Fix an issue when reading blocks in streaming mode, when some produce…

…rs did not write any block to output. (ornladios#4332)

(cherry picked from commit 75d801f)

source/adios2/toolkit/format/bp5/BP5Deserializer.cpp

@@ -1580,7 +1580,7 @@ BP5Deserializer::GenerateReadRequests(const bool doAllocTempBuffers, size_t *max
                     MetaArrayRecOperator *writer_meta_base =
                         (MetaArrayRecOperator *)GetMetadataBase((struct BP5VarRec *)Req->VarRec,
                                                                 Step, WriterRank);
-                    if (!writer_meta_base)
+                    if (!writer_meta_base || !writer_meta_base->BlockCount)
                     {
                         continue; // Not writen on this step
                     }

testing/adios2/engine/bp/TestBPWriteReadLocalVariables.cpp

@@ -1798,6 +1798,200 @@ TEST_F(BPWriteReadLocalVariables, ADIOS2BPWriteReadLocal2DChangeCount)
     }
 }
 
+template <class T>
+void print_vector(std::vector<T> &v)
+{
+    std::cout << "{ ";
+    for (auto &e : v)
+    {
+        std::cout << e << " ";
+    }
+    std::cout << "}" << std::endl;
+}
+
+template <class T, size_t N>
+void print_array(std::array<T, N> &a)
+{
+    std::cout << "{ ";
+    for (auto &e : a)
+    {
+        std::cout << e << " ";
+    }
+    std::cout << "}" << std::endl;
+}
+
+TEST_F(BPWriteReadLocalVariables, ADIOS2BPWriteReadLocalVaryingNumberOfBlocks)
+{
+    /* Write different number of blocks per step, skipping some rank in some steps.
+       Each block size is different too. Test reading each block properly.
+       Only the first 8 MPI ranks do work, the others just loop empty.
+    */
+    constexpr int NSTEPS = 3;
+    constexpr int MAXMPISIZE = 8;
+    const int blocks[NSTEPS][MAXMPISIZE] = {
+        {1, 1, 1, 1, 1, 1, 1, 1},
+        {1, 0, 1, 0, 1, 0, 1, 0},
+        {0, 1, 0, 1, 0, 1, 0, 1},
+    };
+    const size_t blocksizes[NSTEPS][MAXMPISIZE] = {
+        {9, 8, 7, 6, 5, 6, 7, 3},
+        {2, 0, 4, 0, 6, 0, 9, 0},
+        {0, 1, 0, 4, 0, 7, 0, 5},
+    };
+
+    int mpiRank = 0;
+    int mpiSize = 1;
+#if ADIOS2_USE_MPI
+    MPI_Comm_rank(MPI_COMM_WORLD, &mpiRank);
+    MPI_Comm_size(MPI_COMM_WORLD, &mpiSize);
+    const std::string fname("BPWRLocalVaryingNumberOfBlocks_" + engineName + "_MPI.bp");
+#else
+    const std::string fname("BPWRLocalVaryingNumberOfBlocks_" + engineName + ".bp");
+#endif
+
+#if ADIOS2_USE_MPI
+    adios2::ADIOS adios(MPI_COMM_WORLD);
+#else
+    adios2::ADIOS adios;
+#endif
+    {
+        adios2::IO io = adios.DeclareIO("TestIO");
+        const adios2::Dims shape{};
+        const adios2::Dims start{};
+        const adios2::Dims count{(size_t)1};
+
+        auto var_r32 = io.DefineVariable<float>("r32", shape, start, count);
+
+        adios2::Engine bpWriter = io.Open(fname, adios2::Mode::Write);
+
+        for (int step = 0; step < NSTEPS; ++step)
+        {
+            std::cout << "--- generateNewSmallTestData Step " << step << " rank " << mpiRank
+                      << " nprocs " << mpiSize << " ---" << std::endl;
+            SmallTestData currentTestData =
+                generateNewSmallTestData(m_TestData, static_cast<int>(step), mpiRank, mpiSize);
+            print_array(currentTestData.R32);
+
+            int bpos = (mpiRank < MAXMPISIZE ? mpiRank : -1);
+
+            bpWriter.BeginStep();
+            if (bpos >= 0 && blocks[step][bpos])
+            {
+                size_t nx = blocksizes[step][bpos];
+                var_r32.SetSelection({{}, {nx}});
+                bpWriter.Put(var_r32, currentTestData.R32.data());
+            }
+            bpWriter.EndStep();
+        }
+        bpWriter.Close();
+    }
+#if ADIOS2_USE_MPI
+    MPI_Barrier(MPI_COMM_WORLD);
+#endif
+
