[Samples] Add C++ OpenMP example

SConstruct

@@ -248,6 +248,7 @@ defaults.noDebugLinkFlags = ''
 defaults.warningFlags = '-Wall'
 defaults.buildPch = False
 env['pch_flags'] = []
+env['openmp_flag'] = '-fopenmp' # used to generate sample build scripts
 
 if 'gcc' in env.subst('$CC'):
     defaults.optimizeCcFlags += ' -Wno-inline'
@@ -270,11 +271,13 @@ elif env['CC'] == 'cl': # Visual Studio
     defaults.warningFlags = '/W3'
     defaults.buildPch = True
     env['pch_flags'] = ['/FIpch/system.h']
+    env['openmp_flag'] = '/openmp'
 
 elif 'icc' in env.subst('$CC'):
     defaults.cxxFlags = '-std=c++0x'
     defaults.ccFlags = '-vec-report0 -diag-disable 1478'
     defaults.warningFlags = '-Wcheck'
+    env['openmp_flag'] = '-openmp'
 
 elif 'clang' in env.subst('$CC'):
     defaults.ccFlags = '-fcolor-diagnostics'

samples/cxx/CMakeLists.txt.in

@@ -5,7 +5,7 @@ set(CMAKE_VERBOSE_MAKEFILE ON)
 set(CMAKE_CXX_STANDARD 11)
 
 find_package(Threads REQUIRED)
-
+@cmake_extra@
 include_directories(@cmake_cantera_incdirs@)
 link_directories(@cmake_cantera_libdirs@)
 

samples/cxx/SConscript

@@ -4,16 +4,27 @@ Import('env', 'build', 'install', 'buildSample')
 
 # (subdir, program name, [source extensions])
 samples = [
-    ('combustor', 'combustor', ['cpp']),
-    ('flamespeed', 'flamespeed', ['cpp']),
-    ('kinetics1', 'kinetics1', ['cpp']),
-    ('NASA_coeffs', 'NASA_coeffs', ['cpp']),
-    ('rankine', 'rankine', ['cpp']),
-    ('LiC6_electrode', 'LiC6_electrode', ['cpp'])
+    ('combustor', 'combustor', ['cpp'], False),
+    ('flamespeed', 'flamespeed', ['cpp'], False),
+    ('kinetics1', 'kinetics1', ['cpp'], False),
+    ('NASA_coeffs', 'NASA_coeffs', ['cpp'], False),
+    ('rankine', 'rankine', ['cpp'], False),
+    ('LiC6_electrode', 'LiC6_electrode', ['cpp'], False),
+    ('openmp_ignition', 'openmp_ignition', ['cpp'], True)
 ]
 
-for subdir, name, extensions in samples:
+for subdir, name, extensions, openmp in samples:
     localenv = env.Clone()
+    if openmp:
+        localenv.Append(CXXFLAGS=env['openmp_flag'], LINKFLAGS=env['openmp_flag'])
+        localenv['cmake_extra'] = """
+find_package(OpenMP REQUIRED)
+set(CMAKE_CXX_FLAGS ${CMAKE_CXX_FLAGS} ${OpenMP_CXX_FLAGS})
+set(CMAKE_EXE_LINKER_FLAGS ${CMAKE_EXE_LINKER_FLAGS} ${OpenMP_EXE_LINKER_FLAGS})
+"""
+    else:
+        localenv['cmake_extra'] = ''
+
     buildSample(localenv.Program, pjoin(subdir, name),
                 mglob(localenv, subdir, *extensions),
                 CPPPATH=['#include'],

samples/cxx/openmp_ignition/openmp_ignition.cpp

@@ -0,0 +1,97 @@
+// Ignition delay calculation with OpenMP. This example shows how to use OpenMP
+// to run multiple reactor network calculations in parallel by using separate
+// Cantera objects for each thread.
+
+#include "cantera/zerodim.h"
+#include "cantera/IdealGasMix.h"
+
+#include <omp.h>
+
+using namespace Cantera;
+
+void run()
+{
+    // The number of threads can be set by setting the OMP_NUM_THREADS
+    // environment variable before running the code.
+    int nThreads = omp_get_max_threads();
+    writelog("Running on {} threads\n\n", nThreads);
+
+    // Containers for Cantera objects to be used in different. Each thread needs
+    // to have its own set of linked Cantera objects. Multiple threads accessing
+    // the same objects at the same time will cause errors.
+    std::vector<std::unique_ptr<IdealGasMix>> gases;
+    std::vector<std::unique_ptr<IdealGasConstPressureReactor>> reactors;
+    std::vector<std::unique_ptr<ReactorNet>> nets;
+
+    // Create and link the Cantera objects for each thread. This step should be
+    // done in serial
+    for (int i = 0; i < nThreads; i++) {
+        gases.emplace_back(new IdealGasMix("gri30.xml", "gri30"));
+        reactors.emplace_back(new IdealGasConstPressureReactor());
+        nets.emplace_back(new ReactorNet());
+        reactors.back()->insert(*gases.back());
+        nets.back()->addReactor(*reactors.back());
+    }
+
+    // Points at which to compute ignition delay time
+    size_t nPoints = 50;
+    vector_fp T0(nPoints);
+    vector_fp ignition_time(nPoints);
+    for (size_t i = 0; i < nPoints; i++) {
+        T0[i] = 1000 + 500 * ((float) i) / ((float) nPoints);
+    }
+
+    // Calculate the ignition delay at each initial temperature using multiple
+    // threads.
+    //
+    // Note on 'schedule(static, 1)':
+    // This option causes points [0, nThreads, 2*nThreads, ...] to be handled by
+    // the same thread, rather than the default behavior of one thread handling
+    // points [0 ... nPoints/nThreads]. This helps balance the workload for each
+    // thread in cases where the workload is biased, e.g. calculations for low
+    // T0 take longer than calculations for high T0.
+    #pragma omp parallel for schedule(static, 1)
+    for (size_t i = 0; i < nPoints; i++) {
+        // Get the Cantera objects that were initialized for this thread
+        size_t j = omp_get_thread_num();
+        IdealGasMix& gas = *gases[j];
+        Reactor& reactor = *reactors[j];
+        ReactorNet& net = *nets[j];
+
+        // Set up the problem
+        gas.setState_TPX(T0[i], OneAtm, "CH4:0.5, O2:1.0, N2:3.76");
+        reactor.syncState();
+        net.setInitialTime(0.0);
+
+        // Integrate until we satisfy a crude estimate of the ignition delay
+        // time: time for T to increase by 500 K
+        while (reactor.temperature() < T0[i] + 500) {
+            net.step();
+        }
+
+        // Save the ignition delay time for this temperature
+        ignition_time[i] = net.time();
+    }
+
+    // Print the computed ignition delays
+    writelog("  T (K)    t_ig (s)\n");
+    writelog("--------  ----------\n");
+    for (size_t i = 0; i < nPoints; i++) {
+        writelog("{: 8.1f}  {: 10.3e}\n", T0[i], ignition_time[i]);
+    }
+}
+
+int main()
+{
+    try {
+        run();
+        appdelete();
+        return 0;
+    } catch (CanteraError& err) {
+        // handle exceptions thrown by Cantera
+        std::cout << err.what() << std::endl;
+        std::cout << " terminating... " << std::endl;
+        appdelete();
+        return 1;
+    }
+}