324 lines
14 KiB
C++
324 lines
14 KiB
C++
/*==============================================================================
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Solver Manager
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This class handles the Execution Context mssage containing a time stamp and a
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set of variable value assignments.It manages a time sorted queue and dispatches
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the first application execution context to the solver when the solver is ready.
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The solution returned for a given execution context will be published together
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with the execution context and the maximal utility value found by the solver.
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The solver actor class is given as a template argument to the solver manager,
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and at least one solver actor is instantiated at start up. This to allow
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multiple solvers to run in parallel should this be necessary to serve properly
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the queue of waiting application execution contexts. If there are multiple
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objects defined, they have to be optimised individualy, and for this purpose
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it would also be useful to have multiple solvers running in parallel working
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on the same problem, but for different objective functions. This will reduce
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the time to find the Pareto front [1] for the multi-objective optimisation
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problem.
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The functionality of receiving and maintaining the work queue separately from
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the solver is done to avoid blocking the reception of new execution contexts
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while the solver searches for a solution in separate threads. This is done
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for other entities to use the solver to find the optised configuration, i.e.
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feasible value assignments to all propblem variables, maximising the givne
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utiliy for a particular set of independent metric variables, i.e. the
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application execution context. The idea is that other components may use
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the solver in this way to produce training sets for machine learning methods
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that aims to estimate the application's performance indicators or even the
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change in utility as a function of the varying the metric values of the
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application execution context.
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References:
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[1] https://en.wikipedia.org/wiki/Pareto_front
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Author and Copyright: Geir Horn, University of Oslo
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Contact: Geir.Horn@mn.uio.no
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License: MPL2.0 (https://www.mozilla.org/en-US/MPL/2.0/)
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==============================================================================*/
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#ifndef NEBULOUS_SOLUTION_MANAGER
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#define NEBULOUS_SOLUTION_MANAGER
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// Standard headers
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#include <string_view> // Constant strings
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#include <string> // Normal strings
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#include <map> // Multimap for the work queue
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#include <unordered_set> // Solver ready status
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#include <list> // Pool of local solvers
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#include <ranges> // Range based views
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#include <algorithm> // Standard algorithms
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#include <iterator> // For inserters
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#include <sstream> // For nice error messages
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#include <stdexcept> // Standard exceptions
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#include <source_location> // Error location reporting
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#include <condition_variable> // Execution stop management
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#include <mutex> // Lock the condtion variable
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#include <tuple> // For constructing solvers
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// Other packages
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#include <nlohmann/json.hpp> // JSON object definition
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using JSON = nlohmann::json; // Short form name space
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#include <boost/core/demangle.hpp> // To print readable types
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// Theron++ headers
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#include "Actor.hpp" // Actor base class
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#include "Utility/StandardFallbackHandler.hpp" // Exception unhanded messages
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#include "Communication/NetworkingActor.hpp" // Networking actors
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// AMQ communication headers
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#include "Communication/AMQ/AMQjson.hpp" // For JSON metric messages
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#include "Communication/AMQ/AMQEndpoint.hpp" // For AMQ related things
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// NebulOuS headers
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#include "ExecutionControl.hpp" // Shut down messages
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#include "Solver.hpp" // The basic solver class
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namespace NebulOuS
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{
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/*==============================================================================
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Solution Manager
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==============================================================================*/
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template< SolverAlgorithm SolverType >
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class SolverManager
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: virtual public Theron::Actor,
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virtual public Theron::StandardFallbackHandler,
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virtual public Theron::NetworkingActor<
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typename Theron::AMQ::Message::PayloadType >,
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virtual public ExecutionControl
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{
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// There is a topic name used to publish solutions found by the solvers. This
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// topic is given to the constructor and kept as a constant during the class
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// execution.
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private:
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const Theron::AMQ::TopicName SolutionReceiver;
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// --------------------------------------------------------------------------
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// Solver management
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// --------------------------------------------------------------------------
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//
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// The solution manager dispatches the application execution contexts as
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// requests for solutions to a pool of solvers.