+    if (!mpiRank)
+    {
+        adios2::IO io = adios.DeclareIO("ReaderIO");
+#if ADIOS2_USE_MPI
+        adios2::Engine bpReader = io.Open(fname, adios2::Mode::Read, MPI_COMM_SELF);
+#else
+        adios2::Engine bpReader = io.Open(fname, adios2::Mode::Read);
+#endif
+
+        for (int step = 0; step < NSTEPS; ++step)
+        {
+            std::cout << "====== Read Step " << step << " ==========" << std::endl;
+            bpReader.BeginStep();
+            auto var_r32 = io.InquireVariable<float>("r32");
+
+            size_t nblocks = 0;
+            int nproc = (mpiSize < MAXMPISIZE ? mpiSize : MAXMPISIZE);
+            for (size_t b = 0; b < static_cast<size_t>(nproc); ++b)
+            {
+                if (blocks[step][b] == 0)
+                {
+                    continue;
+                }
+
+                std::cout << "  --- generateNewSmallTestData Step " << step << " rank " << mpiRank
+                          << " nprocs " << mpiSize << " b=" << b << " nblocks=" << nblocks << " ---"
+                          << std::endl;
+                SmallTestData currentTestData = generateNewSmallTestData(
+                    m_TestData, static_cast<int>(step), static_cast<int>(b), mpiSize);
+                print_array(currentTestData.R32);
+
+                var_r32.SetBlockSelection(nblocks);
+                std::vector<float> dataIn;
+                bpReader.Get(var_r32, dataIn, adios2::Mode::Sync);
+                EXPECT_EQ(dataIn.size(), blocksizes[step][b]);
+
+                for (size_t i = 0; i < dataIn.size(); ++i)
+                {
+                    EXPECT_EQ(dataIn[i], currentTestData.R32[i]);
+                }
+
+                ++nblocks;
+            }
+            bpReader.EndStep();
+        }
+        bpReader.Close();
+    }
+#if ADIOS2_USE_MPI
+    MPI_Barrier(MPI_COMM_WORLD);
+#endif
+
+    if (!mpiRank)
+    {
+        adios2::IO io = adios.DeclareIO("ReaderIORRA");
+#if ADIOS2_USE_MPI
+        adios2::Engine bpReader = io.Open(fname, adios2::Mode::ReadRandomAccess, MPI_COMM_SELF);
+#else
+        adios2::Engine bpReader = io.Open(fname, adios2::Mode::ReadRandomAccess);
+#endif
+
+        auto var_r32 = io.InquireVariable<float>("r32");
+
+        for (int step = 0; step < NSTEPS; ++step)
+        {
+            std::cout << "====== Read Step " << step << " ==========" << std::endl;
+            var_r32.SetStepSelection({step, 1});
+
+            size_t nblocks = 0;
+            int nproc = (mpiSize < MAXMPISIZE ? mpiSize : MAXMPISIZE);
+            for (size_t b = 0; b < static_cast<size_t>(nproc); ++b)
+            {
+                if (blocks[step][b] == 0)
+                {
+                    continue;
+                }
+
+                std::cout << "  --- generateNewSmallTestData Step " << step << " rank " << mpiRank
+                          << " nprocs " << mpiSize << " b=" << b << " nblocks=" << nblocks << " ---"
+                          << std::endl;
+                SmallTestData currentTestData = generateNewSmallTestData(
+                    m_TestData, static_cast<int>(step), static_cast<int>(b), mpiSize);
+                print_array(currentTestData.R32);
+
+                var_r32.SetBlockSelection(nblocks);
+                std::vector<float> dataIn;
+                bpReader.Get(var_r32, dataIn, adios2::Mode::Sync);
+                EXPECT_EQ(dataIn.size(), blocksizes[step][b]);
+
+                for (size_t i = 0; i < dataIn.size(); ++i)
+                {
+                    EXPECT_EQ(dataIn[i], currentTestData.R32[i]);
+                }
+
+                ++nblocks;
+            }
+        }
+        bpReader.Close();
+    }
+#if ADIOS2_USE_MPI
+    MPI_Barrier(MPI_COMM_WORLD);
+#endif
+}
+
 int main(int argc, char **argv)
 {
 #if ADIOS2_USE_MPI