Fixed error that required Context and Integrator to be deleted in a particular order

openmmapi/include/openmm/Integrator.h

@@ -54,6 +54,7 @@ class ContextImpl;
 class OPENMM_EXPORT Integrator {
 public:
     virtual ~Integrator() {
+        cleanup();
     }
     /**
      * Get the size of each time step, in picoseconds.  If this integrator uses variable time steps,
@@ -92,6 +93,7 @@ public:
      */
     virtual void step(int steps) = 0;
 protected:
+    friend class Context;
     friend class ContextImpl;
     /**
      * This will be called by the Context when it is created.  It informs the Integrator
@@ -103,7 +105,8 @@ protected:
      * This will be called by the Context when it is destroyed to let the Integrator do any necessary
      * cleanup.  It will also get called again if the application calls reinitialize() on the Context.
      */
-    virtual void cleanup() = 0;
+    virtual void cleanup() {
+    };
     /**
      * Get the names of all Kernels used by this Integrator.
      */

openmmapi/src/Context.cpp

@@ -216,6 +216,7 @@ void Context::reinitialize() {
     System& system = impl->getSystem();
     Integrator& integrator = impl->getIntegrator();
     Platform& platform = impl->getPlatform();
+    integrator.cleanup();
     delete impl;
     impl = new ContextImpl(*this, system, integrator, &platform, properties);
 }

openmmapi/src/ContextImpl.cpp

@@ -122,7 +122,6 @@ ContextImpl::~ContextImpl() {
     updateStateDataKernel = Kernel();
     applyConstraintsKernel = Kernel();
     virtualSitesKernel = Kernel();
-    integrator.cleanup();
     platform->contextDestroyed(*this);
 }
 

platforms/cuda/src/CudaContext.cpp

@@ -255,6 +255,7 @@ CudaContext::~CudaContext() {
     string errorMessage = "Error deleting Context";
     if (contextIsValid)
         CHECK_RESULT(cuCtxDestroy(context));
+    contextIsValid = false;
 }
 
 void CudaContext::initialize() {