1 files changed, 114 insertions, 0 deletions
diff --git a/src/mgr/Gil.h b/src/mgr/Gil.h
new file mode 100644
index 000000000..72675a503
--- /dev/null
+++ b/src/mgr/Gil.h
@@ -0,0 +1,114 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab
+/*
+ * Ceph - scalable distributed file system
+ *
+ * Copyright (C) 2017 SUSE LLC
+ *
+ * This is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License version 2.1, as published by the Free Software
+ * Foundation.  See file COPYING.
+ *
+ */
+
+#pragma once
+
+#include <cassert>
+#include <functional>
+
+struct _ts;
+typedef struct _ts PyThreadState;
+
+#include <pthread.h>
+
+
+/**
+ * Wrap PyThreadState to carry a record of which POSIX thread
+ * the thread state relates to.  This allows the Gil class to
+ * validate that we're being used from the right thread.
+ */
+class SafeThreadState
+{
+  public:
+  explicit SafeThreadState(PyThreadState *ts_);
+
+  SafeThreadState()
+    : ts(nullptr), thread(0)
+  {
+  }
+
+  PyThreadState *ts;
+  pthread_t thread;
+
+  void set(PyThreadState *ts_)
+  {
+    ts = ts_;
+    thread = pthread_self();
+  }
+};
+
+//
+// Use one of these in any scope in which you need to hold Python's
+// Global Interpreter Lock.
+//
+// Do *not* nest these, as a second GIL acquire will deadlock (see
+// https://docs.python.org/2/c-api/init.html#c.PyEval_RestoreThread)
+//
+// If in doubt, explicitly put a scope around the block of code you
+// know you need the GIL in.
+//
+// See the comment in Gil::Gil for when to set new_thread == true
+//
+class Gil {
+public:
+  Gil(const Gil&) = delete;
+  Gil& operator=(const Gil&) = delete;
+
+  Gil(SafeThreadState &ts, bool new_thread = false);
+  ~Gil();
+
+private:
+  SafeThreadState &pThreadState;
+  PyThreadState *pNewThreadState = nullptr;
+};
+
+// because the Python runtime could relinquish the GIL when performing GC
+// and re-acquire it afterwards, we should enforce following locking policy:
+// 1. do not acquire locks when holding the GIL, use a without_gil or
+//    without_gil_t to guard the code which acquires non-gil locks.
+// 2. always hold a GIL when calling python functions, for example, when
+//    constructing a PyFormatter instance.
+//
+// a wrapper that provides a convenient RAII-style mechinary for acquiring
+// and releasing GIL, like the macros of Py_BEGIN_ALLOW_THREADS and
+// Py_END_ALLOW_THREADS.
+struct without_gil_t {
+  without_gil_t();
+  ~without_gil_t();
+  void release_gil();
+  void acquire_gil();
+private:
+  PyThreadState *save = nullptr;
+  friend struct with_gil_t;
+};
+
+struct with_gil_t {
+  with_gil_t(without_gil_t& allow_threads);
+  ~with_gil_t();
+private:
+  without_gil_t& allow_threads;
+};
+
+// invoke func with GIL acquired
+template<typename Func>
+auto with_gil(without_gil_t& no_gil, Func&& func) {
+  with_gil_t gil{no_gil};
+  return std::invoke(std::forward<Func>(func));
+}
+
+template<typename Func>
+auto without_gil(Func&& func) {
+  without_gil_t no_gil;
+  return std::invoke(std::forward<Func>(func));
+}