Added class for managing SHMEMSimulators

GPUSimulators/SHMEMSimulator.py

@@ -21,139 +21,17 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 
 import logging
-from GPUSimulators import Simulator, CudaContext
+from GPUSimulators import Simulator
 import numpy as np
 
-import pycuda.driver as cuda
-
-class SHMEMGrid(object):
-    """
-    Class which represents an SHMEM grid of GPUs. Facilitates easy communication between
-    neighboring subdomains in the grid. Contains one CUDA context per subdomain.
-    """
-    def __init__(self, ngpus=None, ndims=2):
-        self.logger =  logging.getLogger(__name__)
-
-        cuda.init(flags=0)
-        self.logger.info("Initializing CUDA")
-        num_cuda_devices = cuda.Device.count()
-        
-        if ngpus is None:
-            ngpus = num_cuda_devices
-
-        assert ngpus <= num_cuda_devices, "Trying to allocate more GPUs than are available in the system."   
-        assert ndims == 2, "Unsupported number of dimensions. Must be two at the moment"
-        assert ngpus >= 2, "Must have at least two GPUs available to run multi-GPU simulations."
-
-        self.ngpus = ngpus
-        self.ndims = ndims
-
-        self.grid = SHMEMGrid.getGrid(self.ngpus, self.ndims)
-        
-        self.logger.debug("Created {:}-dimensional SHMEM grid, using {:} GPUs".format(
-                self.ndims, self.ngpus))    
-
-        self.cuda_contexts = []
-
-        for i in range(self.ngpus):
-            self.cuda_contexts.append(CudaContext.CudaContext(device=i, autotuning=False))
-
-    def getCoordinate(self, index):
-        i = (index  % self.grid[0])
-        j = (index // self.grid[0])
-        return i, j
-
-    def getIndex(self, i, j):
-        return j*self.grid[0] + i
-
-    def getEast(self, index):
-        i, j = self.getCoordinate(index)
-        i = (i+1) % self.grid[0]
-        return self.getIndex(i, j)
-
-    def getWest(self, index):
-        i, j = self.getCoordinate(index)
-        i = (i+self.grid[0]-1) % self.grid[0]
-        return self.getIndex(i, j)
-
-    def getNorth(self, index):
-        i, j = self.getCoordinate(index)
-        j = (j+1) % self.grid[1]
-        return self.getIndex(i, j)
-
-    def getSouth(self, index):
-        i, j = self.getCoordinate(index)
-        j = (j+self.grid[1]-1) % self.grid[1]
-        return self.getIndex(i, j)
-    
-    def getGrid(num_gpus, num_dims):
-        assert(isinstance(num_gpus, int))
-        assert(isinstance(num_dims, int))
-        
-        # Adapted from https://stackoverflow.com/questions/28057307/factoring-a-number-into-roughly-equal-factors
-        # Original code by https://stackoverflow.com/users/3928385/ishamael
-        # Factorizes a number into n roughly equal factors
-
-        #Dictionary to remember already computed permutations
-        memo = {}
-        def dp(n, left): # returns tuple (cost, [factors])
-            """
-            Recursively searches through all factorizations
-            """
-
-            #Already tried: return existing result
-            if (n, left) in memo: 
-                return memo[(n, left)]
-
-            #Spent all factors: return number itself
-            if left == 1:
-                return (n, [n])
-
-            #Find new factor
-            i = 2
-            best = n
-            bestTuple = [n]
-            while i * i < n:
-                #If factor found
-                if n % i == 0:
-                    #Factorize remainder
-                    rem = dp(n // i, left - 1)
-
-                    #If new permutation better, save it
-                    if rem[0] + i < best:
-                        best = rem[0] + i
-                        bestTuple = [i] + rem[1]
-                i += 1
-
-            #Store calculation
-            memo[(n, left)] = (best, bestTuple)
-            return memo[(n, left)]
-
-
-        grid = dp(num_gpus, num_dims)[1]
-
-        if (len(grid) < num_dims):
-            #Split problematic 4
-            if (4 in grid):
-                grid.remove(4)
-                grid.append(2)
-                grid.append(2)
-
-            #Pad with ones to guarantee num_dims
-            grid = grid + [1]*(num_dims - len(grid))
-        
-        #Sort in descending order
-        grid = np.sort(grid)
-        grid = grid[::-1]
-        
-        return grid
-
 
