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BCL

The Berkeley Container Library is a C++ library of distributed data structures with interfaces similar to those in STL containers.

Example

  BCL::HashMap<std::string, int> map(1000);

  map[std::to_string(BCL::rank())] = BCL::rank();

  BCL::barrier();

  if (BCL::rank() == 0) {
    for (size_t i = 0; i < BCL::nprocs(); i++) {
      int value = *map.find(std::string(i), value);
      printf("Got key, val %s, %lu\n",
             std::to_string(i).c_str(), value);
    }
  }

Design

Global Pointers

BCL data structures are designed to operate using only one-sided operations that can be executed with RDMA. Under the hood, BCL data structures are implemented using the BCL Core, which is a small API based around global pointers, which are C++ objects that can be used like regular pointers, but reference memory that may lie on another process or node.

  BCL::GlobalPtr<int> ptr = nullptr;

  if (BCL::rank() == 0) {
    ptr = BCL::alloc<int>(BCL::nprocs());
  }

  ptr = BCL::broadcast(ptr, 0);

  ptr[BCL::rank()] = BCL::rank();

  if (BCL::rank() == 1) {
    for (size_t i = 0; i < BCL::nprocs(); i++) {
      int local_val = local_ptr[i];
      printf("%lu: %lu\n", i, local_ptr[i]);
    }
  }

Backends

The BCL Core works by calling a small set of backend functions that do things like read or write from remote memory. The interface is designed to make it easy to implement new backend functions, and we have implemented backends for MPI, OpenSHMEM, and GASNet-EX.

Compiling BCL Programs

BCL is a header-only library, so to compile a program with BCL, you only need to include the necessary BCL header files and compile as normal for your backend.

[xiii@shini example-dir]$ vi hello.cpp
[xiii@shini example-dir]$ mpic++ hello.cpp -o hello -std=gnu++17 -O3 -I $HOME/src/BCL
[xiii@shini example-dir]$ mpirun -n 4 ./hello
Hello, BCL! I am rank 1/4.
Hello, BCL! I am rank 0/4.
Hello, BCL! I am rank 2/4.
Hello, BCL! I am rank 3/4.

MPI is the default backend, and you can explicitly select a backend with the compiler directives -DMPI, -DSHMEM, and -DGASNET_EX. See /bcl/bcl.hpp for details.

Example Programs

You can find example BCL programs in the /examples directory. We recommend you start with /examples/simple, which covers basic functions in the BCL Core.

Bugs

Please let us know if you identify any bugs or general usability issues by creating an issue on GitHub or directly contacting the authors.

Academic Papers

[ICPP'19] "BCL: A Cross-Platform Distributed Container Library"

Blog Posts

[1] "Creating Expressive C++ Smart Pointers for Remote Memory"

[2] "Storing C++ Objects in Distributed Memory"

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