[llvm] [Offload] Add MPI Plugin (PR #90890)

[Joseph Huber via llvm-commits]

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+//===------- event_system.h - Concurrent MPI communication ------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file contains the declarations of the MPI Event System used by the MPI
+// target.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _OMPTARGET_OMPCLUSTER_EVENT_SYSTEM_H_
+#define _OMPTARGET_OMPCLUSTER_EVENT_SYSTEM_H_
+
+#include <atomic>
+#include <cassert>
+#include <concepts>
+#include <condition_variable>
+#include <coroutine>
+#include <cstddef>
+#include <cstdint>
+#include <exception>
+#include <memory>
+#include <mutex>
+#include <optional>
+#include <queue>
+#include <thread>
+#include <type_traits>
+
+#define MPICH_SKIP_MPICXX
+#include <mpi.h>
+
+#include "llvm/ADT/SmallVector.h"
+
+#include "Shared/EnvironmentVar.h"
+#include "Shared/Utils.h"
+
+// External forward declarations.
+// =============================================================================
+struct __tgt_device_image;
+
+// Helper
+// =============================================================================
+template <typename... ArgsTy>
+static llvm::Error createError(const char *ErrFmt, ArgsTy... Args) {
+  return llvm::createStringError(llvm::inconvertibleErrorCode(), ErrFmt,
+                                 Args...);
+}
+
+/// The event type (type of action it will performed).
+///
+/// Enumerates the available events. Each enum item should be accompanied by an
+/// event class derived from BaseEvent. All the events are executed at a remote
+/// MPI process target by the event.
+enum class EventTypeTy : unsigned int {
+  // Memory management.
+  ALLOC,  // Allocates a buffer at the remote process.
+  DELETE, // Deletes a buffer at the remote process.
+
+  // Data movement.
+  SUBMIT,   // Sends a buffer data to a remote process.
+  RETRIEVE, // Receives a buffer data from a remote process.
+  EXCHANGE, // Exchange a buffer between two remote processes.
+  EXCHANGE_SRC,
+  EXCHANGE_DST,
+
+  // Target region execution.
+  EXECUTE, // Executes a target region at the remote process.
+
+  // Local event used to wait on other events.
+  SYNC,
+
+  // Internal event system commands.
+  LOAD_BINARY, // Transmits the binary descriptor to all workers
+  EXIT         // Stops the event system execution at the remote process.
+};
+
+/// EventType to string conversion.
+///
+/// \returns the string representation of \p type.
+const char *toString(EventTypeTy Type);
+
+// Coroutine events
+// =============================================================================
----------------
jhuber6 wrote:

Doxygen comments (`///`) on top level declarations and omit the big `====` header bar please.

https://github.com/llvm/llvm-project/pull/90890