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diagram_builder.cc
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diagram_builder.cc
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#include "drake/systems/framework/diagram_builder.h"
#include <algorithm>
#include <sstream>
#include <stdexcept>
#include <tuple>
#include <unordered_map>
#include "drake/common/drake_assert.h"
#include "drake/common/drake_throw.h"
namespace drake {
namespace systems {
template <typename T>
DiagramBuilder<T>::DiagramBuilder() {}
template <typename T>
DiagramBuilder<T>::~DiagramBuilder() {}
template <typename T>
std::vector<const System<T>*> DiagramBuilder<T>::GetSystems() const {
std::vector<const System<T>*> result;
result.reserve(registered_systems_.size());
for (const auto& system : registered_systems_) {
result.push_back(system.get());
}
return result;
}
template <typename T>
std::vector<System<T>*> DiagramBuilder<T>::GetMutableSystems() {
std::vector<System<T>*> result;
result.reserve(registered_systems_.size());
for (const auto& system : registered_systems_) {
result.push_back(system.get());
}
return result;
}
template <typename T>
void DiagramBuilder<T>::Connect(
const OutputPort<T>& src,
const InputPort<T>& dest) {
InputPortLocator dest_id{&dest.get_system(), dest.get_index()};
OutputPortLocator src_id{&src.get_system(), src.get_index()};
ThrowIfSystemNotRegistered(&src.get_system());
ThrowIfSystemNotRegistered(&dest.get_system());
ThrowIfInputAlreadyWired(dest_id);
if (src.get_data_type() != dest.get_data_type()) {
throw std::logic_error(fmt::format(
"DiagramBuilder::Connect: Cannot mix vector-valued and abstract-"
"valued ports while connecting output port {} of System {} to "
"input port {} of System {}",
src.get_name(), src.get_system().get_name(),
dest.get_name(), dest.get_system().get_name()));
}
if ((src.get_data_type() != kAbstractValued) &&
(src.size() != dest.size())) {
throw std::logic_error(fmt::format(
"DiagramBuilder::Connect: Mismatched vector sizes while connecting "
"output port {} of System {} (size {}) to "
"input port {} of System {} (size {})",
src.get_name(), src.get_system().get_name(), src.size(),
dest.get_name(), dest.get_system().get_name(), dest.size()));
}
if (src.get_data_type() == kAbstractValued) {
auto model_output = src.Allocate();
auto model_input = dest.get_system().AllocateInputAbstract(dest);
const std::type_info& output_type = model_output->static_type_info();
const std::type_info& input_type = model_input->static_type_info();
if (output_type != input_type) {
throw std::logic_error(fmt::format(
"DiagramBuilder::Connect: Mismatched value types while connecting "
"output port {} of System {} (type {}) to "
"input port {} of System {} (type {})",
src.get_name(), src.get_system().get_name(),
NiceTypeName::Get(output_type),
dest.get_name(), dest.get_system().get_name(),
NiceTypeName::Get(input_type)));
}
}
connection_map_[dest_id] = src_id;
}
template <typename T>
void DiagramBuilder<T>::Connect(const System<T>& src, const System<T>& dest) {
DRAKE_THROW_UNLESS(src.num_output_ports() == 1);
DRAKE_THROW_UNLESS(dest.num_input_ports() == 1);
Connect(src.get_output_port(0), dest.get_input_port(0));
}
template <typename T>
void DiagramBuilder<T>::Cascade(const System<T>& src, const System<T>& dest) {
Connect(src, dest);
}
template <typename T>
InputPortIndex DiagramBuilder<T>::ExportInput(
const InputPort<T>& input,
std::variant<std::string, UseDefaultName> name) {
const InputPortIndex diagram_port_index = DeclareInput(input, name);
ConnectInput(diagram_port_index, input);
return diagram_port_index;
}
template <typename T>
InputPortIndex DiagramBuilder<T>::DeclareInput(
const InputPort<T>& input,
std::variant<std::string, UseDefaultName> name) {
InputPortLocator id{&input.get_system(), input.get_index()};
ThrowIfSystemNotRegistered(&input.get_system());
// The requirement that subsystem names are unique guarantees uniqueness
// of the port names.
std::string port_name =
name == kUseDefaultName
? input.get_system().get_name() + "_" + input.get_name()
: std::get<std::string>(std::move(name));
DRAKE_DEMAND(!port_name.empty());
// Reject duplicate declarations.
if (diagram_input_indices_.count(port_name) != 0) {
throw std::logic_error(
fmt::format("Diagram already has an input port named {}", port_name));
}
// Save bookkeeping data.
const auto return_id = InputPortIndex(diagram_input_data_.size());
diagram_input_indices_[port_name] = return_id;
diagram_input_data_.push_back({id, port_name});
return return_id;
}
template <typename T>
void DiagramBuilder<T>::ConnectInput(
const std::string& diagram_port_name, const InputPort<T>& input) {
DRAKE_THROW_UNLESS(diagram_input_indices_.count(diagram_port_name));
ConnectInput(diagram_input_indices_[diagram_port_name], input);
}
template <typename T>
void DiagramBuilder<T>::ConnectInput(
InputPortIndex diagram_port_index, const InputPort<T>& input) {
InputPortLocator id{&input.get_system(), input.get_index()};
ThrowIfInputAlreadyWired(id);
ThrowIfSystemNotRegistered(&input.get_system());
DRAKE_THROW_UNLESS(
diagram_port_index < InputPortIndex(diagram_input_data_.size()));
// Check that port types match.