 class SHMEMSimulator(Simulator.BaseSimulator):
     """
     Class which handles communication between simulators on different GPUs
+
+    NOTE: This class is only intended to be used by SHMEMSimulatorGroup
     """
-    def __init__(self, sim, grid):
+    def __init__(self, index, sim, grid):
         self.logger =  logging.getLogger(__name__)
         
         autotuner = sim.context.autotuner
@@ -168,14 +46,15 @@ class SHMEMSimulator(Simulator.BaseSimulator):
             sim.block_size[0], sim.block_size[1])
         sim.context.autotuner = autotuner
         
+        self.index = index
         self.sim = sim
         self.grid = grid
         
         #Get neighbor subdomain ids
-        self.east = grid.getEast()
-        self.west = grid.getWest()
-        self.north = grid.getNorth()
-        self.south = grid.getSouth()
+        self.east = grid.getEast(self.index)
+        self.west = grid.getWest(self.index)
+        self.north = grid.getNorth(self.index)
+        self.south = grid.getSouth(self.index)
         
         #Get coordinate of this subdomain
         #and handle global boundary conditions
@@ -185,7 +64,7 @@ class SHMEMSimulator(Simulator.BaseSimulator):
             'east': Simulator.BoundaryCondition.Type.Dirichlet,
             'west': Simulator.BoundaryCondition.Type.Dirichlet
         })
-        gi, gj = grid.getCoordinate()
+        gi, gj = grid.getCoordinate(self.index)
         if (gi == 0 and boundary_conditions.west != Simulator.BoundaryCondition.Type.Periodic):
             self.west = None
             new_boundary_conditions.west = boundary_conditions.west;
@@ -237,7 +116,7 @@ class SHMEMSimulator(Simulator.BaseSimulator):
         self.out_n = np.empty_like(self.in_n)
         self.out_s = np.empty_like(self.in_s)
         
-        self.logger.debug("Simlator subdomain {:d} initialized on {:s}".format(self.grid.comm.rank, MPI.Get_processor_name()))
+        self.logger.debug("Simlator subdomain {:d} initialized on context {:s}".format(self.index, sim.context))
     
         
     def substep(self, dt, step_number):
@@ -254,21 +133,20 @@ class SHMEMSimulator(Simulator.BaseSimulator):
         return self.sim.check()
     
     def computeDt(self):
-        local_dt = np.array([np.float32(self.sim.computeDt())]);
+        local_dt = np.array([np.float32(self.sim.computeDt())])
         global_dt = np.empty(1, dtype=np.float32)
         self.grid.comm.Allreduce(local_dt, global_dt, op=MPI.MIN)
         self.logger.debug("Local dt: {:f}, global dt: {:f}".format(local_dt[0], global_dt[0]))
         return global_dt[0]
         
-        
     def getExtent(self):
         """
-        Function which returns the extent of node with rank 
-        rank in the grid
+        Function which returns the extent of the subdomain with index 
+        index in the grid
         """
         width = self.sim.nx*self.sim.dx
         height = self.sim.ny*self.sim.dy
-        i, j = self.grid.getCoordinate()
+        i, j = self.grid.getCoordinate(self.index)
         x0 = i * width
         y0 = j * height 
         x1 = x0 + width
@@ -276,6 +154,19 @@ class SHMEMSimulator(Simulator.BaseSimulator):
         return [x0, x1, y0, y1]
         
     def exchange(self):        
+        ns_download_before_exchange()
+        # GLOBAL SYNC 
+        ns_do_exchange()
+        # GLOBAL SYNC
+        ns_upload_after_exchange()
+
+        ew_download_before_exchange()
+        # GLOBAL SYNC
+        ew_do_exchange()
+        # GLOBAL SYNC
+        ew_upload_after_exchange()
+
+    def ns_download_before_exchange(self):
         ####
         # First transfer internal cells north-south
         ####
@@ -289,6 +180,7 @@ class SHMEMSimulator(Simulator.BaseSimulator):
                 self.sim.u0[k].download(self.sim.stream, cpu_data=self.out_s[k,:,:], asynch=True, extent=self.read_s)
         self.sim.stream.synchronize()
 
