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35 #ifndef GMXAPI_CONTEXT_IMPL_H
36 #define GMXAPI_CONTEXT_IMPL_H
38 * \brief Declare gmxapi::ContextImpl
40 * \author M. Eric Irrgang <ericirrgang@gmail.com>
47 #include "gromacs/mdrun/legacymdrunoptions.h"
48 #include "gromacs/mdtypes/mdrunoptions.h"
49 #include "gromacs/utility/gmxmpi.h"
51 #include "gmxapi/context.h"
52 #include "gmxapi/session.h"
60 * \brief Provide RAII management of library MPI context.
62 * To acquire an MpiContextManager is to have assurance that any external MPI
63 * environment is ready to use. When the MpiContextManager is released or
64 * goes out of scope, the destructor finalizes the resources.
66 * It is plausible that one or more ranks may not participate in an API session,
67 * but we have not historically handled such use cases at this level.
68 * For GROMACS built with an MPI library, the root communicator in the MpiContextManager
69 * must be valid. For other builds (e.g. tMPI), the communicator member must be MPI_COMM_NULL.
71 * If the client provides a communicator, the client promises to maintain the validity
72 * of the communicator for the life of the MpiContextManager.
74 * Note that thread-MPI chooses the number of ranks and constructs its
75 * MPI communicator internally, so does not and is unlikely to ever
78 * \todo Log errors during set up or tear down.
79 * There is no resource for logging or reporting errors during initialization or when misused.
83 class MpiContextManager
87 * \brief Default constructor.
89 * Construct a valid instance with an appropriate default value for the
90 * base communicator. (Note that appropriate default value depends on whether
91 * the library was compiled with an external MPI library.)
93 * \throws BasicException if library cannot be initialized.
98 * \brief Allow the communicator to be specified.
100 * Supports use cases in which a client provides a non-default communicator.
101 * Ensures that library environment is properly initialized and finalized,
102 * whether or not an externally managed communicator has been provided.
104 * \param communicator Optional communicator representing a client-managed MPI environment.
106 * Note that the communicator must be MPI_COMM_NULL if and only if GROMACS was built without an
107 * external MPI library.
109 * \throws BasicException if library cannot be initialized.
111 * \todo (#3650?) Decide whether to exclude this from tMPI environments or find a sensible invariant.
113 explicit MpiContextManager(MPI_Comm communicator);
115 ~MpiContextManager();
118 * \brief Exclusive ownership of a scoped context means copying is impossible.
122 MpiContextManager(const MpiContextManager&) = delete;
123 MpiContextManager& operator=(const MpiContextManager&) = delete;
127 * \brief Transfer ownership of the managed GROMACS MPI context.
131 MpiContextManager(MpiContextManager&& source) noexcept = default;
132 MpiContextManager& operator=(MpiContextManager&& source) noexcept = default;
136 * \brief Get the communicator for this context.
138 * \return Communicator with an appropriate initialized state for the current library
141 * \throws gmxapi::UsageError if MpiContextManager is in an invalid state, such as after
144 [[nodiscard]] MPI_Comm communicator() const;
148 * \brief The resources provided by this manager.
150 * A valid MpiContextManager has a value for communicator_ that is appropriate
151 * for the library configuration.
153 std::unique_ptr<MPI_Comm> communicator_;
157 * \brief Context implementation.
159 * Execution contexts have a uniform interface specified by the API. Implementations for
160 * particular execution environments can specialize / derive from this base.
162 * \todo Separate interface and implementation.
164 * \warning Definition and semantics depend on configure-time details. For example,
165 * MPI-enabled libraries always hold a valid MPI communicator via MpiContextManager,
166 * whereas tMPI and non-MPI builds hold a meaningless MpiContextManager.
168 * \todo Provide functions or traits for introspection.
172 class ContextImpl final : public std::enable_shared_from_this<ContextImpl>
178 * \brief Factory function
180 * Since this class provides `shared_from_this`, we need to make sure
181 * that it never exists without a shared_ptr owning it.
183 * If we can confirm `shared_from_this` is no longer necessary, implementation may change.
184 * \todo: Use registration/deregistration of launched Sessions to log warnings on shutdown
185 * instead of letting Session keep ContextImpl alive.
