lua-variable-scope
------------------
在代码中导入模块时应注意一些细节,推介使用如下格式:
```
local xxx = require('xxx')
```
而非:
```
require('xxx')
```
理由如下:从设计上讲,全局环境的生命周期和一个Nginx的请求的生命周期是相同的。为了做到会话隔离,每个请求都有自己的Lua全局变量环境。Lua模块在第一次请求打到服务器上的时候被加载起来,通过`package.loaded`表内建的`require()`完成缓存,为后续代码复用。并且一些Lua模块内的`module()`存在边际问题,对加载完成的模块设置成全局表变量,但是这个全局变量在请求处理最后将被清空,并且每个后续请求都拥有自己(干净)的全局空间。所以它将因为访问`nil`值收到Lua异常。
一般来说,在ngx_lua的上下文中使用Lua全局变量真的不是什么好主意:
1. 滥用全局变量的副作用会对并发场景产生副作用,比如当使用者把这些变量看作是本地变量的时候;
1. Lua的全局变量需要向上查找一个全局环境(只是一个Lua表),代价比较高;
1. 一些Lua的全局变量引用只是拼写错误,这会导致出错很难排查。
所以,我们极力推介在使用变量的时候总是使用local来定义以限定起生效范围是有理由的。
使用工具(lua-releng tool)[https://github.com/openresty/nginx-devel-utils/blob/master/lua-releng]查找你的Lua源文件:
$ lua-releng
Checking use of Lua global variables in file lib/foo/bar.lua ...
1 [1489] SETGLOBAL 7 -1 ; contains
55 [1506] GETGLOBAL 7 -3 ; setvar
3 [1545] GETGLOBAL 3 -4 ; varexpand
上述输出说明文件`lib/foo/bar.lua`的1489行写入一个名为`contains`的全局变量,1506行读取一个名为`setvar`的全局变量,1545行读取一个名为`varexpand`的全局变量,
这个工具能保证Lua模块中的局部变量全部是用local关键字定义过的,否则将会抛出一个运行时库。这样能阻止类似变量这样的资源的竞争。理由请参考(Data Sharing within an Nginx Worker)[http://wiki.nginx.org/HttpLuaModule#Data_Sharing_within_an_Nginx_Worker]
[返回目录](#table-of-contents)
> English source:
Lua Variable Scope
------------------
Care must be taken when importing modules and this form should be used:
```lua
local xxx = require('xxx')
```
instead of the old deprecated form:
```lua
require('xxx')
```
Here is the reason: by design, the global environment has exactly the same lifetime as the Nginx request handler associated with it. Each request handler has its own set of Lua global variables and that is the idea of request isolation. The Lua module is actually loaded by the first Nginx request handler and is cached by the `require()` built-in in the `package.loaded` table for later reference, and the `module()` builtin used by some Lua modules has the side effect of setting a global variable to the loaded module table. But this global variable will be cleared at the end of the request handler, and every subsequent request handler all has its own (clean) global environment. So one will get Lua exception for accessing the `nil` value.
Generally, use of Lua global variables is a really really bad idea in the context of ngx_lua because
1. misuse of Lua globals has very bad side effects for concurrent requests when these variables are actually supposed to be local only,
1. Lua global variables require Lua table look-up in the global environment (which is just a Lua table), which is kinda expensive, and
1. some Lua global variable references are just typos, which are hard to debug.
It's *highly* recommended to always declare them via "local" in the scope that is reasonable.
To find out all the uses of Lua global variables in your Lua code, you can run the [lua-releng tool](https://github.com/openresty/nginx-devel-utils/blob/master/lua-releng) across all your .lua source files:
$ lua-releng
Checking use of Lua global variables in file lib/foo/bar.lua ...
1 [1489] SETGLOBAL 7 -1 ; contains
55 [1506] GETGLOBAL 7 -3 ; setvar
3 [1545] GETGLOBAL 3 -4 ; varexpand
The output says that the line 1489 of file `lib/foo/bar.lua` writes to a global variable named `contains`, the line 1506 reads from the global variable `setvar`, and line 1545 reads the global `varexpand`.
This tool will guarantee that local variables in the Lua module functions are all declared with the `local` keyword, otherwise a runtime exception will be thrown. It prevents undesirable race conditions while accessing such variables. See [Data Sharing within an Nginx Worker](#data-sharing-within-an-nginx-worker) for the reasons behind this.