+    def ns_do_exchange(self):
         #Send/receive to north/south neighbours
         comm_send = []
         comm_recv = []
@@ -303,6 +195,7 @@ class SHMEMSimulator(Simulator.BaseSimulator):
         for comm in comm_recv:
             comm.wait()
 
+    def ns_upload_after_exchange(self):
         #Upload to the GPU
         if self.north is not None:
             for k in range(self.nvars):
@@ -315,8 +208,7 @@ class SHMEMSimulator(Simulator.BaseSimulator):
         for comm in comm_send:
             comm.wait()
 
-        
-        
+    def ew_download_before_exchange(self):
         ####
         # Then transfer east-west including ghost cells that have been filled in by north-south transfer above
         ####
@@ -330,6 +222,7 @@ class SHMEMSimulator(Simulator.BaseSimulator):
                 self.sim.u0[k].download(self.sim.stream, cpu_data=self.out_w[k,:,:], asynch=True, extent=self.read_w)
         self.sim.stream.synchronize()
 
+    def ew_do_exchange(self):
         #Send/receive to east/west neighbours
         comm_send = []
         comm_recv = []
@@ -345,6 +238,7 @@ class SHMEMSimulator(Simulator.BaseSimulator):
         for comm in comm_recv:
             comm.wait()
 
+    def ew_upload_after_exchange(self):
         #Upload to the GPU
         if self.east is not None:
             for k in range(self.nvars):

