![]() ![]() You create a pipeline object, then just perform your operations normally. RedisPy also gives you an abstraction around pipelining and transactions. ![]() So, you can see this abstraction is saving you a little bit of code and making your code more readable. ![]() If you run hello() again, it will show only a single EVALSHA. This shows what RedisPy is doing: trying to run the script, getting a NOSCRIPT error, loading the script, then running EVALSHA again. The output should look something like this (if your script cache is empty): What is happening here from the Redis perspective? If you run MONITOR while inputing this script line-by-line, you’ll see activity only when you invoke hello(). For one thing, you don’t have to manage SHA-1 hashes or loading scripts on your own most of the time-RedisPy abstracts this away in a clean, Pythonic style. RedisPy is a full featured client library that improves Lua’s ergonomics in Redis-let’s see what it does to make your life easier. In effect, an application that uses Lua scripting in Redis always needs to be ready to supply Redis with the full Lua source at any given time, and there is no way to ensure that a given script is never evicted from the script cache. If you don’t want to immediately run the script, you can use the SCRIPT EXISTS command to see if a given SHA-1 digest represents a cached script. The problem with EVALSHA is that if you try to run a script that doesn’t exist in the script cache, you’ll get the following error: Redis uses an entirely separate, keyspace-less cache for the scripts: both EVAL and SCRIPT LOAD take the source code, compile it, and store the byte code representation in the cache, but EVAL first checks the script cache so it won’t trigger recompilation of the script if it is already stored in the script cache. This command functions just like EVAL, but points to the SHA-1 digest. Sending the source code over and over is a waste of bandwidth, so SCRIPT LOAD lets you send the Lua source once and receive a SHA-1 digest that you can use later to identify and run this script with EVALSHA. This command accepts the full Lua source followed by the keys count, keys, and finally any arguments that are passed into the script. We need to review Redis’ Lua scripting engine and how you run a script. Of course, at the end, we’ll show you the bullet-proof way to do it when you need everything to always work. Let’s take a look at a Lua scripting corner case in Python with RedisPy where your script can fail despite doing what looks correct. There are many ways to run a script that works most of the time, which can also be articulated as a script that fails some of the time. At the same time, though, Lua scripting can be tricky to “get right.” I don't have zlib or a base64 C library handy, so for example's sake lets say we wanted to let our Lua script use the MessageBox function from the user32.dll library in Windows.Lua scripting is a hugely powerful feature of Redis. Writing a Lua module is actually super easy, and you can tailor the interface to be more idiomatic for Lua. If you had a Lua interpreter with a built-in FFI, or you found a FFI Lua module you could load, you could probably get this to work, but it's really more trouble than it's worth. Your zlib and/or base64 libraries know nothing about Lua. Lua can load the library and call that function, and it's up to that function to actually expose functionality to Lua using the Lua API. How do I actually create or call an existing c library in Lua?Īn arbitrary library, not written for use by Lua? You generally can't.Ī Lua consumable "module" must be linked against the Lua API - the same version as the host interpreter, such as Lua5.1.dll in the root of the Wireshark directory - and expose a C-callable function matching the lua_CFunction signature. ".\\?.dll " LUA_CDIR"?.dll " LUA_CDIR"loadall.dll" ** path of the directory of the executable file of the current process. ** In Windows, any exclamation mark ('!') in the path is replaced by the ![]() The module would be searched in places defined in Your Lua interpreter's luaconf.h file. NOTE: Lua module package managers like LuaRocks orĪlso, simply loading a Lua module usually consists of one line: local zlib = require("zlib") Only difference, there are already plain-Lua libraries for that. The same applies to base64 encoding/decoding. Writing Your own Lua zlib library wrapper, following those standards.There are two ways You could solve Your problem: *.so/*.dll must follow some specific standard, which is bluntly mentioned in programming in Lua#26.2 and lua-users wiki, code sample. You can't load any existing C library, which was not created for Lua, with plain Lua. ![]()
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