[Back to TOC](#table-of-contents)
- Name yuansheng-8.4 WenMing(√)
- Status yuansheng-8.6 WenMing(√)
- Version
- Synopsis yuansheng-8.6 WenMing(√)
- Description yuansheng-8.16 WenMing(√)
- Typical Uses yuansheng-8.16 WenMing(√)
- Nginx Compatibility yuansheng-8.17 WenMing(√)
- Installation yuansheng-8.17 WenMing(√)
- C Macro Configurations yuansheng-8.17 WenMing(√)
- Installation on Ubuntu 11.10 yuansheng-8.18
- Community
- English Mailing List
- Chinese Mailing List
- Code Repository yuansheng-8.20 WenMing(√)
- Bugs and Patches yuansheng-8.20 WenMing(√)
- Lua/LuaJIT bytecode support yuansheng-8.31
- System Environment Variable Support yuansheng-9.1
- HTTP 1.0 support lance-2015.8.13
- Statically Linking Pure Lua Modules yuansheng-9.1
- Nginx Worker内的数据共享 lance-2015.8.5
- Known Issues
- TCP socket connect operation issues yuansheng-9.2
- Lua Coroutine Yielding/Resuming yuansheng-9.2
- Lua Variable Scope yuansheng-9.2
- Locations Configured by Subrequest Directives of Other Modules lance-2015.8.12
- Cosockets Not Available Everywhere yuansheng-9.2
- 特别转义序列 lance-2015.8.5
- Mixing with SSI Not Supported yuansheng-9.2
- SPDY Mode Not Fully Supported yuansheng-9.2
- Missing data on short circuited requests yuansheng-9.2
- TODO yuansheng-9.3
- Changes yuansheng-9.3 WenMing(√)
- Test Suite yuansheng-9.3
- Copyright and License yuansheng-9.3
- See Also yuansheng-9.3
- Directives yuansheng-9.3
- Nginx API for Lua yuansheng-9.3
- Obsolete Sections yuansheng-9.3
- lua_use_default_type hambut 2015.8.5
- lua_code_cache hambut 2015.8.5
- lua_regex_cache_max_entries yuansheng-9.3
- lua_regex_match_limit yuansheng-9.3
- lua_package_path yuansheng-9.4
- lua_package_cpath yuansheng-9.4
- init_by_lua yuansheng-9.4
- init_by_lua_file yuansheng-9.4
- init_worker_by_lua yuansheng-9.6
- init_worker_by_lua_file yuansheng-9.6
- set_by_lua yuansheng-9.6
- set_by_lua_file yuansheng-9.6
- content_by_lua dengshiyong 2015.8.12 WenMing(√)
- content_by_lua_file yuansheng-9.19
- rewrite_by_lua yuansheng-9.19
- rewrite_by_lua_file yuansheng-9.19
- access_by_lua yuansheng-9.27
- access_by_lua_file yuansheng-9.28
- header_filter_by_lua liujinxuan 2015.9.1
- header_filter_by_lua_file yuansheng-9.28
- body_filter_by_lua yuansheng-9.28
- body_filter_by_lua_file yuansheng-9.28
- log_by_lua yuansheng-9.28
- log_by_lua_file yuansheng-9.28
- lua_need_request_body yuansheng-9.28
- lua_shared_dict lance-2015.8.20
- lua_socket_connect_timeout yuansheng-9.28
- lua_socket_send_timeout yuansheng-9.28
- lua_socket_send_lowat yuansheng-9.28
- lua_socket_read_timeout yuansheng-9.28
- lua_socket_buffer_size yuansheng-9.28
- lua_socket_pool_size yuansheng-9.28
- lua_socket_keepalive_timeout yuansheng-9.28
- lua_socket_log_errors yuansheng-9.28
- lua_ssl_ciphers yuansheng-9.29
- lua_ssl_crl yuansheng-9.29
- lua_ssl_protocols yuansheng-9.29
- lua_ssl_trusted_certificate yuansheng-9.29
- lua_ssl_verify_depth yuansheng-9.29
- lua_http10_buffering yuansheng-9.29
- rewrite_by_lua_no_postpone yuansheng-9.29
- lua_transform_underscores_in_response_headers yuansheng-9.29
- lua_check_client_abort yuansheng-9.29
- lua_max_pending_timers yuansheng-9.29
- lua_max_running_timers yuansheng-9.29
- ngx.arg lance-2015.8.19
- ngx.var.VARIABLE lance-2015.8.19
- Core constants lance-2015.8.14 WenMing(√)
- HTTP method constants lance-2015.8.13
- HTTP status constants lance-2015.8.13
- Nginx log level constants lance-2015.8.13
- print lance-2015.8.14
- ngx.ctx lance-2015.8.14
- ngx.location.capture lance-2015.8.11
- ngx.location.capture_multi lance-2015.8.11
- ngx.status lance-2015.8.18 yuansheng(√)
- ngx.header.HEADER lance-2015.9.6 yuansheng(√)
- ngx.resp.get_headers lance-2015.9.7 yuansheng(√)
- ngx.req.start_time lance-2015.9.9 yuansheng(√)
- ngx.req.http_version lance-2015.9.9 yuansheng(√)
- ngx.req.raw_header lance-2015.9.9 yuansheng(√)
