Catalog

Abstract ：

Process handling :

The main thread receives the request , Create a new thread :

The sub thread starts processing the request :

Sequential flow :

Abstract ：

Brief analysis mysql Processing of receiving new connections

Process handling :

The main thread receives the request , Create a new thread :

(gdb) bt
#0  Per_thread_connection_handler::add_connection (this=0x5e7a4d0, channel_info=0x7dc3430) at /data/jenkins/workspace/stonedb5.7-zsl-centos7.9/sql/conn_handler/connection_handler_per_thread.cc:417
#1  0x0000000001db0f66 in Connection_handler_manager::process_new_connection (this=0x5e277a0, channel_info=0x7dc3430)
    at /data/jenkins/workspace/stonedb5.7-zsl-centos7.9/sql/conn_handler/connection_handler_manager.cc:275
#2  0x0000000001d73037 in Connection_acceptor<Mysqld_socket_listener>::connection_event_loop (this=0x7dc18a0)
    at /data/jenkins/workspace/stonedb5.7-zsl-centos7.9/sql/conn_handler/connection_acceptor.h:75
#3  0x0000000001d6a47e in mysqld_main (argc=115, argv=0x5e27c48) at /data/jenkins/workspace/stonedb5.7-zsl-centos7.9/sql/mysqld.cc:5199
#4  0x0000000001d61097 in main (argc=8, argv=0x7ffdd55cdb28) at /data/jenkins/workspace/stonedb5.7-zsl-centos7.9/sql/main.cc:32

The sub thread starts processing the request :

(gdb) c
Continuing.
[New Thread 0x7fdc80137700 (LWP 11313)]
[Switching to Thread 0x7fdc80137700 (LWP 11313)]

Breakpoint 2, pfs_spawn_thread (arg=0x99ee3f0) at /data/jenkins/workspace/stonedb5.7-zsl-centos7.9/storage/perfschema/pfs.cc:2197
2197	  (*user_start_routine)(user_arg);
(gdb) bt
#0  pfs_spawn_thread (arg=0x99ee3f0) at /data/jenkins/workspace/stonedb5.7-zsl-centos7.9/storage/perfschema/pfs.cc:2197
#1  0x00007fdcd505eea5 in start_thread (arg=0x7fdc80137700) at pthread_create.c:307
#2  0x00007fdcd3495b0d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:111
(gdb) p user_start_routine
$1 = (void *(*)(void *)) 0x2597a15 <handle_connection(void*)>
(gdb) s
handle_connection (arg=0x7dc3430) at /data/jenkins/workspace/stonedb5.7-zsl-centos7.9/sql/conn_handler/connection_handler_per_thread.cc:251
251	  Global_THD_manager *thd_manager= Global_THD_manager::get_instance();

Sequential flow :

Be careful :

1. clone The system call returns twice , Parent thread once , Once for the newly created sub thread
2. Cool tone is the main thread of processing , Warm colors for new sub thread processing

The key function :

Per_thread_connection_handler::add_connection

bool Per_thread_connection_handler::add_connection(Channel_info* channel_info)
{
  int error= 0;
  my_thread_handle id;

  DBUG_ENTER("Per_thread_connection_handler::add_connection");

  // Simulate thread creation for test case before we check thread cache
  DBUG_EXECUTE_IF("fail_thread_create", error= 1; goto handle_error;);

  if (!check_idle_thread_and_enqueue_connection(channel_info))
    DBUG_RETURN(false);

  /*
    There are no idle threads avaliable to take up the new
    connection. Create a new thread to handle the connection
  */
  channel_info->set_prior_thr_create_utime();
  error= mysql_thread_create(key_thread_one_connection, &id,
                             &connection_attrib,
                             handle_connection,
                             (void*) channel_info);
#ifndef NDEBUG
handle_error:
#endif // !NDEBUG

  if (error)
  {
    connection_errors_internal++;
    if (!create_thd_err_log_throttle.log())
      sql_print_error("Can't create thread to handle new connection(errno= %d)",
                      error);
    channel_info->send_error_and_close_channel(ER_CANT_CREATE_THREAD,
                                               error, true);
    Connection_handler_manager::dec_connection_count();
    DBUG_RETURN(true);
  }

  Global_THD_manager::get_instance()->inc_thread_created();
  DBUG_PRINT("info",("Thread created"));
  DBUG_RETURN(false);
}

mysql_thread_create

#ifdef HAVE_PSI_THREAD_INTERFACE
  #define mysql_thread_create(K, P1, P2, P3, P4) \
    inline_mysql_thread_create(K, P1, P2, P3, P4)
#else
  #define mysql_thread_create(K, P1, P2, P3, P4) \
    my_thread_create(P1, P2, P3, P4)
#endif

int my_thread_create(my_thread_handle *thread, const my_thread_attr_t *attr,
                     my_start_routine func, void *arg)
{
#ifndef _WIN32
  return pthread_create(&thread->thread, attr, func, arg);
#else
  struct thread_start_parameter *par;
  unsigned int  stack_size;

  par= (struct thread_start_parameter *)malloc(sizeof(*par));
  if (!par)
    goto error_return;

  par->func= func;
  par->arg= arg;
  stack_size= attr ? attr->dwStackSize : 0;

  thread->handle= (HANDLE)_beginthreadex(NULL, stack_size, win_thread_start,
                                         par, 0, &thread->thread);

  if (thread->handle)
  {
    /* Note that JOINABLE is default, so attr == NULL => JOINABLE. */
    if (attr && attr->detachstate == MY_THREAD_CREATE_DETACHED)
    {
      /*
        Close handles for detached threads right away to avoid leaking
        handles. For joinable threads we need the handle during
        my_thread_join. It will be closed there.
      */
      CloseHandle(thread->handle);
      thread->handle= NULL;
    }
    return 0;
  }

  my_osmaperr(GetLastError());
  free(par);

error_return:
  thread->thread= 0;
  thread->handle= NULL;
  return 1;
#endif
}

pfs_spawn_thread

extern "C" void* pfs_spawn_thread(void *arg)
{
  PFS_spawn_thread_arg *typed_arg= (PFS_spawn_thread_arg*) arg;
  void *user_arg;
  void *(*user_start_routine)(void*);

  PFS_thread *pfs;

  /* First, attach instrumentation to this newly created pthread. */
  PFS_thread_class *klass= find_thread_class(typed_arg->m_child_key);
  if (likely(klass != NULL))
  {
    pfs= create_thread(klass, typed_arg->m_child_identity, 0);
    if (likely(pfs != NULL))
    {
      pfs->m_thread_os_id= my_thread_os_id();
      clear_thread_account(pfs);

      pfs->m_parent_thread_internal_id= typed_arg->m_thread_internal_id;

      memcpy(pfs->m_username, typed_arg->m_username, sizeof(pfs->m_username));
      pfs->m_username_length= typed_arg->m_username_length;

      memcpy(pfs->m_hostname, typed_arg->m_hostname, sizeof(pfs->m_hostname));
      pfs->m_hostname_length= typed_arg->m_hostname_length;

      set_thread_account(pfs);
    }
  }
  else
  {
    pfs= NULL;
  }
  my_thread_set_THR_PFS(pfs);

  /*
    Secondly, free the memory allocated in spawn_thread_v1().
    It is preferable to do this before invoking the user
    routine, to avoid memory leaks at shutdown, in case
    the server exits without waiting for this thread.
  */
  user_start_routine= typed_arg->m_user_start_routine;
  user_arg= typed_arg->m_user_arg;
  my_free(typed_arg);

  /* Then, execute the user code for this thread. */
  (*user_start_routine)(user_arg);

  return NULL;
}