pfs_notification.h

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Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA */
 
#ifndef PFS_NOTIFY_SERVICE_H
#define PFS_NOTIFY_SERVICE_H
 
#include <mysql/components/service.h>
#include <mysql/psi/mysql_thread.h>
 
/**
  @page PAGE_PFS_NOTIFICATION_SERVICE Notification service
 
  @section PFS_NOTIFICATION_INTRO Introduction
  The Performance Schema Notification service provides a means to register
  user-defined callback functions for the following thread and session events:
 
  - thread create
  - thread destroy
  - session connect
  - session disconnect
  - session change user
 
  This is a synchronous, low-level API designed to impose minimal performance
  overhead.
 
  @section PFS_NOTIFICATION_CALLBACKS Callback Function Definition
 
  Callback functions are of the type #PSI_notification_cb:
 
  @code
    typedef void (*PSI_notification_cb)(const PSI_thread_attrs *thread_attrs);
  @endcode
 
  For example:
  @code
    void callback_thread_create(const PSI_thread_attrs *thread_attrs)
    {
      set_thread_resource_group(...)
    }
  @endcode
 
  When the callback is invoked, the #PSI_thread_attrs structure will contain the
  system attributes of the thread.
 
  @section PFS_NOTIFICATION_REGISTER Registering Events
 
  To register for one or more events, set the corresponding callback function
  pointers in the #PSI_notification structure, leaving the function pointer
  NULL for unused callbacks.
 
  Use the service function @c register_notification() to register the callbacks
  with the server
 
  @code
    int register_notification(PSI_notification *callbacks,
                              bool with_ref_count);
  @endcode
 
  where
  - @c callbacks is the callback function set
  - @c with_ref_count determines whether a reference count is used for the
                      callbacks. Set TRUE for callback functions in
                      dynamically loaded modules. Set FALSE for callback
                      functions in static or unloadable modules.
 
  For example:
  @code
    PSI_notification my_callbacks;
 
    my_callbacks.thread_create   = &thread_create_callback;
    my_callbacks.thread_destroy  = &thread_destroy_callback;
    my_callbacks.session_connect = &session_connect_callback;
    my_callbacks.session_disconnect  = &session_disconnect_callback;
    my_callbacks.session_change_user = nullptr;
 
    int my_handle =
     mysql_service_pfs_notification->register_notification(&my_callbacks, true);
  @endcode
 
  A non-zero handle is returned if the registration is successful. This handle
  is used to unregister the callback set.
 
  A callback set can be registered more than once. No error is returned
  for calling @c register_notification() more than once for a given callback
  set. Callbacks are invoked once for each time they are registered.
 
  For callback functions that reside in dynamically loaded modules, set
  @verbatim with_ref_count = TRUE @endverbatim so that the module can be safely
  unloaded after the callbacks are unregistered.
 
  For callback functions that reside in static, built-in or otherwise unloadable
  modules, set @verbatim with_ref_count = FALSE @endverbatim to optimize
  callback performance in high-concurrency environments.
 
  Callbacks that reside in a dynamically loaded module such as a server plugin,
  must be successfully unregistered before the module is unloaded.
 
  For callbacks in static or unloadable modules, @c unregister_notification()
  will disable the callback functions, but the function pointers will remain.
 
  @section PFS_NOTIFICATION_UNREGISTER Unregistering Events
 
  To unregister callback functions from the Notification service, use the handle
  returned from @c register_notification(). For example:
 
  @code
    int ret =
  mysql_service_pfs_notification->unregister_notification(my_handle);
 
    if (ret == 0)
    {
      // unload component
    }
    else
    {
      // error
    }
  @endcode
 
  Callbacks that reside in a dynamically loaded module such as a server plugin
  or component must be successfully unregistered before the module is unloaded.
 
  If @c unregister_notification() returns an error, then the module should not
  be unloaded.
 
  If the callbacks were registered with @verbatim with_ref_count = TRUE
  @endverbatim then
  @c unregister_notification() will return an error if any of the functions are
  in use and fail to return after 2 seconds.
 
  If the callbacks were registered with @verbatim with_ref_count = FALSE
  @endverbatim then
  @c unregister_notification() will disable the callback functions, but the
  callback function pointers will be assumed to be valid until the server is
  shutdown.
 
  @c unregister_callback() can be called multiple times for the same handle.
 
  Failing to unregister all callback functions from a dynamically loaded plugin
  or component may result in a undocumented behavior during server shutdown.
 
*/
 
/*
  SERVICE_DEFINITION(pfs_notification)
  Introduced in MySQL 8.0.2
  Removed in MySQL 8.0.17
  Status: Removed, use version 3 instead.
*/
 
/*
  Version 3.
  Introduced in MySQL 8.0.17
  Status: active
*/
 
BEGIN_SERVICE_DEFINITION(pfs_notification_v3)
register_notification_v3_t register_notification;
unregister_notification_v1_t unregister_notification;
END_SERVICE_DEFINITION(pfs_notification_v3)
 
#define REQUIRES_PFS_NOTIFICATION_SERVICE REQUIRES_SERVICE(pfs_notification_v3)
 
#endif