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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"
58 * \brief Provide RAII management of library MPI context.
60 * To acquire an MpiContextManager is to have assurance that any external MPI
61 * environment is ready to use. When the MpiContextManager is released or
62 * goes out of scope, the destructor finalizes the resources.
64 * It is plausible that one or more ranks may not participate in an API session,
65 * but we have not historically handled such use cases at this level.
66 * For GROMACS built with an MPI library, the root communicator in the MpiContextManager
67 * must be valid. For other builds (e.g. tMPI), the communicator member must be MPI_COMM_NULL.
69 * If the client provides a communicator, the client promises to maintain the validity
70 * of the communicator for the life of the MpiContextManager.
72 * Note that thread-MPI chooses the number of ranks and constructs its
73 * MPI communicator internally, so does not and is unlikely to ever
76 * \todo Log errors during set up or tear down.
77 * There is no resource for logging or reporting errors during initialization or when misused.
81 class MpiContextManager
85 * \brief Default constructor.
87 * Construct a valid instance with an appropriate default value for the
88 * base communicator. (Note that appropriate default value depends on whether
89 * the library was compiled with an external MPI library.)
91 * \throws BasicException if library cannot be initialized.
96 * \brief Allow the communicator to be specified.
98 * Supports use cases in which a client provides a non-default communicator.
99 * Ensures that library environment is properly initialized and finalized,
100 * whether or not an externally managed communicator has been provided.
102 * \param communicator Optional communicator representing a client-managed MPI environment.
104 * Note that the communicator must be MPI_COMM_NULL if and only if GROMACS was built without an
105 * external MPI library.
107 * \throws BasicException if library cannot be initialized.
109 * \todo (#3650?) Decide whether to exclude this from tMPI environments or find a sensible invariant.
111 explicit MpiContextManager(MPI_Comm communicator);
113 ~MpiContextManager();
116 * \brief Exclusive ownership of a scoped context means copying is impossible.
120 MpiContextManager(const MpiContextManager&) = delete;
121 MpiContextManager& operator=(const MpiContextManager&) = delete;
125 * \brief Transfer ownership of the managed GROMACS MPI context.
129 MpiContextManager(MpiContextManager&& source) noexcept = default;
130 MpiContextManager& operator=(MpiContextManager&& source) noexcept = default;
134 * \brief Get the communicator for this context.
136 * \return Communicator with an appropriate initialized state for the current library
139 * \throws gmxapi::UsageError if MpiContextManager is in an invalid state, such as after
142 [[nodiscard]] MPI_Comm communicator() const;
146 * \brief The resources provided by this manager.
148 * A valid MpiContextManager has a value for communicator_ that is appropriate
149 * for the library configuration.
151 std::unique_ptr<MPI_Comm> communicator_;
155 * \brief Context implementation.
157 * Execution contexts have a uniform interface specified by the API. Implementations for
158 * particular execution environments can specialize / derive from this base.
160 * \todo Separate interface and implementation.
162 * \warning Definition and semantics depend on configure-time details. For example,
163 * MPI-enabled libraries always hold a valid MPI communicator via MpiContextManager,
164 * whereas tMPI and non-MPI builds hold a meaningless MpiContextManager.
166 * \todo Provide functions or traits for introspection.
170 class ContextImpl final : public std::enable_shared_from_this<ContextImpl>
176 * \brief Factory function
178 * Since this class provides `shared_from_this`, we need to make sure
179 * that it never exists without a shared_ptr owning it.
181 * If we can confirm `shared_from_this` is no longer necessary, implementation may change.
182 * \todo: Use registration/deregistration of launched Sessions to log warnings on shutdown
183 * instead of letting Session keep ContextImpl alive.
185 * \return ownership of a new object
187 static std::shared_ptr<ContextImpl> create(MpiContextManager&& mpi);
190 * \brief Copy disallowed because Session state would become ambiguous.