GPUSimulators/SHMEMSimulatorGroup.py

@@ -0,0 +1,353 @@
+# -*- coding: utf-8 -*-
+
+"""
+This python module implements SHMEM simulator group class
+
+Copyright (C) 2020 Norwegian Meteorological Institute
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program.  If not, see <http://www.gnu.org/licenses/>.
+"""
+
+
+import logging
+from GPUSimulators import Simulator, CudaContext
+import numpy as np
+
+import pycuda.driver as cuda
+
+
+class SHMEMGrid(object):
+    """
+    Class which represents an SHMEM grid of GPUs. Facilitates easy communication between
+    neighboring subdomains in the grid. Contains one CUDA context per subdomain.
+
+    XXX: Adapted to debug on a single GPU. Either remove this possibility or 
+    make it less hacky...
+    """
+    def __init__(self, ngpus=None, ndims=2):
+        self.logger =  logging.getLogger(__name__)
+
+        cuda.init(flags=0)
+        self.logger.info("Initializing CUDA")
+        num_cuda_devices = cuda.Device.count()
+        
+        if ngpus is None:
+            #ngpus = num_cuda_devices
+            ngpus = 2
+
+        #assert ngpus <= num_cuda_devices, "Trying to allocate more GPUs than are available in the system."   
+        assert ndims == 2, "Unsupported number of dimensions. Must be two at the moment"
+        #assert ngpus >= 2, "Must have at least two GPUs available to run multi-GPU simulations."
+
+        self.ngpus = ngpus
+        self.ndims = ndims
+
+        self.grid = SHMEMGrid.getGrid(self.ngpus, self.ndims)
+        
+        self.logger.debug("Created {:}-dimensional SHMEM grid, using {:} GPUs".format(
+                self.ndims, self.ngpus))    
+
+        # XXX: Is this a natural place to store the contexts? Consider moving contexts out of this class.
+        self.cuda_contexts = []
+
+        for i in range(self.ngpus):
+            #self.cuda_contexts.append(CudaContext.CudaContext(device=i, autotuning=False))
+            self.cuda_contexts.append(CudaContext.CudaContext(device=0, autotuning=False))
+
+    def getCoordinate(self, index):
+        i = (index  % self.grid[0])
+        j = (index // self.grid[0])
+        return i, j
+
+    def getIndex(self, i, j):
+        return j*self.grid[0] + i
+
+    def getEast(self, index):
+        i, j = self.getCoordinate(index)
+        i = (i+1) % self.grid[0]
+        return self.getIndex(i, j)
+
+    def getWest(self, index):
+        i, j = self.getCoordinate(index)
+        i = (i+self.grid[0]-1) % self.grid[0]
+        return self.getIndex(i, j)
+
+    def getNorth(self, index):
+        i, j = self.getCoordinate(index)
+        j = (j+1) % self.grid[1]
+        return self.getIndex(i, j)
+
+    def getSouth(self, index):
+        i, j = self.getCoordinate(index)
+        j = (j+self.grid[1]-1) % self.grid[1]
+        return self.getIndex(i, j)
+    
+    def getGrid(num_gpus, num_dims):
+        assert(isinstance(num_gpus, int))
+        assert(isinstance(num_dims, int))
+        
+        # Adapted from https://stackoverflow.com/questions/28057307/factoring-a-number-into-roughly-equal-factors
+        # Original code by https://stackoverflow.com/users/3928385/ishamael
+        # Factorizes a number into n roughly equal factors
+
+        #Dictionary to remember already computed permutations
+        memo = {}
+        def dp(n, left): # returns tuple (cost, [factors])
+            """
+            Recursively searches through all factorizations
+            """
+
+            #Already tried: return existing result
+            if (n, left) in memo: 
+                return memo[(n, left)]
+
+            #Spent all factors: return number itself
+            if left == 1:
+                return (n, [n])
+
+            #Find new factor
+            i = 2
+            best = n
+            bestTuple = [n]
+            while i * i < n:
+                #If factor found
+                if n % i == 0:
+                    #Factorize remainder
+                    rem = dp(n // i, left - 1)
+
+                    #If new permutation better, save it
+                    if rem[0] + i < best:
+                        best = rem[0] + i
+                        bestTuple = [i] + rem[1]
+                i += 1
+
+            #Store calculation
+            memo[(n, left)] = (best, bestTuple)
+            return memo[(n, left)]
+
+
+        grid = dp(num_gpus, num_dims)[1]
+
+        if (len(grid) < num_dims):
+            #Split problematic 4
+            if (4 in grid):
+                grid.remove(4)
+                grid.append(2)
+                grid.append(2)
+
+            #Pad with ones to guarantee num_dims
+            grid = grid + [1]*(num_dims - len(grid))
+        
+        #Sort in descending order
+        grid = np.sort(grid)
+        grid = grid[::-1]
+        
+        return grid
+
+class SHMEMSimulatorGroup(Simulator.BaseSimulator):
+    """
+    Class which handles communication and synchronization between simulators in different 
+    contexts (presumably on different GPUs)
+    """
+    def __init__(self, grid, **kwargs):
+        self.logger =  logging.getLogger(__name__)
+        sims = []
+
+        for i in range(grid.ngpus):
+            local_sim = EE2D_KP07_dimsplit.EE2D_KP07_dimsplit(**kwargs)
+            sims[i] = SHMEMSimulator(i, local_sim, grid)
+        
+        autotuner = sims[0].context.autotuner
+        sims[0].context.autotuner = None;
+        boundary_conditions = sims[0].getBoundaryConditions()
+        super().__init__(sims[0].context, 
+            sims[0].nx, sims[0].ny, 
+            sims[0].dx, sims[0].dy, 
+            boundary_conditions,
+            sims[0].cfl_scale,
+            sims[0].num_substeps,  
+            sims[0].block_size[0], sims[0].block_size[1])
+        sims[0].context.autotuner = autotuner
+        
+        self.nsubdomains = grid.ngpus
+        self.sims = sims
+        self.grid = grid
+        
+        #Get coordinate of this subdomain
+        #and handle global boundary conditions
+        new_boundary_conditions = Simulator.BoundaryCondition({
+            'north': Simulator.BoundaryCondition.Type.Dirichlet,
+            'south': Simulator.BoundaryCondition.Type.Dirichlet,
+            'east': Simulator.BoundaryCondition.Type.Dirichlet,
+            'west': Simulator.BoundaryCondition.Type.Dirichlet
+        })
+        gi, gj = grid.getCoordinate(self.index)
+        if (gi == 0 and boundary_conditions.west != Simulator.BoundaryCondition.Type.Periodic):
