The third available shared memory parallelization provided with Blaze is based on Boost threads.
Boost Thread Setup
In order to enable the Boost thread-based parallelization, two steps have to be taken: First, the
BLAZE_USE_BOOST_THREADS command line argument has to be explicitly specified during compilation:
... -DBLAZE_USE_BOOST_THREADS ...
Second, the according Boost libraries have to be linked. These two simple actions will cause the Blaze library to automatically try to run all operations in parallel with the specified number of Boost threads. Note that the OpenMP-based and C++11 thread-based parallelizations have priority, i.e. are preferred in case either is enabled in combination with the Boost thread parallelization.
The number of threads can be either specified via the environment variable
export BLAZE_NUM_THREADS=4 // Unix systems set BLAZE_NUM_THREADS=4 // Windows systems
or alternatively via the
setNumThreads() function provided by the Blaze library:
blaze::setNumThreads( 4 );
Please note that the Blaze library does not limit the available number of threads. Therefore it is in YOUR responsibility to choose an appropriate number of threads. The best performance, though, can be expected if the specified number of threads matches the available number of cores.
In order to query the number of threads used for the parallelization of operations, the
getNumThreads() function can be used:
const size_t threads = blaze::getNumThreads();
In the context of Boost threads, the function will return the previously specified number of threads.
Boost Thread Configuration
As in case of the other shared memory parallelizations Blaze is not unconditionally running an operation in parallel (see OpenMP Parallelization or C++11 Thread Parallelization). All thresholds related to the Boost thread parallelization are also contained within the configuration file
Please note that these thresholds are highly sensitiv to the used system architecture and the shared memory parallelization technique. Therefore the default values cannot guarantee maximum performance for all possible situations and configurations. They merely provide a reasonable standard for the current CPU generation. Also note that the provided defaults have been determined using the OpenMP parallelization and require individual adaption for the Boost thread parallelization.