multithreading_support - Multithreading Support in Coin The support in
Coin for using multiple threads in application programs and the Coin
library itself, consists of two main features:
· Coin provides platform-independent thread-handling abstraction
classes. These are classes that the application programmer can freely
use in her application code to start new threads, control their
execution, work with mutexes and do other tasks related to handling
The classes in question are SbThread, SbMutex, SbStorage, SbBarrier,
SbCondVar, SbFifo, SbThreadAutoLock, SbRWMutex, and SbTypedStorage. See
their respective documentation for the detailed information.
The classes fully hides the system-specific implementation, which is
either done on top of native Win32 (if on Microsoft Windows), or over
POSIX threads (on UNIX and UNIX-like systems).
· The other aspect of our multi-threading support is that Coin can be
specially configured so that rendering traversals of the scene graph
are done in a thread-safe manner. This means e.g. that it is possible
to have Coin render the scene in parallel on multiple CPUs for
multiple rendering pipes, to better take advantage of such high-end
systems (like CAVE environments, for instance).
Thread-safe render traversals are off by default, because there is a
small overhead involved which would make rendering (very) slightly
slower on single-threaded invocations.
To get a Coin library built with thread-safe rendering, one must
actively re-configure Coin and build a special, local version. For
configure-based builds (UNIX and UNIX-like systems, or with Cygwin on
Microsoft Windows) this is done with the option ’--enable-threadsafe’
to Autoconf configure. For how to change the configuration and re-build
with Visual Studio, get in touch with us at ’firstname.lastname@example.org’.
There are some restrictions and other issues which it is important to
be aware of:
· We do not yet provide any support for binding the multi-threaded
rendering support into the SoQt / SoWin / etc GUI bindings, and
neither do we provide bindings against any specific library that
handles multi-pipe rendering. This means the application programmer
will have to possess some expertise, and put in some effort, to be
able to utilize multi-pipe rendering with Coin.
· Rendering traversals is currently the only operation which we
publicly support to be thread-safe. There are other aspects of Coin
that we know are thread-safe, like most other action traversals
beside just rendering, but we make no guarantees in this regard.
· Be careful about using a separate thread for changing Coin structures
versus what is used for the application’s GUI event thread.
We are aware of at least issues with Qt (and thereby SoQt), where you
should not modify the scene graph in any way in a thread separate from
the main Qt thread. This because it will trigger operations where Qt is