- ngx.req.get_method lance-2015.9.9 yuansheng(√)
- ngx.req.set_method lance-2015.9.9 yuansheng(√)
- ngx.req.set_uri lance-2015.9.9
- ngx.req.set_uri_args lance-2015.9.10
- ngx.req.get_uri_args lance-2015.9.10
- ngx.req.get_post_args lance-2015.9.10
- ngx.req.get_headers lance-2015.9.11
- ngx.req.set_header lance-2015.9.14
- ngx.req.clear_header lance-2015.9.14
- ngx.req.read_body lance-2015.9.16
- ngx.req.discard_body lance-2015.9.24
- ngx.req.get_body_data lance-2015.9.24
- ngx.req.get_body_file lance-2015.9.28
- ngx.req.set_body_data lance-2015.9.28
- ngx.req.set_body_file lance-2015.9.28
- ngx.req.init_body lance-2015.9.28
- ngx.req.append_body lance-2015.9.28
- ngx.req.finish_body lance-2015.9.28
- ngx.req.socket yuansheng-10.12
- ngx.exec yuansheng-10.12
- ngx.redirect yuansheng-10.12
- ngx.send_headers yuansheng-10.12
- ngx.headers_sent yuansheng-10.12
- ngx.print lance-2015.8.7
- ngx.say lance-2015.8.7
- ngx.log lance-2015.8.13
- ngx.flush lance-2015.8.13
- ngx.exit lance-2015.8.13
- ngx.eof lance-2015.8.18
- ngx.sleep lance-2015.8.18
- ngx.escape_uri lance-2015.8.18
- ngx.unescape_uri lance-2015.8.18
- ngx.encode_args lance-2015.8.18
- ngx.decode_args lance-2015.8.18
- ngx.encode_base64 hambut-2015.9.9
- ngx.decode_base64 hambut-2015.9.9
- ngx.crc32_short hambut-2015.9.9
- ngx.crc32_long hambut-2015.9.9
- ngx.hmac_sha1 hambut-2015.9.9
- ngx.md5 hambut-2015.9.9
- ngx.md5_bin hambut-2015.9.9
- ngx.sha1_bin hambut-2015.9.9
- ngx.quote_sql_str hambut-2015.9.9
- ngx.today bells-2015.8.8
- ngx.time bells-2015.8.22
- ngx.now bells-2015.8.22
- ngx.update_time bells-2015.8.16
- ngx.localtime bells-2015.8.22
- ngx.utctime bells-2015.8.22
- ngx.cookie_time yuansheng-10.12
- ngx.http_time yuansheng-10.10
- ngx.parse_http_time yuansheng-10.10
- ngx.is_subrequest yuansheng-10.8
- ngx.re.match lance-2015.8.6
- ngx.re.find lance-2015.8.6
- ngx.re.gmatch lance-2015.8.6
- ngx.re.sub lance-2015.8.6
- ngx.re.gsub lance-2015.8.6
- ngx.shared.DICT lance-2015.8.10
- ngx.shared.DICT.get lance-2015.8.10
- ngx.shared.DICT.get_stale lance-2015.8.10
- ngx.shared.DICT.set lance-2015.8.10
- ngx.shared.DICT.safe_set lance-2015.8.10
- ngx.shared.DICT.add lance-2015.8.10
- ngx.shared.DICT.safe_add lance-2015.8.10
- ngx.shared.DICT.replace lance-2015.8.10
- ngx.shared.DICT.delete lance-2015.8.10
- ngx.shared.DICT.incr lance-2015.8.10
- ngx.shared.DICT.flush_all lance-2015.8.10
- ngx.shared.DICT.flush_expired lance-2015.8.10
- ngx.shared.DICT.get_keys lance-2015.8.10
- ngx.socket.udp yuansheng-10.8
- udpsock:setpeername yuansheng-10.8
- udpsock:send yuansheng-10.8
- udpsock:receive yuansheng-10.8
- udpsock:close yuansheng-10.8
- udpsock:settimeout yuansheng-10.8
- ngx.socket.tcp yuansheng-10.7
- tcpsock:connect yuansheng-10.7
- tcpsock:sslhandshake yuansheng-10.7
- tcpsock:send yuansheng-10.7
- tcpsock:receive yuansheng-10.5
- tcpsock:receiveuntil yuansheng-10.5
- tcpsock:close yuansheng-10.5
- tcpsock:settimeout yuansheng-10.5
- tcpsock:setoption yuansheng-10.5
- tcpsock:setkeepalive yuansheng-10.5
- tcpsock:getreusedtimes yuansheng-10.5
- ngx.socket.connect yuansheng-10.4
- ngx.get_phase yuansheng-10.2
- ngx.thread.spawn yuansheng-10.2
- ngx.thread.wait yuansheng-10.4
- ngx.thread.kill yuansheng-10.4
- ngx.on_abort yuansheng-10.2
- ngx.timer.at yuansheng-10.1
- ngx.config.debug yuansheng-9.30
- ngx.config.prefix yuansheng-9.30
- ngx.config.nginx_version yuansheng-9.30
- ngx.config.nginx_configure yuansheng-9.30
- ngx.config.ngx_lua_version yuansheng-9.30
- ngx.worker.exiting yuansheng-9.30
- ngx.worker.pid yuansheng-9.30
- ndk.set_var.DIRECTIVE yuansheng-9.30
- coroutine.create yuansheng-9.30
- coroutine.resume yuansheng-9.30
- coroutine.yield yuansheng-9.30
- coroutine.wrap yuansheng-9.30
- coroutine.running yuansheng-9.30
- coroutine.status yuansheng-9.30