emacs - Comint 模式每 4096 个字符插入换行符

Question

在 Ubuntu Lucid 上使用 Emacs 23.2.1，任何基于 Comint 的模式都会偶尔插入换行符以获得更大的输出(参见下面的示例 Shell 和 SQL 模式输出)。我在 SQL 模式和 Shell 模式下都试过了，两种情况下的结果都是一样的。在普通终端模拟器中运行类似的命令不会导致这些问题(对于 shell 模式和 mysql 模式命令)。

我尝试过的事情:

• 在 SQL 模式下使用 MySQL，添加以下标志:-A、-C、-t、-f、-n，并将 max_allowed_pa​​cket 设置为 16MB。

• 将 comint-buffer-maximum-size 设置为 10240。

这些都不会对此行为产生任何影响。

如果我向上滚动到有问题的行并删除换行符，则输出会正确显示，因此解决此问题的可能方法是使用一个钩子(Hook)来删除每 4096 个字符(如果可能的话)。

注意:在终端示例中，输出似乎在除每 4096 个字符之外的点处被截断。在 SQL 模式下，正好是每 4096 个(确实是一个可疑的数字)。

这是一些示例输出:

brent@battlecruiser:/$ for i in {1..4096}; do echo -n 0; done; echo;

0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

在这种情况下，它应该打印出一行0，但实际上在904个字符之后插入了一个换行符。

还有一个使用 MySQL 的 SQL 模式示例:

mysql> show variables like '%n%';

+-----------------------------------------+----------------------------------+
| Variable_name                           | Value                            |
+-----------------------------------------+----------------------------------+
| auto_increment_increment                | 1                                |
| auto_increment_offset                   | 1                                |
| binlog_cache_size                       | 32768                            |
| binlog_format                           | STATEMENT                        |
| bulk_insert_buffer_size                 | 8388608                          |
| character_set_client                    | utf8                             |
| character_set_connection                | utf8                             |
| collation_connection                    | utf8_general_ci                  |
| collation_database                      | latin1_swedish_ci                |
| collation_server                        | latin1_swedish_ci                |
| completion_type                         | 0                                |
| concurrent_insert                       | 1                                |
| connect_timeout                         | 10                               |
| delayed_insert_limit                    | 100                              |
| delayed_insert_timeout                  | 300                              |
| div_precision_increment                 | 4                                |
| engine_condition_pushdown               | ON                               |
| error_count                             | 0                                |
| event_scheduler                         | OFF                              |
| foreign_key_checks                      | ON                               |
| ft_boolean_syntax                       | + -><()~*:""&|                   |
| ft_max_word_len                         | 84                               |
| ft_min_word_len                         | 4                                |
| ft_query_expansion_limit                | 20                               |
| general_log                             | OFF                              |
| general_log_file                        | /var/lib/mysql/battlecruiser.log |
| group_concat_max_len                    | 1024                             |
| have_community_features                 | YES                              |
| have_dynamic_loading                    | YES                              |
| have_innodb                             | YES                              |
| have_ndbcluster                         | NO                               |
| have_openssl                            | DISABLED                         |
| have_partitioning                       | YES                              |
| have_symlink                            | YES                              |
| hostname                                | battlecruiser                    |
| identity                                | 0                                |
| ignore_builtin_innodb                   | OFF                              |
| init_connect                            |                                  |
| init_file                               |                                  |
| init_slave                              |                                  |
| innodb_adaptive_hash_index              | ON                               |
| innodb_additional_mem_pool_size         | 1048576                          |
| innodb_autoextend_increment             | 8                                |
| innodb_autoinc_lock_mode                | 1                                |
| innodb_buffer_pool_size                 | 8388608                          |
| innodb_checksums                        | ON                               |
| innodb_commit_concurrency               | 0                                |
| innodb_concurrency_tickets              | 500                              |
| innodb_data_file_path                   | ibdata1:10M:autoextend
           |
| innodb_data_home_dir                    |                                  |
| innodb_doublewrite                      | ON                               |
| innodb_fast_shutdown                    | 1                                |
| innodb_file_io_threads                  | 4                                |
| innodb_file_per_table                   | OFF                              |
| innodb_flush_log_at_trx_commit          | 1                                |
| innodb_flush_method                     |                                  |
| innodb_force_recovery                   | 0                                |
| innodb_lock_wait_timeout                | 50                               |
| innodb_locks_unsafe_for_binlog          | OFF                              |
| innodb_log_buffer_size                  | 1048576                          |
| innodb_log_file_size                    | 5242880                          |
| innodb_log_files_in_group               | 2                                |
| innodb_log_group_home_dir               | ./                               |
| innodb_max_dirty_pages_pct              | 90                               |
| innodb_max_purge_lag                    | 0                                |
| innodb_mirrored_log_groups              | 1                                |
| innodb_open_files                       | 300                              |
| innodb_rollback_on_timeout              | OFF                              |
| innodb_stats_on_metadata                | ON                               |
| innodb_support_xa                       | ON                               |
| innodb_sync_spin_loops                  | 20                               |
| innodb_table_locks                      | ON                               |
| innodb_thread_concurrency               | 8                                |
| innodb_thread_sleep_delay               | 10000                            |
| innodb_use_legacy_cardinality_algorithm | ON                               |
| insert_id                               | 0                                |
| interactive_timeout                     | 28800                            |
| join_buffer_size                        | 131072                           |
| keep_files_on_create                    | OFF                              |
| key_cache_division_limit                | 100                              |
| language                                | /usr/share/mysql/english/        |
| last_insert_id                          | 0                                |
| lc_time_names                           | en_US                            |
| license                                 | GPL                              |
| local_infile                            | ON                               |
| locked_in_memory                        | OFF                              |
| log_bin                                 | OFF                              |
| log_bin_trust_function_creators         | OFF                              |
| log_bin_trust_routine_creators          | OFF                              |
| log_queries_not_using_indexes           | OFF                              |
| log_warnings                            | 1                                |
| long_query_time                         | 10.000000                        |
| lower_case_table_names                  | 0                                |
| max_binlog_cache_size                   | 4294963200                       |
| max_binlog_size                         | 104857600                        |
| max_connect_errors                      | 10                               |
| max_connections                         | 151                              |
| max_error_count                         | 64                               |
| max_insert_delayed_threads              | 20                               |
| max_join_size                           | 18446744073709551615             |
| max_length_for_sort_data                | 1024     
                        |
| max_prepared_stmt_count                 | 16382                            |
| max_sort_length                         | 1024                             |
| max_sp_recursion_depth                  | 0                                |
| max_user_connections                    | 0                                |
| max_write_lock_count                    | 4294967295                       |
| min_examined_row_limit                  | 0                                |
| multi_range_count                       | 256                              |
| myisam_data_pointer_size                | 6                                |
| myisam_recover_options                  | BACKUP                           |
| net_buffer_length                       | 16384                            |
| net_read_timeout                        | 30                               |
| net_retry_count                         | 10                               |
| net_write_timeout                       | 60                               |
| new                                     | OFF                              |
| open_files_limit                        | 1024                             |
| optimizer_prune_level                   | 1                                |
| plugin_dir                              | /usr/lib/mysql/plugin            |
| profiling                               | OFF                              |
| profiling_history_size                  | 15                               |
| protocol_version                        | 10                               |
| query_cache_min_res_unit                | 4096                             |
| query_cache_wlock_invalidate            | OFF                              |
| rand_seed1                              |                                  |
| rand_seed2                              |                                  |
| range_alloc_block_size                  | 4096                             |
| read_only                               | OFF                              |
| read_rnd_buffer_size                    | 262144                           |
| relay_log_index                         |                                  |
| relay_log_info_file                     | relay-log.info                   |
| rpl_recovery_rank                       | 0                                |
| skip_external_locking                   | ON                               |
| skip_networking                         | OFF                              |
| slave_net_timeout                       | 3600                             |
| slave_transaction_retries               | 10                               |
| slow_launch_time                        | 2                                |
| sql_auto_is_null                        | ON                               |
| sql_log_bin                             | ON                               |
| sql_max_join_size                       | 18446744073709551615             |
| sql_notes                               | ON                               |
| sql_slave_skip_counter                  |                                  |
| sql_warnings                            | OFF                              |
| storage_engine                          | MyISAM                           |
| sync_binlog                             | 0                                |
| sync_frm                                | ON                               |
| system_time_zone                        | EDT                              |
| table_definition_cache                  | 256                              |
| table_open_cache                        | 64                               |
| thread_handling                         | one-thread-per-connection        |
| time_zone                               | SYSTEM                           |
| transaction_alloc_block_size            | 8192                             |
| transaction_prealloc_size               | 4096                             |
| tx_isolation                          
  | REPEATABLE-READ                  |
| unique_checks                           | ON                               |
| version                                 | 5.1.41-3ubuntu12.10              |
| version_comment                         | (Ubuntu)                         |
| version_compile_machine                 | i486                             |
| version_compile_os                      | debian-linux-gnu                 |
| warning_count                           | 0                                |
+-----------------------------------------+----------------------------------+
159 rows in set (0.00 sec)

