Added OpenCLPlatformIndex property for selecting platform

platforms/opencl/include/OpenCLPlatform.h

@@ -61,11 +61,18 @@ public:
         static const std::string key = "OpenCLDeviceIndex";
         return key;
     }
+    /**
+     * This is the name of the parameter for selecting which OpenCL platform to use.
+     */
+    static const std::string& OpenCLPlatformIndex() {
+        static const std::string key = "OpenCLPlatformIndex";
+        return key;
+    }
 };
 
 class OPENMM_EXPORT OpenCLPlatform::PlatformData {
 public:
-    PlatformData(int numParticles, const std::string& deviceIndexProperty);
+    PlatformData(int numParticles, const std::string& platformPropValue, const std::string& deviceIndexProperty);
     ~PlatformData();
     void initializeContexts(const System& system);
     void syncContexts();

platforms/opencl/src/OpenCLContext.cpp

@@ -60,7 +60,7 @@ static void CL_CALLBACK errorCallback(const char* errinfo, const void* private_i
     std::cerr << "OpenCL internal error: " << errinfo << std::endl;
 }
 
-OpenCLContext::OpenCLContext(int numParticles, int deviceIndex, OpenCLPlatform::PlatformData& platformData) :
+OpenCLContext::OpenCLContext(int numParticles, int platformIndex, int deviceIndex, OpenCLPlatform::PlatformData& platformData) :
         time(0.0), platformData(platformData), stepCount(0), computeForceCount(0), atomsWereReordered(false), posq(NULL),
         velm(NULL), forceBuffers(NULL), longForceBuffer(NULL), energyBuffer(NULL), atomIndex(NULL), integration(NULL),
         bonded(NULL), nonbonded(NULL), thread(NULL) {
@@ -68,7 +68,9 @@ OpenCLContext::OpenCLContext(int numParticles, int deviceIndex, OpenCLPlatform::
         contextIndex = platformData.contexts.size();
         std::vector<cl::Platform> platforms;
         cl::Platform::get(&platforms);
-        cl_context_properties cprops[] = {CL_CONTEXT_PLATFORM, (cl_context_properties) platforms[0](), 0};
+        if (platformIndex < 0 || platformIndex >= platforms.size())
+            throw OpenMMException("Illegal value for OpenCL platform index");
+        cl_context_properties cprops[] = {CL_CONTEXT_PLATFORM, (cl_context_properties) platforms[platformIndex](), 0};
         context = cl::Context(CL_DEVICE_TYPE_ALL, cprops, errorCallback);
         vector<cl::Device> devices = context.getInfo<CL_CONTEXT_DEVICES>();
         const int minThreadBlockSize = 32;

platforms/opencl/src/OpenCLContext.h

@@ -145,7 +145,7 @@ public:
     class WorkThread;
     static const int ThreadBlockSize;
     static const int TileSize;
-    OpenCLContext(int numParticles, int deviceIndex, OpenCLPlatform::PlatformData& platformData);
+    OpenCLContext(int numParticles, int platformIndex, int deviceIndex, OpenCLPlatform::PlatformData& platformData);
     ~OpenCLContext();
     /**
      * This is called to initialize internal data structures after all Forces in the system

platforms/opencl/src/OpenCLPlatform.cpp

@@ -72,7 +72,9 @@ OpenCLPlatform::OpenCLPlatform() {
     registerKernelFactory(CalcKineticEnergyKernel::Name(), factory);
     registerKernelFactory(RemoveCMMotionKernel::Name(), factory);
     platformProperties.push_back(OpenCLDeviceIndex());
+    platformProperties.push_back(OpenCLPlatformIndex());
     setPropertyDefaultValue(OpenCLDeviceIndex(), "");
+    setPropertyDefaultValue(OpenCLPlatformIndex(), "");
 }
 
 bool OpenCLPlatform::supportsDoublePrecision() const {
@@ -92,10 +94,12 @@ void OpenCLPlatform::setPropertyValue(Context& context, const string& property,
 }
 
