Add threading primitives.

PiperOrigin-RevId: 562649644
Change-Id: I9c35b270e4b3b50cc7eb5a152f24d71def8e2fcd

src/thread/task.h

@@ -0,0 +1,69 @@
+// Copyright 2023 DeepMind Technologies Limited
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+// IWYU pragma: private, include "third_party/mujoco/include/mujoco.h"
+// IWYU pragma: friend "third_party/(py/)?mujoco/.*"
+
+#ifndef MUJOCO_SRC_THREAD_TASK_H_
+#define MUJOCO_SRC_THREAD_TASK_H_
+
+#ifdef __cplusplus
+
+#include <atomic>
+#include <functional>
+#include <thread>
+
+namespace mujoco {
+
+class Task {
+ public:
+  enum Status {
+    QUEUED,
+    COMPLETE,
+  };
+
+  static void Initialize(
+      Task* task,
+      std::function<void*(void*)> start_routine,
+      void* args) {
+    // instantiate a task at the pointer passed in
+    new(task) Task();
+    task->start_routine_ = start_routine;
+    task->args_ = args;
+    task->status_ = Status::QUEUED;
+  }
+
+  void Execute() {
+    args_ = start_routine_(args_);
+    status_ = Status::COMPLETE;
+  }
+
+  void Join() {
+    while (status_ != Status::COMPLETE) {
+      std::this_thread::yield();
+    }
+  }
+
+ private:
+  std::function<void*(void*)> start_routine_;
+
+  void* args_;
+
+  std::atomic<Status> status_ = Status::QUEUED;
+};
+
+}  // namespace mujoco
+
+#endif  // __cplusplus
+
+#endif  // MUJOCO_SRC_THREAD_TASK_H_