+            self.west = None
+            new_boundary_conditions.west = boundary_conditions.west;
+        if (gj == 0 and boundary_conditions.south != Simulator.BoundaryCondition.Type.Periodic):
+            self.south = None
+            new_boundary_conditions.south = boundary_conditions.south;
+        if (gi == grid.grid[0]-1 and boundary_conditions.east != Simulator.BoundaryCondition.Type.Periodic):
+            self.east = None
+            new_boundary_conditions.east = boundary_conditions.east;
+        if (gj == grid.grid[1]-1 and boundary_conditions.north != Simulator.BoundaryCondition.Type.Periodic):
+            self.north = None
+            new_boundary_conditions.north = boundary_conditions.north;
+        sim.setBoundaryConditions(new_boundary_conditions)
+                
+        #Get number of variables
+        self.nvars = len(self.getOutput().gpu_variables)
+        
+        #Shorthands for computing extents and sizes
+        gc_x = int(self.sim.getOutput()[0].x_halo)
+        gc_y = int(self.sim.getOutput()[0].y_halo)
+        nx = int(self.sim.nx)
+        ny = int(self.sim.ny)
+        
+        self.logger.debug("Initialized {:d} subdomains".format(len(self.sims)))
+    
+        
+    # TODO: Re-implement methods below
+    def substep(self, dt, step_number):
+        self.exchange()
+        self.sim.substep(dt, step_number)
+    
+    def getOutput(self):
+        return self.sim.getOutput()
+        
+    def synchronize(self):
+        self.sim.synchronize()
+        
+    def check(self):
+        return self.sim.check()
+    
+    def computeDt(self):
+        local_dt = np.array([np.float32(self.sim.computeDt())])
+        global_dt = np.empty(1, dtype=np.float32)
+        self.grid.comm.Allreduce(local_dt, global_dt, op=MPI.MIN)
+        self.logger.debug("Local dt: {:f}, global dt: {:f}".format(local_dt[0], global_dt[0]))
+        return global_dt[0]
+        
+    def getExtent(self):
+        """
+        Function which returns the extent of the subdomain with index 
+        index in the grid
+        """
+        width = self.sim.nx*self.sim.dx
+        height = self.sim.ny*self.sim.dy
+        i, j = self.grid.getCoordinate(self.index)
+        x0 = i * width
+        y0 = j * height 
+        x1 = x0 + width
+        y1 = y0 + height
+        return [x0, x1, y0, y1]
+        
+    def exchange(self):        
+        ns_download_before_exchange()
+        # GLOBAL SYNC
+        ns_do_exchange()
+        # GLOBAL SYNC
+        ns_upload_after_exchange()
+
+        ew_download_before_exchange()
+        # GLOBAL SYNC
+        ew_do_exchange()
+        # GLOBAL SYNC
+        ew_upload_after_exchange()
+
+    def ns_download_before_exchange(self):
+        ####
+        # First transfer internal cells north-south
+        ####
+        
+        #Download from the GPU
+        if self.north is not None:
+            for k in range(self.nvars):
+                self.sim.u0[k].download(self.sim.stream, cpu_data=self.out_n[k,:,:], asynch=True, extent=self.read_n)
+        if self.south is not None:
+            for k in range(self.nvars):
+                self.sim.u0[k].download(self.sim.stream, cpu_data=self.out_s[k,:,:], asynch=True, extent=self.read_s)
+        self.sim.stream.synchronize()
+
+    def ns_do_exchange(self):
+        #Send/receive to north/south neighbours
+        comm_send = []
+        comm_recv = []
+        if self.north is not None:
+            comm_send += [self.grid.comm.Isend(self.out_n, dest=self.north, tag=4*self.nt + 0)]
+            comm_recv += [self.grid.comm.Irecv(self.in_n, source=self.north, tag=4*self.nt + 1)]
+        if self.south is not None:
+            comm_send += [self.grid.comm.Isend(self.out_s, dest=self.south, tag=4*self.nt + 1)]
+            comm_recv += [self.grid.comm.Irecv(self.in_s, source=self.south, tag=4*self.nt + 0)]
+        
+        #Wait for incoming transfers to complete
+        for comm in comm_recv:
+            comm.wait()
+
+    def ns_upload_after_exchange(self):
+        #Upload to the GPU
+        if self.north is not None:
+            for k in range(self.nvars):
+                self.sim.u0[k].upload(self.sim.stream, self.in_n[k,:,:], extent=self.write_n)
+        if self.south is not None:
+            for k in range(self.nvars):
+                self.sim.u0[k].upload(self.sim.stream, self.in_s[k,:,:], extent=self.write_s)
+        
+        #Wait for sending to complete
+        for comm in comm_send:
+            comm.wait()
+
+    def ew_download_before_exchange(self):
+        ####
+        # Then transfer east-west including ghost cells that have been filled in by north-south transfer above
+        ####
+        
+        #Download from the GPU
+        if self.east is not None:
+            for k in range(self.nvars):
+                self.sim.u0[k].download(self.sim.stream, cpu_data=self.out_e[k,:,:], asynch=True, extent=self.read_e)
+        if self.west is not None:
+            for k in range(self.nvars):
+                self.sim.u0[k].download(self.sim.stream, cpu_data=self.out_w[k,:,:], asynch=True, extent=self.read_w)
+        self.sim.stream.synchronize()
+
+    def ew_do_exchange(self):
+        #Send/receive to east/west neighbours
+        comm_send = []
+        comm_recv = []
+        if self.east is not None:
+            comm_send += [self.grid.comm.Isend(self.out_e, dest=self.east, tag=4*self.nt + 2)]
+            comm_recv += [self.grid.comm.Irecv(self.in_e, source=self.east, tag=4*self.nt + 3)]
+        if self.west is not None:
+            comm_send += [self.grid.comm.Isend(self.out_w, dest=self.west, tag=4*self.nt + 3)]
+            comm_recv += [self.grid.comm.Irecv(self.in_w, source=self.west, tag=4*self.nt + 2)]
+        
+        
+        #Wait for incoming transfers to complete
+        for comm in comm_recv:
+            comm.wait()
+
+    def ew_upload_after_exchange(self):
+        #Upload to the GPU
+        if self.east is not None:
+            for k in range(self.nvars):
+                self.sim.u0[k].upload(self.sim.stream, self.in_e[k,:,:], extent=self.write_e)
+        if self.west is not None:
+            for k in range(self.nvars):
+                self.sim.u0[k].upload(self.sim.stream, self.in_w[k,:,:], extent=self.write_w)
+        
+        #Wait for sending to complete
+        for comm in comm_send:
+            comm.wait()