 void OpenCLPlatform::contextCreated(ContextImpl& context, const map<string, string>& properties) const {
+    const string& platformPropValue = (properties.find(OpenCLPlatformIndex()) == properties.end() ?
+            getPropertyDefaultValue(OpenCLPlatformIndex()) : properties.find(OpenCLPlatformIndex())->second);
     const string& devicePropValue = (properties.find(OpenCLDeviceIndex()) == properties.end() ?
             getPropertyDefaultValue(OpenCLDeviceIndex()) : properties.find(OpenCLDeviceIndex())->second);
     int numParticles = context.getSystem().getNumParticles();
-    context.setPlatformData(new PlatformData(numParticles, devicePropValue));
+    context.setPlatformData(new PlatformData(numParticles, platformPropValue, devicePropValue));
 }
 
 void OpenCLPlatform::contextDestroyed(ContextImpl& context) const {
@@ -103,7 +107,10 @@ void OpenCLPlatform::contextDestroyed(ContextImpl& context) const {
     delete data;
 }
 
-OpenCLPlatform::PlatformData::PlatformData(int numParticles, const string& deviceIndexProperty) : removeCM(false), stepCount(0), computeForceCount(0), time(0.0)  {
+OpenCLPlatform::PlatformData::PlatformData(int numParticles, const string& platformPropValue, const string& deviceIndexProperty) : removeCM(false), stepCount(0), computeForceCount(0), time(0.0)  {
+    int platformIndex = 0;
+    if (platformPropValue.length() > 0)
+        stringstream(platformPropValue) >> platformIndex;
     vector<string> devices;
     size_t searchPos = 0, nextPos;
     while ((nextPos = deviceIndexProperty.find_first_of(", ", searchPos)) != string::npos) {
@@ -115,11 +122,11 @@ OpenCLPlatform::PlatformData::PlatformData(int numParticles, const string& devic
         if (devices[i].length() > 0) {
             unsigned int deviceIndex;
             stringstream(devices[i]) >> deviceIndex;
-            contexts.push_back(new OpenCLContext(numParticles, deviceIndex, *this));
+            contexts.push_back(new OpenCLContext(numParticles, platformIndex, deviceIndex, *this));
         }
     }
     if (contexts.size() == 0)
-        contexts.push_back(new OpenCLContext(numParticles, -1, *this));
+        contexts.push_back(new OpenCLContext(numParticles, platformIndex, -1, *this));
     stringstream device;
     for (int i = 0; i < (int) contexts.size(); i++) {
         if (i > 0)
@@ -127,6 +134,7 @@ OpenCLPlatform::PlatformData::PlatformData(int numParticles, const string& devic
         device << contexts[i]->getDeviceIndex();
     }
     propertyValues[OpenCLPlatform::OpenCLDeviceIndex()] = device.str();
+    propertyValues[OpenCLPlatform::OpenCLPlatformIndex()] = OpenCLExpressionUtilities::intToString(platformIndex);
     contextEnergy.resize(contexts.size());
 }
 

platforms/opencl/tests/TestOpenCLFFT.cpp

@@ -51,7 +51,7 @@ using namespace std;
 void testTransform() {
     System system;
     system.addParticle(0.0);
-    OpenCLPlatform::PlatformData platformData(1, "");
+    OpenCLPlatform::PlatformData platformData(1, "", "");
     OpenCLContext& context = *platformData.contexts[0];
     context.initialize(system);
     OpenMM_SFMT::SFMT sfmt;

platforms/opencl/tests/TestOpenCLRandom.cpp

@@ -48,7 +48,7 @@ void testGaussian() {
     System system;
     for (int i = 0; i < numAtoms; i++)
         system.addParticle(1.0);
-    OpenCLPlatform::PlatformData platformData(numAtoms, "");
+    OpenCLPlatform::PlatformData platformData(numAtoms, "", "");
     OpenCLContext& context = *platformData.contexts[0];
     context.initialize(system);
     context.getIntegrationUtilities().initRandomNumberGenerator(0);

platforms/opencl/tests/TestOpenCLSort.cpp

@@ -51,7 +51,7 @@ void verifySorting(vector<float> array) {
 
     System system;
     system.addParticle(0.0);
-    OpenCLPlatform::PlatformData platformData(1, "");
+    OpenCLPlatform::PlatformData platformData(1, "", "");
     OpenCLContext& context = *platformData.contexts[0];
     context.initialize(system);
     OpenCLArray<float> data(context, array.size(), "sortData");