192 * The API implementation needs to unambiguously determine
193 * which Sessions and Contexts are associated with each other.
196 ContextImpl(const ContextImpl&) = delete;
197 ContextImpl& operator=(const ContextImpl&) = delete;
201 * \brief Objects are not trivial to move.
203 * \todo Implement move semantics. Requires a moveable const MpiContextManager and
204 * LegacyMdrunOptions members.
208 ContextImpl(ContextImpl&&) = delete;
209 ContextImpl& operator=(ContextImpl&&) = delete;
213 * \brief Translate the workflow to the execution context and launch.
215 * \param work workflow graph
216 * \return ownership of a new session
218 * \todo This probably makes more sense as a free function, but we need to determine access policies.
220 * Session is returned with shared_ptr ownership so that Context
221 * can hold a weak_ptr and because Session Resources handles
222 * are still evolving.
223 * \todo Hide lifetime management and ownership from handle object.
224 * We can achieve the necessary aspects of this shared_ptr at a lower level of implementation.
225 * Note also that returned value policies can be implemented in higher level wrappers to ensure
226 * correct object lifetime scope. (See pybind, for instance.)
228 std::shared_ptr<Session> launch(const Workflow& work);
231 * \brief Retain the ability to find a launched session while it exists.
233 * The client owns the Session launched by a Context, but it is helpful
234 * for the Context to know if it has an active Session associated with it.
236 * \todo Use registration/deregistration protocol instead.
237 * Requires logging facility.
239 std::weak_ptr<Session> session_;
242 * \brief mdrun command line arguments.
244 * Store arguments provided by the client and pass them when launching
245 * a simulation runner. This allows client code to access the same
246 * options as are available to mdrun on the command line while the API
252 * \brief Legacy option-handling and set up for mdrun.
254 * This object should not exist, but is necessary now to introduce
255 * the API in a way that means CLI and API work similarly and do not
256 * duplicate definitions e.g. of command-line options.
258 gmx::LegacyMdrunOptions options_;
261 * \brief Scoped MPI management.
263 * Part of the ContextImpl invariant establishes a point where MPI initialization status is
266 * Note that the MpiContextManager invariant is dependent on configure-time options to the
267 * GROMACS library. Specifically, MpiContextManager::communicator() is guaranteed to be
268 * MPI_COMM_NULL if and only if the library was built without an external MPI library.
269 * This is confusing and we should split either this class or the
270 * MpiContextManager class. Another alternative would be to use a std::optional here and to
271 * allow the std::unique_ptr<MpiContextManager> provided to ContextImpl::create() to be null,
272 * but that means a slight change of documented behavior protocol. See #3688 and #3650 for
275 * To ensure the MpiContextManager is initialized only once, we use a const member that must
276 * be initialized at construction.
278 const MpiContextManager mpi_;
282 * \brief Basic constructor.
284 * Don't use this. Use create() to get a shared pointer right away.
285 * Otherwise, shared_from_this() is potentially dangerous.
287 explicit ContextImpl(MpiContextManager&& mpi) noexcept(std::is_nothrow_constructible_v<gmx::LegacyMdrunOptions>);
291 * \brief Allow client code to hold a library communicator.
293 * MPI-enabled client code and thread-MPI GROMACS libraries cannot share headers
294 * in which MPI symbols (such as MPI_Comm) are defined. This class allows a
295 * client to refer to a library communicator opaquely. See gmxapi::offerComm().
297 * In the initial gmxapi::ResourceAssignment implementation, CommHandle objects
298 * are the only possible recipients of assigned resources. If future implementations
299 * allow richer resource assignment, CommHandle may be superseded by a more
300 * elaborate interface. Otherwise, all we need is this simple type proxy.
305 using commType = MPI_Comm;
306 MPI_Comm communicator{ MPI_COMM_NULL };
309 } // end namespace gmxapi
310 #endif // GMXAPI_CONTEXT_IMPL_H