shmemTesting.py

@@ -60,8 +60,10 @@ logger.info("File logger using level %s to %s", logging.getLevelName(log_level_f
 ####
 # Initialize SHMEM grid etc
 ####
+nsubdomains = 2
+
 logger.info("Creating SHMEM grid")
-grid = SHMEMSimulator.SHMEMGrid()
+grid = SHMEMSimulator.SHMEMGrid(ngpus=nsubdomains)
 
 
 
@@ -73,29 +75,29 @@ nx = 128
 ny = 128
 gamma = 1.4
 save_times = np.linspace(0, 5.0, 10)
-#outfile = "shmem_out.nc" # XXX: implement grid-support
 save_var_names = ['rho', 'rho_u', 'rho_v', 'E']
 
-sims = []
-for i in range(grid.ngpus):
-    outfile = "shmem_out_" + str(i) + ".nc"
+outfile = outfile[i] = "shmem_out.nc"
 
-    arguments = IC.genKelvinHelmholtz(nx, ny, gamma) # XXX: implement grid-support
+#outfile[i] = "shmem_out_" + str(i) + ".nc"
+#arguments = []
+local_sim = []
+#sim = []
+
+arguments = IC.genKelvinHelmholtz(nx, ny, gamma, grid=grid)
 arguments['context'] = grid.cuda_contexts[i]
 arguments['theta'] = 1.2
-    #arguments['grid'] = grid  # XXX: implement grid-support 
+arguments['grid'] = grid
 
 ####
 # Run simulation
 ####
 logger.info("Running simulation")
 #Helper function to create SHMEM simulator
-    #def genSim(grid, **kwargs):
-    def genSim(**kwargs):
-        sim = EE2D_KP07_dimsplit.EE2D_KP07_dimsplit(**kwargs)
-        #sim = SHMEMSimulator.SHMEMSimulator(local_sim, grid) # implement SHMEMSimulator-support
-        sims.append(sim)
+def genSim(grid, **kwargs):
+    sim = SHMEMSimulatorGroup.SHMEMSimulatorGroup(i, local_sims, grid, **kwargs)
     return sim
+
 outfile = Common.runSimulation(genSim, arguments, outfile, save_times, save_var_names)
 
 
@@ -103,9 +105,9 @@ for i in range(grid.ngpus):
 ####
 # Clean shutdown
 ####
-#sim = None # implement SHMEMSimulator-support
-sims = None
-local_sims = None
+sim = None
+local_sim = None
+cuda_context = None
 arguments = None
 logging.shutdown()
 gc.collect()