这里的输出总是以 4096 个字符的精确间隔被换行符打断。

除了可能的解决方案之外，如果有任何新方法可以找到有关正在发生的事情的更多信息，我们将不胜感激。

Answer 1

我遇到了类似的问题，虽然我的休息时间似乎是 1024 个字符(啊哈! 在 21_1 版本中就是这种情况)。这对我来说没什么大不了的，但我确实写了一些正确连接结果的东西，这样我就可以对它们进行后处理。但这并没有影响输出，因此不会有太大帮助。

问题的根源在于 process.c 中的 read_process_output ，对 4096 进行硬编码:

/* Read pending output from the process channel,
   starting with our buffered-ahead character if we have one.
   Yield number of decoded characters read.

   This function reads at most 4096 characters.
   If you want to read all available subprocess output,
   you must call it repeatedly until it returns zero.

   The characters read are decoded according to PROC's coding-system
   for decoding.  */

static int
read_process_output (proc, channel)
     Lisp_Object proc;
     register int channel;
{
  // ... snip
  int readmax = 4096;

就像您在问题中提到的那样，一个非常可能的解决方案是编写一个函数(调用它，clean-up-comint-output-at-4096-chars)，然后添加comint-output-filter-functions。像这样的东西。 注意:未经测试的代码。

(add-hook 'comint-output-filter-functions 'clean-up-comint-output-at-4096-chars)
(defun clean-up-comint-output-at-4096-chars (&optional str)
  "look for string of 4096 length and remove newline in the buffer"
  (let ((magic-block-size 4096))
    (save-match-data
      (when (= magic-block-size (length str))
        ;; at the magic block size, look for a newline
        (goto-char (point-max))
        (when (and (search-backward str nil t)
                   (progn
                     (forward-char magic-block-size)
                     (looking-at "\n")))
          (delete-char 1))))))