README.md

Pipeline with Library

This example illustrates how to use the node library that was created in ex01_node_library. Following the pipeline in ex00_simple_pipeline, we will simply replace the source with the following:

auto source = s.construct_object<IntSource>("int_source");

Where IntSource is the compiled class from the previous example. The most important thing to note here is the call to construct_object<NodeT>(std::string name, ...args), where NodeT is the type of node to create, name is the node name, and args is a variable number of arguments. To ensure that each node can store the necessary information to function in the pipeline, we wrap all nodes in a mrc::segment::Object class. This alleviates the need to define properties like name on each and every node class. The downside here is that nodes should not be created directly, but instantiated using the construct_object function.

The construct_object function's first argument is the name to assign to the node. The same name that is used in make_source. The remainder of the arguments are passed directly into the node's constructor. So calling the following function:

auto source = s.construct_object<MySource>("source_name", 1, 2.5f, "string_argument");

Would be equivalent to:

auto source = std::make_shared<MySource>(1, 2.5f, "string_argument");

After the node is created using construct_object, the rest of the pipeline is constructed exactly the same as it was in ex00_simple_pipeline.

Running the Example

Exactly the same as ex00_simple_pipeline, we can run the pipeline and get the following output:

$ ${QSG_BUILD_DIR}/docs/quickstart/cpp/ex02_pipeline_with_library/ex02_pipeline_with_library.x
mrc pipeline starting...
sink: 2.5
sink: 5
sink: 7.5
mrc pipeline complete: counter should be 3; counter=3

Where ${QSG_BUILD_DIR} is the output location of the CMake build.