Adding multiprocess unit tests (#312)

Adding multiprocess unit tests for collectives.  

To run, NCCL_COMM_ID=$HOSTNAME:12345 build/release/test/UnitTestsMultiProcess

test/test_ReduceMultiProcess.cpp

@@ -0,0 +1,96 @@
+/*************************************************************************
+ * Copyright (c) 2019-2021 Advanced Micro Devices, Inc. All rights reserved.
+ *
+ * See LICENSE.txt for license information
+ ************************************************************************/
+
+#include "test_ReduceMultiProcess.hpp"
+
+namespace CorrectnessTests
+{
+    TEST_P(ReduceMultiProcessCorrectnessTest, Correctness)
+    {
+        Dataset* dataset = (Dataset*)mmap(NULL, sizeof(Dataset), PROT_READ|PROT_WRITE, MAP_SHARED|MAP_ANONYMOUS, -1, 0);
+        dataset->InitializeRootProcess(numDevices, numElements, dataType, inPlace, ncclCollReduce);
+        Barrier::ClearShmFiles(std::atoi(getenv("NCCL_COMM_ID")));
+
+        int pid1 = 0;
+        int pid2 = 0;
+        int pid3 = 0;
+        pid1 = fork();
+
+        // From this point on, ignore original process as we cannot have it create a HIP context
+        if (pid1 == 0)
+        {
+            pid2 = fork();
+            if (numDevices > 2)
+            {
+                pid3 = fork();
+            }
+            if ((pid2 > 0 && pid3 == 0 && numDevices == 2)  || (pid2 > 0 && pid3 > 0 && numDevices > 2))
+            {
+                // Process 0
+                TestReduce(0, *dataset);
+                if (pid3 > 0)
+                {
+                    waitpid(pid3, NULL, 0);
+                }
+            }
+            else if ((pid2 == 0 && pid3 == 0 && numDevices == 2) || (pid2 == 0 && pid3 > 0 && numDevices > 2))
+            {
+                // Process 1
+                TestReduce(1, *dataset);
+                if (numDevices > 2)
+                {
+                    waitpid(pid3, NULL, 0);
+                }
+                exit(0);
+            }
+            else if (pid2 > 0 && pid3 == 0 && numDevices > 2)
+            {
+                // Process 2 (available when numDevices > 2)
+                TestReduce(2, *dataset);
+                exit(0);
+            }
+            else if (pid2 == 0 && pid3 == 0 && numDevices == 4)
+            {
+                // Process 3 (available when numDevices == 4)
+                TestReduce(3, *dataset);
+                exit(0);
+            }
+            else
+            {
+                exit(0);
+            }
+            waitpid(pid2, NULL, 0);
+            exit(0);
+        }
+        waitpid(pid1, NULL, 0);
+        munmap(dataset, sizeof(Dataset));
+    }
+
+    INSTANTIATE_TEST_SUITE_P(ReduceMultiProcessCorrectnessSweep,
+                            ReduceMultiProcessCorrectnessTest,
+                            testing::Combine(
+                                // Reduction operator
+                                testing::Values(ncclSum, ncclProd, ncclMax, ncclMin),
+                                // Data types
+                                testing::Values(ncclInt8,
+                                                ncclUint8,
+                                                ncclInt32,
+                                                ncclUint32,
+                                                ncclInt64,
+                                                ncclUint64,
+                                                //ncclFloat16,
+                                                ncclFloat32,
+                                                ncclFloat64,
+                                                ncclBfloat16),
+                                // Number of elements
+                                testing::Values(1024, 1048576),
+                                // Number of devices
+                                testing::Values(2,3,4),
+                                // In-place or not
+                                testing::Values(false, true),
+                                testing::Values("")),
+                            CorrectnessTest::PrintToStringParamName());
+} // namespace