const ExportedInputData& data = diagram_input_data_[diagram_port_index];
const InputPortLocator& model_id = data.model_input;
const std::string& port_name = data.name;
const InputPort<T>& model = model_id.first->get_input_port(model_id.second);
if (model.get_data_type() != input.get_data_type()) {
throw std::logic_error(fmt::format(
"DiagramBuilder::ConnectInput: Cannot mix vector-valued and abstract-"
"valued ports while connecting input port {} of System {} to "
"input port {} of Diagram",
input.get_name(), input.get_system().get_name(), port_name));
}
if ((model.get_data_type() != kAbstractValued) &&
(model.size() != input.size())) {
throw std::logic_error(fmt::format(
"DiagramBuilder::ConnectInput: Mismatched vector sizes while "
"connecting input port {} of System {} (size {}) to "
"input port {} of Diagram (size {})",
input.get_name(), input.get_system().get_name(), input.size(),
port_name, model.size()));
}
if (model.get_data_type() == kAbstractValued) {
auto model_model = model.get_system().AllocateInputAbstract(model);
auto model_input = input.get_system().AllocateInputAbstract(input);
const std::type_info& model_type = model_model->static_type_info();
const std::type_info& input_type = model_input->static_type_info();
if (model_type != input_type) {
throw std::logic_error(fmt::format(
"DiagramBuilder::ConnectInput: Mismatched value types while "
"connecting input port {} of System {} (type {}) to "
"input port {} of Diagram (type {})",
input.get_name(), input.get_system().get_name(),
NiceTypeName::Get(input_type),
port_name, NiceTypeName::Get(model_type)));
}
}
// Write down connection information.
input_port_ids_.push_back(id);
input_port_names_.push_back(port_name);
diagram_input_set_.insert(id);
}
template <typename T>
OutputPortIndex DiagramBuilder<T>::ExportOutput(
const OutputPort<T>& output,
std::variant<std::string, UseDefaultName> name) {
ThrowIfSystemNotRegistered(&output.get_system());
OutputPortIndex return_id(output_port_ids_.size());
output_port_ids_.push_back(
OutputPortLocator{&output.get_system(), output.get_index()});
// The requirement that subsystem names are unique guarantees uniqueness
// of the port names.
std::string port_name =
name == kUseDefaultName
? output.get_system().get_name() + "_" + output.get_name()
: std::get<std::string>(std::move(name));
DRAKE_DEMAND(!port_name.empty());
output_port_names_.emplace_back(std::move(port_name));
return return_id;
}
template <typename T>
std::unique_ptr<Diagram<T>> DiagramBuilder<T>::Build() {
std::unique_ptr<Diagram<T>> diagram(new Diagram<T>(Compile()));
return diagram;
}
template <typename T>
void DiagramBuilder<T>::BuildInto(Diagram<T>* target) {
target->Initialize(Compile());
}
template <typename T>
void DiagramBuilder<T>::ThrowIfInputAlreadyWired(
const InputPortLocator& id) const {
if (connection_map_.find(id) != connection_map_.end() ||
diagram_input_set_.find(id) != diagram_input_set_.end()) {
throw std::logic_error("Input port is already wired.");
}
}
template <typename T>
void DiagramBuilder<T>::ThrowIfSystemNotRegistered(
const System<T>* system) const {
DRAKE_DEMAND(system != nullptr);
if (systems_.count(system) == 0) {
throw std::logic_error(fmt::format(
"DiagramBuilder: Cannot operate on ports of System {} "
"until it has been registered using AddSystem",
system->get_name()));
}
}
namespace {
using EitherPortIndex = std::variant<InputPortIndex, OutputPortIndex>;
// The PortIdentifier must be appropriate to use in a sorted collection. Thus,
// we place its two integer indices first, because they form a unique key on
// their own (the variant disambiguates input vs output indices, even though
// their integer values overlap). The SystemBase* field is supplementary (and
// only used during error reporting).
using PortIdentifier = std::tuple<
SubsystemIndex, EitherPortIndex, const SystemBase*>;
bool is_input_port(const PortIdentifier& node) {
const EitherPortIndex& either = std::get<1>(node);
return either.index() == 0;
}
std::string to_string(const PortIdentifier& port_id) {
const SystemBase* const system = std::get<2>(port_id);
const EitherPortIndex& index = std::get<1>(port_id);
return is_input_port(port_id) ?
system->get_input_port_base(std::get<0>(index)).GetFullDescription() :
system->get_output_port_base(std::get<1>(index)).GetFullDescription();
}
// Helper to do the algebraic loop test. It recursively performs the
// depth-first search on the graph to find cycles.