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std::list< SolverType > SolverPool;
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std::unordered_set< Address > ActiveSolvers, PassiveSolvers;
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// --------------------------------------------------------------------------
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// Application Execution Context management
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// --------------------------------------------------------------------------
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//
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// The contexts are dispatched in time sorted order. However, the time
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// to solve a problem depends on the complexity of the the context and the
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// results may therefore become available out-of-order. Each application
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// execution context should carry a unique identifier, and this is used as
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// the index key for quickly finding the right execution context. There is
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// a second view of the queue of application context where the identifiers
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// are sorted based on their time stamp.
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std::unordered_map< Solver::ContextIdentifierType,
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Solver:: ApplicationExecutionContext > Contexts;
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std::multimap< Solver::TimePointType, Solver::ContextIdentifierType >
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ContextExecutionQueue;
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// When the new applicaton execution context message arrives, it will be
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// queued, and its time point recoreded. If there are passive solvers,
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// the handler will immediately dispatch the contexts to each of these in
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// time order. Essentially, it implements a 'riffle' for the passive solvers
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// and the pending contexts.The issue is that there are likely different
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// cardinalities of the two sets, and the solvers should be marked as
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// active after the dispatch and the context identifiers should be
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// removed from the queue after the dispatch.
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void DispatchToSolvers( void )
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{
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if( !PassiveSolvers.empty() && !ContextExecutionQueue.empty() )
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{
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for( const auto & [ SolverAddress, ContextElement ] :
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std::ranges::views::zip( PassiveSolvers, ContextExecutionQueue ) )
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Send( Contexts.at( ContextElement.second ), SolverAddress );
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// The number of contexts dispatched must equal the minimum of the
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// available solvers and the available contexts.
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std::size_t DispatchedContexts
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= std::min( PassiveSolvers.size(), ContextExecutionQueue.size() );
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// Then move the passive solver addresses used to active solver addresses
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std::ranges::move(
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std::ranges::subrange( PassiveSolvers.begin(),
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std::ranges::next( PassiveSolvers.begin(), DispatchedContexts,
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PassiveSolvers.end() ) ),
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std::inserter( ActiveSolvers, ActiveSolvers.end() ) );
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// Then the dispatched context identifiers are removed from queue
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ContextExecutionQueue.erase( ContextExecutionQueue.begin(),
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std::ranges::next( ContextExecutionQueue.begin(), DispatchedContexts,
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ContextExecutionQueue.end() ) );
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}
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}
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// The handler function simply enqueues the received context, records its
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// timesamp and dispatch as many contexts as possible to the solvers. Note
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// that the context identifiers must be unique and there is a logic error
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// if there is already a context with the same identifier. Then an invalid
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// arguemtn exception will be thrown. This strategy should be reconsidered
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// if there will be multiple entities firing execution contexts.
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void HandleApplicationExecutionContext(
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const Solver:: ApplicationExecutionContext & TheContext,
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const Address TheRequester )
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{
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auto [_, Success] = Contexts.try_emplace(
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TheContext[ Solver::ContextIdentifier.data() ], TheContext );
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if( Success )
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{
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ContextExecutionQueue.emplace(
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TheContext[ Solver::TimeStamp.data() ],
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TheContext[ Solver::ContextIdentifier.data() ] );
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DispatchToSolvers();
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}
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else
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{
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std::source_location Location = std::source_location::current();
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std::ostringstream ErrorMessage;
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ErrorMessage << "[" << Location.file_name() << " at line "
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<< Location.line()
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<< "in function " << Location.function_name() <<"] "
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<< "An Application Execution Context with identifier "
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<< TheContext[ Solver::ContextIdentifier.data() ]
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<< " was received while there is already one with the same "
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<< "identifer. The identifiers must be unique!";
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throw std::invalid_argument( ErrorMessage.str() );
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}
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}
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// --------------------------------------------------------------------------
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// Solutions
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// --------------------------------------------------------------------------
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//
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// When a solution is received from a solver, it will be dispatched to all
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// entities subscribing to the solution topic, and the solver will be returned
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// to the pool of passive solvers. The dispatch function will be called at the
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// end to ensure that the solver starts working on queued application execution
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// contexts, if any.
