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       1                 :             : /*
       2                 :             :  * Copyright 2025 Jinwoo Sung
       3                 :             :  *
       4                 :             :  * Licensed under the Apache License, Version 2.0 (the "License");
       5                 :             :  * you may not use this file except in compliance with the License.
       6                 :             :  * You may obtain a copy of the License at
       7                 :             :  *
       8                 :             :  *     http://www.apache.org/licenses/LICENSE-2.0
       9                 :             :  *
      10                 :             :  * Unless required by applicable law or agreed to in writing, software
      11                 :             :  * distributed under the License is distributed on an "AS IS" BASIS,
      12                 :             :  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
      13                 :             :  * See the License for the specific language governing permissions and
      14                 :             :  * limitations under the License.
      15                 :             :  */
      16                 :             : 
      17                 :             : #pragma once
      18                 :             : 
      19                 :             : #include <memory>
      20                 :             : #include <string>
      21                 :             : #include <string_view>
      22                 :             : #include <utility>
      23                 :             : 
      24                 :             : #include "wirestead/diagnostics/logger.hpp"
      25                 :             : 
      26                 :             : // #449: a blocking send (Reliable-mode send()/send_blocking()/send_move()/
      27                 :             : // send_shared()) called from inside a data/message callback deadlocks -
      28                 :             : // clearing backpressure requires progress on the same io thread that a
      29                 :             : // blocking wait would now be stuck on. This thread_local flag, set for the
      30                 :             : // duration of any data/message callback dispatch, lets the blocking-send
      31                 :             : // path detect that scenario and fail fast (return false) instead of
      32                 :             : // blocking forever. It intentionally isn't scoped per-channel: if the
      33                 :             : // current thread is inside ANY callback dispatch, that thread can't make
      34                 :             : // progress on I/O regardless of which channel triggered the callback -
      35                 :             : // including a second channel sharing the same io_context/thread.
      36                 :             : namespace wirestead {
      37                 :             : namespace wrapper {
      38                 :             : namespace detail {
      39                 :             : 
      40                 :             : // A depth counter rather than a bool so that a nested/reentrant
      41                 :             : // CallbackGuard on the same thread doesn't clear the flag out from under an
      42                 :             : // outer guard that's still in scope: the inner guard's destructor would
      43                 :             : // otherwise flip g_callback_depth back to "not in a callback" while the
      44                 :             : // outer dispatch is still running, reopening the #449 deadlock this guard
      45                 :             : // exists to prevent.
      46                 :             : inline thread_local int g_callback_depth = 0;
      47                 :             : 
      48                 :             : class CallbackGuard {
      49                 :             :  public:
      50                 :        2656 :   CallbackGuard() { ++g_callback_depth; }
      51                 :        2656 :   ~CallbackGuard() { --g_callback_depth; }
      52                 :             :   CallbackGuard(const CallbackGuard&) = delete;
      53                 :             :   CallbackGuard& operator=(const CallbackGuard&) = delete;
      54                 :             : };
      55                 :             : 
      56                 :           5 : inline bool in_data_callback() { return g_callback_depth > 0; }
      57                 :             : 
      58                 :             : // Invokes a user-supplied wrapper callback (on_data/on_message/on_connect/
      59                 :             : // on_disconnect/on_error/on_backpressure and their batch variants) and
      60                 :             : // prevents an exception escaping it from propagating further. All channels
      61                 :             : // share one process-wide IoContextManager thread by default
      62                 :             : // (concurrency/io_context_manager.cc); an uncaught exception here would
      63                 :             : // otherwise escape the un-guarded handler call, propagate out of
      64                 :             : // io_context::run(), and stop I/O for every channel sharing that context -
      65                 :             : // not just the one whose callback misbehaved.
      66                 :             : template <typename Callback, typename... Args>
      67                 :        4297 : void invoke_user_callback(std::string_view component, std::string_view operation, const Callback& callback,
      68                 :             :                           Args&&... args) {
      69         [ +  + ]:        4297 :   if (!callback) return;
      70                 :             :   try {
      71                 :        3737 :     callback(std::forward<Args>(args)...);
      72                 :           0 :   } catch (const std::exception& e) {
      73                 :           0 :     WIRESTEAD_LOG_ERROR(component, operation, "Uncaught exception in user callback: " + std::string(e.what()));
      74                 :           0 :   } catch (...) {
      75                 :           0 :     WIRESTEAD_LOG_ERROR(component, operation, "Uncaught non-standard exception in user callback");
      76                 :             :   }
      77                 :             : }
      78                 :             : 
      79                 :             : // Overload for a handler snapshotted as a shared pointer rather than copied
      80                 :             : // out of its guarded member - see interface::SharedCallback. A null pointer
      81                 :             : // means "not registered", exactly as an empty std::function does above.
      82                 :             : template <typename Callback, typename... Args>
      83                 :        3796 : void invoke_user_callback(std::string_view component, std::string_view operation,
      84                 :             :                           const std::shared_ptr<const Callback>& callback, Args&&... args) {
      85         [ +  + ]:        3796 :   if (!callback) return;
      86                 :        3644 :   invoke_user_callback(component, operation, *callback, std::forward<Args>(args)...);
      87                 :             : }
      88                 :             : 
      89                 :             : }  // namespace detail
      90                 :             : }  // namespace wrapper
      91                 :             : }  // namespace wirestead