bool HasCycleRecurse(
const PortIdentifier& n,
const std::map<PortIdentifier, std::set<PortIdentifier>>& edges,
std::set<PortIdentifier>* visited,
std::vector<PortIdentifier>* stack) {
DRAKE_ASSERT(visited->count(n) == 0);
visited->insert(n);
auto edge_iter = edges.find(n);
if (edge_iter != edges.end()) {
DRAKE_ASSERT(std::find(stack->begin(), stack->end(), n) == stack->end());
stack->push_back(n);
for (const auto& target : edge_iter->second) {
if (visited->count(target) == 0 &&
HasCycleRecurse(target, edges, visited, stack)) {
return true;
} else if (std::find(stack->begin(), stack->end(), target) !=
stack->end()) {
return true;
}
}
stack->pop_back();
}
return false;
}
} // namespace
template <typename T>
void DiagramBuilder<T>::ThrowIfAlgebraicLoopsExist() const {
// To discover loops, we will construct a digraph and check it for cycles.
// The nodes in the digraph are the input and output ports mentioned by the
// diagram's internal connections. Ports that are not internally connected
// cannot participate in a cycle, so we don't include them in the nodes set.
std::set<PortIdentifier> nodes;
// The edges in the digraph are a directed "influences" relation: for each
// `value` in `edges[key]`, the `key` influences `value`. (This is the
// opposite of the "depends-on" relation.)
std::map<PortIdentifier, std::set<PortIdentifier>> edges;
// Create a lookup table from system pointer to subsystem index.
std::unordered_map<const SystemBase*, SubsystemIndex> system_to_index;
for (SubsystemIndex i{0}; i < registered_systems_.size(); ++i) {
system_to_index.emplace(registered_systems_[i].get(), i);
}
// Add the diagram's internal connections to the digraph nodes *and* edges.
// The output port influences the input port.
for (const auto& item : connection_map_) {
const SystemBase* const input_system = item.first.first;
const InputPortIndex input_index = item.first.second;
const SystemBase* const output_system = item.second.first;
const OutputPortIndex output_index = item.second.second;
const PortIdentifier input{
system_to_index.at(input_system), input_index, input_system};
const PortIdentifier output{
system_to_index.at(output_system), output_index, output_system};
nodes.insert(input);
nodes.insert(output);
edges[output].insert(input);
}
// Add more edges (*not* nodes) based on each System's direct feedthrough.
// An input port influences an output port iff there is direct feedthrough
// from that input to that output. If a feedthrough edge refers to a port
// not in `nodes`, we omit it because ports that are not connected inside the
// diagram cannot participate in a cycle.
for (const auto& system_ptr : registered_systems_) {
const SystemBase* const system = system_ptr.get();
for (const auto& item : system->GetDirectFeedthroughs()) {
const SubsystemIndex subsystem_index = system_to_index.at(system);
const PortIdentifier input{
subsystem_index, InputPortIndex{item.first}, system};
const PortIdentifier output{
subsystem_index, OutputPortIndex{item.second}, system};
if (nodes.count(input) > 0 && nodes.count(output) > 0) {
edges[input].insert(output);
}
}
}
static constexpr char kAdvice[] =
"A System may have conservatively reported that one of its output ports "
"depends on an input port, making one of the 'is direct-feedthrough to' "
"lines above spurious. If that is the case, remove the spurious "
"dependency per the Drake API documentation for declaring output ports. "
// NOLINTNEXTLINE(whitespace/line_length)
"https://drake.mit.edu/doxygen_cxx/classdrake_1_1systems_1_1_leaf_system.html#DeclareLeafOutputPort_feedthrough";
// Evaluate the graph for cycles.
std::set<PortIdentifier> visited;
std::vector<PortIdentifier> stack;
for (const auto& node : nodes) {
if (visited.count(node) > 0) {
continue;
}
if (HasCycleRecurse(node, edges, &visited, &stack)) {
std::stringstream message;
message << "Reported algebraic loop detected in DiagramBuilder:\n";
for (const auto& item : stack) {
message << " " << to_string(item);
if (is_input_port(item)) {
message << " is direct-feedthrough to\n";
} else {
message << " is connected to\n";
}
}
message << " " << to_string(stack.front()) << "\n";
message << kAdvice;
throw std::runtime_error(message.str());
}
}
}
template <typename T>
std::unique_ptr<typename Diagram<T>::Blueprint> DiagramBuilder<T>::Compile() {
if (registered_systems_.size() == 0) {
throw std::logic_error("Cannot Compile an empty DiagramBuilder.");
}
ThrowIfAlgebraicLoopsExist();
auto blueprint = std::make_unique<typename Diagram<T>::Blueprint>();
blueprint->input_port_ids = input_port_ids_;
blueprint->input_port_names = input_port_names_;
blueprint->output_port_ids = output_port_ids_;
blueprint->output_port_names = output_port_names_;
blueprint->connection_map = connection_map_;
blueprint->systems = std::move(registered_systems_);
return blueprint;
}
} // namespace systems
} // namespace drake
DRAKE_DEFINE_CLASS_TEMPLATE_INSTANTIATIONS_ON_DEFAULT_SCALARS(
class ::drake::systems::DiagramBuilder)