autorejoin.h

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/* Copyright (c) 2018, 2024, Oracle and/or its affiliates.
 
   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License, version 2.0,
   as published by the Free Software Foundation.
 
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   as designated in a particular file or component or in included license
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   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License, version 2.0, for more details.
 
   You should have received a copy of the GNU General Public License
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   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA */
 
#ifndef GR_AUTOREJOIN_INCLUDED
#define GR_AUTOREJOIN_INCLUDED
 
#include "plugin/group_replication/include/member_info.h"
#include "plugin/group_replication/include/plugin_utils.h"
 
/**
  Represents and encapsulates the logic responsible for handling the auto-rejoin
  process within Group Replication. The auto-rejoin process kicks in one of two
  possible situations: either the member was expelled from the group or the
  member lost contact to a majority of the group. The auto-rejoin feature must
  also be explicitly enabled by setting the group_replication_autorejoin_tries
  sysvar to a value greater than 0.
 
  This thread will do a busy-wait loop for group_replication_autorejoin_tries
  number of attempts, waiting 5 minutes between each attempt (this wait is
  achieved via a timed wait on a conditional variable).
 
  We execute the auto-rejoin process in its own thead because the join operation
  of the GCS layer is asynchronous. We cannot actually block while waiting for a
  confirmation if the server managed to join the group or not. As such, we wait
  on a callback invoked by an entity that is registered as a GCS event listener.
 
  @sa Plugin_gcs_events_handler
*/
class Autorejoin_thread {
 public:
  /**
    Deleted copy ctor.
  */
  Autorejoin_thread(const Autorejoin_thread &) = delete;
 
  /**
    Deleted move ctor.
  */
  Autorejoin_thread(const Autorejoin_thread &&) = delete;
 
  /**
    Deleted assignment operator.
  */
  Autorejoin_thread &operator=(const Autorejoin_thread &) = delete;
 
  /**
    Deleted move operator.
  */
  Autorejoin_thread &operator=(const Autorejoin_thread &&) = delete;
 
  /**
    Initializes the synchronization primitives of the thread.
  */
  Autorejoin_thread();
 
  /**
    The dtor for the thread will destroy the mutex and cond_var.
  */
  ~Autorejoin_thread();
 
  /**
    Initializes the auto-rejoin module with a clean slate, i.e. it
    resets any state/flags that are checked in start_autorejoin().
 
    @sa start_autorejoin
  */
  void init();
 
  /**
    Aborts the thread's main loop, effectively killing the thread.
 
    @return a flag indicating whether or not the auto-rejoin procedure was
    ongoing at the time the abort was requested.
    @retval true the auto-rejoin was ongoing
    @retval false the auto-rejoin wasn't running
  */
  bool abort_rejoin();
 
  /**
    Starts the process of auto-rejoin, launches the thread that will call
    attempt_rejoin() until it succeeds or until it reaches a given
    amount of maximum retries, waiting on a conditional variable each
    iteration with a given timeout.
 
    An auto-rejoin can only start if it isn't already running or if the
    auto-rejoin module is not in the process of being terminated.
 
    @param[in] attempts the number of attempts we will try to rejoin.
    @param[in] timeout the time to wait between each retry.
    @return whether or not we managed to launch the auto-rejoin thread.
      @retval 0 the thread launched successfully
      @retval != 0 the thread couldn't be launched
    @sa mysql_thread_create
  */
  int start_autorejoin(uint attempts, ulonglong timeout);
 
  /**
    Returns a flag indicating whether or not the auto-rejoin process is ongoing
    on this thread.
 
    @return the state of the rejoin process.
    @retval true if the auto-rejoin is ongoing
    @retval false otherwise
  */
  bool is_autorejoin_ongoing();
 
 private:
  /**
    The thread callback passed onto mysql_thread_create.
 
    @param[in] arg a pointer to an Autorejoin_thread instance.
 
    @return Does not return.
  */
  static void *launch_thread(void *arg);
 
  /**
    The thread handle, i.e. setups and tearsdown the infrastructure for this
    mysql_thread.
  */
  [[noreturn]] void autorejoin_thread_handle();
 
  /**
    Handles the busy-wait retry loop.
  */
  void execute_rejoin_process();
 
  /** the THD handle. */
  THD *m_thd;
  /** the state of the thread. */
  thread_state m_autorejoin_thd_state;
  /** the thread handle. */
  my_thread_handle m_handle;
  /** the mutex for controlling access to the thread itself. */
  mysql_mutex_t m_run_lock;
  /** the cond_var used to signal the thread. */
  mysql_cond_t m_run_cond;
  /** flag to indicate whether or not the thread is to be aborted. */
  std::atomic<bool> m_abort;
  /**
    flag that indicates that the auto-rejoin module is in the process of
    being terminated.
  */
  bool m_being_terminated;
  /** the number of attempts for the rejoin. */
  ulong m_attempts;
  /** the time to wait in seconds until the next rejoin attempt. */
  ulonglong m_rejoin_timeout;
};
 
#endif /* GR_AUTREJOIN_INCLUDED */