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void PublishSolution( const Solver::Solution & TheSolution,
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const Address TheSolver )
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{
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Send( TheSolution, SolutionReceiver );
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PassiveSolvers.insert( ActiveSolvers.extract( TheSolver ) );
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DispatchToSolvers();
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}
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// --------------------------------------------------------------------------
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// Constructor and destructor
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// --------------------------------------------------------------------------
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//
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// The constructor takes the name of the Solution Mnager Actor, the name of
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// the topic where the solutions should be published, and the topic where the
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// application execution contexts will be published. If the latter is empty,
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// the manager will not listen to any externally generated requests, only those
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// being sent from the Metric Updater supposed to exist on the same Actor
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// system node as the manager.The final arguments to the constructor is a
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// set of arguments to the solver type in the order expected by the solver
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// type and repeated for the number of (local) solvers that should be created.
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//
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// Currently this manager does not support dispatching configurations to
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// remote solvers and collect responses from these. However, this can be
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// circumvented by creating a local "solver" transferring the requests to
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// a remote solvers and collecting results from the remote solver.
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public:
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template< typename ...SolverArgTypes >
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SolverManager( const std::string & TheActorName,
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const Theron::AMQ::TopicName & SolutionTopic,
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const Theron::AMQ::TopicName & ContextPublisherTopic,
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const unsigned int NumberOfSolvers,
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const std::string SolverRootName,
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SolverArgTypes && ...SolverArguments )
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: Actor( TheActorName ),
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StandardFallbackHandler( Actor::GetAddress().AsString() ),
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NetworkingActor( Actor::GetAddress().AsString() ),
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ExecutionControl( Actor::GetAddress().AsString() ),
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SolutionReceiver( SolutionTopic ),
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SolverPool(), ActiveSolvers(), PassiveSolvers(),
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Contexts(), ContextExecutionQueue()
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{
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// The solvers are created by expanding the arguments for the solvers
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// one by one creating new elements in the solver pool. The solvers
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// will be named with a sequence number from 1 and up added to the
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// root solver name, e.g., if the root name is "MySolver" the solvers
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// will have names "MySolver_1", "MySolver_2",... and so forth. Since
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// all solvers are of the same type they should take the same arguments
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// and so the given arguments are just fowarded to each solver constructor.
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for( unsigned int i = 1; i <= NumberOfSolvers; i++ )
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{
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std::ostringstream TheSolverName;
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TheSolverName << SolverRootName << "_" << i;
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SolverPool.emplace_back( TheSolverName.str(),
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std::forward< SolverArgTypes >(SolverArguments)... );
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}
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// If the solvers were successfully created, their addresses are recorded as
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// passive servers, and a publisher is made for the solution channel, and
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// optionally, a subscritpion is made for the alternative context publisher
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// topic. If the solvers could not be created, then an invalid argument
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// exception will be thrown.
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if( !SolverPool.empty() )
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{
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std::ranges::transform( SolverPool,
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std::inserter( PassiveSolvers, PassiveSolvers.end() ),
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[](const SolverType & TheSolver){ return TheSolver.GetAddress(); } );
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Send( Theron::AMQ::NetworkLayer::TopicSubscription(
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Theron::AMQ::NetworkLayer::TopicSubscription::Action::Publisher,
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SolutionTopic ), GetSessionLayerAddress() );
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if( !ContextPublisherTopic.empty() )
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Send( Theron::AMQ::NetworkLayer::TopicSubscription(
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Theron::AMQ::NetworkLayer::TopicSubscription::Action::Subscription,
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ContextPublisherTopic ), GetSessionLayerAddress() );
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}
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else
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{
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std::source_location Location = std::source_location::current();
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std::ostringstream ErrorMessage;
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ErrorMessage << "[" << Location.file_name() << " at line "
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<< Location.line()
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<< "in function " << Location.function_name() <<"] "
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<< "It was not possible to construct any solver of type "
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<< boost::core::demangle( typeid( SolverType ).name() )
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<< " from the given constructor argument types: ";
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(( ErrorMessage << boost::core::demangle( typeid( SolverArguments ).name() ) << " " ), ... );
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throw std::invalid_argument( ErrorMessage.str() );
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}
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}
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};
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} // namespace NebulOuS
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#endif // NEBULOUS_SOLUTION_MANAGER
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