How does MySQL calculate the number of opened files _ MySQL

How does MySQL calculate the number of opened files bitsCN.com?

I. test
We can see from the manual "6.4.8. How MySQL Opens and Closes Tables" that every time a MyISAM table is opened, we need two file descriptors for verification.
1. restart mysqld
/Etc/init. d/mysql restart
2. check that several files are opened.

Lsof | grep/home/mysql
...
Mysqld 24349 mysql 5u unix 0x000001041e8de040 4244009/home/mysql. sock
Mysqld 24349 mysql 6u REG 2048 30425188/home/mysql/host. MYI
Mysqld 24349 mysql 7u REG 8, 33 0 30425189/home/mysql/host. MYD
Mysqld 24349 mysql 8u REG 2048 30425153/home/mysql/user. MYI
Mysqld 24349 mysql 9u REG 8, 33 892 30425155/home/mysql/user. MYD
Mysqld 24349 mysql 10u REG 8, 33 5120 30425126/home/mysql/db. MYI
Mysqld 24349 mysql 11u REG 3080 30425148/home/mysql/db. MYD
Mysqld 24349 mysql 12u REG 8, 33 4096 30425154/home/mysql/tables_priv.MYI
Mysqld 24349 mysql 13u REG 8, 33 0 30425157/home/mysql/tables_priv.MYD
Mysqld 24349 mysql 14u REG 8, 33 4096 30425143/home/mysql/columns_priv.MYI
Mysqld 24349 mysql 15u REG 8, 33 0 30425156/home/mysql/columns_priv.MYD
Mysqld 24349 mysql 16u REG 8, 33 4096 30425127/home/mysql/procs_priv.MYI
Mysqld 24349 mysql 17u REG 8, 33 0 30425136/home/mysql/procs_priv.MYD
Mysqld 24349 mysql 18u REG 8, 33 1024 30425173/home/mysql/servers. MYI
Mysqld 24349 mysql 19u REG 8, 33 0 30425174/home/mysql/servers. MYD
Mysqld 24349 mysql 20u REG 8, 33 2048 30425182/home/mysql/event. MYI
Mysqld 24349 mysql 21u REG 8, 33 0 30425183/home/mysql/event. MYD
...
　　
We can see that a total of eight tables are opened, and each table has two file descriptors, which seems to be correct.
3. check the status result again.

Mysql> show global status like 'open _ % ';
+ ------------------------ + ------- +
| Variable_name | Value |
+ ------------------------ + ------- +
| Open_files | 17 |
| Open_streams | 0 |
| Open_table_definitions | 15 |
| Open_tables | 8 |
| Opened_files | 52 |
| Opened_tables | 15 |
+ ------------------------ + ------- +

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