libcc1/rpc.hh

   1 /* RPC call and callback templates
   2    Copyright (C) 2014-2021 Free Software Foundation, Inc.
   3
   4 This file is part of GCC.
   5
   6 GCC is free software; you can redistribute it and/or modify it under
   7 the terms of the GNU General Public License as published by the Free
   8 Software Foundation; either version 3, or (at your option) any later
   9 version.
  10
  11 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
  12 WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13 FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14 for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GCC; see the file COPYING3.  If not see
  18 <http://www.gnu.org/licenses/>.  */
  19
  20 #ifndef CC1_PLUGIN_RPC_HH
  21 #define CC1_PLUGIN_RPC_HH
  22
  23 #include "status.hh"
  24 #include "connection.hh"
  25 #include "deleter.hh"
  26
  27 namespace cc1_plugin
  28 {
  29   // The plugin API may contain some "const" method parameters.
  30   // However, when unmarshalling we cannot unmarshall into a const
  31   // object; and furthermore we want to be able to deallocate pointers
  32   // when finished with them.  This wrapper class lets us properly
  33   // remove the "const" and handle deallocation from pointer types.
  34
  35   template<typename T>
  36   class argument_wrapper
  37   {
  38   public:
  39
  40     argument_wrapper () { }
  41     ~argument_wrapper () { }
  42
  43     argument_wrapper (const argument_wrapper &) = delete;
  44     argument_wrapper &operator= (const argument_wrapper &) = delete;
  45
  46     T get () const { return m_object; }
  47
  48     status unmarshall (connection *conn)
  49     {
  50       return ::cc1_plugin::unmarshall (conn, &m_object);
  51     }
  52
  53   private:
  54
  55     T m_object;
  56   };
  57
  58   // Specialization for any kind of pointer.
  59   template<typename T>
  60   class argument_wrapper<T *>
  61   {
  62   public:
  63     argument_wrapper () = default;
  64     ~argument_wrapper () = default;
  65
  66     argument_wrapper (const argument_wrapper &) = delete;
  67     argument_wrapper &operator= (const argument_wrapper &) = delete;
  68
  69     typedef typename std::remove_const<T>::type type;
  70
  71     const type *get () const
  72     {
  73       return m_object.get ();
  74     }
  75
  76     status unmarshall (connection *conn)
  77     {
  78       type *ptr;
  79       if (!::cc1_plugin::unmarshall (conn, &ptr))
  80         return FAIL;
  81       m_object.reset (ptr);
  82       return OK;
  83     }
  84
  85   private:
  86
  87     unique_ptr<type> m_object;
  88   };
  89
  90   // There are two kinds of template functions here: "call" and
  91   // "invoker".
  92
  93   // The "call" template is used for making a remote procedure call.
  94   // It starts a query ('Q') packet, marshalls its arguments, waits
  95   // for a result, and finally reads and returns the result via an
  96   // "out" parameter.
  97
  98   // The "invoker" template is used when receiving a remote procedure
  99   // call.  This template function is suitable for use with the
 100   // "callbacks" and "connection" classes.  It decodes incoming
 101   // arguments, passes them to the wrapped function, and finally
 102   // marshalls a reply packet.
 103
 104   template<typename R, typename... Arg>
 105   status
 106   call (connection *conn, const char *method, R *result, Arg... args)
 107   {
 108     if (!conn->send ('Q'))
 109       return FAIL;
 110     if (!marshall (conn, method))
 111       return FAIL;
 112     if (!marshall (conn, (int) sizeof... (Arg)))
 113       return FAIL;
 114     if (!marshall (conn, args...))
 115       return FAIL;
 116     if (!conn->wait_for_result ())
 117       return FAIL;
 118     if (!unmarshall (conn, result))
 119       return FAIL;
 120     return OK;
 121   }
 122
 123   // The base case -- just return OK.
 124   template<int I, typename... T>
 125   typename std::enable_if<I == sizeof... (T), status>::type
 126   unmarshall (connection *, std::tuple<T...> &)
 127   {
 128     return OK;
 129   }
 130
 131   // Unmarshall this argument, then unmarshall all subsequent args.
 132   template<int I, typename... T>
 133   typename std::enable_if<I < sizeof... (T), status>::type
 134   unmarshall (connection *conn, std::tuple<T...> &value)
 135   {
 136     if (!std::get<I> (value).unmarshall (conn))
 137       return FAIL;
 138     return unmarshall<I + 1, T...> (conn, value);
 139   }
 140
 141   // Wrap a static function that is suitable for use as a callback.
 142   // This is a template function inside a template class to work
 143   // around limitations with multiple variadic packs.
 144   template<typename R, typename... Arg>
 145   class invoker
 146   {
 147     // Base case -- we can call the function.
 148     template<int I, R func (connection *, Arg...), typename... T>
 149     static typename std::enable_if<I == sizeof... (Arg), R>::type
 150     call (connection *conn, const std::tuple<argument_wrapper<Arg>...> &,
 151           T... args)
 152     {
 153       return func (conn, args...);
 154     }
 155
 156     // Unpack one argument and continue the recursion.
 157     template<int I, R func (connection *, Arg...), typename... T>
 158     static typename std::enable_if<I < sizeof... (Arg), R>::type
 159     call (connection *conn, const std::tuple<argument_wrapper<Arg>...> &value,
 160           T... args)
 161     {
 162       return call<I + 1, func> (conn, value, args...,
 163                                 std::get<I> (value).get ());
 164     }
 165
 166   public:
 167
 168     // A callback function that reads arguments from the connection,
 169     // calls the wrapped function, and then sends the result back on
 170     // the connection.
 171     template<R func (connection *, Arg...)>
 172     static status
 173     invoke (connection *conn)
 174     {
 175       if (!unmarshall_check (conn, sizeof... (Arg)))
 176         return FAIL;
 177       std::tuple<argument_wrapper<Arg>...> wrapped;
 178       if (!unmarshall<0> (conn, wrapped))
 179         return FAIL;
 180
 181       R result = call<0, func> (conn, wrapped);
 182
 183       if (!conn->send ('R'))
 184         return FAIL;
 185       return marshall (conn, result);
 186     }
 187   };
 188 };
 189
 190 #endif // CC1_PLUGIN_RPC_HH