ceph/src/mgr/Gil.h

   1 // -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
   2 // vim: ts=8 sw=2 smarttab
   3 /*
   4  * Ceph - scalable distributed file system
   5  *
   6  * Copyright (C) 2017 SUSE LLC
   7  *
   8  * This is free software; you can redistribute it and/or
   9  * modify it under the terms of the GNU Lesser General Public
  10  * License version 2.1, as published by the Free Software
  11  * Foundation.  See file COPYING.
  12  *
  13  */
  14
  15 #ifndef GIL_H_
  16 #define GIL_H_
  17
  18 #include "Python.h"
  19
  20 #include "common/debug.h"
  21
  22 #define dout_context g_ceph_context
  23 #define dout_subsys ceph_subsys_mgr
  24 #undef dout_prefix
  25 #define dout_prefix *_dout << "mgr " << __func__ << " "
  26
  27 //
  28 // Use one of these in any scope in which you need to hold Python's
  29 // Global Interpreter Lock.
  30 //
  31 // Do *not* nest these, as a second GIL acquire will deadlock (see
  32 // https://docs.python.org/2/c-api/init.html#c.PyEval_RestoreThread)
  33 //
  34 // If in doubt, explicitly put a scope around the block of code you
  35 // know you need the GIL in.
  36 //
  37 // See the comment below for when to set new_thread == true
  38 //
  39 class Gil {
  40 public:
  41   Gil(const Gil&) = delete;
  42   Gil& operator=(const Gil&) = delete;
  43
  44   Gil(PyThreadState *ts, bool new_thread = false) : pThreadState(ts)
  45   {
  46     assert(pThreadState != nullptr);
  47
  48     // Acquire the GIL, set the current thread state
  49     PyEval_RestoreThread(pThreadState);
  50     dout(20) << "GIL acquired for thread state " << pThreadState << dendl;
  51
  52     //
  53     // If called from a separate OS thread (i.e. a thread not created
  54     // by Python, that does't already have a python thread state that
  55     // was created when that thread was active), we need to manually
  56     // create and switch to a python thread state specifically for this
  57     // OS thread.
  58     //
  59     // Note that instead of requring the caller to set new_thread == true
  60     // when calling this from a separate OS thread, we could figure out
  61     // if this was necessary automatically, as follows:
  62     //
  63     //   if (pThreadState->thread_id != PyThread_get_thread_ident()) {
  64     //
  65     // However, this means we're accessing pThreadState->thread_id, but
  66     // the Python C API docs say that "The only public data member is
  67     // PyInterpreterState *interp", i.e. doing this would violate
  68     // something that's meant to be a black box.
  69     //
  70     if (new_thread) {
  71       pNewThreadState = PyThreadState_New(pThreadState->interp);
  72       PyThreadState_Swap(pNewThreadState);
  73       dout(20) << "Switched to new thread state " << pNewThreadState << dendl;
  74     }
  75   }
  76
  77   ~Gil()
  78   {
  79     if (pNewThreadState != nullptr) {
  80       dout(20) << "Destroying new thread state " << pNewThreadState << dendl;
  81       PyThreadState_Swap(pThreadState);
  82       PyThreadState_Clear(pNewThreadState);
  83       PyThreadState_Delete(pNewThreadState);
  84     }
  85     // Release the GIL, reset the thread state to NULL
  86     PyEval_SaveThread();
  87     dout(20) << "GIL released for thread state " << pThreadState << dendl;
  88   }
  89
  90 private:
  91   PyThreadState *pThreadState;
  92   PyThreadState *pNewThreadState = nullptr;
  93 };
  94
  95 #endif
  96