Limitations - 2024.1 English

There are some limitations with the use of hls::stream_of_blocks that you should be aware of:

• Each hls::stream_of_blocks object must have a single producer and consumer process, and each process must be different. In other words, local streams-of-blocks within a single process are not supported.
• You cannot use hls::stream_of_blocks within a sequential region. The producer and consumer must be separate concurrent processes in a dataflow region.
• You cannot use multiple nested acquire/release statements (write_lock/read_lock), for example in the same or nested scopes, as shown in the following example:

  using ppbuf = int[N];
  void readerImplicitNested(hls::stream_of_blocks<ppbuf>& in, ...) {
      for(unsigned j = 0; j < M; ++j) {
         hls::read_lock<ppbuf> arrA(in); // constructor would acquire A first
         hls::read_lock<ppbuf> arrB(in); // constructor would acquire B second
         for(unsigned i = 0; i < N; ++i)
             ... = arrA[f(i)] + arrB[g(i)];
         // destructor would release B first
         // destructor would release A second
      }
  }

  However, you can use multiple sequential or mutually exclusive acquire/release statements (write_lock/read_lock), for example inside IF/ELSE branches or in two subsequent code blocks. This is shown in the following example:

  void readerImplicitNested(hls::stream_of_blocks<ppbuf>& in, ...) {
   for(unsigned j = 0; j < M; ++j) {
    {
      hls::read_lock<ppbuf> arrA(in); // constructor acquires A
      for(unsigned i = 0; i < N; ++i)
        ... = arrA[f(i)];
      // destructor releases A
    }
    {
      hls::read_lock<ppbuf> arrB(in); // constructor acquires B
      for(unsigned i = 0; i < N; ++i)
        ... = arrB[g(i)];
      // destructor releases B
    }
   }
  }

• Explicit release of locks in producer and consumer processes are not recommended, as they are automatically released when they go out of scope. However, you can use these by adding #define EXPLICIT_ACQUIRE_RELEASE before #include "hls_streamofblocks.h in your source code.