187 * \return ownership of a new object
189 static std::shared_ptr<ContextImpl> create(MpiContextManager&& mpi);
192 * \brief Copy disallowed because Session state would become ambiguous.
194 * The API implementation needs to unambiguously determine
195 * which Sessions and Contexts are associated with each other.
198 ContextImpl(const ContextImpl&) = delete;
199 ContextImpl& operator=(const ContextImpl&) = delete;
203 * \brief Objects are not trivial to move.
205 * \todo Implement move semantics. Requires a moveable const MpiContextManager and
206 * LegacyMdrunOptions members.
210 ContextImpl(ContextImpl&&) = delete;
211 ContextImpl& operator=(ContextImpl&&) = delete;
215 * \brief Translate the workflow to the execution context and launch.
217 * \param work workflow graph
218 * \return ownership of a new session
220 * \todo This probably makes more sense as a free function, but we need to determine access policies.
222 * Session is returned with shared_ptr ownership so that Context
223 * can hold a weak_ptr and because Session Resources handles
224 * are still evolving.
225 * \todo Hide lifetime management and ownership from handle object.
226 * We can achieve the necessary aspects of this shared_ptr at a lower level of implementation.
227 * Note also that returned value policies can be implemented in higher level wrappers to ensure
228 * correct object lifetime scope. (See pybind, for instance.)
230 std::shared_ptr<Session> launch(const Workflow& work);
233 * \brief Retain the ability to find a launched session while it exists.
235 * The client owns the Session launched by a Context, but it is helpful
236 * for the Context to know if it has an active Session associated with it.
238 * \todo Use registration/deregistration protocol instead.
239 * Requires logging facility.
241 std::weak_ptr<Session> session_;
244 * \brief mdrun command line arguments.
246 * Store arguments provided by the client and pass them when launching
247 * a simulation runner. This allows client code to access the same
248 * options as are available to mdrun on the command line while the API
254 * \brief Legacy option-handling and set up for mdrun.
256 * This object should not exist, but is necessary now to introduce
257 * the API in a way that means CLI and API work similarly and do not
258 * duplicate definitions e.g. of command-line options.
260 gmx::LegacyMdrunOptions options_;
263 * \brief Scoped MPI management.
265 * Part of the ContextImpl invariant establishes a point where MPI initialization status is
268 * Note that the MpiContextManager invariant is dependent on configure-time options to the
269 * GROMACS library. Specifically, MpiContextManager::communicator() is guaranteed to be
270 * MPI_COMM_NULL if and only if the library was built without an external MPI library.
271 * This is confusing and we should split either this class or the
272 * MpiContextManager class. Another alternative would be to use a std::optional here and to
273 * allow the std::unique_ptr<MpiContextManager> provided to ContextImpl::create() to be null,
274 * but that means a slight change of documented behavior protocol. See #3688 and #3650 for
277 * To ensure the MpiContextManager is initialized only once, we use a const member that must
278 * be initialized at construction.
280 const MpiContextManager mpi_;
282 /*! \brief Owning handle to the results of the hardware detection.
284 * The hardware is detected across the whole environment described
286 std::unique_ptr<gmx_hw_info_t> hardwareInformation_;
290 * \brief Basic constructor.
292 * Don't use this. Use create() to get a shared pointer right away.
293 * Otherwise, shared_from_this() is potentially dangerous.
295 explicit ContextImpl(MpiContextManager&& mpi) noexcept(std::is_nothrow_constructible_v<gmx::LegacyMdrunOptions>);
299 * \brief Allow client code to hold a library communicator.
301 * MPI-enabled client code and thread-MPI GROMACS libraries cannot share headers
302 * in which MPI symbols (such as MPI_Comm) are defined. This class allows a
303 * client to refer to a library communicator opaquely. See gmxapi::offerComm().
305 * In the initial gmxapi::ResourceAssignment implementation, CommHandle objects
306 * are the only possible recipients of assigned resources. If future implementations
307 * allow richer resource assignment, CommHandle may be superseded by a more
308 * elaborate interface. Otherwise, all we need is this simple type proxy.
313 using commType = MPI_Comm;
314 MPI_Comm communicator{ MPI_COMM_NULL };
317 } // end namespace gmxapi
318 #endif // GMXAPI_CONTEXT_IMPL_H