Gabriele Cosmo
94 lines
3.0 KiB
Plaintext
94 lines
3.0 KiB
Plaintext
$Id$
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///\file ".README.HowToRunMT.txt"
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///\brief Examples Tips How To Run MT README page
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/*! \page README_HowToRunMT Tips how to run an example in multi-threading mode
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Only migrated examples or user applications can be run in multi-threading (MT) mode.
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The instructions for migrating user applications can be found in Geant4 documentation guides
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and a short howto is available here:
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https://twiki.cern.ch/twiki/bin/view/Geant4/QuickMigrationGuideForGeant4V10
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In this file, we give just useful tips for running already migrated examples
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(or user applications).
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\section HowToRunMT_s1 Run example in multi-threading mode
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No special steps are needed to build an example in multi-threading (MT) mode.
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The examples which has been migrated to multi-threading will automatically
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run in MT when they are built against the Geant4 libraries built with MT mode
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activated, otherwise they will run in sequential mode.
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Not migrated examples will run in sequential mode even when built against
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Geant4 libraries built with MT mode activated.
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The examples which support MT can be easily recognized by the following lines
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of code in main ():
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\verbatim
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#ifdef G4MULTITHREADED
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G4MTRunManager* runManager = new G4MTRunManager;
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#else
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G4RunManager* runManager = new G4RunManager;
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#endif
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\endverbatim
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The compiler flag -DG4MULTITHREADED is automatically set when building applications
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using Geant4's CMake (via GEANT4_USE_FILE) and GNUmake systems, and is listed in
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the flags reported by the --cflags option of the geant4-config program.
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\section HowToRunMT_s2 Set number of threads
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When the number of threads is not selected in the application, the default number
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(which is actually 2) will be used. Another number of threads can be set in several
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ways:
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- in the code
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\verbatim
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#ifdef G4MULTITHREADED
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G4MTRunManager* runManager = new G4MTRunManager;
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runManager->SetNumberOfThreads(4);
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#else
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...
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\endverbatim
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- in a macro file via UI command added just before /run/initialize
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\verbatim
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/run/numberOfThreads 4
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\endverbatim
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- by setting the environment variable
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\verbatim
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export G4FORCENUMBEROFTHREADS = 4
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or
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setenv G4FORCENUMBEROFTHREADS 4
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\endverbatim
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The environment variable value is forced and it cannot be changed from a code
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call or a macro. A warning is issued in such situation.
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\section HowToRunMT_s3 Output from threads
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In MT processing each worker produces its output and these messages are interlayed
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on the screen. The messeges from threads are preceded with a predefined string
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G4WTi> where i is the thread number. Users can change this default behaviour
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and choose
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- to buffer the output from each thread at a time, so that the output of each
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thread is grouped and printed at the end of the job
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\verbatim
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/control/cout/useBuffer true|false
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\endverbatim
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- to limit the output from threads to one selected thread only:
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\verbatim
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/control/cout/ignoreThreadsExcept 0
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\endverbatim
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- to redirect the output from threads in a file:
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\verbatim
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/control/cout/setCoutFile coutFileName
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/control/cout/setCerrFile cerrFileName
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\endverbatim
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*/
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