ifcgeom | Internal library for IfcOpenShell | LGPL-3.0-or-later* |
| ifcgeom_schema_agnostic | Internal library for IfcOpenShell | LGPL-3.0-or-later* |
| ifcgeomserver | Internal library for IfcOpenShell | LGPL-3.0-or-later* |
| ifcjni | Internal library for IfcOpenShell | LGPL-3.0-or-later* |
| ifcparse | Internal library for IfcOpenShell | LGPL-3.0-or-later* |
| ifcwrap | Internal library for IfcOpenShell | LGPL-3.0-or-later* |
| qtviewer | Internal library for IfcOpenShell | LGPL-3.0-or-later* |
| serializers | Internal library for IfcOpenShell | LGPL-3.0-or-later* |